Protein Chemistry Lectures (PDF)

Protein chemistry Prof. Dr. Dina Sabry Dr. Shimaa Mohsen Dr. Mai Abdelaziz  LOs Enumerate Biological importance and function of proteins Describe the structure of proteins Explain properties of proteins Classify proteins  protein...

Protein chemistry Prof. Dr. Dina Sabry Dr. Shimaa Mohsen Dr. Mai Abdelaziz  LOs Enumerate Biological importance and function of proteins Describe the structure of proteins Explain properties of proteins Classify proteins  protein They provide the body with nitrogen, sulfur, and some vitamins. They enter in the formation of enzymes and protein hormones e.g. insulin. They enter in the formation of supporting structures in the body as bone, cartilage, skin, nails, hair and muscles. They enter in the formation of buffer system of the blood, which maintains a constant blood pH.  They enter in the formation of hemoglobin which carries 02 from the lung to tissues. They enter in the formation of antibodies (immunoglobulins), which play an important role in the defensive mechanism of the body. They include plasma proteins, e.g albumin which acts as a carrier of many materials (e.g hormones, minerals, and fatty acids) in the blood, also maintains the osmotic pressure.  Structure of Proteins (Protein Organization) Proteins are formed of a large number of amino acids linked together by peptide bonds. At one of peptide chain, there is free - COOH group called C-terminal, while at the other end free - NH2 group called N- terminal. It can be divided into 4 orders of organization:  Structure of proteins 1 - Primary structure: It is the sequence (ASSEMPLY) of - amino acids united by peptide bonds in the polypeptide chain. Peptide bonds are responsible for the maintenance of this primary structure. The polypeptide chain has 2 termini; a free amino terminal group, termed the N-terminus amino acid and a free carboxylic terminal group, termed C-terminus amino acid. It is not affected by denaturation.  I. Primary structure It is the number, type & sequence (arrangement) of amino acids in the peptide chain. It is due to peptide bond. It is not affected by denaturation.  2. Secondary structure: α helix: It is coiling (folding) of primary structure in form of right handed a helix. It is due to hydrogen bond.  b. β -Pleated Sheet This structure exists in the same polypeptide chain or between 2 or more polypeptide chains. The polypeptide chains line side by side to form sheet and the side chains are above or below the plane of the sheet.  3. Tertiary structure: It is the final order of organization of protein structure (3 dimensional structure). It is of 2 types:  Tertiary structure: The tertiary structure is maintained by three types of interactions: A-Hydrophobic interactions B- Electrostatic interactions (ionic bonds) C-Hydrogen bonds 3- Tertiary structure  4. Quaternary structure: Several polypeptides, each forms its own primary, secondary and tertiary structure and finally all polypeptides combine (interact) forming quaternary structure. Examples: Haemoglobin (tetramer i.e 4 polypeptide chains), Hydrogen bond, ionic bond, Van Der Waal's forces, and disulfide bond are present for quaternary structure stabilization. It is affected by denaturation.  Biology/Chemistry of Protein Structure Primary Assembly STRUCTURE PROCESS Secondary Folding Tertiary Packing Quaternary Interaction  Definition: change in the native state of protein (change in secondary, tertiary and quaternary protein structures due to rupture of weak bonds) without any alteration of primary structure due to preservation of strong peptide bond. Denaturation leads to changes in physical, chemical and biological properties of proteins. It may be reversible  Causes of Denaturation Physical: Chemical: - High pressure. - Strong acid. - High temperature. - Strong base. - Ionizing irradiation e.g X- - Alcohol. ray, UV ray. - Heavy metals like Pb2+, - Shaking (agitation). Ag2+ and Cu2+ etc...., organic - Repeated freezing and solvents, urea. thawing.  Effects of denaturation on proteins: 1 - Increased viscosity. 2 - Decreased solubility. 3 - Increased digestibility by proteolytic enzymes. 4 - Loss of biologic activity, if the protein was an enzyme or hormone. 5 - Loss of the secondary, tertiary and quaternary structure of proteins.  Molecular Chaperones Unfolded proteins are toxic to the cell because of their potential to form large aggregates that is difficult to degrade. Machinery for safely "catalyzing" protein folding is therefore an essential part of cell protein with highly advanced function. Chaperones are a class of proteins that enable successful protein folding. It is energy consuming protein.  Properties of proteins: 1- Amphoteric properties : Amino acid and proteins have amphoteric properties i.e. contain both COOH and NH2. Each protein has its own isoelectric point (PI) i.e. the pH at which the number of ionized negatively charged carboxyl groups (COO") equals the number of positively charged amino groups (NH3+).  Separation of plasma proteins by charge typically is done at a pH above the isoelectric point (PI) of the major proteins. Thus, the charge on the proteins is negative. In an electric field, the proteins will move toward the positive electrode at a rate determined by their net negative charge. Amino acids in aqueous solution contain weakly acidic α-carboxyl groups and weakly basic α-amino groups. Thus, both free amino acids and some amino acids combined in peptide linkages like that in hemoglobin can act as buffers.  