Biochemistry carbohydrates classification

carbohydrates classification

1. Fifth semester CELL BIOLOGY AND BIOCHEMISTRY

2. Biomolecules Biomolecules are any molecules that are produced by living organisms. Micromolecules Small, low molecular weight compound Monomers and o ligomers Macromolecules There are 4 major biological macromolecules: proteins, lipids, carbohydrates, and nucleic acids.  Each of these four has their own unique chemical structure and their own specific function within living organisms.  Humans and other organisms are able to consume these macromolecules within the foods we eat every day as well as manufacture some of them within our cells, such as proteins which we assemble from amino acids.  

3. 1. Proteins Building Blocks : Amino Acids Metabolic Intermediates : α- Keto acids, Ammonia (NH₄⁺) Precursors : Carbon skeletons from glycolysis and the citric acid cycle, Nitrogen from ammonia or other nitrogenous compounds Amino Acids : 20 standard amino acids. Metabolic Intermediates : α- Keto acids : Intermediates such as pyruvate , oxaloacetate , and α- ketoglutarate . Ammonia : Source of nitrogen for amino group incorporation. Precursors : Glycolysis and Citric Acid Cycle Intermediates : Pyruvate (from glycolysis ), α- ketoglutarate , oxaloacetate (from the citric acid cycle). Example Pathway : Glutamate Synthesis : α- Ketoglutarate (from the citric acid cycle) + NH₄⁺ → Glutamate (via glutamate dehydrogenase )

4. 2. Nucleic Acids Building Blocks : Nucleotides Metabolic Intermediates : PRPP ( phosphoribosyl pyrophosphate), ATP, GTP Precursors : Ribose-5-phosphate, Nitrogenous bases ( purines and pyrimidines ) Nucleotides : Composed of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose ), and phosphate groups. Metabolic Intermediates : PRPP : Synthesized from ribose-5-phosphate. ATP, GTP : Purine nucleotides used in energy transfer and nucleic acid synthesis. Precursors : Ribose-5-phosphate : From the pentose phosphate pathway. Nitrogenous Bases : Purines (adenine, guanine) and pyrimidines (cytosine, thymine, uracil ). Example Pathway : Purine Synthesis : Ribose-5-phosphate → PRPP → Inosine monophosphate (IMP) → AMP and GMP

5. 3. Carbohydrates Building Blocks : Monosaccharides Metabolic Intermediates : Glucose-6-phosphate, Fructose-6-phosphate, Glyceraldehyde-3-phosphate Precursors : Carbon dioxide (CO₂), Water (H₂O) Monosaccharides : Simple sugars like glucose, fructose, and galactose . Metabolic Intermediates : Glucose-6-phosphate : Central in glycolysis and gluconeogenesis . Fructose-6-phosphate : Intermediate in glycolysis . Glyceraldehyde-3-phosphate : Intermediate in glycolysis and the Calvin cycle. Precursors : CO₂ and H₂O : Used in photosynthesis to produce glucose. Example Pathway : Photosynthesis : 6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ (glucose) + 6 O₂

6. 4. Lipids Building Blocks : Fatty Acids and Glycerol Metabolic Intermediates : Acetyl- CoA , Malonyl-CoA , Glycerol-3-phosphate Precursors : Acetyl- CoA , Dihydroxyacetone phosphate (DHAP) Fatty Acids : Long hydrocarbon chains with a carboxyl group. Glycerol : A three-carbon molecule with hydroxyl groups. Metabolic Intermediates : Acetyl- CoA : Central intermediate in lipid metabolism. Malonyl-CoA : Used in the elongation of fatty acids. Glycerol-3-phosphate : Intermediate in glycolysis and lipid biosynthesis. Precursors : Acetyl- CoA : From carbohydrate, lipid, and protein metabolism. DHAP : From glycolysis . Example Pathway : Fatty Acid Synthesis : Acetyl- CoA + Malonyl-CoA → Palmitate (via fatty acid synthase complex)

7. Building block molecule life is made up of matter Matter  occupies space and has mass All matter is composed of  elements , substances that cannot be broken down or transformed chemically into other substances.  Each element is made of atoms, each with a constant number of protons and unique properties. A total of 118 elements have been defined; however, only 92 occur naturally, and fewer than 30 are found in living cells. 

