Energy Reactions In Cells

Question 1

What are the main functions of cell metabolism?

Answer 1

PRODUCTION OF:

• Energy in the form of ATP (used for various cell processes)
• Building block molecules for biosynthesis
• Organic precursor molecules e.g. Acetyl CoA
• Biosynthetic reducing power e.g. NADH, NADPH and FADH2 (used in synthesis of cell components)

Question 2

What is the difference between CATABOLISM and ANABOLISM?

Answer 2

• CATABOLISM is the breakdown of larger molecules into smaller ones and is OXIDATIVE AND EXERGONIC
• ANABOLISM is the formation of larger molecules from smaller ones and is REDUCTIVE AND ENDERGONIC

Question 3

Give 3 examples of carrier molecules used in biological oxidation

Answer 3

• NAD+
• NADP+
• FAD+

Question 4

Why must carrier molecules cycle between oxidised and reduced states?

Answer 4

• Total concentrations of carrier molecules within cells are fixed
• Carrier molecules must cycle between oxidised and reduced in order to maintain cell function
• e.g. If all NAD+ was reduced to NADH and not converted back there would be no NAD+ available for oxidation

Question 5

Define FREE ENERGY

Answer 5

• Energy released by an exergonic reaction that is able to do work
• If the free energy change ΔG is negative, the reaction will occur spontaneously

Question 6

Explain why catabolic processes are activated by low energy signals and inhibited by high energy signals

Answer 6

• Low energy signals such as ADP and NAD+ suggest that ATP production is low (high concentration of substrates) so rate of metabolism is increased
• High energy signals such as ATP and NADH suggest that ATP production is high (high concentration of products) so rate of metabolism can be decreased

Question 7

Define SUBSTRATE LEVEL PHOSPHORYLATION

Answer 7

The production of ATP by transfer of high-energy phosphoryl group to ADP from another molecule, catalysed by KINASE enzymes

Question 8

Give 3 examples of high energy signals

Answer 8

• ATP
• FADH2
• NADH/NADPH

Question 9

Give 3 examples of low energy signals

Answer 9

• ADP/AMP
• FAD+
• NAD+/NADP+

Question 10

Define CELL METABOLISM

Answer 10

Highly integrated network of chemical reactions that occur within cells to maintain life

Question 11

Describe the formation of CREATINE PHOSPHATE

Answer 11

When ATP is high in muscles:
CREATINE + ATP —> CREATINE PHOSPHATE + ADP
- catalysed by CREATINE KINASE

Question 12

Explain how creatine phosphate can act as a small store of free energy in muscle cells

Answer 12

• Reaction between creatine and creatine phosphate is REVERSIBLE
• When ATP levels fall, creatine phosphate can be converted back to creatine by PHOSPHATASE enzymes, producing ATP which can be used as a short supply of energy for muscle cells

Question 13

Explain how levels of CREATININE can give an indication of muscle mass

Answer 13

• Creatinine is produced by the non-enzymatic breakdown of creatine and creatine phosphate in muscles
• Rate of production of creatinine is proportional to concentration of creatine in muscles (therefore related to muscle mass)
• Daily excretion of creatinine can be measured and used as an indicator of muscle mass or muscle wasting