Classification of proteins: Compound Derived Simple On hydrolysis They are On hydrolysis they produce produced by they produce amino acids hydrolysis of amino acids in addition to a the first two only prosthetic groups group  Simple protein 1-Albumin and Globulin (plasma and milk) 2- Scleroprotein (insoluble fibrous protein): keratin (skin), collagen (tendon, ligament, connective tissue, bone and cartilage)  ALBUMIN The name is derived from the white precipitate formed when egg is boiled (Latin, albus = white). Functions of Albumin 1. Colloid osmotic pressure of plasma Contributes to 80% Colloid osmotic pressure of plasma If protein concentration in serum is reduced leading to accumulation of water in tissues:’’ edema.’’  ALBUMIN 2. Transport Function (As it is hydrophilic protein) Carrier of various hydrophobic substances in blood as: i. Bilirubin. ii. Fatty acids (Albumin–fatty acid complex cannot cross blood–brain barrier and hence fatty acids cannot be taken up by brain). iii. Drugs (sulfa, aspirin, salicylates, dicoumarol, phenytoin). iv. Hormones: steroid hormones, thyroxine. v. Metals: calcium, copper and heavy metals.  Keratins Keratins are fibrous proteins present in hair, skin and nails. They mainly have the alpha helical structure. Each fibril has 2 polypeptide chains. The matrix has cysteine-rich polypeptide chains which are held together by disulfide bonds. The more the number of disulfide bonds, the harder the keratin is. Also, Keratin is rich in hydrophobic amino acids. Keratins  Collagen It is one of structural extracellular matrix protein. Collagen is nondigestible (of low biological value). It is formed of 3 polypeptide chains in Connective Tissue cells (fibroblasts) and skin, bones, cartilages, tendons, lungs, liver, vessels and cornea. It forms 25% of total body proteins.  Compound Protein 1- Phospho-protein: a) Milk casein Both whey and casein are considered high-quality proteins and provide all essential amino acids required to support growth and development in many infant formula. B) Phosphorylated enzymes  Compound Protein 2. Lipoproteins (is the form of lipid in blood circulation) LIPOPROTEIN MOLECULE= HYDROPHOBIC LIPID (T& C) IS CARRIED BY HYDROPHYLIC PROTEINS (ApoA, ApoC, ApoB)  Compound Protein Glycoproteins: 1. Blood group antigens (group A, group B, group AB and group O) on red blood cells. 2. Immunoglobulins (ANTIBODIES) in plasma.  Compound Protein 4. Proteoglycans Are protein covalent attached to GAGs (glycosaminoglycans) in extracellular matrix of connective tissues.  5. Metallo-proteins Containing Iron (Fe) The iron may be in the form of heme or non- heme iron (NHI). A- Hemoproteins These are proteins containing iron in the form of heme. Hemoproteins include hemoglobin, myoglobin, cytochromes, catalase, peroxidase, nitric oxide synthase and tryptophan pyrrolase.  Hemoglobin Function of Hemoglobin Hemoglobin (Hb) is found exclusively in red blood cells, where its main function is to transport oxygen from the lungs to the capillaries of the tissues, and removes CO2 from them. Also the oxy Hb/Hb system acts as a buffer in the RBCs for H2CO3. Structure of Hemoglobin Hb is made up of 4 heme groups attached to a basic protein, globin, that is histone in nature. It contains 3.4mg of iron per gram. Hemoglobin A, the major hemoglobin in adults (98%), is a tetramer composed of four polypeptide chains – two identical alpha (α) chains and two identical (β) chains, held together by noncovalent interactions. The subunit composition of the normal hemoglobin is shown in the following table: Form Chain Fraction of total composition hemoglobin HbA 22 95 – 98% HbF 22 < 2% HbA2 22 2 – 5%  Myoglobin Myoglobin contains a single polypeptide chain (apomyoglobin). It is an oxygen storage protein. Oxygen transported to tissues must be released for utilization. In tissues, such as muscle, with high oxygen demands, myoglobin provides large oxygen reserves. It is present in cardiac and skeletal muscles. It functions in both tissues as a reservoir for oxygen, and as an oxygen carrier that increases the rate of release of oxygen within the muscle cell during severe muscular exercise.  Myoglobin Hemoglobin Heme 4 Heme Apomyoglobin Globin Myoglobin Heamglobin Site muscles RBCs Structure 1 heme + 1chain 4 heme+ 4 chains Apomyoglobin Globin α2 β2 Function -Storage of o2 in -Transport of o2 to tissue muscle -Removal of Co2 from -Release during tissue sever muscular -Buffer exercise  Hemoglobinopathies Are disorders caused either by production of a structurally abnormal Hb molecule; synthesis of insufficient quantities of normal Hb subunits, or both. The sickling diseases sickle cell anemia (hemoglobin S disease) and hemoglobin SC disease as well as hemoglobin C disease and thalassemias are representative hemoglobinopathies that can have severe clinical consequences.  Type of Hemoglobin Abnormalities Hb S Glutamic acid at position 6 of  subunit is replaced by valine (termed S-chain) Hb M Proximal or distal histidine of  or -chain of Hb is replaced by tyrosine Hb C Glutamic acid at position 6 of the  chain is replaced by lysine α-Thalassemias These are defects in synthesis of α-globin chains β-Thalassemias These are defects in synthesis of β-globin chains B- Non-Heme Iron (NHI) Containing Proteins They include ferritin, transferrin, and hemosiderin 1- Ferritin It is the storage form of iron. 2- Transferrin It is the transport form of iron 3- Hemosiderin It is present in cases of hemosiderosis (iron toxicity), as in cases of repeated blood transfusion for treatment of hemolytic anemia. Amino acids chemistry Protein chemistry Prof. Dr. Dina Sabry Dr. Dalia Badran Dr. Shimaa Mohsen Dr. Dina MEKAWY  LOs Identify general formula of amino acid Classify amino acids nutritionally Classify amino acids as hydrophobic or hydrophilic Identify conversion of amino acids to specialized products. Enumerate Biological importance and function of proteins Describe the structure of proteins Explain properties of proteins Classify proteins AMINO ACIDS AMINO ACIDS Proteins are organic compounds with a high molecular weight. Twenty different amino acids are commonly required for synthesis of proteins, all are α-amino acids. Amino acids are organic acids (COOH), which have amino group (NH2). Amino acids are the building units of protein.  