Biochemistry 1 (PTBA 1104) Past Paper PDF - Horus University

Department of Basic Sciences (Biochemistry) Horus University - Egypt Faculty of Physical Therapy Department of Basic Sciences Biochemistry I PTBA 1104...

Department of Basic Sciences (Biochemistry) Horus University - Egypt Faculty of Physical Therapy Department of Basic Sciences Biochemistry I PTBA 1104 Prepared by: Staff Members of Basic Sciences Department Biochemistry Unit Level 1/Semester 1 2024/2025  HORUS UNIVERSITY IN EGYPT FACULTY OF PHYSICAL THERAPY QUALITY ASSURANCE UNIT Vision The Faculty of Physical Therapy at Horus University strives to be a local and regional competitor in educational programs, distinguished by scientific research that supports sustainable development and community service. Mission The aim of the faculty of Physical Therapy at Horus University is to prepare competent graduates in the field of physical therapy, capable of providing high- quality competitive healthcare through the provision of an excellent academic environment and advanced educational programs that encourage self-learning, continuous learning, and systematic scientific research; thereby contributing to development and solving societal problems. Strategic Goals 1. Improving institutional performance efficiency to ensure quality performance. 2. Achieving excellence in the educational program and enhancing graduate competitiveness. 3. Enhancing the scientific research system and supporting excellence and innovation. 4. Providing exceptional community services and contributing to environmental development for sustainable development. 5. Qualifying the faculty for accreditation according to the standards of the National Authority for Quality Assurance and Accreditation in Education.  Introduction This course will be based on the basic knowledge regarding the biochemistry of carbohydrates, lipids, and proteins. In addition, this course was designed to understand the basis of nucleic acids in our bodies, and carbohydrates metabolism. Each lecture the students will have learned to think about and try to find answers by themselves. The aim of this course involves the study of the biochemistry of carbohydrates, lipids, proteins, and nucleic acids, besides carbohydrate metabolism. In addition, this course will discuss the main pathways of metabolism including glycolysis and Krebs Cycle.  Contents Subject Page Biochemistry of Carbohydrates 1 Biochemistry of Lipids 18 Biochemistry of Proteins 29 Biochemistry of Nucleic acids 39 Enzymes 53 Hormones 56 Vitamins 71 Practical part 89  Chapter 1 Biochemistry of Carbohydrates 1. Carbohydrates  Characteristics of carbohydrates: ™ Carbohydrates are organic substances characterized by 3 features: n They are composed of three elements (carbon, hydrogen, and oxygen). o Presence of an aldehyde or ketone group. p Presence of more than one hydroxy group (poly hydroxy). ™ If the sugar has an aldehyde group, it is classified as an aldose. ™ If the sugar has a ketone group, it is classified as a ketose. ™ The aldehyde group is always at the end of the carbon chain. ™ The ketose group is always on the second carbon of the chain. ™ The family name ending (ose) indicates a carbohydrate, e.g., glucose, ribose, and fructose. Classification of Carbohydrates ™ Carbohydrates are classified based on the number of structural units into monosaccharides, disaccharides, oligosaccharides, and polysaccharides. n Monosaccharides: } Monosaccharides are the simplest sugar units which are not hydrolyzed into simpler forms. } Both glucose and fructose are monosaccharides. 1 Chapter 1 Biochemistry of Carbohydrates o Disaccharides: } Disaccharide is a carbohydrate that gives two monosaccharide units upon hydrolysis. } Sucrose (table sugar) and lactose (milk sugar) are disaccharides. p Oligosaccharides: } Oligosaccharide is a carbohydrate that contains three to ten monosaccharide units. } Examples: œ Maltotriose which is a trisaccharide containing three glucose residues. œ Raffinose which is a trisaccharide containing glucose, galactose, and fructose. 2  Chapter 1 Biochemistry of Carbohydrates q Polysaccharides: } A polysaccharide is a polymeric carbohydrate that gives more than ten units of monosaccharide upon hydrolysis. } Both cellulose and starch are naturally occurring polysaccharides. (1) Monosaccharides ’ Definition: They are the simplest carbohydrate units which cannot by hydrolyzed into simpler units. Classification:  According to active group in the sugar:  If monosaccharide contains an aldehyde group ĺ it's called aldose.  If it contains ketone group ĺ LW V FDOOHG ketose. 3 Chapter 1 Biochemistry of Carbohydrates Classification:  According to the number of carbon atoms (n) in the sugar:  3 carbons ĺtriose & 4 carbons ĺ tetrose.  5 carbons ĺ pentose & 6 carbons ĺ hexose.  7 carbons ĺ heptose. n Trioses: p Pentoses: 9 Aldose e.g., Glyceraldehyde. 9 Aldose e.g., Ribose, Xylose, and Arabinose. 9 Ketose e.g., Dihydroxyacetone. 9 Ketose e.g., Ribulose, and Xylulose. o Tetroses: q Hexoses: 9 Aldose e.g., Erythrose. 9 Aldose e.g., Glucose, Galactose and Mannose. Ketose e.g., Erythrulose. 9 Ketose e.g., Fructose. 4  Chapter 1 Biochemistry of Carbohydrates Chiral carbon atom (Asymmetric carbon atom) } A chiral carbon atom is a carbon atom in a molecule that attached to four different groups. } Glyceraldehyde contains one asymmetric carbon atom while, glucose contains four asymmetric carbon atoms. } All sugars contain asymmetric carbon atom except dihydroxy acetone. 5  Chapter 1 Biochemistry of Carbohydrates Stereoisomers in Carbohydrates } Stereoisomers: Compounds that have the same structural formula but differ in the spatial configuration i.e., they have the same number of C, H and O atoms but differ in the arrangement of groups and atoms in the space. } The number of possible isomers of a compound depends on the number of asymmetric carbon n atoms (n) and equal (2) e.g. 1 } Trioses: 1 asymmetric carbon = 2 = 2. 2 } Tetroses: 2 asymmetric carbon atoms = 2 = 4. 3 } Pentoses: 3 asymmetric carbon atoms = 2 = 8. 4 } Hexoses: 4 asymmetric carbon atoms = 2 = 16. 5 } Heptoses: 5 asymmetric carbon atoms = 2 = 32. } N.B: the number of asymmetric carbon atoms in ketoses is less by one than aldoses. e.g., fructose has 3 asymmetric carbons. } The important types of isomers include: c D and L isomers (enantiomers) or (mirror image). d Įand ȕisomers (anomers). e Epimers. f Aldose and ketose isomers. 6  Chapter 1 Biochemistry of Carbohydrates (1) D & L isomers (enantiomers) } They are isomers which are mirror images of each other e.g., D and L sugar. } D and L refer to the configuration of the pre-last carbon (carbon atom before the last one, i.e., preterminal).  If the OH attached to the pre-last carbon is directed to the right ĺLW VD-sugar e.g., D-glyceraldehyde.  If the OH attached to the pre-last carbon is directed to the left ĺLW VL-sugar e.g., L-glyceraldehyde. } Most sugars in human are in D form except L-fucose, L-arabinose, L-xylulose and L-iduronic acid. (2) ɲΘɴisomers (anomers) } They are isomers that differ in the position of OH group attached to the anomeric carbon (asymmetric carbon atom from free active group carbon in the cyclic structure). } If OH group is attached below the plane ĺLW VĮanomer. } If OH group is attached above the plane ĺLW Vȕanomer. 7  Chapter 1 Biochemistry of Carbohydrates (3) Epimers } They are isomers that differ in the position or configuration of one hydroxyl group at one carbon chiral atom [epimeric carbon] (asymmetric carbon atoms other than the carbonyl carbon), e.g. œ Glucose & galactose at C4; Glucose & mannose at C2. œ Ribose & xylose at C3; Ribose & arabinose at C2. (4) Aldose & ketose isomers } They are isomers that differ in the position of the free active group carbon atom whether it is an aldehyde group at C1 or ketone group at C2 e.g. œ Glyceraldehyde and Dihydroxyacetone. œ Erythrose, and Erythrulose. œ Ribose and Ribulose. œ Glucose and Fructose. 8  Chapter 1 Biochemistry of Carbohydrates Monosaccharides of Biological Importance (1) Glucose = Blood Sugar n Glucose (Dextrose or Grape sugar): } It's the major source of energy in human and animal. } Ingested carbohydrates are absorbed in the form of glucose. } It's converted into other sugars e.g., galactose (in mammary gland), fructose (in seminal vesicles) or ribose (in many tissues). } It enters in the formation of all disaccharides, and most of polysaccharides. (2) Fructose o Fructose (Levulose or Fruit sugar): } It is present in the semen (seminal vesicles). } It enters in the formation of disaccharide sucrose, and polysaccharide inulin. } It can be converted into glucose in the liver. (3) Galactose p Galactose: (Brain sugar) } It is present in the mammary gland. } It enters in the formation of disaccharide lactose, glycolipids, and glycoproteins. } It can be converted into glucose in the liver. (4) Ribose & Deoxy ribose r Ribose: } It enters in the structure of: 9 High energy phosphate compounds as ATP. 9 Co-enzymes as NAD and FAD. 9 Nucleic acids as RNA. 9 Second messengers as cyclic AMP. s Deoxyribose: It enters in the structure of DNA. 9  Chapter 1 Biochemistry of Carbohydrates Sugar Derivatives (1) Sugar acids Aldonic Acids Uronic Acids Aldaric Acids œ Definition: They are the oxidation products of monosaccharides. (A) Aldonic acids n Aldonic acid: (If the first aldehyde group is free) occur by mild oxidation.  Oxidation of first aldehyde group to carboxylic group produces aldonic acid  Glucose ĺGluconic acid at C1. (B) Uronic acids o Uronic acid: (if the first aldehyde group is not free). } Oxidation of the last hydroxyl group to carboxylic group produces uronic acid. } Glucose ĺGlucuronic acid at C6. 4 Importance of glucuronic acid: c Detoxication of toxic compounds by conjugation. d Formation of mucopolysaccharides. e Metabolism of bilirubin (conjugation of bilirubin in the liver to increase its solubility in the bile). f Excretion of steroids. (C) Aldaric acids p Aldaric acid: (Dicarboxylic acid) by strong oxidation. } Oxidation of both carbonyl carbon and last hydroxyl carbon produces dicarboxylic acid or aldaric acid. œ Glucose ĺGlucaric acid at C1 and C6. œ Galactose ĺGalactaric acid at C1 and C6. 