Biomolecules carbohydrates, lipids, nucleic acid

properties, classification and nature of carbohydrates, lipids, nucleic acid

1. Biomolecules DEVIPRIYA P V M PHARM CARBOHYDRATES LIPIDS NUCLEIC ACID

2. Biomolecules Biomolecules can be defined as the molecules that are produced by living organisms and form the structural basis of all living organism. Also called Biogenic molecules . Consists manly of carbon and hydrogen with nitrogen , oxygen , sulphur and phosphorous They include macromolecules like carbohydrates, proteins, lipids and nucleic acids It also includes small molecules like primary and secondary metabolites and natural products.

3. The most common biomolecules are carbohydrates, proteins, lipids, nucleic acids and vitamins. Biomolecules are large molecules of many atoms that are covalently bound together.

4. The major complex biomolecules of cells Biomolecule Building block Major functions Protein Amino acids Fundamental basis of structure and function of cell Deoxyribonucleic acid (DNA) Deoxyribonucleotides Hereditary information Ribonucleic acid (RNA) Ribonucleotides Protein synthesis Polysaccharide (glycogen) Monosaccharide (glucose) Storage form of energy to meet short term demands Lipids Fatty acids & glycerol Storage form of energy to meet long term demands

5. Carbohydrates Carbohydrates are the most abundant organic molecules in nature . Primarily composed of carbon , hydrogen & oxygen. The term carbohydrate means hydrates of carbon Carbohydrates may be defined as polyhydroxy aldehydes or ketones or compounds which produce them on hydrolysis . Carbohydrates are often referred as saccharides (sugar)

6. Functions of Carbohydrates Most abundant dietary source of energy (4 cal/g) Precursors for many organic compounds (fats, amino acids) Present (as glycoproteins and glycolipids) participate in the structure of cell membrane and cellular functions such as cell growth, adhesion and fertilization They are structural components of many organisms. These include the cellulose in plants, exoskeleton of some insects, cell wall of microorganisms Serve as the storage form of energy (glycogen) to meet the energy demands of the body.

7. Chemical nature and Classification of carbohydrates Based on number of sugar units : 1. Monosaccharides : aldoses : ketoses 2. Oligosaccharides : disaccharides : trisaccharides etc 3. Polysaccharides : homopolysaccharies : heteropolysaacharides

8. Monosaccharides: Simplest sugars and cannot be further hydrolysed . sweet to taste, crystalline in character and soluble in water General formula Cn (H2O)n. Further classified based on functional group and number of carbon atoms classification based on functional group : 1 . Aldoses : Functional group is aldehyde. Eg : glyceraldehyde, glucose 2. Ketoses: Functional group is keto group. Eg : dihydroxyacetone , fructose. Classification based on no: of c-atoms: :Trioses(3 C), Tetroses (4C), Pentoses(5C) etc

9. . Oligosaccharides: Consists of 2-10 monosaccharide units. Subdivided based on no: of monosaccharide units. Disaccharides : Consists of 2 monosaccharide units (similar or dissimilar) held together by glycosidic bond. They are crystalline, water soluble and sweet to taste It can be reducing or non- reducing Reducing: contain free aldehyde / keto group. - Eg : maltose, lactose Non-reducing: contain no free aldehyde / keto group - Eg:sucrose , trehalose.

10. Polysaccharides ( glycans ) Polymers of monosaccharide units with high molecular weight Liberates 10 or more monosaccharide units on hydrolysis. Usually tasteless and form colloids with water. The polysaccharides are of two types: Homopolysaccharies: Hydrolysis yield only single type of monosaccharide Eg : starch, glycogen, inulin , chitin, cellulose Heteropolysaacharides: Hydrolysis yield a mixture of a few monosaccharide or their derivatives. Eg:proteoglycans , glucosaminoglycans

