Dentistry Biochemistry I PDF

BIOCHEMISTRY I For Dental Students  Protein chemistry Definitions: - Proteins: are organic compounds with a high molecular weight formed of subunits called amino acids linked together by peptide bond. The term protein is applied to describe molecules greater than 50 amino acids...

BIOCHEMISTRY I For Dental Students  Protein chemistry Definitions: - Proteins: are organic compounds with a high molecular weight formed of subunits called amino acids linked together by peptide bond. The term protein is applied to describe molecules greater than 50 amino acids. The word protein is derived from Greek word, “proteios” which means primary. As the name shows, the proteins are of paramount importance for biological systems. Out of the total dry body weight, 3/4ths are made up of proteins. Proteins are used for body building; all the major structural and functional aspects of the body are carried out by protein molecules. Abnormality in protein structure will lead to molecular diseases with profound alterations in metabolic functions. Proteins contain Carbon, Hydrogen, Oxygen and Nitrogen as the major components Nitrogen is characteristic of proteins. On an average, the nitrogen content of ordinary proteins is 16% by weight. Peptides: is applied to describe molecules less than 50 amino acids. Amino acids: structural unite of protein and peptide Amino Acids - They are the structural units of proteins & peptides and are obtained from them by hydrolysis. The general formula of any amino acid is as follows: 1 - Although about 300 amino acids exist in nature, only 20 of them present in protein structure. - All these amino acids are alpha-amino acids. This means that the amino group is attached to the α-carbon atom (next to the carboxyl group). - All amino acids present in mammals are L-amino acids (amino group is on the left side configuration). - D-amino acids are found in the cell walls of bacteria. - Each amino acid (except proline and hydroxyproline) has a carboxyl group (COOH), an amino group (NH2) and a characteristic side chain (R). - In α-amino acids, both-COOH and –NH2 groups are attached to the same (α -) carbon atom. 2 - All amino acids (except glycine) are optically active, i.e., can rotate plane polarized light. - This is because the 4 groups attached to α -carbon are different. In glycine, the α -carbon is attached to 2 hydrogen atoms, therefore, is optically inactive. Classification of Amino Acids Amino acids can be classified by one of three methods: 1. Chemical classification: Based upon the number of amino groups or carboxyl groups in the amino acid: - Neutral amino acids (mono-amino, mono-carboxylic). - Acidic amino acids (mono-amino, dicarboxylic). - Basic amino acids (diamino, mono-carboxylic). 2. Biological classification: Based upon whether the amino acids can be synthesized in human body or not: - Indispensable or essential amino acids: Not synthesized in the body and must be supplied in the diet. - Dispensable or non-essential amino acids: Can be synthesized in the body and hence is not essential to be present in diet. 3 3. Metabolic Classification: Based upon the fate of amino acid inside the body: - Glucogenic amino acids, that can be converted to glucose. - Ketogenic amino acids, that can be converted to ketone bodies. - Mixed amino acids, i.e., can be converted to both glucose and ketone bodies. 1.Chemical classification Based upon the number of amino groups or carboxyl groups in the amino acid: Amino acids can be classified into: Neutral amino acids - They contain one amino group and one carboxyl group. They have 5 types: 1-Aliphatic amino acids: e.g., glycine, alanine, valine, leucine and isoleucine 2-Hydroxy amino acids: contain –OH group in their side chain e.g., serine, threonine, tyrosine, hydroxyproline and hydroxylysine. 3-Aromatic amino acids: e.g., phenylalanine, tyrosine and tryptophan. 4  4-Sulfur-containing amino acids: Cysteine, cystine & methionine 5. Heterocyclic amino acids: e.g., Histidine, Tryptophan Proline and hydroxyproline. N.B Proline gives hydroxyproline that is essential for collagen Proline and hydroxyproline do not have a free -NH2 group but only the imino group.Therefore, they are called as imino acids. Acidic amino acids - They contain 2 carboxyl groups and one amino group, e.g., glutamic acid and asparatic acid. Basic amino acids - They contain 2 amino groups and one carboxyl group, e.g., Ornithine, Citrulline, Arginine, Lysine and Hydroxy lysine. 5  2.Metabolic classification: Amino acids may be classified into: 1- Glucogenic amino acids, i.e., those which can be converted into glucose, 2- Ketogenic amino acids, i.e., those which can be converted into ketone bodies 3- Mixed amino acids, i.e., those which can be converted into both glucose and ketone bodies. Ketogenic Ketogenic & glucogenic Glucogenic Lysine Leucine Isoleucine Rest of amino acids Tyrosine Tryptophan Phenyl alanine 3-Biological or Nutritional Classification: - Some amino acids cannot be synthesized inside the body. If these amino acids are not taken in diet, they will affect the growth and the health. Thus, amino acids may be classified into: 1- Essential amino acids: (Indispensable amino acids): - These are amino acids that cannot be synthesized in the human body and should be taken in the diet, otherwise their deficiency will lead to a nutrition deficiency disease that affect both growth and health. 6 - Arginine and histidine are semi-essential, i.e., they are mainly required in growing children, pregnant and lactating women and convalescent patients. The main source for these amino acids are animal proteins (milk, egg, meat, liver, fish, chicken). - They are as follows (VITTAL LyMPH): Valine Isoleucine Threonine Tryptophan Arginine Leucine Lysine Methionine Phenylalanine Histidine 2- Non essential amino acids: (Dispensable amino acids): The rest of amino acids can be synthesized inside the human body and their deficiency in diet does not affect the growth or the health. Isoelectric Point: - Amino acids can exist as ampholytes or zwitterions (German word "zwitter" = hybrid) in solution, depending on the pH of the medium. The pH at which the molecule carries no net charge is known as isoelectric point or isoelectric pH (pI). In acidic solution, they are cationic in form and in alkaline solution they behave as anions. 7  - At isoelectric point, the amino acid will carry no net charge; all the groups are ionized but the charges will cancel each other. Therefore at iso-electric point, there is no mobility in an electrical field. Solubility and buffering capacity will be minimum at isoelectric pH. Peptides - Peptides are compounds, formed of less than 50 amino acids linked together by peptide bonds, Example: Glutathione: - It is a tripeptide formed of 3 amino acids:γ- glutamic acid, cysteine and glycine. Functions of glutathione: 1) It has a role in absorption of amino acids. 2) It activates many enzymes. 3) It inactivates insulin hormone, by breaking its disulfide bonds. 4) It protects the cell membrane from damage, e.g., prevents hemolysis of erythrocytes. 5) It prevents rancidity of fat as it acts as antioxidant. Bonds Responsible For Protein Structure Protein structures are generally stabilized by 2 classes of strong bonds (peptide and disulphide) and 3 classes of weak bonds (hydrogen, hydrophobic and electrostatic bonds). I- Strong bonds: 1. Peptide bonds: 8  Peptide bonds are formed by a reaction between amino group of one amino acid and a carboxylic group of the next one. 2. Disulfide bonds: The disulfide bond is formed between 2 cysteine residues. It connects 2 polypeptide chains together. II- Weak Bonds: 1. Hydrogen bonds: Hydrogen bonds are formed between the hydrogen atom of –NH of one peptide chain and oxygen of CO- the adjacent peptide chain. 2- Hydrophobic bonds The non-polar side chains of neutral amino acids form it. 3- Electrostatic bonds 9 These are salt bonds formed between oppositely charged groups in the side chains of amino acids e.g., ɛ-amino group of lysine and the β-carboxyl group of aspartate. Structure of Proteins There are 4 levels or orders of organization of the structure protein molecule: primary, secondary, tertiary and quaternary structures. This complication gives the molecule its functional domain to explain its structure-function requirements that if changes due to mutation will give non-functional protein and, therefore, a disease. 1. Primary structure: Primary structure is the number, type and linear sequence of amino acids held together by peptide bonds in its peptide chain. The peptide bonds (primary bond) are responsible for the primary structure. done by the genetic code in specific gene. Substitution(replacement) of a single amino acid for another in the linear sequence of amino acids in the polypeptide chain, may reduce or abolish biologic activity of the protein. An example is Sickle Cell Anemia where the normal glutamic acid at position 6 of the β-chains is replaced by a valine. 10 2. Secondary structure: - It is the fine folding of polypeptide chain into specific regular coiled structure. It is due to the interaction of amino acids located very close to each other. They are held together by hydrogen, ionic and disulfide bonds. 