1.6 - Metabolic Pathways

Question 1

What do all cells produce?

Answer 1

All cells produce substances that are essential for them to function properly.

Cells must perform a series of chemical reactions called a metabolic pathway to produce these required substance’s

Question 2

Metabolic pathways definition

Answer 2

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

Metabolic pathways are controlled by enzymes and together they form a complex network that is necessary to maintain life.

Question 3

Do metabolic pathways involve lots of steps?

Answer 3

Most metabolic pathways involve multiple steps.

Question 4

At each step of a metabolic pathway, what do enzymes do?

Answer 4

At each step of a metabolic pathway, enzymes change the substrate in order to produce the final product at the end of the pathway.

Question 5

What type of steps can metabolic pathways have?

Answer 5

Metabolic pathways can have reversible steps, irreversible steps and alternative routes.

Question 6

What happens in a metabolic pathway if a specific enzyme or substrate is not available?

Answer 6

If a specific enzyme or substrate is not available in a metabolic pathway, an end product may still be made using an alternative metabolic pathway. This might take longer but still results in the same end product that is needed.

Question 7

Activation energy definition

Answer 7

The activation energy is the minimum energy required for a reaction to take place.

Question 8

What lowers the activation energy?

Answer 8

The binding of an enzyme to its substrate lowers the activation energy of a reaction.

Question 9

Presence of an enzyme and activation energy

Answer 9

If an enzyme is present, the amount of energy needed (activation energy) to make a product is lowered.

Question 10

Types of reactions in metabolic pathways

Answer 10

Reactions in metabolic pathways can be anabolic or catabolic.

Question 11

What can anabolic pathways also be known as?

Answer 11

Anabolic pathways can also be referred to as biosynthesis pathways.

Question 12

What do anabolic pathways require?

Answer 12

Energy

Question 13

Anabolic pathways

Answer 13

Anabolic reactions build up large molecules from small molecules and require energy.

Question 14

Catabolic pathways

Answer 14

Catabolic reactions break down large molecules into smaller molecules and release energy.

Question 15

What can catabolic pathways also be known as?

Answer 15

Catabolic pathways can also be referred to as degradation pathways.

Question 16

What do catabolic reactions release?

Answer 16

Energy

Question 17

Why do anabolic pathways requite energy?

Answer 17

Anabolic pathways require energy to build up smaller molecules into larger molecules.

Question 18

Examples of anabolic reactions

Answer 18

DNA replication

Protein synthesis

Question 19

Why do catabolic pathways release energy?

Answer 19

Catabolic pathways release energy because the large molecules are being broken down into smaller molecules.

Question 20

Examples of catabolic reactions/ pathways

Answer 20

Respiration

Digestion

Question 21

Why are metabolic pathways controlled?

Answer 21

All metabolic pathways must be regulated and controlled in order to prevent the build up of an end product which is not needed.

This means the presence and number of enzyme molecules must be tightly controlled to ensure metabolic efficiency.

Question 22

How can a cell control metabolic pathways?

Answer 22

A cell can control a metabolic pathway by the presence or absence of a particular enzyme or by regulating the rate of reaction of key enzymes.

Question 23

How can regulation of enzyme activity be achieved?

Answer 23

Regulation of enzyme activity can be achieved in several ways however the most effective way is by changing the shape of the enzyme.

Question 24

How do enzymes bind to their substrate?

Answer 24

Enzymes bind to their substrate because they have an active site.

Enzyme activity conforms to the induced fit model.

Question 25

When does an induced fit occur?

Answer 25

An induced fit occurs when the active site of an enzyme is changed slightly to better fit the substrate after the substrate binds.

Question 26

How does the affinity of an enzymes active site compare to the substrate?

Answer 26

An enzyme’s active site has a high affinity to the substrate as well as being specific to the substrate.

Question 27

What happens once products are formed?

Answer 27

As the products are made, their shape changes and they are no longer specific to the enzymes active site.

The products therefore have low affinity to the enzymes and are released.

The active site of the enzyme then resumes its normal shape and the enzyme is free to attach to more substrate molecules.

Question 28

What factors effect enzymes?

Answer 28

As enzymes are made of proteins, their structure can be affected by changes in environmental conditions such as temperature and pH.

Enzymes activity can also be affected by:

• the concentration of the enzyme
• the concentration of the substrate

Question 29

What can affect the rate of enzyme reactions?

Answer 29

The rate of enzyme reaction can be affected by substrate concentration.

Question 30

What happens to enzyme rates as substrate concentration increases?

Answer 30

As substrate concentration increases, the rate of the enzyme catalysed reaction increases until all of the active sites are occupied by the substrate.

Question 31

What happens when all active site are occupied?

Answer 31

When all active sites are occupied, the enzyme is saturated.

Question 32

What happens after the saturation point if more substrates are added l?

Answer 32

After the saturation point, adding more substrate will no longer increase the reaction rate.

Question 33

How do inhibitors affect enzymes?

Answer 33

(Enzyme activity can also be affected by the presence of certain chemicals)

Inhibitors stop an enzyme binding to its substrate.

Question 34

Types of inhibitors

Answer 34

• competitive inhibition
• non-competitive inhibition
• feedback inhibition

Question 35

When does competitive inhibition occur?

Answer 35

Competitive inhibition occurs when a competitive inhibitor binds to the active site of an enzyme and therefore prevents the substrate from binding.

The competitive inhibitors compete with the substrate because they have a similar shape to the substrate and enzymes active site.

Question 36

How can competitive inhibition be reversed?

Answer 36

Competitive inhibition can be reversed by increasing the concentration of the substrate. This is because the increased substrate concentration dilutes the inhibitor so that the enzyme molecules bind to the substrate.

Question 37

What do non-competitive inhibitors bind to?

Answer 37

Non-competitive inhibitors bind to a part of the enzyme that is not the active site but they still change that shape of the active site.

This prevents the substrate from binding to the enzyme and therefore decreases the reaction rate.

Question 38

Noncompetitive inhibition - increasing substrate concentration

Answer 38

As the non-competitive inhibitor does not bind to the enzymes active site, their affects cannot be reversed by increasing substrate concentration.

Question 39

How can metabolic pathways be controlled?

Answer 39

Metabolic pathways can be controlled by feedback inhibition.

Question 40

When does feedback inhibition occur?

Answer 40

Feedback inhibition occurs when the end product of a metabolic pathway reaches a critical concentration. The end product then binds to an enzyme at the start of the metabolic pathway, inhibits it and prevents any further synthesis of the end product.

Question 41

What does feedback inhibition do to the metabolic pathway?

Answer 41

Feedback inhibition stops the metabolic pathway and prevents further synthesis of the end product until the end product concentration decreases.

Question 42

Feedback inhibition end product concentration

Answer 42

The higher the concentration of the end product, the quicker the metabolic pathway stops.

Question 43

What does feedback inhibition ensure?

Answer 43

Feedback inhibition ensures that a cell does not produce more end product than necessary.