Tag: biomolecules: chemical constituents of living cells

The vitamins act as part of coenzymes, small molecules that combine with an enzyme to make it active.

Enzymes are biocatalyst. These are proteinaceous substances that are capable of catalysing chemical reactions of biological systems without themselves undergoing any change. The term enzymes were first used by Kuhne in 1877.

Amylase is a protein-based enzyme that is secreted by the salivary glands of mouth and is involved in the breakdown of starch. It functions in a neutral pH (pH 7). Renin is also a protein enzyme secreted in the stomach and involved in the coagulation of milk. It functions in a acidic pH. Trypsin is also a protein enzyme that is produced in the small intestine and is a proteolytic enzyme. It also functions in acidic pH. So, the correct answer is 'These are all proteins'.

The activity of an enzyme can be affected by a change in the conditions which can alter the tertiary structure of the protein. These include temperature, pH, change in substrate concentration or binding of specific chemicals that regulate its activity. Enzymes generally function in a narrow range of temperature and pH. Each enzyme shows its highest activity at a particular temperature and pH called the optimum temperature and optimum pH. Activity declines both below and above the optimum value. Low temperature preserves the enzyme in a temporarily inactive state whereas high temperature destroys enzymatic activity because proteins are denatured by heat. At boiling temperature all proteins including enzymes are denatured.

All proteins are not enzymes. Proteins are most versatile biochemicals fulfilling a diverse set of structural and functional roles. For example, haemoglobin, keratin, albumin, etc., are all proteins but are not enzymes. Similarly, all enzymes are not proteins. In fact, most of the enzymes, are proteinaceous in nature. But ribozymes are not proteins in nature, they are catalytic RNAs.

Enzymes are the specialized proteins which are capable of catalyzing reactions in the living cells.

Enzymes are the biological catalyst which catalyzes biological reactions within a narrow range of temperature and pH. Certain thermophiles have enzymes which remain functional even at very high temperatures. Most of the enzymes are proteins in nature but a few enzymes are RNA in nature. They are called as catalytic RNAs or ribozymes.

The conjugate protein consists of two parts protein and non-protein part. Non-protein part is the cofactor and protein part is apoenzymes. Complete conjugate protein is known as Holoenzymes. Apoenzyme is an inactive enzyme. Thus, the correct option is D.

A constant indicating the substrate concentration at which an enzyme catalysed reaction attains half its maximum velocity or 1/2 V$ _{max}$ is known as Michaelis-Menten constant or K$ _m$. Lower K$ _m$ indicates more affinity between the enzyme and substrate and consequently higher reaction rates.