B3: Metabolic pathways

What is metabolism?

The interconversion of different chemicals in the body.

What is catabolism?

The breakdown of food to release energy.

What is anabolism?

The building of useful macromolecules.

What do metabolic pathways depend on?

Enzymes working in pathways.

What are the three main stages of aerobic cellular respiration?

Glycolysis, TCA cycle, and electron transport chain.

What molecules are important outputs and inputs of metabolism?

ATP, carbon skeletons, and reducing equivalents (NADH, NADPH, FADH₂).

What is oxidation?

Loss of electrons.

What is reduction?

Gain of electrons.

What is the most common type of reaction in food breakdown?

Oxidation.

Name two simple pathway structures.

Linear pathways and branched pathways.

What is a cyclic metabolic pathway?

A pathway where a carrier molecule is regenerated unchanged.

What is a repeating (spiral) pathway?

A pathway where substrates are processed repeatedly, changing length by two carbons.

Give an example of a repeating pathway.

β-oxidation of fatty acids.

What does unidirectional flow in metabolism mean?

Pathways are irreversible.

What characterises the first step of a metabolic pathway?

It is often the rate-limiting and committed step.

Why must metabolic pathways be regulated?

Compounds are only made when they are needed.

Name the three major energy storage forms.

Glycogen, protein, triglycerides.

What are the five circulating fuels?

Glucose, lactate, amino acids, free fatty acids, ketone bodies.

What are the three key metabolic 'crossroads'?

Glucose-6-phosphate, pyruvate, acetyl-CoA.

What is meant by the adenylate pool?

The constant total of ATP, ADP, and AMP in the cell.

Why is AMP an effective regulator of metabolism?

Small changes in ATP cause large relative changes in AMP.

What enzyme interconverts ATP, ADP, and AMP?

Adenylate kinase.

What is gene regulation in metabolism?

Switching genes encoding enzymes on or off.

What is feedback inhibition?

End product of a pathway inhibits an earlier enzyme.

What is positive feedback?

End product accelerates its own production.

What is allosteric regulation?

Binding of a regulator at one site affects activity at another site.

What characterises allosterically regulated enzymes?

Multiple subunits with active and inactive forms.

What is cooperativity?

Binding of one substrate increases binding or activity at another site.

Why is localisation of enzymes important?

It helps organise and regulate metabolic pathways.

Where are enzymes for cellular respiration located in eukaryotic cells?

In mitochondria.