10  Chapter 1 Biochemistry of Carbohydrates (2) Sugar alcohols (Alditols) } Definition: They are the products of reduction of monosaccharides. 4 D-glucose ĺD-glucitol or D-sorbitol. 4 D-mannose ĺD-mannitol. 4 D-fructose ĺD-sorbitol (+) D-mannitol. 4 D-galactose ĺD-galactitol or D-dulcitol. 4 D-ribose ĺD-ribitol. 4 D-xylose ĺD-xylitol. } The reduction of aldoses produces one product, while the reduction of ketoses forms 2 products due to C2. Cyclic sugar alcohol (Inositol) } The cyclic sugar alcohol is derived from glucose. } It is a member of vitamin B complex. } Function:  It is the main muscle sugar (myoinositol).  It enters in the formation of phosphatidyl inositol (a phospholipid) which function as a platelet activating factor.  It is needed as a second messenger in the mechanism of hormone action. (3) Deoxy sugars } Definition: They are monosaccharides with one hydroxyl group replaced by hydrogen, i.e., there is one oxygen missed. } Examples:  If the sugar is pentose (at carbon 2). 6 Ribose will give deoxyribose (component of DNA).  If the sugar is hexose (at carbons 6). 6 L-galactose will give L-fucose (component of glycoprotein). 11 Chapter 1 Biochemistry of Carbohydrates Disaccharides & glycosidic bonds } Disaccharides consist of two monosaccharides joined covalently by O-glycosidic bond. } The glycosidic bond may be (Į or ȕ) as in cyclic monosaccharides, (Į) points below the ring and (ȕ) points above the ring. } The glycosidic bonds are abbreviated by illustrating the participating carbon e.g. [Oĺ]. Homodisaccharides (1) Maltose = Malt Sugar } Maltose, often called (malt sugar), is present in fermenting grains and produced when the polysaccharide starch breaks down. } It is produced during starch digestion by Į-amylase in the small intestine and then hydrolyzed to glucose by a second enzyme, maltase. } Maltose is made up of two Į-D-glucose units. } The glycosidic linkage between the two glucose units is called an (Į-1,4 linkage). } Maltose is a reducing sugar because the glucose unit on the right has a carbon atom with free OH (C-1). (2) Trehalose (3) Cellobiose } Cellobiose is produced as an intermediate } Trehalose is a disaccharide consists of in the hydrolysis of the polysaccharide two glucose molecules linked by Į-(1,1) cellulose. glycosidic bond. } Cellobiose contains two ȕ-D-glucose units. } It is a non-reducing sugar. } The glycosidic linkage is (ȕ-1,4) linkage. } Trehalose found in yeast and fungi. } Cellobiose is a reducing sugar, and upon hydrolysis produces two D-glucose molecules. 12  Chapter 1 Biochemistry of Carbohydrates Heterodisaccharide (1) Lactose = Milk Sugar } Lactose, or (milk sugar), is the major carbohydrate in mammalian milk. Human milk is about 7% lactose. } Lactose is a disaccharide composed of ȕ-D-galactose and ȕ- D-glucose. } The glycosidic linkage in lactose is ȕ-1,4) linkage. } Lactose is a reducing sugar because the glucose ring (on the right) has a free anomeric carbon at C1. } Lactose can be hydrolyzed by the enzyme lactase in the intestine, forming an equimolar mixture of galactose + glucose. (2) Sucrose = Table Sugar } Sucrose (table sugar), is a disaccharide that is produced commercially from the juice of sugar cane & sugar beets. } The two monosaccharide units present in a D-sucrose molecule are Į-D-glucose + ȕ-D-fructose. } The glycosidic linkage is an [Įȕ-(1,2)] linkage. } Sucrose is a nonreducing sugar. } Sucrase, the enzyme needed to break the [Įȕ-(1,2)] linkage in sucrose, is present in the human body. } Sucrose hydrolysis (digestion) produces an equimolar mixture (50:50) of Į-glucose + ȕ-fructose called invert sugar. 13 Chapter 1 Biochemistry of Carbohydrates Polysaccharides (Glycans) } Definition: They consists of more than (10 monosaccharide units) and / or their derivatives bonded to each other by glycosidic linkages. n Homopolysaccharides: is a polysaccharide in which only one type of monosaccharide monomer is present. 4 Examples: starch, glycogen, dextrin, cellulose, and inulin. o Heteropolysaccharides: is a polysaccharide in which more than one type of monosaccharide monomer is present. 4 Examples: hyaluronic acid and heparin. (A) Homopolysaccharides (1) Starch } Starch is a homopolysaccharide containing only Į-D-glucose monosaccharide units. } It is the most common storage polysaccharide in plants. } Sources include Potatoes, cereals (rice, wheat) and other food grains. } Starch granules consist of two layers: n Amylose (straight chain glucose polymer). o Amylopectin (branched glucose polymer). 14  Chapter 1 Biochemistry of Carbohydrates } Hydrolysis of starch by: 6 Enzyme (amylase) gives dextrin, then maltose. 6 Acids (HCl) gives dextrin, then maltose then Į-glucose. œ Salivary amylase & pancreatic amylase are Į- amylases, which act on Į-(1,4) glycosidic bonds to split starch into dextrin then maltose. } Function: acts as a basic source of energy. (2) Dextrin } Dextrin is the partial hydrolytic products of starch. œ It is formed of Į-D-glucose units linked by Į -4) linkage and Į -6) linkage at branching points. 6 Hydrolysis: By a dextrinase into maltose then Į-D-glucose. œ Function: n Mucilage and adhesive binder. o Infant feeding. 15  Chapter 1 Biochemistry of Carbohydrates (3) Glycogen } Glycogen is a polysaccharide containing only Į-glucose units. } It is the major storage polysaccharide in humans and animals. } It is sometimes referred to as animal starch. œ Storage sites: Liver cells (10%) and muscle cells (1%) are the storage sites for glycogen in humans. } Formed of Į-D-glucose units linked by Į -4) linear linkage and Į -6) linkage at the branching points which occur about once every 10 glucose units. } It is a highly branched i.e., more branched than amylopectin of the starch. } Function: breakdown of glycogen (glycogenolysis) occurs during fasting to maintain the blood glucose level. 6 When excess glucose is present in the blood, the liver and muscle tissues convert the excess glucose to glycogen, which is then stored in these tissues. 6 Whenever the glucose blood level drops, some stored glycogen is hydrolyzed back to glucose. } These two processes are called glycogenesis and glycogenolysis, the formation and decomposition of glycogen. 16 Chapter 1 Biochemistry of Carbohydrates (4) Inulin } Inulin is a long chain polymer composed of D-fructose units linked together by ȕ- (1,2) linkages. } Function: n Determination of glomerular filtration rate (inulin clearance test is a renal function test). o Diet for diabetics. (5) Cellulose } Cellulose (the structural component of plant cell walls) is the most abundant naturally occurring polysaccharide. } Cellulose is an unbranched glucose polymer. } It is found in the cell walls of all plants and formed of ȕ-D-glucose units linked together by ȕ l-4) glycosidic bonds. } It is not digested by the human (due to absence of cellulase enzyme i.e., no ȕ> – 4] glycosidase, so its nutritive value is low. } Function: 6 Cellulose serves as dietary fiber that stimulate peristaltic movements of the intestine and thus provides the “bulk” that helps move food through the intestinal tract and 6 It facilitates the excretion of solid wastes (stool), so it used in the treatment of constipation (laxative effect). 6 It is the main structural polysaccharide in cell walls of plants e.g., cotton. 17 Chapter 2 Biochemistry of Lipids Biochemistry of Lipids - Lipids are organic compound known as fats provide a major source of storing chemical energy in the body. - Lipids are hydrophobic. i.e., they are not soluble in water, due to presence of hydrocarbon chain (-CH2-CH2-CH2-) in their structure. - Lipids are soluble in nonpolar organic fat solvents e.g., acetone, ether, and benzene. Classification of Lipids - They are classified into simple, compound (conjugated) and derived lipids. 1- Simple lipids 2- Compound lipids 3- Derived lipids Formed of fatty acids formed of simple lipids and derived from simple lipids and esters with alcohol. other non-lipid part. complex lipids by hydrolysis. 1-Fats and Oils. 1. Phospholipids. 1-Fatty acids. 2-Waxes 2. Glycolipids. 2-Glycerol. 3. Sulpholipids. 3-Steroids. 4. lipoproteins. 4- fat-soluble vitamins. 5-hormones. 1- Simple Lipids - They are esters of fatty acids with alcohols. - The alcohol may be glycerol or long chain alcohol (other than glycerol). )DWW\DFLG$OFRKROĺ(VWHU:DWHU R - COOH + R - 2+ĺ5&225 H2O - They are classified into fats, oils, and waxes, according to the type of alcohol they contain. 1- Fats and oils - They are esters of fatty acids with glycerol. - They are called triglycerides because they are triesters formed of glycerol and 3 fatty acids. 18 Chapter 2 Biochemistry of Lipids - Triacylglycerols (TG) may be: a- Simple TG: The fatty acids are the same e.g., palmitic or stearic acids forming tripalmitate or tristearate respectively. b- Mixed TG: Triglycerides with 3 different fatty acids. 2- Waxes - They are esters of fatty acids with long chain monohydric alcohol. Glycerol It is trihydric alcohol. It is colorless and viscid fluid with sweet taste. x It is miscible with water. Can combine with one or more fatty acids by ester bonds forming mono, di or triacylglycerol. Importance of glycerol: – It is used in pharmaceutical and cosmetic preparations. – It is used in medicine as a vasodilator agent in coronary heart diseases in the form of nitroglycerine. – It is used as an explosive in the form of trinitroglycerin. 19 Chapter 2 Biochemistry of Lipids Fatty acids - The building block for lipid is the structural unit called a fatty acid. - These are monocarboxylic organic acids with unbranched hydrocarbon chains (–CH2–CH2–CH2–), which usually contain an even number of carbon atoms. Classification of fatty acids: They are further classified into saturated fatty acids (SFAs) and unsaturated fatty acids (UFAs). 