-Did changes to sequence occur in the active(substrate binding) site? Why would

Question

-Did changes to sequence occur in the active(substrate binding) site? Why would a mutation in this area be a disadvantage and likely not persist in a species?

-Why would a more flexible enzyme in a cold environment be an advantage and a disadvantage? (include amount of substrate needed for reaction and enzyme activity at various temperatures)

- How can temperature of an environment determine species distributions at the biochemical(amino acid, DNA etc…) level? Think in terms of DNA mutations, resulting proteins, fitness and natural selection.

Explanation / Answer

We all know that enzyme substrate reactions are highly specific depending not only on the 3-dimensional structure of the protein (which is in turn dependent on the amino acid sequence) but also on various non- covalent interactions between the binding site and the substrate. The active site consists of substrate binding site and the catalytic site. Any mutation which would result in greater affinity of the substrate with its binding site would increase the efficiency of the reaction and any mutation resulting in the reduced affinity of the substrate with the binding site would result in reduced efficiency of the reaction.In in-vitro systems the mutations resulting in increasing the affinitywould surely help but as far as biological systems are concerned which are a bundle of complex metabolic pathways either of the mutations would disturb the equilibrium affecting the species in a negative way hence mutation in this area will likely not persist in a species.

Before answering I would like to revise a few basic concepts

Keeping these two things in mind, in a cold environment,

ADVANTAGE: an enzyme would be having a low optimum temperature hence it would catalyse the reaction at that temperature (Saving energy!!!). As with constant substrate concentrations the rate of enzyme catalyzed reactions increase with increasing temperature until the temperature optima is reached after which the enzyme gets denatured.

DISADVANTAGE: But at this temperature larger concentration of substrate would be required as substrate molecules would have less kinetic energy in order to bind to active site. The more the substrate concentration, the more would be the chance of substrate to bind to active site.

3.Temperature of an environment should affect the species distribution at biochemical level.We know all living beings carry out basic metabolic reactions (respiration, digestion etc.) to survive most of which are enzyme catalysed. The enzyme catalysed reactions are dependent on temperature. If the temperatures are too low the enzymes would not be able to perform “as effectively” and if the temperatures are too high the enzymes would get denatured thus again decreasing the rate of reaction. Hence, as an adaptation I feel that different species with low metabolic rates would have certain codon preference depending on the GC ratios (Cold climate-Low metabolic rate – codons with low GC ratio and vice versa; Low rate of reactions so involvement of rare amino acids and so on). This would be an interesting topic to study as my knowledge in biochemical distribution at various temperatures is limited.

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