3. Tertiary structure: - It is the final three-dimensional form due to the more complicated course folding and super-folding of the polypeptide chain in its secondary level into globular or fibrous form of different size. It is due to interaction of amino acids located far apart. It is the biologically active conformation of the polypeptide and the protein in this conformation is called native protein. Therefore, it is the most liable to denaturation. The tertiary structure is maintained by hydrophobic bonds, electrostatic bonds and van der Waals forces. 4. Quaternary structures: - Certain polypeptides will aggregate to form one functional protein. This is referred to as the quaternary structure. 11 - The protein will lose its function when the subunits are dissociated. - If there are two subunits the protein is called dimeric, three subunits it is called trimeric and if formed of several subunits, so it is called multimeric. - The bonds responsible for the quaternary structure are as those in the tertiary structure. It is the most liable to denaturation. - Examples are globin of hemoglobin and lactate dehydrogenase each is composed of 4 polypeptide chains. Misfolded proteins result when a protein follows the wrong folding pathway. Accumulation of misfolded proteins can cause disorders, known as amyloid diseases. Unfortunately, some of them are very common. The most prevalent one is Alzheimer's disease 12 Denaturation: Brief heating, urea, salicylate, X-ray, ultraviolet rays, high-pressure, vigorous shaking and other physico-chemical agents produce non-specific alterations in secondary, tertiary and quaternary structures of protein molecules. This is called denaturation. Significance and Applications: 1. Denatured proteins e.g., cooked meat (since cooking leads to denaturation of proteins), cooked foods are more easily digested. 13  2. Great care to avoid denaturation must be carried out for blood samples used for determination of enzymatic, hormonal or protein contents. If denaturation occurs false results will be obtained. 3. Detection of albumin in urine by heat coagulation test is based on denaturation by heat. Classification of Proteins Classification based on Nutritional Value: 1- Proteins of high biological value: - These are all proteins of animal origin (with a few exceptions) and some proteins of plant origin, that contain all the 10 essential amino acids in well balanced amounts and are easily digestible. - Examples of animal proteins include; milks and its products, egg, liver, fishes, red and white meats. Examples of the few plant proteins of high biological value are lentils and broad beans. 2) Proteins of low biological value: - These are proteins that is deficient in one or more of the essential amino acids or containing very little amount of one of them or are indigestible. - Most of plant protein are of low biological value and a very few animal proteins are also of low biological value such are collagen because is 14 deficient in tryptophan and cysteine and keratins because they are indigestible. - This does not imply that a person should eat only a protein of high biological value to avoid deficiency of essential amino acids, but this can be also avoided by eating two or more proteins of low biological value that complete each other’s deficiency. Classification based on the axial ratio of the protein molecule: - Studies on the shape of the protein molecule using ultramicroscope indicates that there are two types of proteins in nature: 1. Fibrous proteins: - They have an axial ratio of more than 10. Axial ratio = Length/Width of the protein molecule. They are fairly stable proteins forming fibers or sheets. They are usually insoluble and non-motile. Examples: - a. Keratin proteins in hairs, wool and skin. b. collagen c. Myosin (major protein of muscles). 2-Globular proteins: 15  -Their axial ratio is less than 10. are folded or coiled on themselves in a very compact manner. They are less stable than fibrous proteins and they are usually soluble and motile. Examples are albumin, globulin & myoglobin. Classification based on the composition of the Protein: 1-Simple Proteins These are proteins which on hydrolysis produce amino acids only. Simple proteins are subdivided into: - Albumins - Globulins - Histones - Scleroproteins or Albuminoids are sub- subdivided into: 1-Keratins 2-Collagens 3-Elastins 4-Reticulins 1-Keratins: -Locations: hair, nails, and superficial layer of the skin. Structure: -it is fibrous protein. 16 -rich in cysteine & cystine So the sulfur content in keratin is high. The peptide chains cross –linked by "S-S" bonds. 2-Collagens: -Locations: White fibers of connective tissues present in skin, bones,teeth,tendons,and blood vessels. -about 30% of total body protein. -The 3 amino acids distributed “Glycine-X-Y” & so on. Usually X-Y is proline & hydroxyproline - Collagen rich in Glycine. , when boiling for a long time change to "gelatin". NB: Gelatins is the product of denaturation of collagen & Has the properties of gel formation on cooling. -Gelatin is good to patient as it's appetizer & easily digested. 3-Elastins: -Locations: yellow fibers of connective tissues present in lungs, uterine wall, tendons, big arteries. -It's "Rubber like". 4-Reticulins: Location: spleen, liver & lymph gland. 2-Conjugated proteins Definition: They are proteins that on hydrolysis, give amino acids and another group and they include: 1. Phosphoproteins Definition: These are proteins conjugated with phosphate. 17 Phosphate is attached to OH group of serine or threonine present in protein. e.g., Casein( milk protein). 2. Lipoproteins Definition: These are proteins conjugated with lipids converting them into water soluble substances. e.g., Plasma lipoproteins: see lipid chemistry. 3. Glycoproteins Definition: These are proteins conjugated with carbohydrates e.g., Mucous 4. Metalloproteins Definition: These are proteins conjugated with metals e.g., Transferrin: the iron carrier protein in the blood. Chromoproteins Definition: These are proteins conjugated with colored pigmen e.g., Hemoglobin which is red in color. 6. Nucleoprotein Definition: These are proteins (histones) conjugated with nucleic acids (DNA or RNA) e.g., Chromosomes: These are proteins conjugated with DNA. Classification Based on Functions : 1-Catalytic proteins, e.g., enzymes 2-Structural proteins, e.g., collagen, elastin& keratin 3-Contractile proteins, e.g., myosin, actin& flagellar proteins 4-Transport proteins, e.g., hemoglobin, albumin & transferrin 5-Regulatory proteins or hormones, e.g., insulin& growth hormone 18 6-Genetic proteins, e.g., histones 7-Protective proteins, e.g., immunoglobulins& clotting factor ===================================== 19 20  Carbohydrates chemistry Definition: Carbohydrates are the most abundant organic molecules in nature. They have a wide range of functions. The empiric formula for many of the simpler carbohydrates is (CH2O)n , where n ≥3, hence the name “hydrate of carbon.” New definition : Carbohydrates are aldehyde (CHO) or ketone (C=O) derivatives of polyhydric alcohols (have more than one OH group). Importance of carbohydrates: 1) Source of energy (Brain cells and RBCs are almost wholly dependent on carbohydrates as the energy source). 2) In animal and plant cells (Glycoproteins and glycolipids are components of cell membranes and receptors that mediate some forms of intercellular communication). 3) Part of nucleic acids. 4) Structural unit of: Cellulose of plants, exoskeleton of insects, mucopolysaccharides as ground substance. 21  Classification of carbohydrates: - According to the number of sugar units in the molecule there are: 1. Monosaccharides (simple sugars): They contain one sugar unit, i.e., and the simplest form of sugars. –glucose 2. Disaccharides: They contain 2 sugar units ---sucrose 3. Oligosaccharides: They contain 3 – 10 monosaccharide units per molecule and give monosaccharides on hydrolysis. 4. Polysaccharides: They contain more than 10 monosaccharide units per molecule and give monosaccharides on hydrolysis---starch. ----------------------------------------------------------------------------------------------------------------- Monosaccharides - They are classified according to the number of carbon atoms into groups. Each of these groups is subdivided according to the type of functional chemical group into: - Aldoses (sugars containing aldehyde group) - Ketoses (sugars containing ketone group). 