1- Saturated fatty acids (SFAs): - A saturated fatty acid (SFA) is a fatty acid with a carbon chain in which all carbon–carbon bonds are single bonds (no double bonds). - They have the general formula CH3-(CH2)n-COOH; where n is the number of carbon minus two. - Saturated fatty acids are further classified, according to carbon chain length into short chain and long chain fatty acids. The differences between short chain and long chain fatty acids: 2- Unsaturated fatty acids (USFAs): – They have one or more double bonds. I. Mono-saturated fatty acids: contain one double bond e.g.: Oleic that contains 18 carbon atoms and one double bond II. Polyunsaturated fatty acids: contain more than one double bond HJ(VVHQWLDOIDWW\DFLGV Essential fatty acids Def: They are polyunsaturated fatty acids. They include: 20 Chapter 2 Biochemistry of Lipids 1- Linoleic (18 C+ 2 double bonds) 2- Linolenic (18 C+3 double bonds) 3- Arachidonic acids (20 C+ 4 double bonds). Importance: - They are essential for growth. - They must be taken in diet because the body cannot synthesize them. - They are essential for phospholipids formation. - Arachidonic acid is important for biosynthesis of prostaglandins. 2- Compound Lipids They are lipids conjugated with other substances. They include: - Phospholipids. - Glycolipids. - Sulpholipids. - Lipoproteins. 1- Phospholipids - Phospholipids are the major lipid constituents of cell membranes. - They are a group of compound lipids formed of alcohol, fatty acids, phosphoric acid and nitrogenous base. Classification of Phospholipids: - There are two classes of phospholipids according to the alcohol present into: 1. Glycerophospholipids (phosphoglycerides), that contain glycerol as the alcohol. 2. Sphingophospholipids (sphingomyelins) that contain sphingosine as the alcohol. 21 Chapter 2 Biochemistry of Lipids a) Phosphoglycerides: 1- Phosphatidic acid: It is formed of: – Glycerol. – Saturated fatty acid. – Unsaturated fatty acid. – Phosphoric acid. - Function: It acts as intermediate compound in the biosynthesis of other phosphoglycerides. 2- Lecithin: It is formed of: – Glycerol. – Saturated fatty acid, – Unsaturated fatty acid, – Phosphoric acid, – Choline attached to phosphoric acid. Function: - It is the most abundant phospholipids in the cell membrane. - It acts as a lipotropic factor preventing fatty liver. 22 Chapter 2 Biochemistry of Lipids 3- Cephalins: It is formed of: – Glycerol. – Saturated fatty acid – Unsaturated fatty acid, – Phosphoric acid. – (WKDQRODPLQHRUVHULQH Function: They are important in blood clotting. b) sphingomyelins: - Structure: ƒ Sphingosine base. ƒ Unsaturated fatty acid (to the amino group of sphingosines). ƒ Phosphoric acid (to the first carbon of sphingosine). ƒ Choline base attached to phosphoric acid. Function: ƒ It is abundant in the nervous system in the myelin sheath. ƒ It is present to lesser extent in liver, spleen, and bone marrow. 23 Chapter 2 Biochemistry of Lipids Nimann Pick disease: It is a disease caused by deficiency of sphingomyelinase enzyme, which catabolizes sphingomyelin. This leads to accumulation of large amounts of sphingomyelin in brain, liver, and spleen. 2- Lipoproteins - Lipoproteins are compound lipids formed of lipid part (which may be triglycerides, cholesterol or phospholipids) and protein part (which may be Įor ȕglobulin). - Function: Lipoproteins are important for lipid transport in the blood. Lipids are insoluble in water so they cannot be transported alone. Proteins (as they contain charged amino acids) bind to lipids to increase their polarity i.e., lipoproteins are more water soluble. ƒ There are four major classes of plasma lipoproteins: - Chylomicrons. - Very-low-density lipoproteins (VLDL). - Low-density lipoproteins (LDL). (Bad cholesterol) (Less healthy) - High-density lipoproteins (HDL). (Good cholesterol) (Healthy) 24 Chapter 2 Biochemistry of Lipids 25 Chapter 2 Biochemistry of Lipids 3- Derived Lipids These are substances derived from simple lipids and compound lipids by hydrolysis & substances associating lipids in nature. They include: - Fatty acids and Glycerol. - Steroids. - Isoprenoids. - (LFRVDQRLGV - Fat soluble vitamins. Steroids -They are a large group of biologically important compounds that contain a steroid nucleus. - Steroid compounds include: a) Sterols (cholesterol and ergosterol). b) Steroid hormones (Sex hormones, adrenal cortex hormones) c) Vitamin D d) Bile acid and bile salts. 1- Sterols: Sterols include cholesterol and ergosterol. Cholesterol is present in animal tissues and ergosterol in plant tissues. Cholesterol: 26 Chapter 2 Biochemistry of Lipids 1. enters in the structure of cell membrane. 2. It is the precursor of all steroid hormones. 3. It is oxidized in the liver to give bile acids and bile salts. 4. It gives 7- dehydrocholesterol which is a provitamin D3. Ergosterol: It is plant sterol, and it is provitamin D2. 2. Bile acids: A bile acid is a cholesterol derivative that functions as a lipid emulsifying agent that facilitate the absorption of dietary lipids in the intestine. An emulsifier is a substance that can disperse and stabilize water insoluble substances as colloidal particles in an aqueous solution. Two major types of bile acids produced from cholesterol by biochemical oxidation: 1- Primary bile acids are formed in the liver and include cholic acid and chenodeoxycholic acid. 2- Secondary bile acids are formed in the small intestine and include deoxycholic acid and lithocholic acid. ƒ Function: They have a role in digestion and absorption of lipid: ƒ They help emulsification of lipid particles. ƒ They activate the pancreatic lipase enzyme responsible for digestion of triglycerides. 3. Steroid hormones: 1-Adrenocortical hormones e.g cortisol, aldosterone. 27 Chapter 2 Biochemistry of Lipids 2-Male sex hormones e.g testosterone. 3-Female sex hormones e.g estrogen & progesterone. 28  Chapter 3 Biochemistry of Proteins Protein Chemistry x Twenty percent of the human body is made up of proteins. Proteins are the large, complex molecules that are critical for normal functioning of cells. x They are essential for the structure, function, and regulation of the body’s tissues and organs. x Proteins are organic nitrogenous compounds of high molecular weight formed of C,H,O,N (N=16 % ). x -Proteins are made up of smaller units called amino acids, which are building blocks of proteins. They are attached to one another by peptide bonds forming a long chain of proteins. x -The carboxylic group of the first amino acid units with the amino group of the second amino acid, and so on. x -Amino acids are the structural units of proteins and are obtained from them by acid, alkali, or enzymatic hydrolysis. x Other elements, such as sulfur, phosphorus and iron, are essential constituents of certain specialized proteins. EX: 1-phosphorus e.g. Casein (milk protein) 29  Chapter 3 Biochemistry of Proteins 2-Iron e.g. Hemoglobin (oxygen- transporting protein of blood). x Only twenty (20) naturally occurring amino acids are present in proteins called standard amino acids. ¾ 20 different amino acids: -12 made by body -8 essential amino acids (must get from food) Classification of amino acids A-According to number of amino and carboxylic groups(chemical) : 1- Neutral amino acids (NH2 group = COOH group): 1-Aliphatic amino acids 9 ( glycine- alanine- valine- isoleucine- leucine). 2-Hydroxy amino acids 9 ( serine- threonine). 3-Sulphur amino acids 9 (cysteine- cystine- methionine). 4-Aromatic amino acids 9 (phenylalanine, tyrosine, tryptophan). 2- Basic amino acids ((NH2 group more than COOH group) : 9 Histidine- arginine- lysine. 3- Acidic amino acids ( COOH group more than NH2 group) 9 Glutamic acid- aspartic acid. 4- Imino acids ( contain an imino group ,NH ): 9 Proline- hydroxyproline. 30  Chapter 3 Biochemistry of Proteins B-Nutritional classification: This based on the requirement of amino acids in diet and synthesis of them in body. They include : 1- Essential amino acids: -Not synthesized in the body. -Should be taken in diet. -Their deficiency in diet leads to various deficiency diseases. -They include : Valine- leucine- isoleucine- histidine- Phenyl alanine- tryptophan- Threonine- methionine. 2- Non essential amino acids:.Synthesized in the body. -Not essential to be taken in diet- -They include : the rest of amino acids. C-Biological (metabolic) classification : -Depend on metabolic fate of amino acids in the body whether they give glucose (carbohydrate, ketone bodies or both. -They include : 1- Glucogenic amino acids : x All amino acids are glucogenic except leucine. x They are converted in body into glucose (carbohydrate) only. 2- Ketogenic amino acids : x Leucine - Lysine (pure ketogenic) x Converted in body to ketone bodies only. 3- Both glucogenic & ketogenic amino acids : x Tyrosine- phenylalanine- tryptophan-isoleucine. x Converted in body to both glucose & ketone bodies. Classification of proteins: According to peptide bond structure: A-Simple proteins ¾ Definition: on hydrolysis they produce only amino acids. ¾ Examples : 1-Albumin: in egg white, serum & milk. 2-Globulin: in egg white, serum & milk. 3-Histones : in combination with nucleic acid (chromatin) & in globin part of HB. 4-Scleroproteins (albuminoids): e.g. 31  Chapter 3 Biochemistry of Proteins x Keratin: hair, nail & dermis. x Elastin: elastic tissues e.g. : wall of lung. x Collagen: skin & connective tissue e.g. bone, cartilage, tendons, ligaments, joints x Fibrin: fibrous tissue. x Myosin: muscles.   B-Conjugated proteins ¾ Definition: Formed of protein part and non protein part. ¾ According to the non-protein part they are classified into : 1-Glycoproteins:.Proteins conjugated with carbohydrates e.g. hormones: FSH, LH, TSH. 2-Lipoproteins: Proteins conjugated with lipids. e.g. chylomicrons, VLDL, LDL, HDL. 3-Phosphoproteins Proteins conjugated with phosphoric acid. e.g casinogen ( in milk) & vitellin (in egg yolk) 4-Metalloproteins: proteins conjugated with metals. e.g : insulin ( protein + zinc) & ferritin (protein + iron). 