The cell has four primary ways of controlling the activity of enzymes in order t

Question

The cell has four primary ways of controlling the activity of enzymes in order to keep a tight control on the levels of metabolites. Match the following examples to the appropriate mode of enzyme regulation.

Drag the appropriate items to their respective bins. Fructose-6-phosphate (F6P) is converted into fru ctose-1,6 bisphosphate (FBP) by phosphofructokinase the reverse Phosphorylation of the kinase domain The activation of p53, a tumor Hexokinase, a key enzyme of catalyzed by fructose-1,6 reaction is suppressor, is directly regulated by glycolys is strongly inhibited by its is, acetylation of its ine residues. own product, glucose-6-phosphate bisphosphatase. If left unchecked, the production of FBP would lead right of protein kinase C regulates its activity back to the formation of FBP again. To prevent such inefficiency, the two enzymes are regulated reciprocally. When lactose levels rise in bacteria The small molecule 2,3-BPG inhibits genes are turned on to increase the the binding of oxygen to hemoglobin levels of those enzymes that by binding at a site distinct from that metabolize lactose. for oxygen (i.e. allosteric inhibition). Changing enzyme concentration Reversible inhibition Covalent modification Substrate cycling

Explanation / Answer

Changing enzyme concentration: When the level of lactose increases the lac operon is induced leading to the transcription by turning on of the genes leading to increase in the level of enzymes metabolizing lactose.

Reversible inhibition:

Phosphofructokinase-1 is an allosteric enzyme; hence it has reversible inhibitors and activators for feedback inhibition or activation.

Covalent modification

Phosphorylation is an example of covalent modification. The enzymes catalyzing phosphorylation reactions are called protein kinases. The phosphate group is covalently attached to the serine and threonine residues.

Substrate cycling

Substrate cycling occurs when two metabolic pathways run simultaneously in opposite directions and this leads to wastage of energy as it has no overall effect. This is stopped in cells as in case of Hexokinase; a glycolytic enzyme, which is strongly inhibited by its product glucose -6- phosphate.

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