Chemical Classification of amino acids Neutral: monocarboxcylic and monoamino groups Acidic: Dicaboxcylic and monoamino groups Basic: Diamino and monocaboxcylic groups  Neutral amino acids Neutral: monocarboxcylic and monoamino groups Glycine Alanine  Neutral amino acids Neutral: monocarboxcylic and monoamino groups Hydroxyl Serine containing amino acids Therionine Sulphate Cysteine containing amino acids Methionine Methionine in the active form S-adenosyl methionine (SAM) is used as methyl donor. Trans-methylation reactions are catalyzed by different methyl transferases. methyl transferase - Nor-epinephrine Epinephrine (hormone metabolism) SAM  Acidic amino acids Acidic: Dicaboxcylic and monoamino groups Aspartic acid Glutamic acid  Basic amino acids Basic: Diamino and monocaboxcylic groups: Lysine, Arginine and Histidine Lysine Mid term short essay exam: Explain on biochemical basis The chemical structure of lysine is essential for DNA epigenetic regulation by histone modification  ANSWER Lysine amino acid is basic hydrophilic amino acid is essential for nucleosome structure (DNA packaging and epigenetic regulation by histone modification through Lysine acetylation and lysine methylation in ACTIVATION AND A) Model of a nucleosome composed of 8 INACTIVATION OF DNA histone proteins with exposed tails (darker grey which is rich in hydrophilic lysine a.a.) and REPLICRION). wrapped DNA (lighter grey). B) Structure of euchromatin (“beads on a string”). C) Structure of heterochromatin. Epigenetic regulations for activation and inactivation of DNA replication Histidine: Hydrophilic polar basic amino acid It is precursor for histamine, an amine produced by the body in inflammation and hypersensitivity allergic reactions by Histidine by decarboxylation reaction.  Nutritional Classification of Amino Acids I- Essential Amino Acids They are not formed in the body. It is essential to supply them in diet. Their deficiency decreases the rate of growth and protein synthesis. They are 9 in number: 1- Valine 2- Leucin 3-Isoleucine 4-Threonine 5- Methionine 6- Lysine 7- Phenylalanine 8- Tryptophan 9- Histidine II- Half-essential or Semi-essential Amino Acids They are formed in the body at a rate enough for adult but not for growing animals (Arginine ) III- Non-essential Amino Acids They are formed in the body mostly from carbohydrates at a rate enough for growing and adult animals. These include the rest of amino acids Proteins that contain all the essential amino acids are of high biological value, e.g. milk and egg proteins. Proteins that are deficient in one or more of the essential amino acids are of low biological value, e.g. collagen and elastin. Classification of amino acids as hydrophobic or hydrophilic  Depending on the interaction of side chains with water.  In general, proteins fold so that amino acids with hydrophobic side chains are in the interior of the molecule where they are protected from water, while those with hydrophilic side chains are on the surface in contact to water on the outside of the molecule. Hydrophobic amino acids: 1. Phenylalanine and tyrosine. 2. Tryptophan. 3. Valine, leucine, and isoleucine. Hydrophilic amino acids Have side chains that contain O or N atoms; some of the hydrophilic side chains are charged at physiologic pH. The acidic amino acids (aspartic and glutamic acids) have carboxyl groups that are negatively charged, Whereas The basic amino acids (lysine, arginine, and histidine) have nitrogen atoms that are positively charged.  Location of nonpolar amino acids in soluble and membrane proteins Nitrogen Balance Nitrogen balance is the (normal) condition in which the amount of nitrogen incorporated into the body each day exactly equals the amount excreted. Negative nitrogen balance occurs when nitrogen loss exceeds incorporation. Positive nitrogen balance occurs when the amount of nitrogen incorporated exceeds the amount excreted.  Positive nitrogen balance Occurs when the amount of nitrogen incorporated exceeds the amount excreted. It is associated with: Growth Pregnancy Recovery phase (of injury or surgery or condition associated with negative nitrogen balance)  Negative nitrogen balance Negative nitrogen balance occurs when nitrogen loss exceeds incorporation. It is associated with: Protein malnutrition (kwashiorkor) Dietary deficiency of even 1 essential amino acid Starvation Uncontrolled diabetes Infection Conversion of amino acids into specialized products  Glycine Specialized products synthesized from Glycine: 1.Creatine :it is used to store energy in the form of creatine phosphate in muscles. 2.Collagen :it is abundant protein in the connective tissue, bone, cartilage. 3.Hemoglobin formation. 