Chapter 3 (Enzymes) F.Sc 1st Year Biology Short Questions

What is difference between pepsin and pepsinogen?

Pepsin is an enzyme that breaks down proteins into smaller peptides. Pepsinogen is an inactivated form of pepsin which is released by the chief cells in the stomach wall, and upon mixing with the hydrochloric acid of the gastric juice, pepsinogen activates to become pepsin.

Describe. lock and key model of enzyme action or What do you know about lock and key model?

A Lock and Key model was proposed by Emil Fischer (1890). It visualizes substrate and enzyme interaction. A specific enzyme can transform only one substrate into products(s) just like a special key which can open only a specific lock. The active site is a rigid structure in this model. There is no modification or flexibility in the active site before, during or after the enzyme action. Active site is used only as a template.

At high substrate concentration, rate of reaction does not increase. Give reason.

This is because all the active sites of the enzyme are occupied by high substrate concentration and further increase in the substrate does not increase the reaction rate.

Give effect of pH on enzyme action. or What is the effect of changed pH on the working of enzymes?

A slight change in pH can change the ionization of the amino acids at the active site. A change in PH may also affect the ionization of the substrates. Under these changed conditions enzyme activity is either retarded or blocked completely. Extreme changes in pH cause the bonds in the enzyme to break, resulting in the enzyme denaturation.

How substrate concentration affects rate of enzyme action?

If substrate concentration is low, the reaction rate is directly proportional to the substrate available. If the amount of substrate is increased at constant enzyme concentration, a point is reached when a further increase in the substrate does not increase the rate of the reaction anymore. This is because all the active sites of the enzyme are occupied by high substrate concentration and further increase in the substrate does not increase the reaction rate.

Define feedback inhibition of enzyme with diagram.

A cellular control mechanism in which an enzyme that catalyzes the production of a particular, substance in the cell is inhibited when that substance has accumulated to a certain level, thereby balancing the amount provided with the amount needed. Feedback inhibition Initial substrate intermediate substances Enzyme Enzyme Enzyme Enzyme Final product Precursor activation.

Differentiate between activator and coenzyme.

The detachable co-factor is known as an activator if it is an in janic ion e.g. Mg2+, Fe2+, Cu2+ & Zn2+ etc. If non-protein part is loosely attached to the protein part or enzyme it is known as coenzyme.

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