11. Monosaccharide Biochemical importance Glyceraldehyde Glyceraldehyde 3-phosphate is an intermediate in glycolysis Dihydroxyacetone Its 1-phosphate is an intermediate in glycolysis D- Erythrose Its 4-phosphate is an intermediate in carbohydrate metabolism D-Ribose For the structure of RNA and nucleotide coenzymes(ATP, NAD+ , NADP+) D- Deoxyribose For the structure of DNA D- Ribulose It is an important metabolite in hexose monophosphate shunt D- Xylose Involved in the function of glycoproteins L- Xylulose Excreted in urine in essential pentosuria D- Lyxose As a constituent of lyxoflavin of heart muscle D-Glucose The sugar fuel of life ; excreted in urine in diabetes ; structural unit of cellulose in plants D-Galactose Converted to glucose, failure leads to galactosemia D-Mannose For the structure of polysaccharides D-Fructose Its phosphates are intermediates of glycolysis D- Sedoheptulose Its 7-phosphate is an intermediate in HMP shunt, and in photosynthesis

12. Disaccharides Biochemical importance Sucrose Most commonly used table sugar supplying calories Lactose Exclusive carbohydrate source to breast fed infants. Lactose deficiency (lactose intolerance) leads to diarrhea and flatulence Maltose An important intermediate in the digestion of starch

13. LIPIDS Lipids may be regarded as organic substances relatively insoluble in water, soluble in organic solvents (alcohol, ether etc.), actually or potentially related to fatty acids and utilized by living cells. Lipids are heterogeneous group of compounds

14. Functions of lipids They are the concentrated fuel reserve of the body ( triacylglycerols ). Lipids are the constituents of membrane structure and regulate the membrane permeability (phospholipids and cholesterol). They serve as a source of fat soluble vitamins(A, D, E & K). Lipids are important cellular metabolic regulators (steroid hormones and prostaglandins). Lipids protect the internal organs, serve as insulating materials and give shape and smooth appearance of the body

15. Classification and chemical nature of lipids CLASSIFICATION OF LIPIDS

16. Classified into Simple lipids Complex lipids Derived lipids Miscellaneous lipids Simple lipids: Esters of fatty acids with alcohol. Fatty acids(carboxylic acid with hydrocarbon side chain) are the simplest form of lipids. Both saturated (do not contain double bonds) and unsaturated fatty acids (contain one or more double bonds) almost equally occur in the natural lipids. The fatty acids that cannot be synthesized by the body and hence supplied through diet are essential fatty acids (EFA) eg : arachidonic acid.

17. EFA are required for the membrane structure and function, transport of cholesterol, formation of lipoproteins, synthesis of eicosanoids , prevention of fatty liver etc Simple lipids are of two types: (a)Fats and oils ( triacylglycerols ): These are esters of fatty acids with glycerol. Triacylglycerols (triglycerides) are the most abundant group of lipids that primarily function as fuel reserves of animals Triacylglycerols undergo properties like Hdrolysis , Saponification, Rancidity and In-vivo lipid peroxidation The difference between oil and fat is only physical (oil is a liquid and fat is solid at room temperature) Insoluble in water and non-polar in character

18. (b)Waxes: Esters of fatty acids(usually long chain) with alcohol (aliphatic or alicyclic ) other than glycerol. Cetyl alcohol is most commonly found in waxes

19. Complex(compound lipids): These are esters of fatty acids with alcohols containing additional groups such as phosphate, nitrogenous base, carbohydrate, protein etc. They are further divided as follows: (a)Phospholipids: In addition to alcohol and fatty acids, they contain phosphoric acid and frequently a nitrogenous base. Glycerophospholipids (major lipids that occur in the biological membrane) contain glycerol as alcohol Eg : lecithin. Spingophospholipids contain sphingosine as alcohol Eg : sphingomyelin (b)Lipoproteins Macromolecular complexes of lipids with proteins They are transport vehicles for lipids in the circulation.

