9 BIOMOLECULES

Biomolecules

All the carbon compounds that we get from living tissues.

Biomicromolecules:

Molecules which have molecular weights less than one thousand Dalton. They are also known as monomers.

Biomacromolecules:

Have molecular weight more than 10000 Daltons (generally 10,000 Daltons and above). They are generally polymers. A biomolecule a with molecular weight in the range of ten thousand daltons and above; found in acid insoluble fraction. e.g. polysaccharides, nucleic acids, proteins and lipids.

Primary and secondary metabolites

• Primary metabolites:

• have identifiable functions and play important roles in normal physiological process eg. Amino acids, nitrogenous bases, proteins and nucleic acid.
• Secondary metabolites: are product of certain metabolic pathways from primary metabolites, eg. carotenoids, drugs, alkaloids, essential oils, rubber, gum, cellulose and resins etc.

Amino acids

Organic compounds containing an amino group and one carboxyl group (acid group) and both these groups are attached to the same carbon atom called α carbon and so they are called amino acids.

e.g. In Glycine R = H

In alanine R = CH₃

In serine R = CH₂ – OH

Twenty types of amino acids. Amino acid exists in Zwitterionic form at different pHs.

Based on number of amino and carboxyl groups, amino acids can be:

Aromatic:

Tryptophan, phenylalanine and Tyrosine are aromatic (give smell) amino acids.

Proteins:

Proteins are polypeptide chains made up of amino acids. There are 20 types of amino acids joined together by peptide bond between amino and carboxylic group. There are two kinds of amino acids.

Essential amino acids are obtained by living organism along with food.

Non-essential amino acids can be prepared by our body from raw materials.

Biological macromolecules

There are three main types of biological macromolecules, according to mammalian systems:

• Carbohydrates
• Nucleic acids
• Proteins
• Lipids

Carbohydrates:

Carbohydrates are polymers of carbon, hydrogen and oxygen. They can be classified as monosaccharides, disaccharides and polysaccharides. Carbohydrates are found in starch, fruits, vegetables, milk and sugars. They are an important source of a healthy diet.

Nucleic Acids:

The nucleic acids include DNA and RNA that are the polymers of nucleotides. Nucleotides comprise a pentose group, a phosphate group, and a nitrogenous base group. All the hereditary information is stored in the DNA. The DNA synthesized into RNA and proteins.

Proteins:

Proteins are the polymers of amino acids. These include the carboxylic and the amino group. There would be no lipids or carbohydrates without proteins because the enzymes used for their synthesis are proteins themselves.

Lipids:

Lipids are a hydrophobic set of macromolecules, i.e., they do not dissolve in water. These involve triglycerides, carotenoids, phospholipids, and steroids. They help in the formation of the cell membrane, formation of hormones and in the and as stored fuel.

 

Fatty Acids & Saturated

With single bonds in carbon chain, e.g., Palmitic acid, butyric acid.

Unsaturated

With one or more double bonds, e.g., oleic acid, linoleic acid.

Glycerol

A simple lipid, is trihydroxy propane.

Some lipid have fatty acids esterified with glycerol. Example of fatty acid (Palmitic acid)

(CH₃ — (CH₂)₁₄ — COOH)

Triglyceride (R₁, R₂, R₃ are alkyl groups in fatty acids.)

Nitrogen bases (Carbon compounds with heterocyclic rings)

Purine:

Adenine, Guanine,

Pyrimidine:

Cytosine, Uracil, Thymine.

Nucleoside:

Nitrogenous base + Sugar e.g., Adenosine, guanosine.

Nucleotide:

Nitrogenous base + Sugar + Phosphate group. e.g. Adenylic acid, Guanylic acid. Thymidylic acid.

Nucleic acids:

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

Examples of Macromolecules:

Synthetic Fibres

• Nylon, rayon and spandex consist entirely of macromolecules. These are created in certain steps:
• The monomers are reacted to make prepolymers or a liquid, primitive macromolecule. In the next step, the prepolymers are fed through a cell where it solidifies and attains the desired thickness. This process is called spinning.

Genetic Transfer:

DNA is a genetic material that contains nucleic acids which code for genetic material. During meiosis, the DNA is no longer a whole, and the nucleotides that remain are responsible for transferring the genetic information to the gametes.

Monomers and Polymers

Macromolecules are basically polymers, long chains of molecular sub-units called monomers. Carbohydrates, proteins and nucleic acids are found as long polymers. Due to their polymeric nature and large size, they are known as macromolecules.

Structure of Proteins

• Primary structure:

• Is found in the form of linear sequence of amino acids. First amino acid is called N-terminal amino acid and last amino acid is called C-terminal amino acid.