1-Trioses: are monosaccharides containing 4 carbon atoms: A- Aldotetroses: B- Ketotriose: e.g., 22  CH2OH CH3 C = O C = O CH2OH CH3 Dihydroxyacetone, the hydroxylated form of Acetone 2- Tetroses: are monosaccharides containing 4 carbon atoms: A- Aldotetroses: - D- and L-isomers are mirror images to each other that is only recognizable when there are more than one asymmetric carbon atom CHO CHO CHO CHO H C OH HO C H HO C H H C OH H C OH HO C H H C OH HO C H CH2OH CH2OH CH2OH CH2OH D-Erythrose L-Erythrose D-Threose L-Threose B-Ketotetroses: CH2OH CH2OH C=O C=O H C OH HO C H CH2OH CH2OH D-Erythrulose L-Erythrulose 3- Pentoses: they contain 5 carbon atoms. -Ribose is the most important pentose because it enters in the structure of DNA and RNA and important free nucleotides such as ATP and coenzymes NAD ,FAD & NADP- A- Aldopentoses: CHO CHO CHO CHO CHO CHO H C OH HO C H HO C H H C OH H C OH HO C H H C OH HO C H H C OH HO C H HO C H H C OH H C OH HO C H H C OH HO C H H C OH HO C H CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH D-Ribose L-Ribose D-Arabinose L-Arabinose D-Xylose L-Xylose B- Ketopentose: CH2OH CH2OH CH2OH CH2OH C=O C=O C=O C=O H C OH HO C H HO C H H C OH H C OH HO C H H C OH HO C H CH2OH CH2OH CH2OH CH2OH D-Ribulose L-Ribulose D-Xylulose L-Xylulose 23 4- Hexoses: are monosaccharides containing 6 carbon atoms. They are the most important monosaccharides particularly glucose. A- Aldohexoses: Glucose: -Is called grape sugar, blood sugar or Dextrose because it is dextrorotatory. -It is fermentable& reducing -It is produced by hydrolysis of starch, glycogen, sucrose, maltose and lactose. CHO CHO CHO CHO CHO CHO H C OH HO C H HO C H H C OH H C OH HO C H HO C H H C OH HO C H H C OH HO C H H C OH H C OH HO C H H C OH HO C H HO C H H C OH H C OH HO C H H C OH HO C H H C OH HO C H CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH D-Glucose L-Glucose D-Mannose L-Mannose D-Galactose L-Galactose They are epimers to each other B- Ketohexoses: Fructose: (or levulose) because is levorotatory and is the sweetest sugar known. It is the main sugar in bee's honey and fruits. High-fructose corn syrup: High-fructose corn syrups (HFCSs) are prepared through enzymatic processing to convert glucose into fructose. Pure corn syrup (100% glucose) is then added to fructose to produce a desired sweetness. HFCS 55 (containing 55% fructose and 42% glucose) is commonly used as a substitute for sucrose in beverages, including soft drinks, with HFCS 42 used in processed foods. Most studies have shown no significant difference between 24 sucrose and HFCS meals in either postprandial glucose or insulin responses. (Note: The rise in the use of HFCS parallels the rise in obesity, but a causal relationship has not been demonstrated. CH2OH CH2OH C=O C=O HO C H H C OH H C OH HO C H H C OH HO C H CH2OH CH2OH D-Fructose L-Fructose Asymmetric carbon atom - Asymmetric carbon atom (chiral carbon) is the carbon atom attached to which 4 different groups or atoms. - Importance of asymmetric carbon atom: 1. It makes the compound optically active 2. Isomerism is created around it. 25  Optical activity Definition: It is the ability of the sugar to rotate the plane polarized light. The sugar that rotates the light to the right is called dextrorotatory (d or +) such as glucose, and that rotating light to the left is called levorotatory (l or -) such as fructose Isomerism - Isomers are substances which have the same molecular formula but differ in distribution of their atoms into groups or distribution of these groups and atoms in the space around carbon atoms. Notes: 1- D and L isomerism (enantiomers): D form has the OH group to the right of the sub-terminal carbon atom whereas, it is on the left in L form. This difference makes the two forms (D and L) mirror image to each Metabolizable sugars in human body are D-forms only. Examples are D-glucose and L-glucose or D-mannose and L-mannose. - Glyceraldehyde is called the reference sugar because it contains one asymmetric carbon atom. CHO CHO H C OH HO C H CH2OH CH2OH D-Glyceraldehyde L-Glyceraldehyde OH group on sub-terminal OH group on sub-terminal carbon is written on right side. carbon is written on left side. 26 b. Anomers: - They are stereoisomers which differ in distribution of H and OH group around the asymmetric anomeric carbon atom C1 in aldoses or C2 in ketoses after cyclization of the molecule, e.g., - and -glucose are anomers. CH2OH CH2OH O O OH H H H H H OH H OH H OH H OH OH H OH H OH -D-Glucose -D-Glucose -A sugar can have its anomeric carbon linked to an –NH2 or an –OH group on another structure through N- and O-glycosidic bonds, respectively. Three Representations of Glucose Structure: - The 1st carbon aldehyde group is condensed with the hydroxyl group of the 5th carbon to form a ring. The open chain projection formula and the ring structure of glucose were proposed by Emil Fischer (Nobel Prize, 1902). - Later it was shown that the glucose is existing in biological systems, not as a rectangle, but as a pyranose ring. This was established by Sir Walter Haworth (Nobel prize, 1937). - Monosaccharides have three forms of structure, open chain, closed hemiacetal and the Haworth’s ring structure. 27 C. Epimers: - They are stereoisomers which differ in distribution of H and OH groups around a single asymmetric carbon atom other than the anomeric and DL- form creating carbon before the last i.e., without difference on other carbon atoms. - Ribose is an epimer to each of arabinose and xylose. Glucose is an epimer to each of mannose and galactose. Arabinose and xylose as well as galactose and mannose are not epimers to each other because they differ around distribution of H and OH in more than one asymmetric center. CHO CHO CHO H C OH HO C H H C OH H C OH H C OH HO C H H C OH H C OH H C OH CH2OH CH2OH CH2OH Ribose Arabinose Xylose CHO CHO CHO H C OH HO C H H C OH HO C H HO C H HO C H H C OH H C OH HO C H H C OH H C OH H C OH CH2OH CH2OH CH2OH Glucose Mannose Galactose 28 Carbon-2 (C-2) and C-4 epimers and an isomer of glucose. 29  Chemical reactions of monosaccharides Oxidation of sugars (Sugar acids): - The product of oxidation depends on the nature of oxidizing reagent, 1. Oxidation by mild or weak oxidizing reagent: It oxidizes the first carbon and gives Aldonic acid, e.g., Bromine water, and examples include: 1- Glyceraldhyde give Glyceric acid(glycerate): found in metabolism of carbohydrates in the body. 2- Glucose give Gluconic acid: 2. Oxidation by moderate oxidizing reagents: - Such as H2O2 (hydrogen peroxide) or diluted HNO3. They oxidize the last carbon (CH2OH) to give uronic Acids. Example include: Glucuronic acid which enters in the structure mucopolysaccharides and detoxication of several toxins by conjugation. 3. Oxidation by strong oxidizing reagent: -Concentrated HNO3 oxidizes the first and last carbon to give aldaric acid. 30  This reaction is important to differentiate between glucose and galactose since glucaric acid is water soluble, whereas, mucic acid is insoluble in water and precipitates in the form of insoluble crystals of specific shape. Oxidation of fructose: The molecule is cleaved into two acids with shorter chain length. One is glycollic acid and the other is trihydroxy- butyric acid a derivative of Butyric acid (CH3 – CH2 – CH2 – COOH), as follows, CH2OH CH2OH O2 COOH C=O O2 Glycollic acid HO C H + Conc. HNO3 COOH H C OH H C OH O2 H C OH H C OH CH2OH CH2OH D-Fructose Trihydroxy-butyric acid ---------------------- Reduction of monosaccharides (sugar alcohols): - Reduction of monosaccharides gives sugar alcohols. 31 1-Glucose is reduced to sorbitol 2-But ketose forms two alcohols, Fructose is reduced to mannitol and sorbitol. 3-Similarly, galactose is reduced to dulcitol and ribose to ribitol. The osmotic effect of sorbitol and dulcitol produces changes in tissues when they accumulate in abnormal amounts, e.g. cataract of lens. Amino sugars (sugaramines): - Replacing OH group on C2 by an amino group (NH2) produces them: Glucosamine (chitosamine): Enters in the structure of exoskeleton of insects (chitin) and mucopolysaccharides Deoxysugars These are sugars in which OH group is replaced by H. 1-Deoxyribose that enters in structure of DNA., 2- L-galactose gives L-fucose L-fucose enter in the structure of blood group. N.B: Benedict's Reaction: Benedict's reagent is very commonly employed to detect the presence of glucose in urine (glucosuria) and is a standard laboratory test employed in diabetes mellitus. In practice, 0.5 ml of urine and 5 ml of Benedict's reagent (Benedict’s reagent contains sodium carbonate, copper sulphate and sodium citrate) are boiled for 2 minutes. If 32 sugar is present, copper is reduced to produce green, yellow, orange or red precipitate, depending on the concentration of sugar. Therefore, this can be used as a semiquantitative test. Any sugar with free aldehyde/keto group will reduce the Benedict's reagent. Therefore, this is not specific for glucose. Disaccharides Reducing disaccharides 1-maltose: - It consists of 2 -glucose units linked by -1,4-glucosidic linkage, 33  CH2OH CH2OH O O H H OH..... H H H 1 4 H H OH H OH O H..... OH OH H OH H OH -Glucose Glucose − and −Maltose 2-Isomaltose: 3-Lactose: - It is formed of -galactose and -glucose linked by -1,4-glucosidic linkage -galactose participates by C1 while -glucose participates by C4. CH2OH CH2OH O O H OH..... H OH H H 1 O 4 H OH H OH H H..... OH H H OH H OH -Galactose Glucose − and −Lactose Non-reducing disaccharides: Sucrose: It is table sugar and sugar of cane and molasses and is formed of -glucose linked to -fructose by --1,2-linkage. It is a fermentable sugar. - The 2 anomeric carbons (C1 of glucose and C2 of fructose) are involved in the linkage, therefore it is non-reducing sugar. 34  CH 2OH O H H -Glucose H 1 OH H OH H OH CH 2OH O O -Fructose OH 2 H H CH 2OH OH H Sucrose Polysaccharides - They are classified into: 1. Homopolysaccharides. 