Biomolecules and Enzymes

This option is correct because urease is a nickel-containing metalloenzyme of high molecular weight that catalyses the hydrolysis of urea into carbon dioxide and ammonia, and dopamine β-hydroxylase is a copper-containing enzyme that synthesises norepinephrine from dopamine.

Ceruloplasmin is an enzyme synthesized in the liver containing 6 atoms of copper in its structure. Laccases are copper-containing oxidase enzymes that are found in many plants, fungi and microorganisms.

It is correct. Proteins help our body in its growth, formation of muscles and repair of worn out tissues. 

The binding site of receptors is analogous to the active site of enzymes. However, no reaction is catalysed. 

A chemoreceptor also known as chemosensor is a sensory receptor that transduces a chemical signal into an action potential. A chemosensor detects certain chemical stimuli in the environment. Attractants and repellents are detected by chemoreceptors. These chemoreceptor proteins may be located in the periplasmic space or the plasma membrane.

Amylase helps in the digestion of carbohydrates and renin helps in the control of blood pressure through angiotensin. Both are enzymes thus biocatalysts.

Ser and Cys residues have reactive –OH and –SH groups respectively. The compound diisopropylphosphofluoridate (DIPF) reacts with Ser residue in the active site of the enzyme acetylcholinesterase, irreversibly inhibiting the enzyme and preventing the transmission of nerve impulses. Iodoacetamide modifies Cys residues and hence, may be used as a diagnostic tool in determining whether one or more Cys residues are required for enzyme activity.

Zymogen is an enzyme’s inactive precursor which must be cleaved for the formation of active enzyme. For example, trypsin and chymotrypsin are synthesised as precursor trypsinogen and chymotrypsinogen.

Subtilisin, a serine protease, is present in prokaryotes. Subtilisin uses a catalytic triad for creating a nucleophilic serine. Trypsins are proteases which cleave peptide bonds after arginine or lysine and this particularity is guided by the residue present at the bottom of the S1 pocket of the enzyme. Elastase proteases have a smaller S1 aperture than chymotrypsin and trypsin proteases. Therefore, residues like glycine, valine and alanine are preferred. Chymotrypsin proteases have more hydrophobic S1 pocket than trypsin proteases. Therefore, medium and large hydrophobic residues like phenylalanine, tryptophan and tyrosine are preferred. Thus, all the enzymes belong to the category of serine proteases.

Papain is a proteolytic enzyme belonging to cysteine protease family. Papain is found in unripe papaya and also in mountain papaya. Papain has a sulfhydryl group required for enzyme activity and a polypeptide chain accompanied by 3 disulfide bridges. Papain can digest protein substrates. Bromelain is a combination of proteolytic enzyme and small amounts of other substances like acid phosphatase, peroxidase, calcium and protease inhibitors. Bromelain is obtained from both stem and fruit of pineapples. Bromelain has anti-inflammatory effects and interferes with slow blood clotting.

Ligases are also known as synthetases. Ligases act as catalysts in reactions where bonds are formed between two compounds. They utilise the energy obtained from cleaving the ATP. Formation of C-N, C-S, C-C, and C-O bonds are catalysed by ligases.

Core histone of nucleosome is a histone octamer consisting of 2 copies each of H2A, H2B, H3 and H4. All the core histones are rich in lysine and arginine (amino acids with basic side chains) and their positive charges can effectively neutralise the negatively charged DNA backbone.

This amino acid has a free amino group for the formation of peptide bond. Peptidoglycan of bacterial cell wall is made up of N-acetyl glucosamine (NAG)-N-acetyl muramic acid (NAM). To NAM, a tetra-peptide chain is attached consisting of L-alanine, D-glutamic acid, L-lysine and D-alanine. The L-lysine is attached to a penta-glycine chain sideways, which is further attached to D-alanine of the neighbouring NAG-NAM complex. Since L-lysine needs to form the penta-glycine chain, it should have a free amino group for peptide bond formation. This extensive cross linking gives rigid structure to the peptidoglycan moiety.

Most peptidases can only cleave L-amino acids. Peptidases are enzymes that act on short protein chains into individual amino acids. Many bacteria secrete peptidases that act on L-amino acids and help in their nutrition. But these enzymes cannot degrade their cell walls due to the presence of D-amino acids in their cell walls.

Integrins are heteromeric protein which bind to tripeptide sequence Arg-Gly-Asp and expressed in a cell-specific manner.