U2 Metabolic pathways

Question 1

What is metabolism?

Answer 1

All of the chemical reactions that take place inside living cells

Unicellular and multicellular organisms must control their metabolisms in order to survive

Question 2

examples of Metabolic reactions

Answer 2

respiration
protein synthesis
photosynthesis
starch synthesis

Question 3

What are metabolic pathways?

Answer 3

a series of chemical reactions which take place within a cell involving several enzymes

The products of one reaction will become the substrate of the next

Question 4

What can metabolic pathways have?

Answer 4

reversible steps
irreversible steps
alternative routes

Question 5

Catabolic metabolic pathway?

Answer 5

Involves breaking down (degrading) large molecules into smaller ones

Releases energy

Question 6

Anabolic metabolic pathways

Answer 6

Involves building up (synthesising) large molecules from smaller ones

requires energy

Question 7

What is the cell membrane made up of?

Answer 7

Phospholipid molecules
proteins

(external surface membrane
protein molecule
channel protein
phospholipid bilayer)

Question 8

In what ways can materials pass through the membrane?

Answer 8

diffusion
osmosis
active transport (pump mechanism)

Question 9

What functions can proteins in the plasma membrane have?

Answer 9

protein pores (diffusion)
pumps (active transport)
enzymes (atp synthase)

these are embedded in the phospholipid membranes

Question 10

What are metabolic pathways controlled by!

Answer 10

the presence or absence of particular enzymes (embedded in the cell membrane which catalyse the steps in metabolic pathways)

Question 11

What are the 3 reasons that enzymes are essential in to metabolic pathways?

Answer 11

They speed up chemical reactions

They remain unchanged after the reaction so can be used again

They lower the activation energy required to carry out the reaction

Question 12

When does induced fit occur?

Answer 12

When the active site changes shape to better fit the substrate after the substrate binds.

The active site of an enzyme is flexible and dynamic. When a substrate enters the active site, the shape of the active site changes slightly making it fit exactly (induced fit)

Question 13

What is affinity?

Answer 13

Attraction

Question 14

Why do substrate molecules bind readily to the active site

Answer 14

They have a high affinity for the active site

Question 15

What affinity do products have?

Answer 15

Low affinity, allowing them to leave the active site and leaving the active site free to catalyse another reaction

Question 16

What is enzyme action affected by?

Answer 16

pH and temperature

They also require an adequate supply of substrate. If the substrate concentration is too low, the rate of reaction is low. This improves as the substrate concentration increases.

Question 17

What drives a sequence of reactions in a particular direction?

Answer 17

Some metabolic reactions are reversible

-The presence of a substrate
-Removal of a products

Question 18

What are inhibitors?

Answer 18

Substances which can slow down the rate of an enzyme and they are split into 2 main groups:
-competitive inhibitors
-non-competitive inhibitors

Question 19

Competitive inhibitors

Answer 19

Have a similar shape to that of the substrate and so they also fit the enzymes active substrate

If the inhibitor joins the enzyme, this prevents the substrate from doing so, and so this therefore reduces the number of substrate molecules being used by the enzyme (reduced rate of reaction in presence of inhibitor)

Question 20

How is the effect of a competitive inhibitor reversed?

Answer 20

By increasing the substrate conconcentration

with more substrate molecules present, there is a higher chance that the active site will be occupied by a substrate molecule rather than the inhibitor

At high substrate conc., the inhibitor is out-competed by the substrate and the maximum rate of reaction is achieved

Question 21

Non-competitive inhibitors

Answer 21

Doesn’t interfere with the active site

It binds to another part of the enzyme but results in the shape of the enzyme being altered so changes the shape of the active site

Substrate can now no longer let fit the enzyme’s active site and therefore the reaction cannot take place

(no inhibitor: maximum rate of reaction achieved at high substrate concentration
with inhibitor: max reaction rate never achieved)

Question 22

Can the effect of a non-competitive inhibitor be reversed by increasing substrate concentration?

Answer 22

no

Question 23

Examples of non-competitive inhibitors

Answer 23

heavy metals like lead, silver, etc

Question 24

What is end product feedback inhibition

Answer 24

Another way in which a metabolic pathway can be regulated (saves energy/end-product only produced when required)

As the concentration of the end product builds up to a critical level, some of the product binds to an earlier enzyme in the pathway and blocks this enzyme’s action (inhibits enzyme)

This prevents (unnecessary) synthesis of the end-product

Question 25

What 3 things play a part controlling metabolic pathways?

Answer 25

Competitive inhibition
Non-competitive inhibition
Feedback inhibition