5-Nucleoproteins: Proteins conjugated with nucleic acid. e.g : chromatin in chromosomes (histone + DNA). C-Derived proteins : 32  Chapter 3 Biochemistry of Proteins ¾ Definition: Denaturized or hydrolytic products of either simple or conjugated proteins. ¾ -They are classified into : Primary protein derivatives Result from alteration of protein from it native state without hydrolysis i.e : denaturation. Examples: - Coagulated proteins by heat e.g : coagulated albumin & coagulated globulin. Secondary protein derivatives Result from alteration of protein from its native state but with hydrolysis i.e: they are the hydrolytic products of protein. Examples: - proteoses : result from partial hydrolysis of proteins. -Peptones: result from further hydrolysis of proteoses. -Peptides: result from further hydrolysis of peptones. According to chemical structure : A. Primary Structure The simplest level of protein structure, primary structure is simply the sequence of amino acids in a polypeptide chain. 33  Chapter 3 Biochemistry of Proteins The hormone insulin has two polypeptide chains A, and B. The sequence of the A chain, and the sequence of the B chain can be considered as an example for primary structure. B.Secondary structure refers to local folded structures that form within a polypeptide due to interactions between atoms. dŚĞŵŽƐƚĐŽŵŵŽŶƚLJƉĞƐŽĨƐĞĐŽŶĚĂƌLJƐƚƌƵĐƚƵƌĞƐĂƌĞƚŚĞɲŚĞůŝdžĂŶĚƚŚĞ ɴ ƉůĞĂƚĞĚ ƐŚĞĞƚ͘ ŽƚŚ ƐƚƌƵĐƚƵƌĞƐ ĂƌĞ ŚĞůĚ ŝŶ ƐŚĂpe by hydrogen bonds, which form between the carbonyl O of one amino acid and the amino H of another. 34  Chapter 3 Biochemistry of Proteins C.Tertiary structure The overall three-dimensional structure of a polypeptide is called its tertiary structure. The tertiary structure is primarily due to interactions between the R groups of the amino acids that make up the protein. Important to tertiary structure are hydrophobic interactions, in which amino acids with nonpolar, hydrophobic R groups cluster together on the inside of the protein, leaving hydrophilic amino acids on the outside to interact with surrounding water molecules. Also, Disulfide bonds, covalent linkages between the sulfur-containing side chains of cysteines, are much stronger than the other types of bonds that contribute to tertiary D. Quaternary structure When multiple polypeptide chain subunits come together, then the protein attains its quaternary structure. An example for quaternary structure is hemoglobin. The hemoglobin carries oxygen in the blood and is made up of four subunits, two each of ƚŚĞɲĂŶĚɴƚLJƉĞƐ͘ 35  Chapter 3 Biochemistry of Proteins According to function: 1-Catalytic proteins Act as biochemical catalyst act as enzyme -Glucokinase. -Dehydrogenase. -Transaminase. 2-Defense proteins Bind to foreign substances, such (bacteria and viruses) to help combat invasion of the body by foreign Particle -Immunoglobulins. 3-Transport proteins Bind to small biomolecules and transport them to other locations -Hemoglobin transports oxygen. -Transferrin transports iron. 4-Storage proteins Bind and store small molecules for future Use -Ferritin stores iron in liver. -Myoglobin stores oxygen in muscles. 5-Nutrient Proteins important in the early stages of life, from embryo to infant -Casein in milk. 6-Regulatory proteins regulate cellular and physiological activities. -Insulin regulate glucose metabolism. 7-Messenger proteins 8-Structural proteins 9-Fluid-balance proteins 36  Chapter 3 Biochemistry of Proteins Bonds in proteins 1- Covalent = strong= chemical : ¾ Peptide bond: Strong bond between amino group of one amino acid & carboxyl group of adjacent amino acid. ¾ Not affected by denaturation 2- Non covalent =weak = physical : ¾ Hydrogen bond : x Weak bond between electronegative atoms e.g O- of carboxyl group of one peptide chain & H+ of amino group of adjacent antiparallel peptide chain. x Affected by denaturation. ¾ Ionic bond = electrostatic bond. x Weak bond between oppositely charged groups and atoms e.g between COOH group of acidic amino acid & NH2 of basic amino acids. x Affected by denaturation. Denaturation ¾ Definition: Change of native state of protein due to rupture of weak bonds leading to loss of its function -Causes (factors of denaturation) : A-Physical: High pressure, High temperature or Ionizing radiation e.g X-ray , UV rays. 37  Chapter 3 Biochemistry of Proteins B-Chemical: Strong acid, Strong base. 38 Chapter 4 Biochemistry of Nucleic acids Nucleic Acids  Nucleic acids are intracellular components which are required for the storage and expression of genetic information.  They are polymers made of monomers units called nucleotides.  They include: n DNA (deoxyribonucleic acid). o RNA (ribonucleic acid). Deoxyribonucleic acid (DNA)  Types of DNA: c Double stranded linear e.g., nuclear (chromosomal) DNA of eukaryotic cells, some DNA viruses. d Double stranded circular e.g., mitochondrial DNA, Chloroplast DNA (in Plants), some DNA viruses. e Single stranded circular e.g., some small DNA viruses.  Functions of DNA: n Replication: synthesis of daughter DNA (which are smaller in size and carry the same genetic information (using parent DNA strands as a templates). o Transcription: synthesis of RNA which is translated later on into a protein (using one parent sense strand as a template). 39 Chapter 4 Biochemistry of Nucleic acids Structure of DNA (base pairing rule of Watson and Crick)  It is a polydeoxyribonucleotide that contains many monodeoxyribonucelotides covalently linked by 3’,5’ phospho- diester bonds.  Each monodeoxyribonucleotide is composed of 3 elements:  Sugar pentose; 2'-deoxyribose.  Nitrogenous base (adenine, guanine, cytosine, and thymine).  Phosphate. 9 The sugar is linked to the nitrogenous base forming a nucleoside. ’ Nucleotide: the basic unit of DNA is phosphorylated nucleoside.  It exists as a double-stranded molecule, where the two strands wind around each other forming a helix.  In the double stranded helix, the two chains are coiled around a common axis, the chains are paired in an antiparallel manner, that is the 5'- end of one strand is paired with the 3'- end of the other strand.  The hydrophilic (polar), deoxyribose-phosphate backbone of each chain is on the outside of the molecule, while the hydrophobic (non- 40 Chapter 4 Biochemistry of Nucleic acids 41 Chapter 4 Biochemistry of Nucleic acids  The spatial relationship between the two strands in the helix creates a major (wide) groove and a minor (narrow) groove, these grooves are of different size due to the asymmetry of the base-pairs. Base pairing  The bases of one strand are paired with bases of the second so that an adenine (A) is paired with thymine (T) whereas a cytosine (C) is paired with a guanine (G) therefore, one polynucleotide chain of the DNA helix is the complement of the other.  Given the sequence of bases on one chain, the sequence of bases on the complementary chain can be determined.  The base pairs are held together by hydrogen bonds, two between A and T, and three between G and C.  These hydrogen bonds plus the hydrophobic interactions between the 42 Chapter 4 Biochemistry of Nucleic acids 43 Chapter 4 Biochemistry of Nucleic acids Ribonucleic acid (RNA)  They are polymer of ribonucleotides (e.g., AMP, GMP, CMP, and UMP).  Ribonucleotides are interconnected by phosphodiester bonds between the 5' hydroxyl group of ribose of one nucleotide and the 3' hydroxyl group of ribose of the next nucleotide.  Types of RNA: n Messenger RNA (mRNA). o Transfer RNA (tRNA). 44 Chapter 4 Biochemistry of Nucleic acids (1) Messenger RNA (mRNA)  It constitutes about 5% of total RNA of the cell.  It is a single strand which is complementary to the sense (template) DNA strand.  It is synthesized in the nucleus by transcription (using DNA dependent RNA polymerase II enzyme), then it passes to the cytoplasm.  The chain length of mRNA is variable due to the heterogeneous nature of the protein chain length (it must contain at least 100 nucleotide residues). ’ Functions:  It is the key component of the translation process (protein synthesis).  It carries the genetic information about the protein to be synthesized, from the nucleus to the cytoplasm where it binds to ribosomes (the machinery site for protein synthesis). 45 Chapter 4 Biochemistry of Nucleic acids 46 Chapter 4 Biochemistry of Nucleic acids (2) Transfer RNA (tRNA)  It constitutes about 15% of total RNA of the cell.  It is synthesized in the nucleus by transcription (using DNA dependent RNA polymerase III enzyme), then it passes to the cytoplasm.  There are about 31 tRNA (some amino acids have more than one tRNA).  It is arranged in the form of a cloverleaf, having 2 free ends, and 3 loops: ’ The 2 free ends: c One free end (3-0H terminus) = acceptor arm which ends by a specific sequence formed of CCA. 9 The specific activated amino acid is connected to the 3’ OH terminus by an ester link, (charged tRNA), while when tRNA is not bound to its specific activated amino acid, it is called uncharged tRNA. d One free end (5’ phosphate terminus) which ends by a base guanine (over 85% of tRNA) or base cytosine (less than 15% of tRNA). ’ The 3 loops (poles): c The anticodon loop:  Central loop which is a distant from the free end carrying the amino acid.  Contains 3 bases responsible for recognition, and complementary base pairing with the 3 bases on the genetic codon of mRNA. d D loop which contains the unusual base dihydrouracil. e T loop which contains the unusual thymine and pseudouridine bases. 47 Chapter 4 Biochemistry of Nucleic acids 48 Chapter 4 Biochemistry of Nucleic acids (3) Ribosomal RNA (rRNA)  It constitutes about 80% of total RNA of the cell.  It is synthesized in the nucleus by transcription (using DNA dependent RNA polymerase 1 enzyme for r18s, r5.8s, and r28s, and RNA polymerase III for r5s.  The ribosomes are very large complex ribonucleoproteins, having been self-assembled from at least 4 distinct RNA molecules (18s, 5.8s, 28s and 5s) and about 100 specific protein molecules. ’ Organization in eukaryotic cells e.g., human: o They occur in the form of polysomes (associated with mRNA) in the rough endoplasmic reticulum. o The ribosome contains 2 major nucleoprotein subunits: 9 A larger one (60S). 