8. Carbohydrate Classification Structure Functions of simple sugar and compound carbohydrates

9. Carbohydrates “Hydrate of carbon” H & O 2:1 ratio Carbohydrates are defined as biomolecules containing a group of naturally occurring carbonyl compounds ( aldehydes or ketones ) and several hydroxyl groups . It consists of carbon (C), hydrogen (H), and oxygen (O) atoms (1;2;1), usually with a hydrogen-oxygen atom ratio of 2:1 (as in water). It’s represented with the empirical formula Cm(H 2 O)n (where m and n may or may not be different) or (CH 2 O)n. Aldehyde group – aldoses Keto group - ketoses Neutral have only hydroxyl & carboxyl group Basic : contain amino group in addition to hydroxyl & carboxyl group Acidic : additional carboxyl groups

10. Classification of carbohydrates Simple sugars Compound sugars

11. Monosaccharide Monosaccharides are the simplest carbohydrates and cannot be hydrolyzed into other smaller carbohydrates. The “mono” in monosaccharides means one, which shows the presence of only one sugar unit. simple sugars colorless, crystalline solids that are soluble in water and insoluble in a nonpolar solvent. general formula representing monosaccharide structure is Cn (H2O)n or CnH2nOn. Dihydroxyacetone and D- and L-glyceraldehydes are the smallest monosaccharides – here, n=3. The monosaccharides containing the aldehyde group (the functional group with the structure, R-CHO) are known as aldolases and the one containing ketone groups is called ketoses (the functional group with the structure RC(=O)R′). Some examples of monosaccharides are glucose, fructose, erythrulose , and ribulose .

12. Glucose ( C 6 H 12 O 6 ) Dextrose/grape sugar/corn sugar Sweet, solid, colourless , water soluble, crystalline Right handed configuration and dextrorotatory 5 hydroxyl grp , free terminal aldehyde group hence its reducing sugar Biological roles Immediate sources of energy and food Indispensable for functioning of brain cells Forms storage products starch in plants, glycogen in animals Building block of cellulose Essential constituent of blood

13. Fructose (C 6 H 12 O 6 ) Levulose or fruit sugar Sweet, solid, colourless , water soluble, crystalline ketohexose Found in sweet fruits and honey Obtained by hydrolysis of corn sugar Fructose is a hexose sugar with a ketone functional group, making it a ketohexose. In its most common form in solution, It exists as a six- membered ring ( furanose form). Functions Produce energy. It enters glycolysis after being converted to intermediates such as fructose-6-phosphate or fructose-1-phosphate. Fructose combines with glucose to form sucrose, a disaccharide. Fructose is primarily metabolized in the liver, where it is converted to intermediates such as fructose-1-phosphate by the enzyme fructokinase . Excess fructose can be converted into triglycerides (fat) in the liver through a process called de novo lipogenesis .

14. Galactose Galactose , a member of a group of carbohydrates known as simple sugars ( monosaccharides ). less sweet than glucose and fructose It is usually found in nature  combined  with other sugars, as, for example, in  lactose  (milk sugar). Galactose is also found in complex carbohydrates and in carbohydrate-containing lipids called glycolipids , which occur in the brain and other nervous tissues of most animals. Found in honey, celery, beets, and yogurt Galactose has a carbonyl carbon at carbon number one and can be formed into a six- membered ring. Glucose and galactose have similar structures but differ in their hydroxyl group orientation

15. Functions of Monosaccharides Glucose (C6H12O6) is an important source of energy in humans and plants. Plants synthesize glucose using carbon dioxide and water, which in turn is used for their energy requirements. • The presence of galactose is in milk sugar (lactose), and fructose in fruits and honey makes these foods sweet. • Ribose is a structural element of nucleic acids and some coenzymes. • Mannose is a constituent of mucoproteins and glycoproteins required for the proper functioning of the body.

16. Disaccharides Disaccharides consist of two sugar units (two monosaccharides ) When subjected to a dehydration reaction (condensation reaction or dehydration synthesis), they release two monosaccharide units. The covalent bond formed between the two sugar molecules is known as a glycosidic bond. Some examples of disaccharides are lactose, maltose, and sucrose. Sucrose is the most abundant disaccharide of all and is composed of one D-glucose molecule and one D-fructose molecule.

17. Sucrose (C 12 H 22 O 11 ) Cane sugar or table sugar, Non reducing disaccharide Sucrose is a molecule composed of two monosaccharides , namely glucose and fructose. Bind by glycosidic linkage This non-reducing disaccharide has a chemical formula of C 12 H 22 O 11 . Sweet, water soluble, crystalline solid Storage form of beetroot and sugarcane C 12 H 22 O 11  can be obtained from sugar beets or sugar canes, but it must be refined to be fit for human consumption. Refined sucrose (or sugar) is a popular ingredient in many food recipes because of its sweet taste. There are no anomeric hydroxyl groups in a sucrose molecule. It can, therefore, be classified as a non-reducing sugar (since it does not act as a reducing agent).

