1. metabolism and survival

Question 1

what is metabolism

Answer 1

the term used to describe the large number of integrated and complex biochemical reactions that occur in an organism

Question 2

what are metabolic pathways

Answer 2

integrated (linked together) and controlled pathways of enzyme-catalysed reactions within a cell.

they can have reversible steps, irreversible steps and alternative routes.

Question 3

describe annabolic reactions

Answer 3

(synthesis) reactions build up large molecules from small molecules and require energy. (eg protein synthesis)

Question 4

describe catabolic reactions

Answer 4

(degradation) reactions break down large molecules into smaller molecules and release energy (eg respiration)

Question 5

what 3 types of proteins are found in cell membranes (that help to aid metabolism)

Answer 5

1) protein pores
2) pumps
3) enzymes which are embedded in membranes

Question 6

why are protein pores needed in the membrane

Answer 6

they allow larger molecules (eg. glucose) to diffuse across the membrane

Question 7

why are protein pumps needed in the membrane

Answer 7

they transport molecules across membranes that often require energy provided by ATP (active transport)

Question 8

why are enzymes needed in the membrane

Answer 8

enzymes that are embedded in the membrane help to speed up specific reactions in metabolic pathways

Question 9

what is a metabolite

Answer 9

a substance formed in, or necessary for, metabolism

Question 10

metabolic pathways are controlled by…

Answer 10

• the presence and absence of particular enzymes
• regulation of the rate of reactions of key enzymes*

*Some enzymes may be absent due to mutations in the gene. Some enzymes are only present when their substrate causes them to be produced.

Question 11

when does induced fit occur

Answer 11

when the active site changes shape to better fit the substrate after the substrate binds

Question 12

what does affinity mean

Answer 12

attraction to the enzyme

Question 13

how do enzymes lower the activation energy (Ea)

Answer 13

by forming an enzyme-substrate complex that accelerates the rate of reaction.

This is an alternative pathway allowing a small amount of energy needed and so the reactions can take place at lower temperatures

Question 14

explain why the reaction rate increases then becomes constant as the substrate concentration increases

Answer 14

At low substrate concentrations, not all enzyme active sites are filled, low concentration of products produced = low enzyme activity.

Increased substrate concentration means more active sites are filled with substrates means more product = more enzyme activity.

When substrate concentration exceeds enzyme concentration, no extra active sites available, no extra product formed

Question 15

what is an inhibitor

Answer 15

a substance which slows down or prevents a particular chemical reaction i.e. it reduces the activity of an enzyme.

Question 16

describe a competitive inhibitor

Answer 16

-Very similar shape to substrate.

-Bind directly to the active site, preventing substrate molecules binding.

-This is a temporary blockage, meaning a proportion of active sites are temporarily unavailable.

-Competitive inhibition can be reversed by increasing the substrate concentration.

Question 17

describe a non-competitive inhibitor

Answer 17

-Does not bind to active site but binds to an area on the enzyme away from the active site

-This changes the shape of the active site, preventing the substrate from binding.

-This is a more permanent inhibition of the active site, meaning the substrates can’t bind.

-Non-competitive inhibition cannot be reversed by increasing substrate concentration.

Question 18

when does feedback inhibition (end-product inhibition) occur?

Answer 18

when the end-product in the metabolic pathway reaches a critical concentration.

The end-product then inhibits an earlier enzyme (not earliest), blocking the pathway, and so prevents further synthesis of the end-product.

this slows down/stops the metabolic pathway, saving energy and resources as well as offering finely tuned control over the volume of end metabolite produced.