20. Lipoproteins are of 5 types, namely chylomicrons , very low density lipoproteins (VLDL), low density lipoproteins (LDL), high density lipoproteins (HDL) and free fatty acid- albumin complexes. (c)Glycolipids: These lipids contain a fatty acid, carbohydrate and nitrogenous base. The alcohol is sphingosine , hence they are also called as glycosphingolipids . Glycerol and phosphate are absent Eg : cerebrosides , gangliosides (d)Other complex lipids: sulpholipids , aminolipids and lipopolysaccharides are among the other complex lipids

21. Derived lipids: These are the derivatives obtained on the hydrolysis of simple and complex lipids which posses the characteristics of lipids . These include glycerol and other alcohols, fatty acids, mono and diglycerols , fat soluble vitamins, steroid (cholesterol, bile acids, vitamin D, sex hormones, adrenocortical hormones), hydrocarbons and ketone bodies. Miscellaneous lipids: These include a large number of compounds posessing the characteristics of lipids. Eg : carotenoids , squalene , hydrocarbons such as pentacasone (in bees wax), terpenes etc. NEUTRAL LIPIDS : The lipids which are uncharged These are mono, di and triacylglycerols , cholesterol and cholesteryl esters

22. NUCLEIC ACID There are two types of nucleic acids, namely Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA). Nucleic acid serve as repositories and transmitters of genetic material

23. Functions of nucleic acids DNA is the chemical basis of heredity and regarded as the reserve bank of genetic information DNA is exclusively responsible for maintaining the identity of different species of organisms. Every aspects of cellular information is under the control of DNA. The DNA is organized into genes , the fundamental units of genetic information. The genes control the protein synthesis through the mediation of RNA. DNA RNA Proteins The interrelationship of these three classes of biomolecules (DNA, RNA and proteins) constitute the central dogma of molecular biology or central dogma of life

24. Components of Nucleic acids: Nucleic acids are the polymers of Nucleotides ( polynucleotides ) held by 3´ and 5´ phosphate bridges ie , nucleic acids are build up of monomeric units-nucleotides (building blocks of nucleic acids) Nucleotides are composed of a nitrogenous base, a pentose sugar and a phosphate. The term nucleoside refers to base+ sugar Thus Nucleotide is nucleoside + phosphate

25. The nitrogenous bases found in nucleotides are of two types – purines and pyrimidines (these are aromatic heterocyclic compounds)

26. DNA and RNA contain the same purines namely adenine(A) and Guanine(G). Further the pyrimidine Cytosine(C) is also present in both DNA nad RNA. They differ in the second pyrimidine base. DNA contain Thymine(T) whereas RNA contains Uracil (U)

27. Sugars of Nucleic acid: The five carbon monosaccharides ( pentoses ) are found in the nucleic acid structure. RNA contains D-ribose while DNA contains D-deoxyribose Ribose and deoxyribose differ in structure at carbon-2. Deoxyribose has one oxygen less at C2 compared to ribose

28. The pentoses are bound to nitrogenous bases by β -N- glycosidic bonds Nucleoside monophosphates possess only one phosphate moiety(AMP, TMP etc) The addition of second or third phosphates to the nucleoside results in nucleoside diphosphates ( eg : ADP) or triphosphates ( eg : ATP) respectively

29. DNA: Polymer of deoxyribonucleotides . The monomeric deoxynucleotides in DNA are held together by 3´,5´-phosphodiester bridges. The salient features of Double helical structure of DNA proposed by Watson and Crick are follows: (1)The DNA is a right handed double helix consists of gtwo polydeoxyribonucleotide cahins twisted around each other on a common axis. (2)The 2 strands are antiparallel ( one strand runs in 5´ to 3´ direction while the other in 3´ to 5´ direction) (3)The diameter of a double helix is 20 Å(2nm) (4)Each turn of helix is 34 Å with 10 pairs of nucleotides, each pair placed at a distance of 3.4 Å

30. (5)Each strand of DNA has 3´,5´-phosphodiester bonds (hydrophilic) on the periphery and the hydrophobic bases are stacked inside (6)The two polynucleotide chains are complementary to each other due to base pairing. (7)The 2 strands are held by hydrogen bonds formed by the complementary base pairs. (8)The H-bonds are formed between a purine and pyrimidine only (9)The content of adenine equals to thymine (A=T) and guanine equals to that of cytosine(G=C) (10)The genetic information resides on one of the two strands known as template strand or sense strand. The opposite strand is antisense strand

31. RNA RNA is a polymer of ribonucleotides held together by 3´,5´-phosphodiester bridges. The 3 major types of RNA are : Messenger RNA(mRNA) Transfer RNA( tRNA ) Ribosomal RNA( rRNA )