CHAPTER 1: BIOMOLECULES PART 1- CARBOHYDRATES
BIOMOLECULES: An organic compound normally present as an essential component of living organism.
CARBOHYDRATES
- Carbohydrates (German: Kohlenhydrate, French: hydrates de carbone) were once thought to be made up entirely of carbon and water in a 1:1 ratio.
- Saccharide is a name taken from the Latin word for sugar (origin = "sweet sand").
- Carbohydrate is most commonly used in biochemistry as a synonym for saccharide.
- Glyceraldehyde or dihydroxy acetone are the simplest polyhydroxy aldehyde or ketone with the empirical formula (CH2O)n. Carbohydrates are defined as polyhydroxy aldehyde or ketone with the empirical formula (CH2O)n.
- Sugars, starches, cellulose, and a variety of other chemicals present in living creatures are examples of carbohydrates.
STRUCTURE
- Monosaccharides make up the majority of saccharides found in biological systems.
- H - (CHOH)x (C = O) - (CHOH)y - H, having a ketonic functional group, or H - (C = O) - (CHOH)x - H, containing an aldehydic functional group, is a typical monosaccharide structure.
- Each carbon atom, with the exception of the functional group carbon atom, possesses hydroxyl groups.
THE CONCEPT OF ISOMERISM IS REQUIRED IN THE STUDY OF CARBOHYDRATES.
There are two major kinds of isomeric forms:
- Structural isomers and isomers with the same molecular formula but distinct structures.
- Stereo isomers have the same chemical and structural formula but differ in their configuration, or how the atoms are arranged in space.
Stereo isomers are further divided into optical and geometrical isomers.
- In carbohydrate chemistry, optical isomerism is increasingly important.
- The existence of a chiral centre causes optical isomerism (asymmetric carbon atom).
Chiral centre refers to the carbon atom with four distinct groups connected to it.
As a result, there are two ways to arrange the atoms as shown:
- The hydroxyl group on the right hand side is denoted by D, whereas the hydroxyl group on the left is denoted by L.
- Enantiomers are two forms that are mirror images of one another.
- Distereoisomers are stereoisomers that are neither enantiomers nor diastereoisomers.
Enantiomers are I and II, III and IV, whereas diastereomers are I, III, IV and II,III, IV.
- Enantiomers have the same physical qualities as one another, such as melting and boiling points and solvent solubility, but they rotate planar polarised light in opposing directions.
- Dextrorotatory (marked by +) devices rotate plane polarised light in a clockwise manner.
- Levorotatory are those that revolve in an anticlockwise way (represented by -).
- As a result, D-glucose can be both dextrorotatory (+) and levorotatory (-). (-).
- Only at C - 2 carbon do D - Glucose and D - Mannose have distinct configurations.
- Epimers of each other are carbohydrate molecules that differ only in one carbon atom's structure.
- Carbohydrates are frequently categorised based on how many saccharide units they contain.
- Carbohydrates are simple sugars or monosaccharides in their most basic form.
- These simple sugars can be combined to create more complex carbs.
SIMPLE CARBOHYDRATES
- Only at C - 2 carbon do D - Glucose and D - Mannose have distinct configurations.
- Epimers of each other are carbohydrate molecules that differ only in one carbon atom's structure.
- Natural foods such as fruits, vegetables, milk, and milk products contain a lot of simple sugars. Honey, molasses, maize, and maple syrup are other excellent sources of simple sugars.
MONOSACCHARIDES
- The term'mono' refers to a solitary person.
- Monosaccharides are sweet-tasting, colourless crystalline solids that are readily soluble in water but insoluble in nonpolar solvents.
- They are made up of carbon, hydrogen, and oxygen in the ratio 1:2:1 and have the emperical formula (CH2O)n
- Glucose, fructose and galactose are types of monosaccharides.
- Monosaccharides have a backbone made up of an unbranched single bonded carbon chain.
- A carbonyl group is formed when one of the carbon atoms is doubly linked to an oxygen atom.
- The monosaccharides may be an aldehyde (carbonyl group at the end of the carbon chain) or a ketone (carbonyl group at any other position in the chain) and are referred to as ALDOSE or KETOSE, respectively.
- Triose, tetroses, pentoses, hexoses, and heptoses are monosaccharides with 3,4,5,6, or 7 carbon atoms in their backbone, respectively. Glyceraldehyde, for example, is an aldose, whereas Dihydroxy acteone is a ketose.
- Many simple sugars can be found in a ring or chain configuration. The aldehyde/ketonic carbonyl group carbon (C = O) and hydroxyl group (- OH) combine to produce a hemiacetal with a new C - O - C bridge when the open-chain form of a monosaccharide coexists with a closed ring form.
- Because to its low angle and eclipsing strain, five and six-membered rings are preferred over other ring sizes. Furanose (five-membered cyclic structures) and pyranose (three-membered cyclic structures) are two types of cyclic structures (six-membered)
- Example: The glucose ring form is formed when the oxygen on carbon number 5 binds to the carbonyl group's carbon (carbon number 1) and transfers its hydrogen to the carbonyl oxygen, resulting in the formation of a hydroxyl group.
- When the hydroxyl group is on the opposite side of the -CH2OH group, alpha glucose is produced; when the hydroxyl group is on the same side as the -CH2OH group, beta glucose is produced.
DIASACCHARIDES
- A disaccharide is produced when two monosaccharides join together in a condensation reaction, releasing a molecule of water in the process.
- A glycosidic bond in an anomeric carbon connects the two monosaccharide units. Sucrose, maltose, and lactose are three common disaccahrides.