9 A smaller one (40S). 49 Chapter 4 Biochemistry of Nucleic acids ’ Organization in prokaryotic cells e.g., bacteria: o They occur in the form of polysomes (associated with mRNA) or as a monosomes (free forms). o The ribosome contains 2 major nucleoprotein subunits: 9 A larger one (50S). 9 A smaller one (30S). ™ N.B. Svedberg unit (sedimentation or S unit) is a measure of the sedimentation velocity by high-speed centrifuge (which depends on the M.W. and the size of ribosomal particles).  Functions:  Ribosomes are the machinery site of translation process (protein synthesis).  The specific ribosomal proteins are directly involved in binding mRNA and tRNA (ribosomes have 2 bindings sites for tRNA): o A site: aminoacyl tRNA. o P site: peptidyl tRNA.  The specific ribosomal RNA molecules are necessary for ribosomal self-assembly and serve as a structural polymer holding the multiprotein particles in a compact configuration which helps the binding of mRNA to the ribosomes which increases the efficiency of 50 Chapter 4 Biochemistry of Nucleic acids A summary of transcription and translation process 51 Chapter 4 Biochemistry of Nucleic acids Comparison between DNA & RNA DNA RNA Shape Double strand helix. Single strand helix. Site Nucleus & Mitochondria. Cytoplasm. Synthesis By replication. By transcription. Significance o Formation of DNA by o Biosynthesis of proteins replication. through translation. o Formation of RNA by transcription Sugar Deoxyribose. Ribose. Types One. Three. Bases A, G, C and T. A, G, C and U. 52  Enzymes Enzymes: Special proteins that act as biological catalysts. The first discovered enzyme is called diastase in 1833 an used for conversion of starch to saccharificate, and the second enzyme to be discovered is pepsin enzyme in 1836 Enzyme was first identified as a substance that accelerate chemical reactions in which the progress of the reaction is affected by a substance that is not consumed in the reaction. Catalyst: substance that stresses chemical bonds & speeds up reaction in forward and/or reverse directions. Catalysts lower the activation energy needed for the reaction to occur. Enzymes are not changed or consumed by the reaction. Activation energy: energy to start a reaction. Requires energy input to break bonds. 1) Globular proteins with specialized 3-D shapes. 2) Lower activation energy by: a) bringing two substrates together (greater chance to react). b) stress bonds of a substrate (to break them). Substrate: The reactant/s that the catalyst or enzyme binds with to in turn speed up the reaction.  Site of enzymes Enzymes may present extracellular as digestive enzymes or intracellular as other body enzymes. These intracellular enzymes may be present in cytoplasm like enzymes of glycolysis (glucose oxidation cycle) or intranuclear like those of krebs cycle and B-oxidation. Nomenclature of enzymes Old nomenclature: They named by addition of suffix ase to substrate on which they act. e.g The enzyme act on protein is protease & on starch (amylon) is called amylase and on lipids called lipase. Recently, the enzymes classified according to both reaction type and reaction mechanism.The most recent attempt of classification By I.U.B (International Union of Biochemistry) to prevent confusion due to increase number of enzymes. The major feature of this system are :- (A)Enzymes are classified into six major groups. (B) The enzymes name has two parts: The first part is the name of substrate, the second part is ending in (ase) indicating the type of reaction catalyzed. (C) Additional information, if needed to clarify the nature of reaction may follow in parenthesis. (D)Each enzyme has systemic code number. This code number is formed from four digits: The first digit is (class), second digit is subclass, third digit is (subsubclass) and fourth digit is for specific enzyme. Ex. 2.7.1.1 hexokinase. 2 (Transferase) & 7 (Transfer phosphate group), 1 (phosphate acceptor) and 1 (hexokinase). Classification of enzymes  Enzymes are classified into six main groups: oxidoreductases, transferases, hydrolases Lyases, isomerases and ligases. 1-Oxidoreductases: Including enzymes necessary for oxidation-reduction reaction. Oxidation means removal of electron or addition of oxygen while reduction means addition of electron or hydrogen. 2- Transferases: In biochemistry, a transferase is an enzyme that catalyzes the transfer of a functional group (e.g. a methyl or phosphate group) from one molecule (called the donor) to another (called the acceptor). For example, an enzyme that catalyzed this reaction would be a transferase: A–X + B → A + B–X In this example, A would be the donor, and B would be the acceptor. The donor is often a coenzyme. Ex. Hexokinase, transaminase. 3- Hydrolases: Including enzymes catalyzing the hydrolysis process ex. peptidase hydrolyse peptide bond. 4- Lyases: Enzymes catalyzing addition or removal of one group from substrate by mechanism other than hydrolysis ex. Fumarase and aconitase.  5- Isomerases: Enzymes catalyzing the interconversion of two isomers. This group include : Isomerase, mutase, and epimerase. 6- Ligases: Including enzymes catalyzing the linking of two compounds. ex.. glutamate + NH3 glutamine Glutamine synthetase Mechanisms of action of enzymes Binding of the substrate to the enzyme, to form the enzyme-substrate complex: E+S E−S Reaction of the enzyme-substrate complex to form the enzyme-product complex : E−S E−P Breakdown of the enzyme-product complex, with release of the product: E−P E+P I- Enzyme substrate combination: The enzymes act mainly through combination with their substrates to give enzyme - substrate complex (E-S complex). The breakdown of this complex results in formation of the end product and leave enzyme molecule again unchanged. Models of enzyme - substrate combination: 1. Rigid model: In which there is no change in the shape of enzymes after substrate combination. This model also called " Lock and Key" model since enzyme act as a lock and substrate like a ky. Rigid model  2. Flexible model(induced fit model): In which substrate produce conformational change in active site of enzyme through arranging the chemical groups correctly for proper substrate combination II- Coenzymes and cofactors 1- Coenzymes: Coenzymes are organic molecules that are required by certain enzymes to carry out catalysis. They bind to the active site of the enzyme and participate in catalysis but are not considered substrates of the reaction. Coenzymes often function as intermediate carriers of electrons, specific atoms or functional groups that are transferred in the overall reaction (Carrier of one reaction product). An example of this would be the role of NAD in the transfer of electrons in certain coupled oxidation reduction reactions. Some coenzymes and the reactions they are involved in are shown in the following table coenzymes in group transfer reactions Coenzyme Abbreviation Entity transferred Nicotine NAD - partly adenine composed of Electron (hydrogen atom) dinucelotide niacin Nicotine NADP - adenine Partly Electron (hydrogen atom) dinucelotide composed of phosphate niacin FAD - Partly Flavine composed of adenine Electron (hydrogen atom) riboflavin dinucelotide (vit. B2) Coenzyme A CoA Acyl groups  CoenzymeQ CoQ electrons (hydrogen atom) Thiamine Thiamine Aldehydes pyrophosphate (vit. B1) Pyridoxal Pyridoxine amino groups phosphate (vit B6) Biotin Biotin Carbon dioxide Carbamide Vit. B12 Alkyl groups coenzymes 2-Cofactors: Cofactors are often classified as inorganic substances that are required for, or increase the rate of, catalysis. Examples of some enzymes that require metal ions as cofactors is shown in the table below Cofactor Enzyme or protein Zn++ Carbonic anhydrase Zn++ Alcohol dehydrogenase Fe+++ or Fe++ Cytochromes, hemoglobin Fe+++ or Fe++ Ferredoxin Cu++ or Cu+ Cytochrome oxidase K+ and Mg++ Pyruvate phosphokinase Enzyme Specificity Enzymes are characterized by high degree of specificity and there are several types according to specificity: 1-Absolute specificity: In which the enzyme is specific only to one substrate. Ex. uricase and uric acid. & urease and urea. 2- Relative specificity: In which the enzymes act on group of compounds have the same bond. Ex. Lipase act on lipid & amylase act on glycogen and dextrins. 3- Structural specificity: In which the enzymes are specific not only to types of bonds but also to structure surrounding these bonds. Ex. pepsin hydrolyze peptide bond formed by amino group of phenyl Alanine and carboryl group of tyrosine. 4- Streo-specificity (optical specificity): In which the enzyme is specific only to one isomer of substrate Ex. L. amino acid oxidase act only on L- amino acid. 5- Dual specificity: In which one enzyme act on different Substrates. Ex. Xanthine-oxidase enzyme oxidize both hypoxanthine and xanhine to give uric acid. Factors affecting enzyme activity 1- Effect of temperature: Within limited range, the enzyme velocity is directly proportional to temperature i.e. As temperature increases, the enzyme activity will increase till optimum temperature is reached , at which the enzyme activity is maximum. After that the increase in temperature will decrease enzyme activity due to denaturation of enzyme. 2- Effect of pH : Each pH Temperature enzyme has an optimum pH at which the activity is maximum. pH affect only  on ionic state of substrates and enzymes. Change in pH below or above the optimum pH will denaturate the enzyme and decrease the enzyme activity. 3- Effect of enzyme concentration : Within limits, increased concentration will result in increase the rate of enzyme velocity. 4- Effect of end products: The accumulation of end products will result in inhibition in the enzyme activity. This is called feed - back inhibition. So the removal of end product will increase the rate of the reaction. Feed-back inhibition is usually proceeded by an allosteric type of inhibition. 