• Secondary structure:

• Polypeptide chain undergoes folding or coiling which is stabilized-by hydrogen bonding. Right handed helices are observed; e.g., fibrous protein in hair, nails.

• Tertiary structure:

• Long protein chain is folded upon itself like a hollow woollen ball. Gives a 3-dimensional view of protein, e.g., myosin.

• Quaternary structure:

• Two or more polypeptides with their folding’s and coiling’s are arranged with respect to each other, e.g., Human haemoglobin molecule has 4 peptide chains – 2 α and 2 β Subunits.

Monosaccharides

Monosaccharides are joined by glycosidic bond, right end is reducing and left end is non reducing.

Polysaccharides

Are long chain of polymers of monosaccharides.

• Starch:

• Store house of energy in plant tissues. Forms helical secondary structures, made of only glucose monomers.

• Cellulose:

• Homopolymer of glucose. It does not certain complex helices. Cotton fibre is cellulose.

• Glycogen:

• Is a branched homopolymer, found as storage polysaccharide in animals.

• Insulin:

• Is a polymer of fructose.

• Chitin:

• Chemically modified sugar (amino-sugars) N-acetyl galactosamine form exoskeleton of arthropods; heterpolymer.

Metabolic Pathways

There are two types of metabolic pathways:

• Anabolic pathways:

• Lead to formation of more complex structure from a simpler structure with the consumption of energy, e.g., Protein from amino acids., also known as biosynthetic pathways.

• Catabolic pathway:

• Lead to formation of simpler structure from a complex structure, e.g., Glucose → Lactic Acid + energy The most important energy currency in living systems is ATP (adenosine tri – phosphate).

Bonds linking monomers in a polymer

Peptide bond:

Formed between the carboxyl (–COOH) group of one amino acid, and the amino (– NH₂) group of the next amino with the elimination of water moiety, (dehydration).

Glycosidic bond:

Bond formed between two carbon atoms of two adjacent monosaccharides., by dehydration.

Phosphodiester bond:

Bond formed in nucleic acids where in a phosphate moiety links the 3-carbon of one sugar of one nucleotide to the 5-carbon of the sugar of the succeeding nucleotide. (The bond between phosphate group and hydroxyl group of sugar)

Enzymes

• Enzymes are commonly proteinaceous substances which are capable of catalysing chemical reactions of biological origin without themselves undergoing any change. They are commonly called as biocatalysts.
• The nucleic acids that behave like enzymes are called ribozymes.
• The tertiary structure of protein/Enzyme has pockets or crevice into which substrate fit to form ES complex.
• The formation of the ES complex is essential for catalysis. E + S = ES → EP → E + P
• The structure of substrate gets transformed into the structure of product through formation of transient state structure.
• The major difference between inorganic and organic catalyst is inorganic catalyst works effectively at high temperature and pressure but enzyme get damaged at high temperature.
• The external energy required to start a chemical reaction is called activation energy.
• 

Factors influencing Enzyme Activity:

• Temperature:

• An enzyme is active within a narrow range of temperature. Temperature ate which enzyme is most active is called optimum temperature. The enzyme activity decrease above and below this temperature.

• pH:

• Every enzyme has an optimum pH at which it is maximum active. Most of the intracellular enzymes work at neutral pH.

• Concentration of Substrate:

• Increase in substrate concentration increases the rate of reaction due to occupation of more active sites by substrate.

• Competitive Inhibitor:

• When the molecular structure of inhibitor resembles the substrate, it inhibits the function of enzymes.

Enzymes are classified as:

Oxidoreductases/ Dehydrogenases:

S reduced + S’ oxidized S oxidized + S’ reduced

Transferases: S – G + S’ S + S’ – G

Hydrolases: Catalyses the hydrolysis of peptide, ester, glycosidic bonds et

Lyases: Remove the groups from substrate.

Isomerases: Inter conversion of optical, geometrical or positional isomers.

Ligases: Catalyses the linking together of two compounds.

Co-factors

Co-factors are the non-protein constituent of an enzyme which make the enzyme more catalytically active. The protein portions of enzyme are called apoenzyme.

• Prosthetic group:

• These are organic compound which tightly bound to the apoenzyme.

g., Haem is prosthetic group in peroxidase and catalase.

• Coenzyme: These are organic compounds whose association with the apoenzyme is only transient, usually occurring during the course of catalysis.

e.g., Coenzyme Nicotinamide adenine dinucleotide (NAD) and NADP contain vitamin niacin.

• Metal ions: Metal ions form coordination bond with side chains at the active site and at the same time form one or more coordination bond with substrate.

e.g., zinc in enzyme carboxy peptidase.

PRACTICE QUESTIONS

CELL

ALSO READ