2.1 Metabolic Pathways

Question 1

describe ‘the term metabolism’

Answer 1

all the reactions which take place in a living cell

Question 2

describe ‘the 2 types of reactions that occur in cells’

Answer 2

Anabolic Reaction
- small molecules are built into larger molecules
- energy is required
- e.g. building amino acids into proteins

Catabolic Reaction
- large molecules are broken down into smaller molecules
- energy is released
- e.g. the breakdown of glucose to carbon dioxide and water

Question 3

which molecule supplies cells directly with energy?

Answer 3

ATP

Question 4

what 3 steps can metabolic pathways have?

Answer 4

• reversible steps (the same enzyme can catalase the reaction in both directions)
• irreversible steps
• alternative routes

Question 5

what is the function of the plasma membrane?

Answer 5

to control which substances enter and leave the cell

Question 6

what are the 2 main components of the plasma membrane?

Answer 6

• phospholipids
• proteins

Question 7

what 3 ways can molecules cross the plasma membrane?

Answer 7

• diffusion
• osmosis
• active transport

Question 8

why can oxygen and carbon dioxide pass through he phospholipid layer easily?

Answer 8

because they are small molecules

Question 9

describe ‘the pore proteins within the plasma membrane’

Answer 9

• they form a channel through the phospholipid bi-layer
• allows larger molecules to cross the membrane by diffusion
• e.g. passage of glucose across the membrane

Question 10

describe ‘the pump protein within the plasma membrane’

Answer 10

• it’s the carrier molecule which spans (goes all the way through) the membrane
• moves substances across the membrane against their concentration gradient
• e.g. sodium-potassium pump

Question 11

describe ‘the enzymes within the plasma membrane’

Answer 11

• they are proteins found embedded on the outside or inside of the membrane
• it catalyses (speeds up) chemical reactions
• e.g. ATP synthase

Question 12

what are metabolic pathways controlled by?

Answer 12

• presence or absence of particular enzymes
• the regulation of the rate of reaction of key enzymes

Question 13

what is activation energy and what does the presence of enzymes have on this?

Answer 13

Activation energy is the quantity of energy required for a reaction to progress.

The presence of enzymes lowers the activation energy.

Question 14

what is the substance acted on by an enzyme called?

Answer 14

the substrate

Question 15

what is the substance that’s produced called?

Answer 15

the product

Question 16

describe ‘the induced fit model of an enzyme reaction’

Answer 16

The substrate has a high affinity for the active site (this means that the substrate has a high tendency to bind with the enzyme. The products have a low affinity for the active site (this means the products have a low tendency to bind with the enzyme). This allows the products to leave the active site.

Question 17

explain ‘the effect increasing substrate concentration has on the rate of an enzyme-controlled reaction’

Answer 17

The activity of the enzyme increases with increasing substrate concentration until a maximum rate is reached. At this point, all the active sites at any given moment are occupied with a substrate and the reaction cannot proceed faster.

Question 18

what are inhibitors?

Answer 18

substances which interfere with enzyme action and decrease the rate of reaction

Question 19

describe ‘the 3 types of inhibitor’

Answer 19

Competitive Inhibitor
- is a molecule with a shape similar to that of a substrate, they bind to the active site preventing the substrate from doing so
- can be reversed by increasing substrate concentration

Non-Competitive Inhibitor
- is a molecule which binds away from the active site, it changes the shape of the active site preventing the substrate from binding
- cannot be reversed by increasing substrate concentrations

Feedback Inhibitor
- occurs when the end-product in the metabolic pathway reaches a critical concentration, the end-product then inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end-product
- when the concentration of the end-product decreases, the inhibition is lifted, the enzyme will start working again and the metabolic pathway will progress