2. Heteropolysaccharides. Homopolysaccharides - They yield only one type of monosaccharides on hydrolysis 1-Glucoans: - They produce only glucose on hydrolysis. They include; starch, glycogen and cellulose Dietary fiber is the edible part of plants which is nondigestible, non-starch carbohydrates, cellulose and lignin. it is completely or partially fermented by the gut bacteria to short-chain fatty acids (SCFA) in the large intestine. 35 SCFAs play an essential role in regulating host metabolism, immune system, and cell proliferation. Dietary fiber provides little energy but has several beneficial effects: 2-Fructosans: Inulin composed of D-fructose units It is the reserve carbohydrate present in various bulbs and tubers such as chicory, dahlia, onion, garlic, etc. It is clinically used to find renal clearance value and glomerular filtration rate -Inulin and Insulin are different Heteropolysaccharides They are polysaccharides that on hydrolysis produce several types of sugars 3 types: 1- Non-nitrogenous heteropolysaccharides: - They do not contain sugar amines such as plant gums & Pectin 36  2- Nitrogenous heteropolysaccharides: - They contain sugar amines and are of two types: neutral and acidic nitrogenous heteropolysaccharides. Neutral nitrogenous heteropolysaccharides or Glycoproteins: - They do not contain acids or sulfate - They are formed of a large protein core to which are attached smaller chains of carbohydrate. Distribution: - Cell membrane & cell-surface recognition - Blood group (cell surface antigenicity) - Collagen of connective tissue (Extracellular matrix). - Mucins. 37 Acidic nitrogenous heteropolysaccharides 38  or mucopolysaccharides: They have two types: sulfate-free and sulfated. 1- Sulfur-free mucopolysaccharides: - Their sugar units are not sulfates, e.g., hyaluronic acid It is present in connective tissue matrix, vitreous humor of the eye, skin, synovial fluid, around the ovum, and in the umbilical cord to preserve the full-form of these structures. It contains glucosamine and glucuronic acid. B. Sulfur-containing mucopolysaccharides: Their sugar units are sulfates, e.g., heparin. It is an anticoagulant prevents intravascular clotting. Therefore, it is used in cases of increased coagulability, e.g., cardiac ischemia or deep venous thrombosis. - Glycoprotein & mucoprotein (mucopolysaccharides): When carbohydrate are attached to a protein it is called a proteoglycan. If the carbohydrate content is less than 10%, it is generally named as a glycoprotein. If the carbohydrate content is more than 10% it is a mucoprotein (mucopolysaccharides). 39  3- Agar It is prepared from sea weeds and contains galactose, glucose and other sugars. Agar cannot be digested by bacteria and hence used widely as a supporting agent to culture bacterial colonies & supporting medium for electrophoresis. N.B: Salivary α-amylase initiates digestion of dietary polysaccharides (e.g., starch or glycogen), producing oligosaccharides. Pancreatic α-amylase continues the process. The final digestive processes occur at small intestine. Several disaccharidases (e.g., lactase & sucrase) produce monosaccharides (glucose, galactose, and fructose). If carbohydrate degradation is deficient undigested carbohydrate will pass into the large intestine, where it can cause osmotic diarrhea. Bacterial fermentation of the material produces large volumes of carbon dioxide and hydrogen gas, causing abdominal cramps, diarrhea, and flatulence. 40 Lactose intolerance: caused by loss of lactase 41  lipids chemistry Definition: - Lipids are organic compounds formed mainly from fatty alcohol and fatty acids combined together by ester linkage. O H2O O R CH2 OH HO C R R CH2 O C R + Fatty alcohol Fatty acid Esterase (lipase) ester (lipid) Lipids are a heterogeneous group of water-insoluble (hydrophobic) organic molecules. Because of their insolubility in aqueous solutions, body lipids are generally found compartmentalized, as in the case of membrane associated lipids or droplets of triacylglycerol (TAG) in adipocytes, or transported in blood in association with protein, as in lipoprotein particles. Biological Importance of Lipids: - Lipids are important dietary constituents, because of the following reasons: 1. They are more palatable and storable to unlimited amount compared to carbohydrates. 2. They have a high-energy value (25% of body needs) and they provide more energy per gram than carbohydrates and proteins but carbohydrates are the preferable source of energy. 3. Supply the essential fatty acids that cannot be synthesized by the body. 4. Supply the body with fat-soluble vitamins (A, D, E and K). 5. They are important constituents of the nervous system. 42 6. Tissue fat “constant fat” is an essential constituent of cell membrane and nervous system. It is mainly phospholipids in nature that are not affected by starvation. 7. Stored lipids “depot fat” are stored mainly in adipocytes. It is mainly triglycerides in nature and acts as: i. A store of energy. ii. A pad for the internal organs to protect them from outside shocks. iii. Insulator against loss of body heat. 8. Understanding biochemistry of lipids provide bases for dealing with diseases such as obesity Excessive fat deposits cause obesity, (Truncal obesity is a risk factor for heart attack), atherosclerosis, lipid-storage diseases, essential fatty acid deficiency, respiratory distress syndrome, in diabetes mellitus, the metabolisms of fatty acids and lipoproteins are deranged, leading to ketosis... etc. 43  Classification of Lipids Lipids are classified into: I- Simple lipids: - They are esters of fatty acids with fatty alcohol. They are classified according to the alcohol present into: 1-Neutral fats: are esters of fatty acids with glycerol (triacylglycerols, or triglycerides). 2-Waxes: Esters of fatty acids with any alcohols other than glycerol that is mostly monohydric. Cholesterol esters with any fatty acid are waxes. Esters of vitamin A and vitamin D with fatty acid, e.g., palmitic or stearic acid are waxes, too. II- Compound lipids: They are esters of fatty acids and alcohols in additions to other groups. They include the following types: 1-Phospholipids (phosphatides): Compound lipids containing fatty acids, alcohol, phosphoric acid and often a nitrogenous base. 2-Glycolipids: Compound lipids containing fatty acids, carbohydrate and sphingosine, but not phosphoric acid nor glycerol. 3-Lipoproteins: Compound lipids composed of a lipid part associating by secondary bonds with proteins as plasma and membranous lipoproteins. III- Derived Lipids: 44  - They are products of hydrolysis of simple and compound lipids and/or their derivatives that still possess the general characteristics of lipids. They include: i. Fatty acids. ii. Alcohols. iii. Sterols, steroids and hormonal derivatives of vitamin D. iv. Eicosanoids: They are 20 C compounds (Greek, eikosi = twenty), derived from arachidonic acid. (Prostaglandins, leukotrienes and thromboxane). The effects of prostaglandins on different tissues are different and some of these may oppose each other. Prostaglandins are local hormones. In most tissues, PGE increases cAMP (cyclic AMP) level. Effects on CVS: Prostacyclin or PGI2 is synthesized by the vascular endothelium. Major effect is vasodilatation. It also inhibits platelet aggregation and has a protective effect on vessel wall against deposition of platelets. Thromboxane (TXA2) is the main PG produced by platelets. The major effects are vasoconstriction and platelet aggregation. Prostacyclin and thromboxane are opposing in activity. Prostaglandins increase the contractility and lowers the blood pressure. Hence, it may be used in the treatment of hypertension. Effects on ovary and uterus: PGF2 stimulates the uterine muscles. So use in inducing labor and arresting postpartum hemorrhage. Respiratory tract: PGF is a constrictor of bronchial smooth muscle; but PGE is a potent bronchodilator. PGE is used in aerosols for treating bronchospasm. 45 Effects on immunity: PGE2 and D2 produce inflammation by increasing capillary permeability. Cortisol and aspirin are strong anti-inflammatory drugs, because they inhibit prostaglandin synthesis. v. Ketone bodies. Alcohols Alcohols associated with lipids include: Glycerol: - It is a trihydric alcohol (i.e., containing three OH groups) and has the popular name glycerin. - It is synthesized in the body from glucose. -On heating with sulfuric acid or KHSO4 (dehydration), it gives acrolein (acryl aldehyde) that has a bad odor. -This reaction is used for detection of free glycerol or any compound containing glycerol. CH2 OH 2 H 2O CHO HO CH CH Heating, KHSO4 CH2 OH CH2 Glycerol Acrolein It combines with three molecules of nitric acid to form trinitroglycerin that is used as explosive and vasodilator. Uses of Glycerol: 46 i- Glycerol enters in pharmaceutical and cosmetic preparations (hygroscopic). ii- Nitroglycerin is used as vasodilator thus it is used in treatment of angina pectoris. CH2 ONO2 O2NO CH CH2 ONO2 Trinitroglycerine iii- Glycerol is used in treatment of glaucoma due to its ability to dehydrate the tissue from its water content. Sphingosine: - It is the alcohol present in sphingolipids. OH CH3-(CH2)12-CH CH CH CH NH2 CH2OH Sphingosine - It is synthesized in the body from serine and palmitic acid. - It is not positive with acrolein test. Fatty Acids 47 Definition: Fatty acids are aliphatic mono-carboxylic acids. Fatty acids can be classified as follows: Saturated Fatty Acids They are classified into: A- Short chain B-long chain (2-10 C) (More than 10 C) A-Short-chain fatty acids: They have 2-10 carbons. -present in milk in high amount. -They are further classified into: 1- Volatile short-chain fatty acids: -Contain 2-6 carbon atoms. -Volatile at room temperature. 