18. Uses of Sucrose most important components of soft drinks and other beverages. used in many pharmaceutical products. It serves as a chemical intermediate for many emulsifying agents and detergents. It also serves as a food thickening agent and as a food stabilizer. The shelf lives of many food products, such as jams and jellies, are extended with the help of this compound. The use of sucrose in baking results in the brown colour of the baked products. This compound also serves as an  antioxidant  (a compound that inhibits oxidation). Sucrose is widely used as a food preservative.

19. Lactose (C 12 H 22 O 11 Lactose is a disaccharide sugar composed of one molecule of glucose and one molecule of galactose . It is commonly known as "milk sugar" because it is the primary carbohydrate found in milk and dairy products. Milk from cows and goats is used to make cheese and yogurt, but not all milk products contain the same amount of lactose . For example, hard cheeses such as cheddar, parmesan and Swiss contain very little or no lactose , whereas milk, ice cream and yogurt contain higher amounts of lactose. Hard cheeses are lower in lactose due to the removal of whey (a liquid solution of fat, lactose and protein) while they are being made as well as the continued breakdown of lactose by bacteria during the aging process. Lactose intolerance  is a condition that stems from the body not producing enough lactase and results in the expression of physical symptoms such as abdominal bloating and cramps, diarrhea and gas

20. maltose Maltose , also known as malt sugar, is a disaccharide made up of two alpha D-glucose units. Colourless , crystalline, water soluble, reducing disaccharide, found in starch and glycogen The two units of glucose undergo condesation polymerization through alpha 1,4 glycosidic linkage In the small intestinal lining in humans, the enzyme maltase and isomaltase break down the molecules of maltose into two glucose molecules, which is then absorbed by the body. In higher animals, maltose is the end product of oral and intestinal digestion of starch by amylases and further hydrolysed into glucose molecules by intestinal enzyme maltase

21. Uses of Maltose Maltose lacks sweetness and is not used as a sweetener. Instead, it is used in the malting of barley for the manufacturing of beer. It is used extensively in alcohol production. Free maltose, as well as maltose formed by the digestion of starch in the mouth, can cause dental caries. Enzyme maltase and isomaltase present in the small intestine break down maltose into two glucose units which are then absorbed. Our body has the capacity to absorb maltose directly, which later on can be broken down into glucose units for producing energy. Due to a high glycemic index, maltose increases blood sugar levels.

22. Functions of Disaccharides • Sucrose is a product of photosynthesis, which functions as a major source of carbon and energy in plants. • Lactose is a major source of energy in animals. Maltose is an important intermediate in starch and glycogen digestion. • Trehalose is an essential energy source for insects. • Cellobiose is essential in carbohydrate metabolism. • Gentiobiose is a constituent of plant glycosides and some polysaccharides

23. Oligosaccharides Oligosaccharides are complex compounds that yield 2 to 10 molecules of the same or different monosaccharides on hydrolysis joined through glycosidic linkage. Based on the number of monosaccharides attached, the oligosaccharides are classified as trisaccharides , tetrasaccharides , pentasaccharides , and so on. The general formula of trisaccharides is Cn (H2O)n-2, and that of tetrasaccharides is Cn (H2O)n-3, and so on. The oligosaccharides are normally present as glycans . They are linked to either lipids or amino acid side chains in proteins by N- or O- glycosidic bonds known as glycolipids or glycoproteins . The glycosidic bonds are formed in the process of glycosylation , in which a carbohydrate is covalently attached to an organic molecule, creating structures such as glycoproteins and glycolipids .

