C1.1- Enzymes and metabolism - IB Biology

Question 1

List examples of cyclical pathways in metabolism

Answer 1

Krebs cycle
Calvin cycle

Question 2

List an example of a linear pathway in metabolism

Answer 2

Glycolysis

Question 3

Explain the aim of glycolysis

Answer 3

Glycolysis happens in the cytoplasm. Glycolysis breaks glucose into pyruvate. Glucose is too big of a molecule to fit into the mitochondria of a cell. So, glucose has to be broken down into pyruvate so it can fit into the mitochondria.

After glycolysis happens, only a very small amount of energy is produced. However, after in the mitochondria, the metabolism of sugar is completed, and a much higher amount of energy is produced.

Question 4

Explain what happens after pyruvate enters the cell

Answer 4

In eukaryotic cells, the pyruvate molecules produced at the end of glycolysis are transported into the matrix, which is the innermost compartment of mitochondria.

There, pyruvate will be transformed into an acetyl group that will be picked up and activated by a carrier compound called coenzyme A (CoA).

Question 5

How is pyruvate broken down

Answer 5

Step 1. A carboxyl group is removed from pyruvate, releasing a molecule of carbon dioxide into the surrounding medium. The result of this step is a two-carbon hydroxyethyl group bound to the enzyme (pyruvate dehydrogenase). This is the first of the six carbons from the original glucose molecule to be removed. This step proceeds twice (remember: there are two pyruvate molecules produced at the end of glycolsis) for every molecule of glucose metabolized; thus, two of the six carbons will have been removed at the end of both steps.

Step 2. The hydroxyethyl group is oxidized to an acetyl group, and the electrons are picked up by NAD+, forming NADH. The high-energy electrons from NADH will be used later to generate ATP.

Step 3. The enzyme-bound acetyl group is transferred to CoA, producing a molecule of acetyl CoA.

Upon entering the mitochondrial matrix, a multi-enzyme complex converts pyruvate into acetyl CoA. In the process, carbon dioxide is released and one molecule of NADH is formed.

Question 6

Explain the effects of a substrate binding to an allosteric site

Answer 6

Only specific substances can bind to an allosteric site. Binding causes interactions within that lead to conformational changes, which alter the active site enough to prevent catalysis. Binding is reversible.

The allosteric site is like a second active site. The allosteric site is located somewhere else on the enzyme.

Question 7

Examples of competitive inhibitors

Answer 7

Statins are an example of competitive inhibitors

Question 8

Distinguish the difference between a competitive inhibition and a non-competitive inhibition

Answer 8

A competitive inhibitor competes with other substrates to bind with the active site. Whereas, a non-competitive inhibitor aims to bind with the allosteric site. So it doesn’t compete with any other substrate.

An inhibitor will increase substrate concentration

Question 9

Effect of non-competitive inhibitor and competitive inhibitor on substrate concentration

Answer 9

A competitive inhibitor will increase substrate concentration. Whereas, a non-competitive inhibitor will decrease substrate concentration.

Question 10

Effect of binding of either inhibitor

Answer 10

Binding causes interactions within an enzyme that lead to conformational changes, which alter the active site enough to prevent catalysis. Binding is reversible. If the binding is weak between the inhibitor and the active site, it will eventually detach and the active site will be free again. This is useful to slow down a metabolic reaction (eg. the need to lower body temperature).

However, some inhibitors create a strong bind between the inhibitor and the active site and this is permanent. But the enzyme will eventually be digested. (eg. venom in poisonous snakes have this and it’s how they catch their prey)