2C Acetic acid CH3-COOH 3C Propionic acid CH3-CH2-COOH 4C Butyric acid CH3-(CH2)2-COOH, 5C Valeric acid CH3-(CH2)3-COOH 6C Caproic acid CH3-(CH2)4-COOH 2- Non-volatile short-chain fatty acids: -Contain 7-10 carbon atoms. -Non-volatile at room temperature. 8C Caprylic acid CH3-(CH2)6-COOH 10C Capric acid CH3-(CH2)8-COOH B- Long-chain fatty acids: They contain more than 10 carbon atoms. 48  -They occur in hydrogenated oils& animal fats, -They are non-volatile. -Water-insoluble 16C Palmitic acid CH3-(CH2)14-COOH 18C Stearic acid CH3-(CH2)16-COOH Unsaturated fatty acids - They are called unsaturated because of the presence of double bonds. - The presence of double bonds affects their physical properties, e.g., decreasing the melting temperature, therefore, all unsaturated fatty acids are liquids at room temperature. They are further classified according to the number of double bonds into: Monounsaturated fatty Polyunsaturated fatty acid acid (one double bond) (more than one double bond) 1. Monounsaturated fatty acids: A) Palmitoleic acid (unsaturated palmitic acid): 49  CH3-(CH2)5-CH=CH-(CH2)7-COOH - It is found in all fats, it is C16:1∆9, i.e., has 16 carbons and one double bond located between carbon number 9 and carbon 10 from the carboxyl end of the fatty acid. - ω7: indicates a double bond on the 7 th carbon counting from the methyl end of the fatty acid (ω -carbon). B) Oleic acid is the most common fatty acid in natural fats. CH3-(CH2)7-CH=CH-(CH2)7-COOH - It is C18:1∆9, i.e., has 18 carbons and one double bond located between carbon number 9 and carbon 10. It is equivalent to ω 9. 2. Polyunsaturated fatty acids P.U.F.A (Essential fatty acids ) Definition: They are essential fatty acids that can not be synthesized in the human body (due to lack of enzymes that can form more than one double bond) and must be taken in adequate amounts in the diet. They are required for normal growth and metabolism. They are liquids at room temperature. Function: 1- They are useful in the treatment of atherosclerosis. 2- Eicosanoids are synthesized from them. 3- They participate in structure of cell membranes. 4- They are essential for skin integrity, normal growth, health of the retina and vision. 5- Important in preventing fatty liver. 50 6- Energy production. Source: vegetable oils such as corn oil, linseed oil, peanut oil, olive oil, cottonseed oil, soybean oil and fish oils. Examples: Include: 1-Linoleic: C18:29, 12. CH3-(CH2)4-CH=CH-CH2-CH=CH-(CH2)7-COOH 2--Linolenic acid: C18:39, 12, 15. CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH 3--Linolenic acid: is a positional isomer for -Linolenic acid, C18:36, 9, 12. CH3-(CH2)4-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)4-COOH 4-Arachidonic acid: C20:45, 8, 11, 14. CH3-(CH2)4-CH=CH-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)3-COOH Simple Lipids 1-Neutral Fats Definition: 51  - They are called neutral because they carry no charge. The neutral fats are the most abundant lipids in nature. - They are esters of glycerol with various fatty acids. Since the 3 hydroxyl groups of glycerol are esterified, the neutral fats are also called “Triglycerides” or more correctly triacylglycerols. - Esterification of glycerol with one molecule of fatty acid gives monoglyceride, and that with 2 molecules gives diglyceride. O O HO C R1 CH2 OH H2C O C R1 O O R2 C O C H HO C R2 + HO C H O O CH2 OH 3 H2 O H2C O C R3 HO C R3 Glycerol Triglycerides Fatty acids (Triacylglycerol) - The commonest fatty acids in animal fats are palmitic, stearic and oleic acids. - The main difference between fats and oils is for oils being liquid, whereas, fats are solids at room temperature. This is mainly due to the presence of larger percentage of unsaturated fatty acids in oils than fats that has mostly saturated fatty acids. Chemical Properties of fats and oils: 1-Hydrolysis: - They are hydrolyzed into their constituents (fatty acids and glycerol) by the action of steam, acid, alkali or enzyme (e.g., lipase of pancreas). glycerol and free fatty acids are produced. O O CH2 O C R1 H2C OH R1 C OH O Lipase or Acid O R2 C O C H HO C H + R C OH 2 O O CH2 O C R3 3 H2O H2C OH R3 C OH Triacylglycerol Glycerol Free fatty acids 52 - Alkaline hydrolysis produces glycerol and salts of fatty acids (soap). This is why alkaline hydrolysis of fats and oils is called saponification (Salt Formation). O O CH2 O C R1 H2C OH R1 C ONa O O R2 C O C H HO C H + R C ONa 2 O O CH2 O C R3 3 NaOH H2C OH R3 C ONa Triacylglycerol Glycerol Sodium salts of fatty acids (soap) Sodium and potassium salts of long chain fatty acids are called soaps. Calcium and magnesium soaps are insoluble so, Calcium soaps are used in grease. 2- Hydrogenation or hardening of oils: - The hydrogenation is done under high pressure of hydrogen and is catalyzed by nickel or copper and heat. It is the base of hardening of oils (margarine manufacturing), e.g., change of oleic acid of fats (liquid) into stearic acid (solid). Oils Hydrogen, high pressure, nickel Hard fat (liquid) (margarine, solid) (with unsaturated (with saturated fatty acids, e.g., oleic) fatty acids, e.g., stearic) - Disadvantages of hydrogenated fats include: lack of fat- soluble vitamins (A, D, E and K) and essential fatty acids. Rancidity Fats and oils have a tendency to become rancid. The term rancidity refers to the appearance of an unpleasant smell and taste for fats and oils. 53  PUFA are more easily oxidized; so vegetable oils with a high content of PUFA are usually preserved with addition of antioxidants. Fats and oils are preferred cooking media. However, overheating and repeated heating would lead to the formation and polymerization of cyclic hydrocarbons. These will impart an unpleasant taste and color to the oil. Coconut oil having medium chain saturated fatty acids will withstand such polymerization. Hazards of Rancid Fats: 1. The products of rancidity are toxic, i.e., causes food poisoning and cancer. 2. Rancidity destroys the fat-soluble vitamins (vitamins A, D, K and E). 3. Rancidity destroys the polyunsaturated essential fatty acids. 4. Rancidity causes economical loss because rancid fat is inedible. 2-Waxes Definition: - Waxes are solid simple lipids containing a monohydric alcohol other than glycerol esterified to long-chain fatty acids. Like bee & carnauba waxes. Compound Lipids 54  Definition: - They are lipids that contain additional substances, e.g., phosphorus, carbohydrate, or proteins beside fatty acid and alcohol. - Compound or conjugated lipids are classified into the following types according to the nature of the additional group: a) Phospholipids b) Glycolipids. c) Lipoproteins a) Phospholipids Definition: Phospholipids or phosphatides are compound lipids, which contain phosphoric acid group in their structure. Classification: Phospholipids are classified into 2 groups according to the type of the alcohol present: I) Glycerophospholipids: They contain glycerol &include: 1) Phosphatidic acid. 2) Lecithins 3) Cephalins. 4) Cardiolipin. 5) Inositides. 6) Plasmalogens. II) Sphingophospholipids: They contain sphingosine as an alcohol &include: -Sphingomyelins. a) Glycerophospholipids: 55  1- Lecithins: Definition: Lecithins are glycerophospholipids that contain choline as a base beside phosphatidic acid. They exist in 2 forms - and -lecithins. O CH2 O C R1 O R2 C O C H O CH3 CH2 O P O CH2 CH2 N + CH3 OH Choline CH3 -Lecithin O CH2 O C R1 CH3 O + CH3 N CH2 CH2 O P C H OH O CH3 Choline CH2 O C R2 -Lecithin Properties: 1) They are extremely hygroscopic. 2) The toxic effect of snake or scorpion venom, poisonous spiders and stinging insects. The venom contains lecithinase, which hydrolyzes the polyunsaturated fatty acid converting lecithin into lysolecithin, lysolecithin causes hemolysis of RBCs (inside the box in the figure above is replaced by an H atom). 3) Phospholipase A2 hydrolyses polyunsaturated fatty acid from cell membrane phospholipids for synthesis of eicosanoids. 4) Lung surfactant is a complex of lecithin, sphingomyelin and a group of apoproteins. It is produced by type II alveolar cells.It lowers alveolar surface tension and improves gas exchange besides activating macrophages to kill pathogens. In premature babies, this surfactant is deficient and they suffer from respiratory distress syndrome. 