4.Purine base synthesis :(Adenine and guanine) 5.Glutathione formation: Antioxidant and cofactor for enzymes)  Methionine Specialized products synthesized from Methionine: SAM S-adenosyl methionine Active methionine: Is the methyl donor needed for formation of epinephrine, choline & creatine)  Glutamic acid Specialized products synthesized from glutamic acid 1.GABA ( γ-amino butyric acid):CNS Neurotransmitter inhibitor 2. Glutathione (Antioxidant and cofactor for enzymes)  Phenylalanine Specialized products synthesized from Phenylalanine 1.Biosynthesis of tyrosine Biosynthesis of tyrosine An inborn error of phenylalanine metabolism : Phenylketonuria (PKU) Cause –Phenylalanine hydroxylase deficiency Accumulation of: –Phenylalanine –phenylpyruvic –phenyllactic –phenylacetic Signs Infants with classic phenylketonuria (PKU) are normal at birth but if untreated show slow development, severe mental retardation, autistic symptoms, and loss of motor control. Children may have pale skin and white-blonde hair. Treatment A diet restricted in phenylalanine (small quantities are necessary because it is an essential amino acid).  Tyrosine Specialized products synthesized from of Tyrosine 1.Biosynthesis of thyroid hormones 2.Biosynthesis of neurotransmitter (catecholamines ) 3.Biosynthesis of melanin pigment Thyroid hormones Neurotransmitters Melanin pigment Folic acid=tetrahydrobiopterin (BH4) PLP= Vitamin B6 Vitamin C &Cu SAM An inborn error of Tyrosine metabolism : Albinism Albinism is a condition in which then normal conversion of tyrosine to melanin is altered. Cause The most severe form is a deficiency of tyrosinase. Symptoms: Absence of melanin pigment in the skin, hair, and eyes.  Tryptophane Specialized products synthesized from of Tryptophane 1.Melatonin: Hormone & antioxidant. 2. Nicotinic acid (vitamin B3): for synthesis of NAD+ and NADP+. (Cofactor hydrogen carrier in oxidation reduction reactions)  Tryptophane 3. Serotonin: Neurotransmitter *Which has multiple physiologic roles including pain perception, regulation of sleep, appetite, temperature, blood pressure, cognitive functions, and mood (causes a feeling of well-being, thereby functioning as antidepressants). *The largest amount of serotonin is found in the intestinal mucosa. *Smaller amounts occur in the CNS, where it functions as a neurotransmitter , and in platelets.  Conversion of amino acids into specialized products Amino Acid Functions Glycine Creatine (it is used to store energy in the form of creatine phosphate in muscles) Collagen (it is abundant protein in the connective tissue, bone, cartilage) Hemoglobin Purine (Adenine and guanine) Glutathione (Antioxidant and cofactor for enzymes) Methionine SAM (active methionine), (which is methyl donor needed for formation of epinephrine, choline & creatine) Glutamic acid GABA ( γ-amino butyric acid):CNS neurotransmitter inhibitor Glutathione (Antioxidant and cofactor for enzymes) Tyrosine 1. Catecholamine (neurotransmitters): Dopamine, norepinephrine & epinephrine. 2. Melanin: A dark brown pigment present mainly in skin, hair and iris. Tyrosinase Tyrosine Melanin Deficiency of tyrosinase causes Albinism (decrease melanin formation and patients suffer from skin burns). 3. Thyroid hormones (T3 &T4).  Conversion of amino acids into specialized products Amino Acid Functions Tryptophane 1. Melatonin: Hormone & antioxidant. 2. Nicotinic acid (vitamin B3): for synthesis of NAD+ and NADP+. (Cofactor hydrogen carrier in oxidation reduction reactions) 3. Serotonin: has multiple physiologic roles including pain perception, regulation of sleep, appetite, temperature, blood pressure, cognitive functions, and mood (causes a feeling of well-being, thereby functioning as antidepressants). The largest amount by far is found in the intestinal mucosa. Smaller amounts occur in the CNS, where it functions as a neurotransmitter , and in platelets. Phenylalanine Tyrosine synthesis Phenylalanine hydroxylase Phenylalanine Tyrosine Deficiency of phenylalanine hydroxylase causes Phenylketonuria (decrease tyrosine amino acid & increase phenylalanine which will be metabolized to phenylpyruvate & phenylacetate. All these metabolites increase in blood then excreted in urine giving the urine mousy odor, the patients has also mental retardation). Treatment: diet low in phenylalanine rich in tyrosine. Carbohydrates of Biological Importance Dr. Dina Sabry Professor of Medical Biochemistry & Molecular Biology  Chemical nature of carbohydrates: Carbohydrates are polyhydroxyalcohols with a functional aldehyde or keto group. Biomedical importance of Carbohydrates -Carbohydrates are the most abundant organic molecules in nature. -They have a wide range of functions, including: Providing a significant fraction of the dietary calories for most organisms. Storage form of energy in the body. Serving as cell membrane component mediate some forms of intercellular communication. Classification of Carbohydrates  MONOSACCHARIDES Monosaccharides are the simplest sugars. Monosaccharides are classified by two methods according to Number of Functional carbon atoms groups Trioses (3 carbons) Aldehyde group: Ketone group: Tetroses (4 carbons) Aldoses Ketoses Pentoses (5 carbons) Hexoses (6 carbons) I- Aldoses The mother compound of all aldoses is the aldotriose glyceraldehyde. D-sugars: the hydroxyl group of the penultimate carbon atom to the right. L- sugars: contain hydroxyl group on the left side of the penultimate carbon atom. Most of the naturally occurring monosaccharides are of the D type.  Aldoses are further subclassified according to the number of carbon atoms present into : 1.Aldotrioses (C3) 2.Aldotetroses (C4) 3. Aldopentoses (C5) 4. Aldohexoses (C6) Adotetrose Aldopentose Aldohexoses II- Ketoses The simplest ketose is the triose dihydroxyacetone. Ketoses are further subclassified according to the number of carbon atoms present into : 1.Ketotrioses (C3) e.g. dihydroxyacetone. 2.Ketotetroses (C4) e.g. D-erythrulose. 3.Ketopentoses (C5) e.g. D- ribulose. 4.Ketohexoses (C6) e.g. D- fructose. Ketotetrose Ketopentoses Ketohexose  Forms of Isomerism of Monosaccharides Isomers Compounds which have the same molecular formula = the same number and types of atoms But have different: -structural formula (connection of these atoms ) -or steric formulae.  