Metabolism

Question 1

List:

FOUR proposed ‘problems’ cells face.

Answer 1

1. Responding to their environment.
2. Making/breaking molecules - How?
3. Obtaining energy.
4. Maintaining self and appropriate replication.

Question 2

Define:

Biological transduction

(General definition)

Answer 2

A cell’s conversion of one stimulus/signal/component into another.

A more specific definition in the context of bacteria refers to the viral transfer of bacterial genetic material to another bacteria or organism’s cells.

Question 3

Fill-in-the-Blank:

Life deals with different ____ and ____ to maintain itself.

Answer 3

Life deals with different inputs and outputs to maintain itself.

Question 4

Define:

Metabolic pathway

Answer 4

A sequence of enzyme catalysed reactions in which the product of one reaction becomes the substrate for the next.

Question 5

Define:

Metabolism

Answer 5

A collection of all the life-sustaining chemical reactions of a cell, which are interlinked (by intermediates), enzyme catalysed, and regulated by various mechanisms.

Question 6

True or False:

Most metabolites appear once in a metabolic network.

Answer 6

True

However, there are some key, central intermediates (‘hub metabolites’) that can feed into multiple metabolic pathways and act as a link between them.

Question 7

What is a major control mechanism of metabolic pathways?

Answer 7

The activation/inhibtion of allosteric enzymes.

Such enzymes usually are controlled by negative feedback, whereby the product of the reaction inhibits the enzyme activity, whilst the substrate activates or enhances it.

Question 8

Why are allosteric enzymes typically located at the beginning of linear metabolic pathways?

Answer 8

They act as key pathway regulators (i.e. a biochemical ‘on-off switch’), and so having the main regulation point at the beginning of a linear pathway reduces wasted energy/resources on non-functional metabolites.

This way, the reaction pathway is stopped/inhibited before fully comitting.

Question 9

Define:

Anabolism

Answer 9

The synthesis of more complex molecules and components from simpler ones.

Such reactions are endergonic and reductive.

Question 10

Define:

Catabolism

Answer 10

The breakdown of more complex molecules and components into their constituents.

Such reactions are exergonic and oxidative.

Question 11

Where is the energy of ATP stored?

Answer 11

In its phosphoanhydride bonds.

Question 12

What does NAD⁺ derive from?

(NAD stands for nicotinamide adenine dinucleotide)

Answer 12

Niacin (vitamin B₃).

It accepts one hydride to become its reduced form, NADH.

Question 13

What does FAD derive from?

(FAD stands for flavin adenine dinucleotide.)

Answer 13

Riboflavin (vitamin B₂).

It accpets two hydrides to become its reduced form, FADH₂.

Question 14

What is the approximate ΔG°’ (standard gibbs free energy) of the hydrolysis of ATP?

ATP ⇌ ADP + P_i

Answer 14

ΔG°’ ≈ -30.5 kJ mol^-1

And therefore, going from ADP to ATP (phosphorylation) is the same value, but endergonic (+30.5).

Question 15

True or False:

Lipids contain more energy than carbohydrates.

Answer 15

True

They are more reduced than carbohydrates and so can undergo more oxidation and thus energy release. However, more work is required to do so.

However, neither lipids nor carbohydrates have nearly as much stored energy as fossil fuels!

Question 16

Why must glucose (and other fuel molecules) be catabolised in a step-wise manner?

Answer 16

If fuel molecules were to be combusted in one step, none of the energy would be stored and instead released as heat.

In step-wise reactions, the energy released can be captured in the form of ATP production and put towards doing work in the cell.

Question 17

Which fuel molecule is conserved across the tree if life?

Answer 17

Glucose

Hence its importance for even anaerobic organisms, due to its partial oxidation via glycolysis.