5- Effect of substrate: Increase substrate concentration will increase the rate of enzyme velocity till certain limit at which the enzyme will attain a maximum velocity (Vmax). Further increase in substrate concentration will not lead to any increase in the enzyme activity due to saturation of all binding site (catalytic site) of enzyme.  Km value or Michaelis constant: is substrate concentration that produces half- maximal velocity. The Michaelis - menten equation: It describes the behavior of enzymes as substrate concentration is varied Vmax (S) S = Substrate concentration. Vi = Initial velocity. Vi = _________ Km + (S) At point (A) : When (S) is much lesser than Km the addition of (S) to Km change its value very little. So (S) can be dropped from denominator - - Vmax (S) Vmax  Vi ≈ ________ ∴ Vi ≈ ______ (S) Km Km ( ≈ approximately equal) Vi ≈ constant (S) ≈ K (S) ∴Vi depends on substrate concentration, When substrate concentration is below that required to produce half maximal velocity (Km). At (C) point: When (S) is much greater than Km value. The addition of Km to (S) has a very little value. So Km Can be dropped from denominator. Vmax (S) ∴ Vi = _________ ≈ Vmax (S) So the initial velocity (Vi) is maximal (Vmax) when substrate concentration is for exceed the Km value. (3) At point (B): When S = Km Vmax (S) Vmax Vi = _________ = __________ 2S 2 When S equal Km the initial velocity is half maximum. What if the reciprocal of the current equation is done? Michealis-Menton equation: V0 = (Vmax x [S]) / (Km + [S]) Reciprocal of this equation: 1 / V0 = (Km / Vmax [S]) + (1 / Vmax) Finally: 1 / V0 = (Km / Vmax ) (1 / [S]) + (1 / Vmax)  (6) Effect of reactants: A + B → AB As reactants increase the rate of reaction will increase due to increase the rate of collision. Doubling of A or B will double the reaction rate. Doubling of A and B will increase the rate of collision four folds. (7) Oxidizing agent: will oxidize SH group of enzyme and decrease the rate of reaction. (8) Atomic radiation: X-rays and infra red will denaturate the enzyme and decrease the rate of enzyme activity. Enzyme Inhibitors Inhibitors are substances which can combine with enzymes to inhibit their activities. There are two types of inhibitors: 1-Competitive inhibitors: In which there is structural similarity between substrate and inhibitor. The reaction is reversible and depends on concentration of substrate. The combination usually occur at catalytic site. In this type there is competition between substrate and inhibitor. The classic example is competition between succinate (S) and malonate (I) for succinate dehydrogenase. Malonate (COOH__CH2-COOH) Can combine with succinic acid dehydrogenase forming (Enz I) complex. Another examples: Sulphanilamide resemble PABA (paraamino benzoic acid) in structure. Since PABA is necessary for folic acid formation in bacteria. These bacteria may take sulphanilamide istead PABA, that inhibit bacterial growth.  Vitamin K and dicumarol. N.B: Competitive inhibitor affect Km value mainly but not Vmax. (2) Non competitive inhibitors: Which may be reversible or irreversible. (A)-Reversible: Since the substrate and inhibitor may combine at different sites, (catalytic and allosteric sites) formation of Enz IS or Enz I is possible. The reversible non competitive affect the Km value. (B-) Irreversible: Which may be specific or non specific. 1-Non specific: These including factors which affect all enzymes like denaturation. 2-Specific: Including inhibitors which are specific to certain group: ++ ++ ++ Ex: Inhibitors of SH group like heavy metals (Hg , Pb , Cu ), Iodoacetate, and oxidizing agent. The reaction is irreversible and there is no structural similarity between substrates and inhibitors. Diagnostic importance of plasma enzymes There are two types of plasma enzymes: (A) Functioning plasma enzymes: Including enzymes that present in plasma with their substrates and have important physiological functions in blood. They have not any diagnostic importance. (B) Non functioning plasma enzymes: Including enzymes which have neither specific function nor substrate in blood. In normal individual they are present inside tissue cells of organs and in very minute amount in blood. When these enzymes are elevated in blood, this indicate destruction of tissue cells. So these enzymes are very important in diagnosis and prognosis of diseases. These enzymes include: 1. Creatine phospho kinase (CPK): in myocardial infarction and muscular dystrophy they will increase. 2. Lactate dehyogenase (LDH): Elevated in myocardial infarction, leukemia and hepatic disease (hepatocellular). 3. Transaminases (GOT & GPT ): Increased in myocardial infarction, and hepatitis (hepatocellular) mainly GPT. 4. Alkaline phosphatase (AP): increased in carcinoma of bone & hepatic disorders (hepato biliary). 5. Acid phosphatase: elevated in metastatic prostatic carcinoma. 6. Gamma-glutamyl transferase: Increase in liver disorder (hepatobiliary). 7. Amylase: Elevated in acute pancreatitis and salivary disorders.(8) 8. Lipase : Increase in acute pancreatitis. 9. Trypsin: Increase in pancreatic disorders. Isoenzymes Isoenzymes or Isozymes are distinct forms (fractions) of given enzymes having the same catalytic activity. They differ from each other in some physical and chemical properties e.g. heat stability, electrophoretic mobility and immunogenic properties (Like two faces of the same coin). Ex. Lactate dehydrogenase present in blood in the form of five fractions, each derived from one organ e.g, Liver, heart.... These fractions are LD1, LD2, LD3, LD4 and LD5.  These five fractions are derived from two protomers (H and M) produced from two different genes, which when arranged give five fractions as follow: LD1 (HHHH) & LD2 (HHHM), LD3 (HHMM) & LD4 (HMMM) and LD5 (MMMM). If LDH is elevated in patient and electrophoresis is carried out to determine the fraction (isoenzyme) responsible for such elevation. When LD1 isoenzyme is found to be increased. The myocardial infarction is confirmed. Regulation of enzyme activity The enzyme activity is regulated through two main mechanisms: A) Changing the absolute quantity of enzyme: altering the catalytic efficiency of enzyme. The quantity of enzyme affected mainly by changing the rate of synthesis and the rate of degradation. The quantity can be increased by elevation of the rate of synthesis or by decreasing the rate of degradation or by both. Factors affecting quantity enzymes are: 1. Genetic factors: Since DNA gene is responsible for enzyme synthesis so any defect in synthesis may result from mutation of gene. 2. Induction and repression: Since the enzyme biosynthesis is genetically controlled. The synthesis of certain key enzymes can be selectively stimulated to produce more enzyme molecules if the cell is loaded with some substrate like substances (Inducer). The presence of other metabolites may repress (inhibit) synthesis of some enzymes. The inducer may inhibit the repressor and result in stimulation. The process is called derepression. 3. Hormonal effect: Some hormones may act on genetic apparatus of the cell and stimulate the process of transcription and formation of mRNA specific for formation of specific enzyme ex. glucagon and glucocoticoids stimulate the biosynthesis of key enzyme of gluconeogenesis. B) By altering the catalytic efficiency of enzyme: The catalytic activity is affected by: 1. Activation of enzymes: some enzymes are secreted in the form of inactive (pro-enzyme or zymogen) and the conversion to active form need proteolysis. e.g. The digestive enzyme pepsin is secreted in the form of pepsinogen and can be changed to active form by proteolytic enzyme. 2. Allosteric effectors: In the case if feedback inhibition and precursor activation, the activity of the enzyme is being regulated by a molecule which is not its substrate. In these cases, the regulator molecule binds to the enzyme at a different site than the one to which the substrate binds. When the regulator binds to its site, it alters the shape of the enzyme (conformational changes) so that its activity is changed. This is called an allosteric effect. In feedback inhibition, the allosteric effect lowers the affinity of the enzyme for its substrate. In precursor activation, the regulator molecule increases the affinity of the enzyme in the series for its substrate. 3. Covalent modification: Reversible modulation of the catalytic activity of enzyme can occurs by covalent attachment of phosphate group to enzyme. Phosphorylation may activate some enzymes like phosphorylase and inactivate the other like glycogen synthetase through production of an opposite effect. (dephosphorylation).  Hormones Hormones are chemical substances, secreted by one type of tissue and carried by blood to target tissue elsewhere in the body (endocrine hormones) to stimulate specific biochemical and physiological activities. The exceptions are paracrine hormones that produced by one tissue to act on neighboring tissues or cells and autocrine hormones that released to act on the same tissues or cells, like hormones of digestive system. The main function of hormones is to catalyze and control various metabolic functions. They resemble enzymes in two ways: 1-They are catalyst and needed in very small amount. 2-They are not used in the reaction. They differ from enzymes in several aspects: 1-Enzymes are utilized at the site where they are produced, while in case of endocrine hormones the site of origin is far from the site of action. 2-Hormones have to be discharged into blood stream whereas enzymes show their action in the cell. 3-Hormones are not only proteins but also have diverse structures while all enzymes are protein in nature. Classification of hormones I-According to chemical nature of hormones: 1-Hormones which are amino acid derivatives: Like thyroid hormones (T3 &T4) and catecholamine (epinephrine and norepinephrine derived from amino acid tyrosine. Melatonin is derived from amino acid tryptophan. 