56 2- Cephalins (or Kephalins): Definition: They are phosphatidyl-ethanolamine or serine. Cephalins occur in association with lecithins in tissues and are isolated from the brain (Kephale = head). Structure: Cephalins resemble lecithins in structure except that choline is replaced by ethanolamine, serine or threonine amino acids. O CH2 O C R1 O R2 C O C H O CH2 O P O CH2 CH2 NH2 Ethanolamine OH HO CH2 CH COOH Serine -Cephalin NH2 HO CH CH COOH Threonine CH3 NH2 3- Plasmalogens: -Unsaturated CH2 O CH CH R1 fatty alcohol O R2 C O C H O CH3 CH2 O P O CH2 CH2 N + CH 3 OH CH3 -Plasmalogen Definition: Plasmalogens are found in cell membranes of brain and muscle. Structure: Plasmalogens resemble lecithins and cephalins in structure but differ in the presence of ,-unsaturated alcohol rather than a fatty acid at C1 of the glycerol connected by ether bond. At C2 there is fatty acid 57  The nitrogenous base may be choline, ethanolamine, serine or threonine. b)Sphingophospholipids Ceramide Sphingosine Fatty acid OH O CH3 (CH2)12 CH CH CH CH NH C R1 CH2 Choline O CH3 O P O CH2 CH2 N + CH3 OH CH3 Phosphate Sphingomyelin All sphingolipids have sphingosine, which is attached to a fatty acid in amide linkage to form a ceramide. Phosphosphingosides They contain phosphoric acid group. A common phosphosphingoside present abundantly in biomembranes, especially of the nervous system, is sphingomyelin. It contains ceramide, phosphate and choline. Sphingomyelins are the only sphingolipid that contain phosphate and have no sugar moiety. b) Glycolipids Glycosphingolipids (Glycolipids): They are seen widely in nerve tissues. This group of lipids do not contain phosphoric acid; instead, they contain carbohydrates and ceramide. 58  Ceramide Sphingosine Fatty acid OH O CH3 (CH2)12 CH CH CH CH NH C R1 CH2 CH2OH O OH O H Galactose OH H H H H OH Psychosin Cerebroside Deficiency of enzymes of sphingolipid metabolism results in sphingolipidoses, a group of inborn metabolic disorders resulting in accumulation of specific lipid residues. Mental retardation, neurological deficit and skeletal abnormalities are common presenting symptoms Niemann Pick's Disease This is an inborn error of metabolism due to failure of degradation of sphingomyelin. The enzyme sphingo-myelinase is deficient in this condition and sphingomyelin is accumulated in tissues. Salient features are severe mental retardation, hepatosplenomegaly and cherry red spot in macula of retina. Death usually occurs by the age of 2 years. c) Lipoproteins Definition: Lipoproteins are lipids combined with proteins in the tissues. They include: 1) Structural lipoproteins: present in cell membranes. In lung tissues it is found as a surfactant. 59 2) Transport lipoproteins or Plasma lipoproteins: These are the forms present in blood plasma. They are composed of a protein called apolipoprotein and lipids. As the lipid content increases, the density of plasma lipoproteins decreases and the diameter increases and vice versa. Polar lipids (phospholipids) Polar apolipoproteins Nonpolar lipids (cholesterol and its esters and triacylglycerols) Structure of a plasma lipoprotein complex - Plasma lipoproteins can be separated by two methods: 1) Electrophoresis: is the migration of charged particles in an electric field either to the anode or to the cathode. It sequentially separates the lipoproteins into chylomicrons, -, pre--, and -lipoproteins and albumin-free fatty acids complex. 2) Ultra-centrifugation: Using the rate of floatation in sodium chloride solution leading to their sequential separation into:- 1-Chylomicrons: - They have the largest diameter and the least density. - They contain 1-2% protein only and 98-99% fat. - The main lipid fraction is triglycerides absorbed from the intestine. 2- Very low-density lipoproteins (VLDL) or pre--lipoproteins: They contain about 7-10% protein and 90-93% lipid. -The lipid content is mainly triglycerides formed in the liver. 60  3- Low-density lipoproteins (LDL) or -lipoproteins: - They contain 10-20% proteins Their lipid content varies from 80-90%. - They contain about 60% of total blood cholesterol As their percentage increases, the liability to atherosclerosis increases. 4- High-density lipoproteins (HDL) or -Lipoproteins: - They contain 35-55% proteins - They contain 45-65% lipids formed of cholesterol and phospholipids - They act as cholesterol scavengers, as their percentage increases, the liability to atherosclerosis decreases. 5- Albumin-free fatty acids complex: It is a proteolipid (the protein part is lager than the lipid part) complex with 99% protein associated with long-chain free fatty acids (1%) for transporting them. Steroids Definition: Steroids constitute an important class of biological compounds. Steroids are usually found in association with fat. - Biologically important groups of substances, which contain steroid ring are: 1) Sterols. 2) Adrenal cortical hormones. 3) Male and female sex hormones. 4) Vitamin D group. 5) Bile acids. 6) Cardiac glycosides. 61  18 12 CH3 19 11 13 17 16 CH3 C D 1 9 14 15 2 A 5 10 B 8 HO 3 4 6 7 Steroid ring Cholesterol: - It is the most important sterol in animal tissues as free alcohol or in an esterified form with fatty acids Steroid hormones, bile salts and vitamin D are derivatives from it. Source: - It is synthesized in the body from acetyl-CoA and is also taken in the diet as in, butter, milk, egg, brain, meat and animal fat. CH3 CH3 CH3 CH3 CH3 HO Cholesterol ------------------------------------------------------------------------ 62 63  Vitamins characters: 1. They are essential organic compounds for normal health and growth since they are not synthesized in human body. 2. They must be supplied in the diet in the required very small amounts and deficiency of any vitamin in the body results in a disease. 3. They are present in normal food in small amounts. 4. They do not enter in tissue structure as carbohydrates, fats and proteins. 5. Vitamins are essential food factors, which are required for the proper utilization of the proximate principles of food like carbohydrates, lipids and proteins. All the vitamins are usually available in an ordinary diet. 6. They are not oxidized for energy production as carbohydrates, fats and proteins. 7. Provitamins: These are precursors of vitamins that converted into vitamins inside the body e.g. Carotenes are provitamin A. 8. Vitaimers: These are different forms of one vitamin e.g. Vitamin D has 2 vitamers; D2, & D3. Classification: The vitamins are mainly classified into two: 1. The fat soluble vitamins are A, D, E and K 2. Water soluble vitamins are B complex and C. 64  Fat-soluble vitamins Vitamin A (retinol) the provitamin is called carotenoids or carotenes Sources 1. Animal sources: (RETINYL ESTER) a- Liver, eggs and milk fat. b- Fish. 2. Plant sources: a- Vitamin A is present in plants as provitamin A; Carotenes. b- Carotenes. Present in carrots, potato and tomatoes. 65 Functions of vitamin A: It has the following functions: 1-Wald's Visual Cycle: Wald was awarded Nobel prize in 1967, for identifying the role of vitamin A in vision. Rhodopsin is a protein found in the photoreceptor cells of the retina. Rhodopsin is made-up of the protein opsin and 11-cis retinal. When light falls on the retina, the 11-cis-retinal isomerises to all- transretinal lead to generation of Nerve Impulse. Bright light depletes stores of rhodopsin in rods. Therefore, when a person shifts suddenly from bright light to a dimly lit area, there is difficulty in seeing, for example, entering a cinema theater. After a few minutes, rhodopsin is resynthesized and vision is improved. This period is called dark adaptation time. It is increased in vitamin A deficiency. In the retina, there are two types of photosensitive cells, the rods and the cones. Rods are responsible for perception in dim light. It is made up of 11- cisretinal + opsin. Deficiency of cis-retinal will lead to increase in dark adaptation time and night blindness. 2-Vitamin A has a role in reproduction , growth, bone , teeth formation & differentiation of tissues. 3- Antioxidant property: Fresh vegetables containing carotenoids were shown to reduce the incidence of cancer. 66  Deficiency of vitamin A - Eye: -Night Blindness or Nyctalopia: Visual acuity is diminished in dim light. - Xerophthalmia: The conjunctiva becomes dry, thick and wrinkled. The conjunctiva gets keratinized and loses its normal transparency. Cornea is also keratinized. Infections may supersede -Keratomalacia: When the xerophthalmia persists for a long time, it progresses to keratomalacia (softening of the cornea). Later, corneal opacities develop. Bacterial infection leads to corneal ulceration, and total blindness. - Skin and mucus membranes: Roughness of skin and mucus membranes. 67  Vitamin K (Anti-haemorrhagic vitamin) The letter "K" is the abbreviation of the German word "koagulation vitamin" Have three vitamers: K1 K2 and K3 Naturally occurring vitamin K (fat soluble): -Vitamin K1 (phylloquinone): is the major form of vitamin K in plants e.g. spinach, cauliflower and cabbage. -Vitamin K2 (menaquinone): is formed inside the intestine by intestinal bacteria. Synthetic (e.g. K-viton drug)) is water-soluble: - Vitamin K3 (Menadione) and it is most potent member. Functions of vitamin K: 1. Synthesis of some blood clotting factors in liver: prothrombin (factor II), and factors VII, IX and X. 2. in bones: Synthesis of osteocalcin (calcium binding protein). Deficiency of vitamin K: is rare because intestinal bacteria synthesize it. Vitamin K deficiency is manifested as bleeding, Very minor injuries will go on bleeding. Vitamin E 68 Sources: Vegetables and seed oils e.g. cotton, olive and coconut oils. Functions: Vitamin E is the most powerful natural antioxidant Free radicals are continuously being generated in living systems. Their prompt inactivation is of great importance. Vitamin E prevents early aging. It reduces the risk of myocardial infarction by reducing oxidation of LDL. 69  Vitamin D (Calciferol): vitamin D is called the "sun-shine vitamin". As sunshine is less in winter months, vitamin deficiency is seen in winter. Functions: - Calcitriol is the physiologically active form of vitamin D. It increases the blood calcium level & mineralization of bones. Deficiency: The deficiency diseases are rickets in children and osteomalacia in adults. Hence vitamin D is known as antirachitic vitamin. Rickets in children: characterized by bone deformities. Osteomalcia in adults: characterized by bone fractures. WATER SOLUBLE VITAMINS 70  Vitamin C = L-Ascorbic Acid Sources: - Fruits especially citrus fruits (lemon, orange) melon and strawberry. Guava is very rich in vitamin C. - Vegetables especially green leafy vegetables such as lettuce, tomatoes, raw cabbage, green peppers and germinating seeds are rich source of the vitamin. 