Forms of Isomerism of Monosaccharides Stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in space. Forms of Isomerism of Monosaccharides  Forms of Isomerism of Monosaccharides 4. Aldose-Ketose Isomers (Functional Group Isomerism): -They have the same molecular formulae but differ in their functional groups. -For example: Fructose is a functional group isomer of glucose, galactose or mannose.  Important ImportantMonosaccharides Monosaccharides 1- Trioses: Glyceraldehyde 3-phosphate and dihydroxyacetonephosphate are intermediates during glucose oxidation in living cells. 2- Tetroses : Erythrose 4-phosphate is formed during glucose oxidation in living cells. 3- Pentoses : - D-ribose is a component of many nucleosides and nucleotides and ribonucleic acids (RNA). - 2-deoxyribose is a component of deoxyribonucleic acid (DNA).  Important Monosaccharides 4- Hexoses : - D-glucose ( grape sugar) is the main sugar present in blood and is present in all animal and plant cells, honey and fruits. - It enters in the formation of many disaccharides and polysaccharides. - D-fructose (fruit sugar) is present in honey, fruits and semen. - It is a component of sucrose and inulin. - D-galactose is a component of lactose which is present in milk. - It is also found in glycosaminoglycans (GAGS), glycolipids and glycoproteins.  Monosaccharide Derivatives 1- Sugar acids: Uronic acids : The primary alcohol group of monosaccharides is oxidized to form the corresponding uronic acid. - Glucose is oxidized to form glucuronic acid (GlcUA). -Galactose is oxidised to form galacturonic acid (GalUA).  Monosaccharide Derivatives 2- Sugar Alcohols: -These are sugars in which the carbonyl group is reduced to alcohol group. Sorbitol is the alcohol of glucose dulcitol is the alcohol of galactose mannitol is the alcohol of mannose.  2- Sugar Alcohols: H2 carbonyl group= functional group Corresponding alcohol Glyceraldhyde or Dihydroxyacetone H2 Glycerol Ribose H2 Ribitol H2 Glucose Sorbitol Galactose H2 Mannose Dulcitol H2 Fructose H2 Manitol Sorbitol +Manitol  Monosaccharide Derivatives -The reduction of ketones produces 2 alcohols.  Monosaccharide Derivatives Important members of sugar alcohols: a- Glycerol: It is the alcohol of glyceraldehyde or dihydroxyacetone. -It is a component of triacylglycerol and most phospholipids. b- Ribitol: It is the alcohol of ribose. It is a component of riboflavin (vitamin B2).  Monosaccharide Derivatives 3- Deoxysugars : – OH group is replaced by a hydrogen atom 2-deoxy β-D-ribofuranose: It is present in the structure of DNA.  Monosaccharide Derivatives 4-Aminosugars Amino group (NH2) replaces the –OH group on the second carbon e.g. glucosamine (GluN), galactosamine (GlaN) and mannosamine (ManN). Aminosugars are important constituents of glycosaminoglycans (GAGs ) and some types of glycolipids and glycoproteins. Several antibiotics contain aminosugars which are important for their antibiotic activity  Monosaccharide Derivatives 6- Ester formation The hydroxyl groups of monosaccharides can form esters with acids A- Phosphate esters: Glucose 1-P and glucose 6-P  7-Glycosides products of condensation of the anomeric carbon of the sugar with: Non-Carbohydrate compound Another sugar (Glycon): e.g. (Aglycon): disaccharides polysaccharides. alcohols, phenols or nitrogenous bases.. Monosaccharide Derivatives  Disaccharides Disaccharides consist of two monosaccharides united together by glycosidic linkage.  Disaccharides Reducing Nonreducing -Maltose -Isomaltose Sucrose -Lactosae II- DISACCHARIDES Disaccharides consist of two monosaccharides united together by O-glycosidic linkage. Non-Reducing Reducing Disaccharides Disaccharides Because they has free Carbonyl group Because they has no free Carbonyl at Second sugar (α or β) group at Second sugar as both involved in the linkage. Maltose Sucrose Isomaltose Lactose Cellobiose  Disaccharides Name of Chemical nature Type of linkage Hydrolytic products disaccharide Maltose Reducing disacchrides, α1,4 glucosidic link 2 glucose CHO Isomaltose Reducing disacchrides, α1,6 glucosidic link 2 glucose CHO Lactose Reducing disacchrides, β1,4 galactisidic Galactose + Glucose CHO link Cellobiose Reducing disacchrides, β1,4 glucosidic link 2 glucose units CHO Sucrose Non Reducing α1,2 glucosidic link Glucose + Fructose disacchrides, CHO OR β2,1fructosidic link  Disaccharides If the glycosidic linkage involves the carbonyl group of one of its two sugars (e.g. lactose and maltose ) the resulting disaccharide is reducing. Free anomeric carbon  Disaccharides If the glycosidic linkage involves the carbonyl group of both sugars (e.g. sucrose) the resulting disaccharide is non-reducing.  A. Reducing disaccharides Maltose Isomaltose Lactose Galactose+ Glucose + Glucose Glucose Free anomeric carbon in the second sugar unit 1. Maltose (Malt sugar) Disaccharides Formed of two molecules of D-glucopyranose united by 1, 4- glucosidic linkage 1. Maltose ( Malt sugar) Disaccharides Starch amylase Maltose Maltase OR acid D-glucose 2- Isomaltose Disaccharides It is formed of two molecules of D-glucopyranose. United by 𝛼 1, 6-glucosidic linkage. 2- Isomaltose Disaccharides It is one of the hydrolysis products of starch and glycogen by amylase It represents the branching point of the molecule. 3. Lactose ( milk sugar) It is formed of β-D-galactopyranose and D-glucopyranose united by β1,4-galactosidic linkage. It is hydrolyzed by lactase enzyme or by acids into D-glucose and D-galactose. B.Nonreducing disaccharide Sucrose. Sucrose (Cane sugar) (Table sugar) It is present in plants as sugar cane and beets. Sucrose (Cane sugar) (Table sugar) -It is formed of β-D-fructofuranose and 𝛼 -D-glucopyranose united by :- -𝛼 1,2-glucosidic linkage or - Β 2,1-fructosidic linkage.  