24. Tri and Tetrasaccharides Both present in plants in small amount Trisaccharides – Raffinose (found in sugar beet, cotton seed and fungi); Formed of glucose, fructose and galactose Gentianose – rhisome of some plants; two molecules of glucose and one molecule of fructose Tetrasaccharide – Stachynose – found in plants stachys species ; one mol. of glucose, one mol. Of fructose, two mol. of galactose

25. Functions of Oligosaccharides Glycoproteins are carbohydrates attached to proteins involved in critical functions such as antigenicity , solubility, and resistance to proteases. Glycoproteins are relevant as cell-surface receptors, cell-adhesion molecules, immunoglobulins , and tumor antigens. • Glycolipids are carbohydrates attached to lipids that are important for cell recognition and modulate membrane proteins that act as receptors. • Cells produce specific carbohydrate-binding proteins known as lectins , which mediate cell adhesion with oligosaccharides. • Oligosaccharides are a component of fiber from plant tissues. cell recognition and cell adhesion

26. Polysaccharides ( glycan ) (C 6 H 10 O 5 ) n Polysaccharides are a chain of more than 10 carbohydrates joined together through glycosidic bond formation. They are ubiquitous and mainly involved in the structural or storage functions of organisms. All the glycosidic linkages between the sugar monomers of a polysaccharides are not of same type They include α -(1-2)linkage, α -(1-4)linkage, α -(1-6)linkage, β -(1-2)linkage, β -(1-4)linkage classified into two groups: homopolysaccharides (similar kinds of monosaccharides ) and heteropolysaccharides (different kind of monosaccharides ) Eg : starch, glycogen, cellulose, chitin

27. a) Homoglycan - contains only one type of monosaccharide unit - eg . Starch, glycogen, cellulose Starch Storage form of polysaccharide abundant in tubers, corms, seeds Formed of two kinds of glucose polymers, α - amylose (10-20%) and β - amylose (80-90%) α - amylose is long, , linear, unbranched, curved, helically coiled, water soluble, formed of 200 glucose unit linked by α -(1-4) glycosidic bonds Amylopectin branching and water insoluble, 30 subunits linked by α -(1-4) glycosidic bonds Glycogen Highly branched. Short term storage polysaccharide of animal tissue abundant in liver and skeletal muscles. Present in small amt in bacteria and plants It differs from starch in the abs. of unbranched α - amylose type

28. Cellulose Linear, unbranched, water soluble structural polysaccharides Formed of 1,200-12,500 β -glucose units through β -(1-4) glycosidic bonds Occurs in plants b) Heterogylcan contains only different type of monosaccharide unit Include agar, neutral sugars and mucopolysaccharides Agar is starch-like heteropolymer from sea weeds ( gelidium , gracilaria ) ; hydrophillic , swells strongly in cold water and forms gels; dissolves in water to form sol sets to gel on cooling Cannot digested by bacteria hence used as supporting agent in bacterial culture medium

29. LIPIDS Classification (Simple lipids, Complex lipids, Derived lipids) Fatty acids – saturated and unsaturated Triacyl glycerols Phospholipids Sphingolipids

30. Lipids Esters of fatty acids and alcohol fatty acids –long chain aliphatic organic acids Alcohol in both plants and animal are glycerol but in plant some contain cholesterol Chemically diverse group of organic compound which are insoluble, or poorly soluble in water Hydrophobic nature is due to predominance of hydrocarbon chains -(CH 2 -CH 2 -CH 2 )-in their structure Non-polar, hydrophobic, fatty, oily, waxy, Include broad range of molecules such as fatty acids, phospholipids, sterols, sphingolipids , terpenes Functions of biological lipids Storage form of metabolic fuel Provide structural components of membranes Have protective function in bacteria, fungi, plant, insects, vertebrates,

31. Classification of Lipids Three major groups of Lipids - Simple lipids - Compound lipids - Derived lipids ADD PICTURE IN PAGE 256

32. Simple lipids Homolipids , alcohol esters of fatty acids Yield fatty acids and alcohol on hydrolysis Formed of carbon, hydrogen, oxygen They include neutral fats and waxes Fats : esters of fatty acids and glycerol ( acyl glycerols or glycerides Waxes : esters of fatty acids and non-glycerol aliphatic alcohols. Neutral fats Waxes Neutral fats Mixtures of triacylglycerols (triglycerides) Ester of fatty acids and glycerols Have fa

33. Amino acids, peptides and proteins Amino acids Classification based on polarity Zwitterions dipeptides

34. Proteins Primary, secondary, tertiary, quaternary structures of proteins Native conformations Biological functions of proteins Denaturation and renaturation

35. Nucleotides Structures, functions of nucleotides Nucleotide derivatives

36. Secondary metabolites A brief account of secondary metabolites Physiological roles Significance : ecological importance

37. Enzymes Classification Mechanism of enzyme action Optimization of weak interactions in the transition state Co-enzymes Inhibition, regulation Allosteric enzymes Covalently modulated enzymes Isoenzymes