71 Functions of Vitamin C: 1- Hydroxylation of proline: Ascorbic acid is necessary for the post-translational hydroxylation of proline and lysine residues. Hydroxyproline and hydroxylysine are essential for the formation of cross-linkings in collagen, which gives the tensile strength of the fibers. This process is absolutely necessary for the normal production of supporting tissues such as osteoid, collagen and intercellular cement substance of capillaries. 2- Iron metabolism: Ascorbic acid enhances the iron absorption from the intestine. Ascorbic acid reduces ferric iron to ferrous state, which is preferentially absorbed. 3- Hemoglobin metabolism: It is useful for reconversion of met– hemoglobin to hemoglobin. 4- Antioxidant property: As an antioxidant , it may prevent cancer formation. 72 Deficiency (scurvy) Manifestations due to decrease collagen formation: - Bleeding. - Osteoporosis. - Oral cavity: In severe cases of scurvy, the gum becomes painful, swollen, and spongy. The pulp is separated from the dentine and finally teeth are lost. - Delayed wound healing - Easy bruising. -Anemia 73  Vitamin B Complex (Thiamine, Riboflavin, Niacin, Pyridoxine, Pantothenic Acid, Biotin, Folic Acid and Vitamin B12) These vitamins are chemically not related to one another. They are grouped together because all of them function in the cells as coenzymes. Thiamin = Vitamin B1 THYMINE is the base present in DNA. THIAMINE is the vitamin B1 Sources:- Seeds as peas, beans, whole cereal grains, bran , yeast,eggs&milk. Function: The main role of thiamine (TPP) is in carbohydrate metabolism. So, the requirement of thiamine is increased along with higher intake of carbohydrates. Deficiency Manifestations of Thiamine: Beriberi: Deficiency of thiamine leads to beriberi. The early symptoms are anorexia and weakness. 1-Wet Beriberi: Here cardiovascular manifestations are prominent. Edema of legs, face, and serous cavities are the main features. Death occurs due to heart failure. 2-Dry Beriberi: In this condition, CNS manifestations are the major features. Peripheral neuritis with sensory disturbance leads to complete paralysis. 1- Wernicke-Korsakoff syndrome: It is also called as cerebral beriberi. Clinical features are those of encephalopathy plus psychosis. It is seen only when the nutrition is severely affected. 2- Polyneuritis: It is common in chronic alcoholics. 74  Riboflavin = Vitamin B2 Sources of Riboflavin: Rich sources are liver, dried yeast, egg and whole milk. Good sources are fish, whole cereals, legumes and green leafy vegetables. H O H3C N 3NH 5 10 4 flavin 6 7 8 9 1 2 H3C N N O H H C H H OH D-ribitol H OH H OH CH2OH Riboflavin, B2 - Riboflavin is converted to its active coenzyme forms (FMN and FAD) with the help of ATP. H O flavin H O N N H3C NH H3C NH flavin H3C H3C N N O N N O H H H C H NH2 H C H H OH H OH ribitol H N ribitol OH N H OH O O O H OH H OH CH2 O P O P O CH2 N CH2 O P OH O N OH OH H H adenine OH 2 phosphates phosphates H H Flavin Adenine Dinucleotide, FAD HO OH Flavin Mononucleotide, FMN ribose 75  Functions: FMN and FAD are coenzymes act as hydrogen carriers that are wide spread and involved in the oxidation-reduction reactions in: 1- Carbohydrate metabolism. 2- Lipid metabolism. 1- metabolism of amino acids, purine and pyrimidine. Deficiency: Natural deficiency of riboflavin in man is uncommon, because riboflavin is synthesized by the intestinal flora. Riboflavin deficiency usually accompanies other deficiency diseases such as beriberi, and kwashiorkor. Symptoms are confined to skin and mucous membranes. - Glossitis (Greek, glossa = tongue). - Magenta-colored tongue - Cheilosis (Greek, cheilos = lip) - Angular stomatitis (inflammation at the corners of mouth). -Circumcorneal vascularization. 76  Niacin Niacin and Nicotinic acid are synonyms. It is also called as pellagra preventing factor. The term nicotinic acid should not be confused with nicotine. Nicotinic acid is a vitamin; but, nicotine is the potent poison from tobacco. Sources: The richest natural sources of niacin are dried yeast, rice polishing, liver, peanut, whole cereals, legumes, meat and fish. About half of the requirement is met by the conversion of tryptophan to niacin. About 60 mg of tryptophan will yield 1 mg of niacin. H H CO.NH2 NH2 2H N N + N CO.NH2 O O N N N+ adenine H2C O P O P O CH2 O O H H OH OH H H H H 2 phosphates H H OH HO OH HO ribose ribose Nicotinamide Adenine Dinucleotide, NAD H H NH2 CONH2 N N O O N+ H2C O P O P O CH2 N N O O H H OH OH H H adenine H H 2 phosphates H H O HO OH OH P OH O ribose ribose-2-phosphate OH Nicotinamide Adenine Dinucleotide Phosphate, NADP 77 Functions: 1- Niacin is essential for the formation of the coenzymes NAD+ (Also called Coenzyme I ), NADP+ (Also called Coenzyme II) NAD+ and NADP+ Coenzymes act as hydrogen carrier and they are essential for many biochemical oxidation-reduction reactions. These reactions are important in carbohydrate, protein and lipid metabolism. Deficiency: It leads to a disease called: Pellagra. Pellagra is called a disease of (4 Ds) including: 1. Dermatitis: The exposed skin becomes dry, rough and scaly with brown discoloration, glossitis and stomatitis are seen. 2. Diarrhea. 3. Dementia. 4. Death (if not treated). Pyridoxine “Vitamin B6” Vitamin B6 is the term applied to a family of 3 related pyridine derivatives; pyridoxine (alcohol), pyridoxal (aldehyde) and pyridoxamine. Active form of pyridoxine is pyridoxal phosphate (PLP). It is synthesized by pyridoxal kinase, utilizing ATP. 78  CHO CH2NH2 CH2OH HO HO HO CH2OH 4 CH2OH CH2OH 3 5 2 1 6 CH3 N CH3 N CH3 N + + + Pyridoxine Pyridoxal Pyridoxamine CHO O HO CH2 - O - P - OH OH CH3 N + Pyridoxal phosphate Sources: Rich sources are yeast, rice polishing, wheat germs, cereals, legumes (pulses), oil seeds, egg, milk, meat, fish and green leafy vegetables.Royal Jelly of bees (very rich in vitamin B6) Function: The pyridoxal phosphate (PLP) acts as coenzyme for many reactions in amino acid metabolism Thiamine pyrophosphate is involved with carbohydrate metabolism. Pyridoxal phosphate is involved in protein metabolism. Deficiency: 1- Pellagra may result, because pyridoxal phosphate is needed for the conversion of tryptophan to niacin. 2- Disturbance in amino acids metabolism. This leads to growth retardation and may be mental retardation. 3- Convulsions in young infants due to deficient formation of GABA. 4- Anemia due to deficient formation of haemoglobin. Pantothenic Acid The Greek word “pantos” means everywhere. As the name suggests, it is widely distributed in nature. Sources: 79 It is widely distributed in plants and animals. Moreover, it is synthesised by the normal bacterial flora in intestines. Therefore, deficiency is very rare. Functions: A) Coenzyme A (CoASH) Function Coenzyme A acts as acid carrier e.g. acetic acid, succinic acid, fatty acids and other carboxylic acids. B) Acyl carrier protein (ACP): Functions: ACP used for fatty acid synthesis. Biotin (Vitamin H or Coenzyme R) Sources: - The intestinal bacteria synthesize most of the human requirements of biotin - Egg yolk, animal tissues, tomatoes and yeast are excellent sources of biotin. 80 Functions: Biotin functions as coenzyme of the carboxylase enzyme that catalyz carbon fixation (carboxylation) reactions. Deficiency: Deficiency of biotin does not occur in man because the intestinal bacteria supply all the human needs but, biotin deficiency may result from: 1) Ingestion of large amounts of avidin which is a protein present in raw egg white. 2) Deficiency of holocarboxydase synthetase enzyme in children. The enzyme is responsible for the attachement of biotin to carboxylase enzyme. Biotin deficiency include: Dermatitis Growth retardation. 81  Vitamin B12 = Cyanocobalamin (Anti-pernicious anemia or extrinsic factor) 82  Sources: Meat, egg, milk and milk products. Vitamin B12 is not present in vegetables. Functions Cobalamin acts as a coenzyme for: Methylation of homocysteine to methionine important for cell proliferation & Isomerization of L-methyl malonyl COA to succinyl COA. This is the final reaction in the oxidation of odd number fatty acids. Thus, vitamin B helps in the formation of myelin sheath through the metabolism of odd number fatty acids. Deficiency: 1-Megaloblastic anemia It is a macrocytic hyperchromic anemia. It is due to abnormal replication of DNA in hematopoietic tissue. 