On biochemical bases explain, sucrose is non-reducing? Both anomeric carbons are involved in the linkage.  Polysaccharides Polysaccharides are composed of >10 monosaccharide units linked by glycosidic bonds.  Polysaccharides  Why polysaccharides are non reducing ? Since the condensation of the monosaccharide units involves the carbonyl groups of the sugars, leaving only one free carbonyl group at the end of a big molecule, polysaccharides are nonreducing.  Polysaccharides A.Homopolysaccharides B.Heteropolysaccharides  A.Homopolysaccharides These are polysaccharides which are entirely made up of only one type of monosaccharide units. They are given names according to the nature of their building units as follows: 1. Glucans: formed of D-glucose units and include starch, dextrins, glycogen and cellulose. 2. Fructans: formed of D-fructose units e.g. inulin present in plants  A.Homopolysaccharides Glucans D-Glucose Units 1.Starch 4.Cellulose 2.Dextrin 3.Glycogen  A.Homopolysaccharides 1. Starch Starch is the chief storage form of carbohydrates in chlorophyll- containing plants. It is present in large amounts in: - cereals (rice and wheat) -tubers (potatoes and sweet potatoes) -legumes (beans).  A.Homopolysaccharides Starch Granules Amylose (15- 20%) Amylopectin(80-85%) Inner part Outer part  A.Homopolysaccharides 2. Dextrin They are produced during the hydrolysis of starch by salivary or pancreatic amylase.  A.Homopolysaccharides 3. Glycogen Glycogen is the storage form carbohydrates in animals (animal starch). It is mainly present in skeletal muscles and liver.  A.Homopolysaccharides 4. Cellulose Cellulose forms the principal part of the cell wall of plants. It is formed of a long non-branched chain of β-D-glucopyranose units. Connected together by β1,4-glucosidic linkage. Why is the presence of cellulose in diet is important ? Bulk of food Intestinal contractions Prevents constipation.  Glucans: 4- Cellulose: Cellulose forms the principal part of the cell wall of plants. It is formed as bundle of fibers in nature. It is formed of a long non-branched chain of glucose units connected together by β1,4-glucosidic linkage. Cellulose is insoluble in water. It is non-hydrolysable by amylase that present in human body because it contains a β1,4-glucosidic linkage. It was hydrolysed by cellulase enzyme. The presence of cellulose in diet is important as it increases the bulk of food, which stimulates intestinal contractions and prevents constipation. (on biochemical basis explain: Cellulose used in treatment of constipation)  B. Heteropolysaccharides These are polysaccharides which are formed of more than one type of monosaccharide unit. They include glycosaminoglycans (GAGs) formly called mucopolysaccharides.  B. Heteropolysaccharides Glycosaminoglycans (GAGs) -Unbranched, -Long chains (usually >50 sugar units) heteropolysaccharides -Composed of repeating disaccharide units, usually made up of an amino sugar and a uronic acid.  B. Heteropolysaccharides Glycosaminoglycans GAGs Sulfate free GAGS Sulfate containing GAGS  B. Heteropolysaccharides I- Sulfate free glycosaminoglycans: e.g. hyaluronic Acid. II-Sulfate containing glycosaminoglycans: - chondroitin sulphate -keratan sulphate -dermatan sulphate -heparin and heparan sulphate.  B. Heteropolysaccharides GAGs and proteoglycans Most of the GAGs are covalently conjugated to a protein core, the product of which is termed proteoglycans. They are formed mainly of carbohydrates (95%) and only (5%) proteins. Site: GAGs are present mainly in the extracellular matrix (ECM) or ground substance in association with other extracellular proteins  GAGs Name Chemical nature Hyaluronic acid Sulfate free GAGs-heteropolysaccharides- CHO Chondrotein sulphate Sulfate containing GAGs-heteropolysaccharides- CHO Dermatan sulphate Sulfate containing GAGs-heteropolysaccharides- CHO Keratan sulphate Sulfate containing GAGs-heteropolysaccharides- CHO Heparin Sulfate containing GAGs-heteropolysaccharides- CHO Heparan sulphate Sulfate containing GAGs-heteropolysaccharides- CHO  Importance of GAGs: 1- They are important components of the extracellular matrix. 2- GAGs present are producing its gel like matrix to act as lubricant and shock absorbant. 3- Aggrecan in cartilage contributes to its compressibility. It has a very complex structure containing many types of GAGs (hyaluronic, chondroitin sulfate and keratan sulfate).  Importance of GAGs: 4- Hyaluronic acid is essential for wound repair. 5-Keratan sulfate proteoglycans are important for maintenance of corneal transparency. 6- Dermatan sulfate proteoglycans are important for maintenance of shape of the sclera of the eye. 7- Heparan sulfate proteoglycans play an important role in cell-cell interactions and in cell membrane receptors.  Importance of GAGs: 8- Heparin is a well known anticoagulant i.e. prevents thrombus formation. It activates antithrombin & inactivates coagulation factors IX, XI. Heparin also binds to the lipoprotein lipase and releases it from the capillary wall to blood, this enzyme helps in removal and clearance of blood lipids (so heparin is known as clearing factor).  B. Heteropolysaccharides Functions of GAGs and proteoglycans 1- GAGs important constituents of extracellular matrix. The proteoglycans interact with a variety of proteins in the matrix, such as collagen and elastin, determining the structural organization of the matrix.  