2-Polypeptide or protein hormones: These hormones are formed from polypeptide chain(s) e.g. hypothalamic, pituitary, parathyroid and pancreatic hormones. 3-Steroid hormones: These hormones are steroid in nature. Like adrenocortical hormones and calcitriol hormone. II-According to location of receptors: 1-Hormones bind to intracellular receptors (Group I): a- Intracytoplasmic receptors: Like steroid hormones. b- Intranuclear receptors: Like thyroid hormones. 2-Hormones bind to Extracellular receptors (Group II): Like catecholamine, glucagons, calcitonin and pituitary hormones. Mechanisms of action of hormones Group I: Hormones have intracellular receptors  These are lipophilic hormones (fat-soluble) diffuse through plasma membrane of the cell to combine with high-affinity receptors in target cell to form "hormone receptor complex". These receptors may be located intracytoplasmic or intranuclear. This hormone receptor complex binds to a specific region of DNA called hormone response element (HRE) of DNA and activated the inactivated a specific gene. Then the hormone affecting the genetranscription and production of a specific mRNA. This mRNA is translated to a specific protein (enzyme). The newly formed enzyme then activates the metabolic process.  Group II: Hormones have extracellular (membrane) receptors The largest number of hormones is water soluble and gives their effect through interaction with plasma membrane receptors. The combination of these hormones with their receptors results in activation or inactivation of adenylate cyclase. Activation of adenylate cyclase results in formation of cAMP from ATP. cAMP is a second messenger for hormone which considered as a first messenger. cAMP activates protein kinase, which in turn phosphorylates proteins to phosphoproteins, which elicit the physiological effects Hormones which activate adenylate cyclase are: Epinephrine, norepinephrine, glucagone, parathyroid hormones, FSH, LH, ACTH, MSH,….. N.B. Epinephrine acts in muscle and liver while, glucagons acts only on the liver. These hormones through activation of adenylate cyclase can increase the level of cAMP. cAMP is destroyed by the enzyme phosphodiestrase to 5'-AMP. Activated by insulin. Effects of cAMP activation: 1- cAMP stimulates glycogenolysis through activation of phosphorylase enzyme.  2- Stimulation of lipolysis through stimulation of lipase enzyme. 3- cAMP inhibits glycogenesis through inhibition of glycogen synthetase enzyme. G-Protein and hormonal action: Neurotransmitter/hormone binds to external face of receptor. Receptor undergoes a conformational change, which is propagated to the G-protein binding site G-protein binding site binds to trimetric G protein (αβγ), and causes it to exchange bound GDP for GTP. Exchange of GDP to GTP causes G protein to dissociate into α-GTP and β γ subunits. α-GTP diffuses across inner face of the plasma membrane to interact with adenylate cyclase. Adenylate cyclase becomes activated, and cyclized ATP to cyclic AMP, as long as α-GTP is bound to it. However, the α-subunit has GTPase activity, and eventually hydrolyzes its bound GTP to GDP + Pi. At this point, α-subunit dissociated from Adenylate cyclase to diffuse back and re-associate with β γ to form αβγ inactive molecule.  Pituitary hormones The pituitary gland is sometimes called the "master" gland of the endocrine system, because it controls the functions of the other endocrine glands. The pituitary gland is no larger than a pea, and is located at the base of the brain. The gland is attached to the hypothalamus (a part of the brain that affects the pituitary gland) by nerve fibers. The pituitary gland itself consists of three sections: a) The anterior lobe (adenohypophysis). b) The intermediate lobe (pars intermedia). c) The posterior lobe (neurohypophysis). I-Hormones of anterior lobe: 1. Growth hormone. 2. ACTH (adrenocorticotropic hormone). 3. TSH (thyroid-stimulating hormone) : stimulates the thyroid gland 4. FSH (follicle-stimulating hormone). 5. LH (luteinizing hormone). 6. Prolactin. II-Intermediate lobe: It secretes melanocyte stimulating hormone which controls skin pigmentation III-Posterior lobe: 1- ADH (antidiuretic hormone) or vasopressin. 2- Oxytocin. 1-Growth hormone  Human growth hormone is a single polypeptide hormone formed from 191 amino acids. In sheep and cows, growth hormone is formed from 2 polypeptide chains. Metabolic effects: 1 On carbohydrates metabolism: It is a hyperglycemic hormone (increase glucose level in blood) through: 2 1t decreases glucose uptake. 3 It inhibits glycolysis by inhibition of glucokinase enzyme. II-On proteins metabolism: It has an anabolic effect, increasing amino acid uptake by cells, increases protein synthesis and produces a positive nitrogen balance and gain of weight. III- On lipids metabolism: It stimulates lipolysis and so increases amount of fatty acids and ketone bodies in blood. Major Pituitary Hormone target Major Physiologic Effects gland organ(s) Promotes growth (indirectly), Liver, adipose Growth hormone control of protein, lipid and tissue carbohydrate metabolism Thyroid-stimulating Stimulates secretion of thyroid Thyroid gland Anterior hormone hormones Pituitary Adrenocorticotropic Adrenal gland Stimulates secretion of adrenal hormone (cortex) hormones. Mammary Prolactin Milk production gland  Ovary and Luteinizing hormone Control of reproductive function testis Follicle-stimulating Ovary and Control of reproductive function hormone testis Conservation of body water Antidiuretic hormone Kidney increases blood pressure and Posterior decreases urine volume. Pituitary Ovary and Stimulates milk ejection and Oxytocin testis uterine contractions (ecobolic) FSH, LH and TSH are glycoprotein in nature, while ACTH is a polypeptide hormone formed from 39 amino acids. These hormones act through activation of cAMP. Oxytocin and vasopressin are cyclic nanopeptide (formed from 9 amino acids). They contain cysteine amino acids at position 1 and 6 linked by Disulphide Bridge. Diabetes insipidus: is a disease characterized by increased thirst and increased urination (polyuria). These can result from deficiency of a body chemical (antidiuretic hormone) normally produced by the pituitary gland, or may be due to the kidney's inability to respond properly to the hormone. In this condition a specific gravity is low since there is no glucosuria. Thyroid gland The thyroid gland produces thyroid hormones. These are peptides containing iodine. The two most important hormones are tetraiodothyronine (thyroxine or T4) and triiodothyronine (T3). These hormones are essential for life and have many effects on body metabolism, growth, and development.  Iodine plays an important role in the function of the thyroid gland. It is the chief component of thyroid hormones, and is essential for their production. Iodine is obtained from the water we drink and the food we eat. In areas of the world where there is an iodine deficiency, iodine must be added to the salt or bread. Factors like cold, acute psychosis, circadian and pulsatile rhythms positively affect hypothalamus in the brain to send signals to anterior pituitary gland which secretes TSH or thyroid stimulating hormone which acts on receptor sites of the thyroid gland causing it to produce the hormones T3 and T4. These in turn negatively affect the hypothalamus causing it to send signal to anterior pituitary so it does not continue to produce TSH Severe stress, Corticoids, Dopamine and excess Iodide from outside sources cause a negative influence, checking hormone production. The thyroid gland is composed of 2 lobes (left and right) located on both sides of the trachea. The lobes contain follicular spheres of colloid (thyroid follicles) surrounded by microvillous cells (follicular cells). The follicle walls are tightly and completely enmeshed in capillaries for efficient hormone uptake. Steps of thyroid hormones biosynthesis 1. Concentration of iodide: Follicle cells actively (using ATP) take up iodide (I-) from the blood against electrochemical gradient. This step is inhibited by thiocyanate or perchlorate 2. Oxidation of iodide: Follicle cells "oxidize" iodide (I-) to active iodine (I). Remember, oxidation means to lose an electron. This step is inhibited by thiouria and thioracil. 3. Iodination of tyrosine: Iodine is attached to tyrosine (Tyr) to give mono-iodotyrosine (MIT) and di-iodotyrosine (DIT). 4. Coupling of iodotyrosine: MIT's and DIT's are joined to form T3 (tri- iodothyronine) and T4 (thyroxine).  5. Release of T3 and T4: after thyroglobin hydrolysis. 6. N.B. T3 (tri-iodothyronine) is the bioactive (active) thyroid 7. hormone. However, most cells in the body can readily convert T4 to T3 so, clinically, we measure both of these important thyroid hormones. Mechanism of action:  Thyroid hormones act through nuclear stimulation of DNA for transcription of mRNA and synthesis of specific protein that modulate the action of thyroid hormone. Biochemical functions: 1-Caloregenic effect: Thyroid hormones increase the basal metabolic rate through increase consumption of O2 and ATP utilization. So these hormones increase energy production as a heat. 2-Effect on carbohydrates metabolism: Thyroid hormones have mild hyperglycemic effect through: a- They increase absorption of glucose from small intestine. b- They increase the sensitivity of tissues to epinephrine. c- They increase utilization and oxidation of glucose in tissues. 2-On lipid metabolism: They stimulate lipolysis and so increase free fatty acids in blood. They decrease cholesterol level in blood through increasing its turnover to bile salts. 3-On proteins metabolism: Physiological dose is anabolic while, overdose is catabolic. Goiter  A Goiter is an enlargement of the thyroid gland. Apart from iodine deficiency, other causes of goiter involve conditions of the thyroid such as nodules, cancer, hyperthyroidism and hypothyroidism. Symptoms 1. The symptoms of a Goiter include: 2. Enlargement of the throat, ranging from a small lump to a huge mass. 3. Swallowing problems, if the goiter is large enough to press on the esophagus. 