Enzymes what factors are responsible?

Question

What are the metabolic processes responsible for the 3D structure of enzymes? What specific examples of metabolic processes can alter pH and Temperature?

Answer 1

As far as I'm aware metabolic processes are not responsible for the 3D structure of enzymes. Enzymes adopt their shapes because of hydrogen bonding and charge attraction/repulsion within the molecule.

Increased respiration within the cell from increased energy demand will result in increased CO2 production which will tend to make the cell more acidic and also increase temperature. Natural homostatic processes act to counter both these effects in most normal circumstances so that the changes will in general be small and transient.

Answer 2

pH is extremely important for enzyme function.

When eating, HCl is released in the stomach which is extremely acidic. This causes the pepsinogen (inactive enzymes, or 'zymogens') to convert to the active form known as pepsin. When the food passes into the small intestine, the pH needs to return to a normal level or the enzymes in the small intestine will not work properly.

Answer 3

Enzymes are proteins which are translated and transcribed from our DNA using ribosomes etc. The primary structure of any protein is purely the order of amino acids which make it. Following this, the polypeptide chain may curl up into an alpha helix due to hydrogen bonds forming between oxygen atoms in a -CO group and hydrogen atoms in a -NH group in the amino acid four places ahead of it. Similarly, it may form a beta pleated sheet - both alpha helixes and beta pleated sheets are desribed as the secondary structure.

The tertiary structure is the way in which the polypeptide coils up to form a precise 3D shape. In the case of an enzyme, this may be complimentary to the substrate molecule it acts on. The tertiary structure includes hydrogen bonds, disulphide bridges, ionic bonds and hydrophobic interactions. Quaternary structures are the association of different polypeptide chains.

Enzymes are affected by a range of factors which relate to their structure and bonding. These include: heat, pH, presence of enzyme inhibitors, the concentration of the enzyme and the concentration of the substrate. Changing the heat or pH beyond a set range will permanently denature an enzyme.

At set points during the alimentray canal, the pH changes e.g. pH1 in the stomach and a pH ~neutral or slightly alkali passing from the duodenum into the ileum. pH1 in the stomach is caused by the secretion of HCl by oxyntic cells. This is neutralised by HCO3- ions in pancreatic juice as the bolus travels into the small intestine.

Some enzymes are secreted as precursors and are then changed to their active forms upon exposure to certain conditions e.g. pepsinogen. Upon exposure to acid in the stomach, short chain amino acids are removed to convert it to pepsin for protein digestion. Two different examples are the precursors trypsinogen and chymotrypsinogen (also proteases) in pancreatic juice, converted to their active forms by another enzyme called enterokinase (in the duodenum) and trypsin itself.