Functions of GAGs and proteoglycans 2- They are highly polar and attract water molecules, forming hydrated gel. This gel: Provides flexible mechanical support for the ECM. Acts as a lubricant in synovial fluid.  Functions of GAGs and proteoglycans This gel: Is compressible: when a GAG solution is compressed, water is squeezed out and GAGs occupy a smaller volume. When released return to its volume. -This gives GAGs the shock absorbing properties and explains their role as shock absorbents in joints and making the eyeball resilient (flexible).  Functions of GAGs and proteoglycans 4-Hyaluronic acid : Present in high concentrations in embryonic tissues, plays an important role in cell migration and morphogenesis. Wound healing (repair). Hyaluronic acid D-glucuronic acid and N-acetyl-D- glucosamine. It is present in synovial fluid, has a high molecular weight and function as a lubricant and shock absorbent. As the age advances hyaluronic acid is replaced by dermatan sulfate in synovial fluid. Dermatan sulfate is not a good lubricant; hence age related joint pains that develop in old people.  Functions of GAGs and proteoglycans 5-Heparin Anticoagulant (prevents thrombus formation), it acts by binding with factor IX and XI. Also, it produces activation of antithrombin.  Functions of GAGs and proteoglycans Heparin helps in removal and clearance of blood lipids. It binds specifically to lipoprotein lipase enzyme and increases its release form the capillary wall to the plasma Removal of blood lipids  Functions of GAGs and proteoglycans 6- Keratan sulfate proteoglycan is important for transparency of the cornea. 7- Heparan sulfate proteoglycans are associated mainly with plasma membrane of cells and play an important role in cell membrane receptors and cell-cell interactions.  Functions of GAGs and proteoglycans 8- Aggrecan: It is the major proteoglycan present in cartilage. It has a very complex structure containing: several types of GAGs: -hyaluronic acid -chondroitin sulfate -keratan sulfate attached to a protein.  Functions of GAGs and proteoglycans GAGs side chains bind to collagen fibrils. GAGs side chains are acidic and therefore negatively charged, they attract water in between causing the molecule to form a Gel. It plays an important role in compressibility of cartilage. Code of the module: BIO 1104 lecture no: 4 lecture topic: Lipid chemistry Fall 2024-25 Presented by : Medical Biochemistry and molecular biology Department Coordinator : Dr Dina Mekawy Lipid chemistry Medical Biochemistry and Molecular Biology department Prof. Dr. Dina Sabry Ass. Prof. Dalia Badran Ass. Prof. Shimaa Mohsen Ass. Prof. Noura Sliem Lecturer Dr Dina Mikawy  LOs Define Lipids Describe the types of fatty acids Explain properties of Lipids Classify Lipids and enumerate their functions  LIPID OF BIOLOGICAL IMPORTANCE Definition: Lipids are organic compounds, which have the following common properties: 1- They are esters of fatty acids or substances associated with them in nature. 2- Most of them are insoluble in water but soluble in fat solvents (non polar solvents) e.g.: benzene, chloroform, acetone and ether.  Classification: Lipids are classified into three main groups: Simple Lipids Derived Lipids Compound lipids Esters of fatty Esters of fatty They are acids with various acids with various produced by types of alcohols types of alcohols hydrolysis of in addition to a the first two prosthetic group groups  Fatty Acids Fatty acids that occur in natural fats are usually monocarboxylic acids containing an even number of carbon atoms. The chain may be saturated (containing no double bonds) or unsaturated (containing one or more double bonds).  I- Saturated Fatty Acids (SFA): They contain no double bonds. They are either short chain (from C2 to C10) or long chain (from C12 to C24) All have the following general formula: CH₃- (CH₂)n- COOH Where n = Total number of carbons – 2  I- Saturated Fatty Acids (SFA): A- Short chain fatty acids include: Acetic acid (C2) Butyric acid (C4) B- Long chain fatty acid, the most common include mainly: Palmitic acid (C16) Stearic acid (C18) II- Unsaturated Fatty Acids (USFA): They contain one or more double bonds. Unsaturated fatty acids are classified according to the number of double bonds in their chains into two main groups: 1- Monoethenoid: one double bond: Palmitoleic acid Oleic acid II- Unsaturated Fatty Acids (USFA): Polyethenoid They have more than one double bond in their structure, termed polyunsaturated fatty acids (PUFA). Linoleic acid Linolenic acid Arachidonic acid Unsaturated fatty acids may occur in two structural configurations – cis and trans isomers Cis: The hydrogen atoms attached to the carbon double bond are on the same side Trans: The hydrogen atoms attached to the carbon double bond are on different sides Cis fatty acids are commonly occur in nature and are responsible for cell membrane fluidity. Trans fatty acids do not commonly occur in nature and are typically produced by an industrial process called hydrogenation  Nutritional classification of fatty acids: a)- Essential Fatty Acids: They are not synthesized in our body, so it is essential to take them in diet. They include Linolenic, Linoleic and arachidonic acids. Deficiency of essential fatty acids produces: Fatty liver and sterility in adults. Impaired growth, mental retardation and dermatitis in infants. Sources of PUFA: They are present mainly in fish and vegetable oils e.g.: maize, cottonseed, linseed, olive, sun flower and soya been oils. b)- Non Essential Fatty Acids: They include all other fatty acids because they are formed in our body in good amounts mainly from carbohydrates. It is not essential to take them in diets.  