4. Breathing problems, if the goiter is large enough to press on the windpipe (trachea). Types of goiter: Goiters are broadly classified into two groups including: 1-Endemic Goiter: in which a whole community is affected by insufficient dietary iodine. One common reason is that the soil in which foods are grown is iodine depleted. Certain areas of Australia, including Tasmania and areas along the Great Dividing Range (for example, the Australian Capital Territory), have low iodine levels in the soil. There is also evidence of a re-emergence of iodine deficiency in cities like Melbourne and Sydney. Mountainous areas and areas far from the sea are the ones most likely to be iodine deficient. However, endemic Goiters tend to be more prevalent in developing countries. They are rare in developed countries because of widespread iodine supplementation. 2-Sporadic Goiter - in which only the individual is affected. Risk factors for sporadic goiter include family history, diet, age (over 40 years) and gender (women are more susceptible than men). Causes of goiter: 1. Insufficient iodine in the diet. 2. High consumption of certain foods that neutralize iodine, such as cabbage and cauliflower. Other foods, like soy, may also induce Goiters. 3. Certain drugs, such as lithium and phenylbutazone. 4. Thyroid cancer. 5. Nodules growing on the thyroid gland. 6. Hyperthyroidism (overactive thyroid gland). 7. Hypothyroidism (under active thyroid gland). Hyperthyroidism: Hyperthyroidism means the thyroid gland is overactive. A common cause is Graves' disease, in which the immune system produces antibodies that act like TSH and stimulate the thyroid gland uncontrollably. The gland responds by producing an excessive amount of hormones. Goiter is caused by this massive over stimulation. Some of the symptoms of hyperthyroidism include a racing and irregular heart, restlessness, unexplained weight loss, heat intolerance and diarrhea. Hypothyroidism: Hypothyroidism means the thyroid gland is under active. The pituitary gland keeps sending its chemical messages, instructing the thyroid to produce its hormones. The thyroid gland enlarges as it attempts to comply. Apart from iodine deficiency, other causes of hypothyroidism include Hashimoto's disease (which, like Graves' disease, is an autoimmune  disease), treatment for hyperthyroidism, and dysfunction of the pituitary gland. Some of the symptoms of hypothyroidism include low energy, depression, cold intolerance and constipation. Thyroid nodules: Thyroid nodules are lumps that grow on the gland. Nodules are classified into two groups: Hot or warm: These nodules account for around 15 percent of cases, and can cause hyperthyroidism. The cancer risk is low. Cold: These nodules account for around 85 percent of cases. Around 20 per cent of these are cancerous Calcium homeostasis (Hormones regulate calcium metabolism) The normal level of calcium in blood is 9-11mg %. There are three hormones which are responsible for regulation of calcium level in blood are: 1. Parathyroid hormone. 2. Calcitriol (active form of vitamin D). 3. Calcitonin. I-Parathyroid hormone This is polypeptide hormone formed of 84 amino acids which is secreted by parathyroid gland It is secreted as preprohorohormone composed of 107 amino acids. Mechanism of action: It acts through activation of cAMP. Biochemical effects: It is a hypercalcimic hormone that increases calcium level in blood through: 1. It increases calcium mobilization from the bone. 2. It increases renal absorption of calcium and increases urinary excretion of phosphorus 3. It stimulates calcium absorption from intestine through promotion of vitamin D activation in the kidney (indirect effect). II-Calcitriol (active form of vitamin D) Calcitriol is formed by activation of cholecalciferol in the liver (by hydroxylation at C-25 followed by hydroxylation in kidney at C-1. to form 1, 25 dihydroxycholecalciferol. Mechanism of action: It acts through stimulation of process of transcription. Biochemical effects: 1. It stimulates calcium absorption from small intestine, through stimulation of biosynthesis of calcium binding proteins in the intestinal mucosa. 2. It stimulates calcium re-absorption from kidney. 3. Mobilization of calcium from the bone.  III- Calcitonin Is a polypeptide hormone formed from 32 amino acids? Mechanism of action: It acts through activation of camp. Biochemical effects: Calcitonin is a hypocalcaemia hormone through stimulation of calcium deposition in bone tissues. Pancreatic hormones Pancreas is an organ of endocrine and exocrine functions. The endocrine portion is formed from two types of cells that perform its function. These two types of cells: 1. α-cells: Secrete glucagon. 2. β-cells: Secrete insulin. 1- Insulin hormone Biochemical structure: It is a polypeptide hormone, its crystallization requires traces of zinc and secreted from β-cells of islets of Langerhans. It is produced as an inactive form (proinsulin), in the form of a single polypeptide chain of 84 amino acids. The active form formed from 2 polypeptide chains (A and B chains)  A-chain formed from 21 amino acids with glycine as a first amino acid and aspargine as a last one. B-chain is composed of 30 amino acids, the first one is phenylalanine and the last one is alanine in dog and pork. The two polypeptide chains are connected with two disulphide linkages. One in between amino acid no. 7 in both chains. The second disulphide linkages connect between amino acid no. 20 in A- chain and amino acid no. 19 in B-chain. There is a third disulphide bond between amino acids no. 6 and no. 11 in chain A. Insulin receptors and mechanism of action Insulin receptors are glycoprotein in nature. It is a heterodimer consisting of two subunits called as α and β. This is represented as α2 β2. The two subunits are linked by two disulphide bonds. α-Subunit is extracellular and binds to insulin and β-subunit is a transmembrane protein and serves as the purpose of signal transduction of cytoplasmic portion of α-subunit.  This subunit has tyrosine kinase activity and an autophosphorylation site. Binding of insulin to insulin receptors produces activation of tyrosine kinase activity which results in: 1. Insulin increases activity of some enzymes by phosphorylation- dephosphorylation mechanism. 2. Insulin also decreases transcription of enzymes of gluconeogenesis. Biochemical effects: 1- On carbohydrates metabolism:  It is a hypoglycemic hormone through: 1. 1nsulin stimulates glucose uptake by extra hepatic tissues due stimulation the synthesis of glucose transporter. 2. Insulin stimulates glucose oxidation in tissues, through stimulation of enzymes of glycolysis, citric acid cycle and HMP-shunt. 3. Insulin stimulates glycogenesis and lipogenesis (formation of lipids from glucose). 4. Insulin inhibits gluconeogenesis. 2- On lipids metabolism: It is a lipogenic hormone. 1. It stimulates lipogenesis through stimulation of acetyl CoA carboxylase and providing NADP necessary for lipogenesis. 2. It inhibits lipolysis. 3. 3It is a ketolytic hormone (breakdowns ketone bodies). 3- On proteins metabolism: It is an anabolic hormones i.e. increases protein biosynthesis. Abnormalities in β-cells: Results in diabetes mellitus (DM), characterized by polyuria, glucosuria and increase specific gravity. There are two types of diabetes mellitus: Type 1 DM: Peoples with type 1 diabetes mellitus (also called insulin-dependent diabetes mellitus or IDDM) don't produce insulin and need regular shots of it to keep their blood glucose levels normal.  Type1diabetes was once called juvenile-onset diabetes, but that name has been dropped because type1 diabetes also strikes young and older adults alike. Type 1 diabetes accounts for about 5% to 10% of those who have the disease. Type 2 DM: Approximately 95 percent of people with diabetes mellitus have type 2 diseases (also called non-insulin-dependent diabetes mellitus or NIDDM). Those with type 2 produce insulin, but the cells in their bodies are "insulin resistant", they don't respond properly to the hormone, so glucose accumulates in their blood. Some people with type 2 diabetes must inject insulin, but most can control the disease through a combination of weight loss, exercise, a prescription oral diabetes medication, and tight control. 2- Glucagon hormone Is a polypeptide hormone secreted from α-cell of pancreas. It is formed from 29 amino acids and acts through activation of cAMP. Metabolic effects: 1- On carbohydrates metabolism: it is a hyperglycemic hormone through: Stimulation of glycogenolysis through activation of phosphorylase enzyme. Stimulation of gluconeogenesis through stimulation of transcription of PEPCK. 2- On lipids metabolism: It is lipolytic hormone since, it stimulates lipase enzyme. It increases fatty acids and ketone bodies in blood. 3- On protein metabolism: It is a catabolic hormone  Hormones of adrenal gland The hormones of adrenal gland are two types: 1- Hormones of adrenal medulla. 2- Hormones of adrenal cortex. 1- Hormones of adrenal medulla Catecholamines are hormones of adrenal medulla. Including epinephrine, norepinephrine and dopamine. They are found to contain catechol group and an amino group so they are called collectively "catecholamines" Catecholamines are derived from amino acid phenylalanine through the following steps; 1-Tyrosine hydroxylase: Is a rate-limiting enzyme in catecholamines biosynthesis. It functions as oxidoreductase to convert L- tyrosine to L- dihydroxyphenylalane (L- dopa). 2-Dopa decarboxylase: It requires pyridoxal phosphate for conversion of L- dopa to 3,4 dihydroxypheylethylamine 3-Dopamine β-hydroxylase: Catalyzes the conversion of dopamine to norepinephrine. 4-Phenylethanolamine-N-methyl transferase (PNMT): Catalyzes the methylation of norepinephrine for production of epinephrine. Catabolism of catecholamines: The catabolism of catecholamines is carried out by catechol-o-methyl transferase (COMT) an