12.Metabolism

Question 1

What is metabolism?

Answer 1

the chemical processes which occur in a living organism in order to maintain life.

Question 2

What are the functions of metabolism?

Answer 2

1. provide a source of energy by high energy electrons
2. for reductive power for anabolic processes
3. need a source of carbon to build cellular components

Question 3

Where does energy come from?

Answer 3

the sun

• hydrogen fuses with helium, creating energy for photosynthesis
• plants synthesis macromolecules such as glucose and oxygen via photosynthesis
• these macromolecules oxidise to produce ATP
• ATP can therefore drive biosynthetic reactions as long as there is oxygen in the sun- energy transfer is continuous

Question 4

What 2 reactions are involved in metabolism?

Answer 4

catabolism and anabolism

Question 5

What is catabolism? does it require energy?

Answer 5

Large, complex organic molecules are degraded into smaller molecules

• It is a degradative/oxidative/converging reaction
• no, energy is liberated

Question 6

What does converging mean?

Answer 6

High number of starting reactants/small number of end products.

Question 7

What is anabolism? does it require energy?

Answer 7

Large, complex organic molecules are constructed from smaller molecules

• It is a biosynthetic/reductive/diverging reaction
• yes, energy is required

Question 8

What kind of agent do oxidation/reductive reactions require?

Answer 8

oxidation = reducing agent 
reduction = oxidising agent

Question 9

What is a ‘REDOX’ reaction?

Answer 9

• the transfer of electrons from 1 molecule to another
• oxidation - loss of electrons
• reduction - gain of electrons

Question 10

What is the most reduced state of carbon?

Answer 10

methane (CH4) - high free energy

Question 11

What is the Most oxidised state of carbon?

Answer 11

carbon dioxide (CO2) - low free energy

Question 12

What are the steps of glucose oxidation?

Answer 12

• changes in free energy ( a decrease in energy will then become oxidised and energy will be released)
• it reduces the activation energy so that a reaction can happen at 37°C
• The release of energy is reduced- can be coupled to endergonic reactions in cells and doesn’t damage the cell
• provides convenient control points
• can be integrated with other cellular metabolism

Question 13

What is an endergonic reaction?

Answer 13

anabolic/reductive reactions

Question 14

What is an exergonic reaction?

Answer 14

catabolic/oxidative reactions

Question 15

Describe electron flow in chemotrophs

Answer 15

• organic compounds e.g. carbohydrates, amino acids etc. are oxidised to release high energy electrons
• organic cofactors act as electron acceptors (to carry to the next stage of metabolism)
• NAD and 2H+ is reduced to NADH and H+
• FAD and 2H+ is reduced to FADH2
• a terminal electron acceptor is reduced aerobically; O2 to H20.

Question 16

Enzymes

Answer 16

• proteins that catalyse the conversion of a substrate to a product, often requiring the coenzyme ATP
• perform most chemical reactions in cells
• named by SUBSTRATEaction-ase

Question 17

Oxidoreductase

Answer 17

• enzymes catalysing oxido-reductions

- e.g. alcohol dehydrogenase

Question 18

Transferase

Answer 18

• transfer of a group onto a substrate

- e.g. UMP kinase

Question 19

Hydrolase

Answer 19

• catalyses the hydrolysis of various bonds

- e.g. aminoacyl-tRNA-hydrolase

Question 20

Lyase

Answer 20

• catalyse the breakdown of various chemical bonds, often forming a ring structure or new double bond
• e.g. decarboxylates

Question 21

Isomerase

Answer 21

• converting a molecule from one isomer to another

Question 22

Ligase

Answer 22

• the joining of 2 large molecules, forming a new chemical bond, often with the hydrolysis of a small molecule present on one of the larger molecules

Question 23

What enzymes transfer phosphate groups

Answer 23

kinases