- Disaccharides cannot be absorbed into the circulation through the small intestinal wall.
- As a result, they are degraded into monosaccharides by sucrase or invertase, maltase, and lactase (- galactosidase).
Sucrose:
- The main carbohydrate found in cane sugar, also known as table sugar.
- (1 --> 1) glycosidic linkages connect glucose and fructose.
- Sucrase, also known as invertase, is an enzyme that catalyses the hydrolysis of sucrose in the gut into D-glucose and D-fructose, which are then rapidly absorbed into the bloodstream.
Lactose:
- A common sugar found in milk and dairy products.
- (1 --> 4) glycosidic linkages connect glucose + galactose molecules.
- Lactase is an enzyme that catalyses the breakdown of this disaccharide in mammals during digestion.
- Lactose intolerance is a clinical disease caused by a lack of these enzymes. Due to a lactase deficiency, the subjects in these studies are unable to digest lactose.
Maltose:
- The most basic sugar, found in barley malt and as a byproduct of starch breakdown.
- Glucose + glucose are connected by glycosidic linkages (1 --> 4).
- The intestinal enzyme maltase hydrolyzes maltose into two molecules of Dglucose, which particularly cleaves the (1 --> 4). bond
Oligosaccharides:
- Oligosaccharides are carbohydrates with more than two or up to 10 monosaccharide units.
- Raffinose and stachyose are two examples of oligosaccharides, which are made up of fructose, galactose, and glucose chains that repeat themselves.
- Raffinose is a trisaccharide found in beans, peas, soy, cabbage, brussels sprouts, and broccoli, among other legumes and vegetables.
- Galactose is linked to sucrose through a glycosidic connection (1 --> 6).
Polysaccharides:
- Polysaccharides are polymeric carbohydrate compounds made up of repeated units (mono- and disaccharides) linked by glycosidic linkages.
- The standard formula for polysaccharides is Cx (H2O)y, where x is generally a high value between 200 and 2500.
- These structures are usually linear, although they can have a variety of branching levels.
- They might be amorphous or even water insoluble.
- Polysaccharides are classified into two groups based on the monosaccharide units: homopolysaccharides and heteropolysaccharides.
Heteropolysaccharides: Heteropolysaccharides are polysaccharides that contain more than one type of monosaccharide, such as pectin (a polymer of galactouranic acid and its methylated ester).
Starch:
- Starch is the most abundant storage polysaccharide in nature, and it is a storage sugar found in all plant cells.
- Tubers, such as potatoes and maize seeds, are high in this.
- Starch is a glucose polymer that comprises two kinds of glucose polymers:
- is made up of hundreds of D-glucose residues in linear, unbranched chains.
- A (1 --> 4) glycosidic bond connects the C1 and C4 carbon atoms of the glucose residues.
- Such chains can have a molecular weight of up to 50000.
- The total number of glucose residues in an amylopectin molecule might be in the thousands.
- Every 24 to 30 glucose units, (1 --> 6) bonds form, resulting in branching.
Glycogen:
- In animal cells, glycogen is the primary store polysaccharide, but in plant cells, starch is the primary storage polymer.
- Glycogen is a branching polysaccharide made up of D glucose monomer units linked together by a glycosidic connection (1 --> 4).
- Glycogen's (1 --> 6) branches are shorter, more frequent, and more widespread than amylopectin's. In this case, the overall structure is more compact.
- alpha- amylases, which are found in saliva and pancreatic juice and released into the digestive system, hydrolyze both glycogen and starch in the digestive tract.
- alpha- amylases hydrolyze the (1 --> 4) glycosidic linkage of glycogen and amylopectin's outer branches, yielding Dglucose, maltose, and a refractory core known as "limit dextrin."
- alpha- because to their inability to cleave ( 1 --> 6 ) bonds, amylases cannot hydrolyze limit dextrins any further. This is accomplished by a “debranching” enzyme, (1-6) glucosidase, which acts on the branch connections.
- alpha- amylase and (1-6) glucosidase work together to fully breakdown glycogen and starch (amylopectin)
- Cellulose is the most common structural carbohydrate found in plant cell walls.
- Cellulose is present in stalks, stems, trunks, and woody parts of plant tissues' cell walls.
- Like starch, cellulose is made up of monomer units of glucose that are connected in a linear way by (1 --> 4) glycosidic linkages.
- Because cellulose molecules lack side chains, they may lay close together and create stiff structures.
Functions:
- ENERGY SOURCE: Monosaccharides provide 3.74 kcal/g, disaccharides 3.95 kcal/g, and starch 4.18 kcal/g, with an average of 4 kcal/g.
- ENERGY STORAGE: Starch and glycogen are stored carbohydrates in plants and mammals, respectively.
- STRUCTURAL COMPONENT: Chitin exoskeletons of almost a million species of arthropods Cellulose is the structural unit of cell walls (e.g. insects, lobsters, and crabs).
- Ribose and deoxyribose are two sugars that are found in the nucleotide structure and are part of the carrying structure of RNA and DNA, respectively.
- They're also related to a variety of proteins and lipids. They function as signals within cells, determining the metabolic fate or intracellular localisation of the attached molecules.
- Detoxifying processes: At the hepatic level, glucuronic acid, which is made from glucose, combines with endogenous substances such as hormones, bilirubin, and exogenous substances such as chemical or bacterial toxins or drugs to render them atoxic, increase their solubility, and allow their elimination.
- Glucose is required for the preservation of neural tissue integrity (certain parts of the central nervous system can only use glucose for energy generation).