2- Neurological manifestations It is due to the lack of myelin sheath formation due to the deficiency of methionine and disturbance in the metabolism of odd number fatty acids. Folic acid (Folacin = Peteroyl Glutamic Acid) Sources: The major source is leafy vegatables. Functions: Tetrahydrofolic acid (H4 folate) act as a carrier for one–carbon groups. 83  All the manifestations of folate deficiency is due to decrease rate of cell division secondary to decreased biosynthesis of DNA. They include: 1- Pancytopenia: i.e., a) Megaloblastic anemia b) Leucopenia:  W.B.Cs. c) Thrombocytopnea:  Platelets. 2- Impaired growth. ========================================================= 84  Biochemistry of Minerals According to the body needs, minerals may be divided into two groups: A. Macro-minerals: - They are required in amounts greater than 100 mg/day. - They include seven elements: calcium, phosphorus, magnesium, sodium, potassium, chloride and sulfur. B. Micro-minerals (trace elements): - They are required in amounts less than 100mg/day. - Trace elements: Elements present in the body in very low amounts (micrograms/gram or less). - Some are essential trace elements e.g., chromium, cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, selenium and zinc. 85  Macro-Minerals Calcium (Ca2+) Sources: Milk and milk products (the richest sources). Beans, leafy vegetables and egg yolk. Functions of Calcium: Unionized calcium: - It enters in the structure of bones and teeth. Ionized calcium: It is important for: -Transmission of nerve impulses. -Contraction of muscles. -Neuromuscular excitability. Deficiency of ionized calcium causes tetany. -Blood and milk clotting. -Mediation of some hormone responses e.g. it acts together with calmodulin as second messenger for hormones depending on cAMP. Factors affecting calcium absorption: Factors promoting calcium absorption: 1) High protein diet: amino acids form soluble calcium salts with calcium, which are easily absorbed. 2) pH: an acidic pH in the upper small intestine is essential for calcium absorption. 3) High dietary lactate or citrate that form soluble salts with calcium. Factors inhibiting calcium absorption: 1)High dietary phosphate, oxalate and phytate which form insoluble salts with calcium. 2)Alkalinity: excessive alkali intake as during treatment of peptic ulcer decreases calcium absorption. 86 3)Presence of free fatty acid: Impairment of fat absorption causes presence of large amount of free fatty acids which react with calcium producing insoluble calcium soaps. Body Calcium: - Calcium is the most abundant mineral in the body (about 1200g). Most of calcium is present in the skeleton (bones and teeth) 99%, in the form of hydroxyapatite: 3 Ca3(PO4)2.Ca(OH)2. - The remaining 1% of calcium is present in body fluids and other tissues. Normal calcium levels: - Blood calcium level ranges from 9-11 mg/dl (average: 10mg/dl). - Blood calcium lies entirely in the plasma, no calcium inside red blood cells. Requirements: - Adult men and women: 800 mg/day. Children, pregnant and lactating women: 800 – 1200 mg/day. Phosphorus (P) Sources: Milk and milk products, fish, meat, liver and kidney, leafy vegetables and egg yolk. Function: 1. 80% of the phosphorous share in bone and teeth formation. 2. The remaining enters in the structure of the following cellular components: - Nucleic acids: DNA and RNA. - Phospholipids: e.g. lecithins, cephalins. 87 - Phosphoproteins. - Coenzymes: e.g., NAD, NADP. - High-energy phosphate, e.g., ATP, GTP, creatine phosphate. - Blood buffers. Body phosphorus: - Total body phosphorus is about 800g. - Most of phosphorus (80%) is present in the skeleton (bones and teeth) in the form of hydroxyapatite: 3 Ca3(PO4)2. Ca(OH)2. - The other 20% is present in other tissues (mostly intracellular) and body fluids. Magnesium (Mg2+) Sources: - It is present in meat, fish, sea foods, green vegetables, legumes, peas and nuts. Functions: 1. It enters in the structure of skeleton (bones and teeth). 2. It activates many enzymes e.g., kinase enzymes. 3. It is important for muscle contraction, nerve impulse transmission and it decreases neuromuscular excitability. Body magnesium: - Body contains about 21 g of magnesium. - 70% of magnesium is present in bones and teeth. - The remaining 30% are mostly intracellular in other tissues and body fluids. Daily requirements: About 300 mg/day are needed for adults. 88  Micro-minerals (Trace elements) IRON (Fe3+) Sources: Meats, liver, kidney , spleen, egg yolk, fish, nuts, dates and beans. Spinach is a poor source, because of its lower content of iron and some iron is bound to phytate. Functions of Iron: 1. As a component of hemoglobin and myoglobin, it is required for O 2 and CO2 transport. 2. As a component of cytochromes required for oxidative phosphorylation. 3. As a component of the essential enzyme, (lysosomal) myeloperoxidase, it is required for phagocytosis and killing of bacteria by neutrophils. 4. Lactoferrin binds iron in milk, it facilitates the transfer of iron to intestinal receptor in the infant. It also inhibits microbial growth. Body Iron: - The total body iron of an adult male is 3-5g. It is distributed as follows: RBCs iron (hemoglobin): 66%, tissue iron (33%) and plasma iron 1%. Factors affecting iron absorption: a) Factors increasing iron absorbtion: 1. Gastric HCl: The acidity of gastric HCl liberates free Fe+3 from chemically combined dietary iron. 2. Reducing substances: e.g., cysteine (SH), ascorbic acid and glutathione convert Fe+3  Fe+2 (ferrous) which is more soluble and easily absorbed. Proteins in diet enhance iron absorption due to its cysteine content. 3. Body needs: Absorption occurs only if the body is in need to iron. 89  b) b) Factors decreasing iron absorbtion: 1. A high phosphate diet: Inhibits iron absorption due to the formation of insoluble compounds of iron phosphate. 2.Phytic acid (of cereals) and oxalate: Inhibit iron absorption due to the formation of insoluble iron salts (ferric phytate, ferric oxalate). 3.Steatorrhea: Inhibits iron absorption due to the formation of insoluble iron soaps with fatty acids. Alterations of plasma iron: a) Iron deficiency anemia: Causes: 1. Deficient intake. 2. Impaired absorption: e.g. Steatorrhea, abdominal surgery. 3. Excessive loss e.g. menstrual loss, gastrointestinal bleeding, bleeding due to some parasites (anchylostoma). b) Iron overload: Causes: 1. Repeated blood transfusion. 2. Intravenous administration of iron. 3. Hemochromatosis (hemosiderosis, Bronz diabetes): - This is a rare hereditary disease characterized by abnormal increase of iron absorption. Iron is deposited in the form of hemosiderin in: 1. Liver: Causing liver cirrhosis. 2. Pancreas: Causing fibrosis and diabetes mellitus. 3. Skin: Causing Bronz discoloration of skin. Requirements: - Adults: 10 mg/day. Pregnant and lactating women: 30 mg/day. Copper (Cu2+) 90 - Sources: - The richest sources of copper are nuts, liver& kidney Functions: 1. It is essential for hemoglobin synthesis. 2. It enters in the formation of bone. 3. Maintains the myelin within the nervous system. 5. Copper is a component of the following enzymes: 1. cytochrome oxidase and superoxide dismutase. 2. tyrosinase, lysyl oxidase and dopamine--oxidase Zinc (Zn2+) Sources: liver, eggs, seafood and milk. Functions: 1. Zinc is important for growth and reproduction. It is a cofactor for RNA and DNA polymerases, so RNA and DNA synthesis. 2. It plays a role in tissue repair, wound healing and hair and nail integrity. 3. Zinc is required for mobilization of vitamin A from the liver. 4. Insulin forms complex with zinc, in the B cells of the pancreas is used to store and release insulin. 5. Immunostimulant and essential for male reproductive system 6. Anti-inflammatory. Iodine (I-) Sources: Iodized table salt will provide daily body needs. Fish, seafood, weeds and vegetables grown near seaboard are good sources. Functions: 91 - The only known function of iodine is the formation of thyroid hormones (T3 and T4). Deficiency: It results in thyroid hypertrophy (enlargement) and goiter. Selenium (Se2+) - Selenium is an essential component of the enzyme glutathione peroxidase Fluoride (Fl-) - Fluoride is an essential component of bones and teeth. - F (as fluoride [F− ]) is added to water in many parts of the world to reduce the incidence of dental caries. F − replaces the hydroxyl group of hydroxylapatite, forming fluoroapatite that is more resistant to the enamel- dissolving acid produced by mouth bacteria. - Fluoride ions are also potent inhibitors of the Enolase enzyme of the glycolytic pathway. This results in the inhibition of the glycolytic pathway in bacteria with decreased lactic acid formation. 92  Enzymes Enzymes are biocatalysts. Life is possible due to the coordination of numerous metabolic reactions inside the cells. Proteins can be hydrolyzed with hydrochloric acid by boiling for a very long- time; but inside the body, with the help of enzymes, proteolysis takes place within a short-time at body temperature. Lack of enzymes will lead to block in metabolic pathways causing inborn errors of metabolism. The substance upon which an enzyme acts, is called the substrate. The enzyme will convert the substrate into the product or products. Almost all enzymes are proteins. Enzymes follow the physical and chemical reactions of proteins. They are heat labil