Biomolecules
Introduction to Biomolecules
A living organism is a collection of organic molecules.
The compounds in a cell mostly consist of carbon, hydrogen, oxygen, nitrogen,
phosphorus and sulphur.
Biomolecules are bigger and more complicated.
Sugars, lipids, proteins, polysaccharides and vitamins are some examples of
biomolecules.
Carbohydrates: Classification
Carbohydrates are polyhydroxy aldehydes or ketones.
Carohydrates can be classified based on their behaviour during hydrolysis. These broad
groups include monosaccharides, oligosaccharides and polysaccharides.
Monosaccharides are the basic building blocks of carbohydrates.
Monosaccharides can be classified based on the number of carbons and the functional
group present.
Oligosaccharides yield two to ten monosaccharide units when hydrolysed.
Polysaccharides yield a large number of monosaccharide units when hydrolysed.
Tollen’s and Fehling’s test can be used to identify reducing sugars.
Carbohydrates: Glucose-Preparation and Structural Determination
Glucose is an aldohexose with the chemical formula C6 H12O6.
Fischer projections are a convenient way to show stereochemistry of carbohydrates. The
Relative configuration of carbohydrates can be determined by comparison with the
configuration of two enantiomers of glyceraldehydes.
Glyceraldehyde is chosen as a standard of reference as it is a simplest carbohydrate that
has a single asymmetric carbon which shows optical isomerism.
The carbohydrate or monosaccharide which can be chemically correlated to (+) isomer
of Glyceraldehyde is said to possess D configuration and the carbohydrate or
monosaccharide which can be chemically correlated to (-) isomer of Glyceraldehyde is
said to possess L configuration.
D or L represent the relative configuration of a particular stereoisomer and doesn’t hold
any relation with the optical activity of the compound.
Carbohydrates: Cyclic Structure of Glucose and Fructose
Glucose can form open-chain and two cyclic ring structures, called pyranoses.
The cyclic structure is attributed to the formation of hemiacetal from the reaction
between the aldehydlic group and the C-5 hydroxyl group in the same molecule. The
cyclic structure thus formed is a six-membered ring.
Haworth projections are useful for showing cyclic structures.
Fructose is a ketohexose with the chemical formula C6 H12O6. It is laevorotatory.
Fructose is found in both open-chain and cyclic ring structures.
The cyclic structure is obtained when the hydroxyl group at C 5 gets added to the
carbonyl group at C 2. The cyclic structure thus obtained is a five-membered ring.
Cyclic ring structures with five-membered rings are called furanoses.
Carbohydrates: Disaccharides
Glycosidic bonds link monosaccharides through an oxygen atom.
Sucrose, a non-reducing sugar, is made from glucose and fructose.
Solutions of sucrose are dextrorotatory, but when sucrose is hydrolysed, it becomes
laevorotatory.
• The hydrolysis of sucrose produces a mixture that is laevorotatory. A change in the sigh
of optical rotation from dextrorotatory to laevorotatory that takes place during the
process of hydrolysis is called the inversion of sugar.
Maltose is made from two glucose units, while lactose is made from galactose and
glucose.
Carbohydrates: Polysaccharides and Importance of Carbohydrates
Polysaccharides contain many monosaccharide units joined together by glycosidic
linkages.
Chemically, starch is a polymer of α isomer of D-(+)-glucose.
Starch is made of two components: amylase and amylopectin.
Cellulose is a straight-chain polysaccharide. It is made up of chains of β-D-glucose
units.
Cellulose is a polysaccharide that makes up plant cell walls.
Glycogen is the storage form of glucose in animals.
Carbohydrates have a variety of important uses
Proteins: Amino Acids
Proteins are polymers of α-amino acids. Naturally occurring proteins are made from L –
amino acids only.
Amino acids contain an-NH2 group and a –COOH group, with a side chain, all attached
to the α-carbon.
Amino acids can be classified as acidic, basic or neutral on the basis of their nature.
Amino acids form zwitter-ions in aqueous solutions.
The high melting points and solubility of most of the amino acids is due to their dipolar
ion structure.
Proteins: Structure and Denaturation, Enzymes
Proteins are polymers of α-amino acids that are linked by peptide bonds.
Protein structures can be described as primary, secondary, tertiary and quaternary.
α-helices and β-sheets are important examples of secondary structure.
Proteins can be denatured by a change in temperature or pH.
Enzymes are proteins that catalyse specific reactions.
Vitamins
Vitamins are necessary part of our diet, and deficiencies lead to specific diseases.
Vitamins A, D, E and K are fat soluble vitamins. Vitamin C an B group vitamins are
water soluble vitamins.
Vitamin A deficiency leads to xeropthalmia.
Vitamin D deficiency leads to rickets in children and osteomalacia in adults.
Vitamin K deficiency leads to slower blood clotting.
Vitamin E deficiency leads to fragile red blood cells and muscular weakness.
Vitamin C deficiency causes scurvy.
Vitamin B1 deficiency causes beriberi.
Nucleic Acids
Nucleic acids are the biomolecules present in all living cells, and are responsible for
transmitting genetic information from one generation to the next.
The basic components of nucleic acids include a pentose sugar, a phosphate group and
nitrogen bases.
DNA contains D-2-Deoxyribose, but RAN contains D-Ribose.
The nitrogenous bases in DNA are adenine, guanine, cytosine and thymine. RNA use
uracil in place of thymine.
The double helix structure of DNA is held together by A-T and C-G base pairing.
There are 3 types of RNA in cells.
Nucleic acids store genetic information and encode protein sequences.
