Unit 1 - Metabolic Pathways

Question 1

What are Metabolic Pathways?

Answer 1

Metabolic pathways are integrated and controlled pathways of enzyme-catalysed reactions within a cell

Question 2

What categories are Metabolic Pathways divided into?

Answer 2

1. Catabolism​
2. Anabolism

Question 3

Describe Catabolism

Answer 3

Catabolic pathways breakdown complex molecules to simple molecules​

This (usually) releases energy

Question 4

Describe Anabolism

Answer 4

Anabolic pathways involve the biosynthesis (build up) of complex molecules from simpler molecules​

This requires energy

Question 5

What does the use of irreversible steps in metabolic pathways mean?

Answer 5

After that point substrates cannot be converted back and are committed to continuing on the pathway

Question 6

Describe reversible steps in metabolic pathways

Answer 6

Reversible steps are important if too much of a substrate builds up​

It allows it to be converted back to the previous substrate​

Some products of metabolism in the body are potentially toxic, this can prevent toxicity

Question 7

When do you use alternative routes in metabolic pathways?

Answer 7

When substrates are plentiful or in short supply

Question 8

What is the result of Alternative routes in metabolic pathways?

Answer 8

This can conserve energy, (or prevent the build-up of toxic intermediate products).​

Question 9

What controls metabolic pathways?

Answer 9

The presence or absence of particular enzymes

Question 10

What is activation energy?

Answer 10

An initial input of energy to start a reaction

Question 11

Describe the effect of enzymes on activation energy

Answer 11

Enzymes reduce Ea, this conserves energy

Question 12

What is Enzyme Specificity?

Answer 12

Enzymes only work with one type of substrate​

The substrate fits exactly into the active site

Question 13

Name the chemical attraction between substrate and enzyme

Answer 13

Affinity

Question 14

Describe an Induced Fit in Enzymes

Answer 14

The active site is flexible and slightly alters its shape when the substrate enters​

This close fit ensures the active site is in very close contact with the substrate

End products are released because there is low affinity with the active site.​

The enzyme will return to its original conformation.

Question 15

Describe Substrate Orientation

Answer 15

In a reaction with 2 or more substrates, the shape of the active site ensure they are held in the correct position​

This weakens the ​chemical bonds

This reduces Ea required to get reactants to ‘transition state’​

Question 16

Define the Transition State in terms of enzyme activity

Answer 16

Transition state is where the structure is no longer a substrate but not yet a product

Question 17

To function efficiently enzymes must have…

Answer 17

• Suitable temperature​
• Appropriate pH​
  *Adequate supply of substrate

Question 18

Talk about Substrate Concentration in terms of Rates of Reaction

Answer 18

Substrate concentration refers to the relative number of substrate molecules present that could bind to an available enzyme. ​

At low concentrations, the rates of reaction in a cell are low because there are too few substrate molecules to bind to active sites of enzymes. ​

An increase in substrate concentration means that there will be more substrate to bind to active sites therefore reaction rate will increase. ​

This trend will continue until all of the active sites are occupied. At this point, enzyme concentration becomes a limiting factor and rates of reaction will plateau.

Question 19

What are the 3 types of Enzyme inhibition?

Answer 19

1. Competitive inhibition​
2. Non-competitive inhibition​
3. End-product inhibition

Question 20

Describe Competitive Inhibition

Answer 20

Competitive inhibitors compete with a substrate for the active site of an enzyme​

These inhibitors are a similar structure to the substrate so can block an active site

Question 21

Describe Non-Competitive Inhibition

Answer 21

Non-competitive inhibitors become attached to a non-active (allosteric) site on an enzyme​

This alters the shape of the enzyme and in turn the active site

Question 22

Describe Allosteric regulation

Answer 22

If the allosteric site is occupied by an activator (regulatory molecule) the enzyme will be in an active form​

If occupied by a non-competitive inhibitor, the enzyme will change shape

Question 23

Describe End product inhibition

Answer 23

When the end product of an enzyme catalysed reaction builds up it can bind to an enzyme found earlier within the pathway.

This slows down the conversion of A to B, and in turn regulates the whole pathway, preventing wasteful conversion of substrates and accumulation of products​