Physical Properties of Fatty Acids 1. Solubility in water: fatty acids are insoluble in water but soluble in fat solvents. 2. Physical state at room temperature: The saturated fatty acids are solid at room temperature Unsaturated long chain fatty acids are liquids due to the presence of double bonds.  I- Simple Lipids They are esters of fatty acids with alcohols, according to the types of alcohols there are two main sub-groups: 1. Neutral fats or Triacylglycerol (TAG): They are esters of three fatty acids with glycerol. It is the stored simple lipid in adipose tissue 2. Waxes: They are esters of one fatty acid with long chain monohydroxyalcohol higher than glycerol (e.g: Bee wax). I- Simple Lipids TAG esterified with PUFA at C3 and mono-unsaturated FA at C2 and saturated FA at C1 of glycerol TAG was esterified with Saturated fatty acids at C1, C2 and C3 of glycerol  Complex lipids (Compound or Conjugated lipids) Phospholipids: Lipids Glycolipids containing, in addition (glycosphingoLipids:) to fatty acids and an containing a fatty acid, alcohol, a phosphoric sphingosine, and acid residue. carbohydrate. Proteolipids: fatty acid, alcohol and protein  II- Conjugated Lipids (Compound Lipids) They contain fatty acids, alcohols and other (prosthetic) groups. According to the type of prosthetic group they are classified into: 1- Phospholipids: Containing phosphate radicals. 2- Glycolipids: Containing carbohydrate radicals. 3- Proteolipids: Containing protein radicals and they are water insoluble.  Phospholipids: were classified according to type of alcohol A- Glycerophospholipids (Alcohol is glycerol): B- Sphingomyline 1- Phosphatidic acid (Alcohol is sphingol) 2- Phosphatidyl serine 3- Phosphatidyl ehanolamine 4- Phosphatidyl choline 5- Phosphatidyl inositol A- Glycerophopholipids  Importance and functions of phospholipids: 1- Amphipathic molecules that contain non- polar groups (fatty acid side chains) and polar groups (phosphate, serine, ethanolamine, glycerol, choline and inositol) they form micelles in water. 2- They are good emulsifying factors, important for digestion and absorption of dietary fats.  Importance and functions of phospholipids: 3-They are good hydrotropic substances, they prevent deposition of cholesterol as cholesterol stones (biliary calculi). 4- They are important constituents of lipid bilayer in cell membranes. 5- They are important constituents of plasma lipoproteins.  Importance and functions of phospholipids: 6- Lung surfactant is formed mainly of dipalmitoyl-lecithin, the lack of which is responsible for respiratory distress syndrome in premature infants. 7- They provide arachidonic acid for synthesis of eicosanoids. 8- They are essential for blood clotting, as they provide the platelet activating factor (PAF)  B- Sphingomyelin: This type is present in cell membranes specially of the lungs and brain mainly in the myelin sheath. It contains sphingosine (sphingol) which is 18 carbon amino alcohol fatty acids are linked to sphingosine to form ceramide, which is connected to phoshocholine to form sphingomyelin.  Sphingosine containing lipids Phospho FA choline Sphingosine Ceramide Sphingomyline Glycolipids types are ganglosides, cerebrosides and sulpholipids  Importance of glycolipids: They are found mainly in the myelin sheath and cell membrane of RBCs. They act as cell membrane receptors for hormones and external stimuli also they provide recognition properties.  III- Derived Lipids They are produced by hydrolysis of either simple or conjugated lipids. They include the following : 1. Fatty acids. 2. Alcohols. 3. Steroids. 4. Carotenoids. 5. Fat soluble vitamins: as vitamins A, D, E & K. Steroids  Classification of steroids Steroid hormones. Sterols. Bile acids.  Cholesterol It is the most important animal sterol. It is present either free (non esterified) or esterified with fatty acid to form cholesteryl ester. Free cholesterol contains 27 carbon atoms. Distribution of cholesterol: It is widely distributed in all tissues but higher concentrations are present in brain, nervous tissue, liver, adrenals, gonads, skin and adipose tissue.  Cholesterol Precursor of cholesterol: It is formed from active acetate (acetyl-CoA). Blood level of cholesterol: Normally it is present in the plasma in concentrations ranging from 100 to 200 mg/dL (30% as free cholesterol and 70% as cholesteryl esters) Hazards of hyperchosterolemia: Increased plasma level of cholesterol predisposes to atherosclerosis and coronary heart diseases.  Importance and derivatives of cholesterol: It is important constituent of cell membranes. It is converted into bile acids and bile salts in the liver. It is the precursor of all steroid hormones. It can be oxidized in the liver into 7-dehydro cholesterol which can be converted under the skin into vitamin D3 by ultra violet  Bile Acids 1. Primary bile acids: they are formed in the liver from cholesterol 2- Secondary bile acids: they are formed of primary bile acid in large intestine.  Bile salts: They are formed by conjugation of cholic acid with glycine (80%) or taurine (20%) then are excreted by liver in bile secretions as sodium glycocholate or sodium taurocholate. Bile salts pass to the intestine where they are reabsorbed and return back to the liver to be excreted again in bile (entero-hepatic circulation). Enterohepatic circulation Enterohepatic circulation  Importance of bile salts: Conversion of cholesterol to bile salt is an important mechanism for removal of excess cholesterol from blood. They are good emulsifying factors important for digestion and absorption of fats. They prevent precipitation of cholesterol in the bile as cholesterol stones. They stimulate liver cells to secrete more bile (choleretic effect).