2 - ICH - Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts that interact with substrate molecules to facilitate chemical reactions. Usually globular proteins.

Question 2

2 main functions of enzymes?

Answer 2

1. Biological catalysts - Speeds up a reaction in a living organisms/ cells without getting used up in the process.
2. Controls reactions - The amount of enzyme available determines how quickly a reaction can proceed (as it lowers to amount of activation energy required).

Question 3

Name:

1. Substance that the enzyme reacts on
2. New substance formed

Equation?

Answer 3

1. Substrate
2. Product

Substrate + Enzyme → Product + Enzyme

Question 4

Name:

1. Sum of all reactions taking place in a cell/organism
2. All break down reactions
3. All build up reactions

Answer 4

1. Metabolism (metabolic reactions)
2. Catabolism (catabolic reactions)
3. Anabolism (anabolic reactions)

Question 5

Catabolic reactions?

Answer 5

Reactions used to break down large molecules into smaller molecules e.g. Hydrolysis

Are exergonic = They release energy (a net loss of energy) and will form ATP.

Question 6

Anabolic reactions?

Answer 6

Reactions used to join smaller molecules together to form larger molecules e.g. Condensation.

Anabolic reactions require energy and is usually provided by the temporary energy storage molecule called ATP.

Are endergonic = Takes in energy

Question 7

What is a metabolic pathway?

What are B, C and D?

Answer 7

A series of connected metabolic reactions.

B,C and D are called intermediates.

Each step of the pathway is controlled by a different enzyme.

Question 8

Relationship between enzymes and substrate?

Explain enzyme specificity.

Answer 8

They are complementary. The active site is preceisly the right shape for the substrate molecule to slot in.

Enzyme specificity = Different enzymes have different shapes of active sites so each enzyme can only bind with a particular substrate.

Question 9

Collisions and the reactions? (Think collision theory)

Answer 9

Enzyme and substrate molecules are constantly moving as a result of their KE. They must collide with each other before they react.

Collisions are at random.

More collisions = greater rate of reaction

Question 10

Define activation energy

Example of H₂O₂?

Answer 10

Activation energy = Energy required to initiate a reaction

E.G

The thermal decomposition of H₂O₂

Providing the activation energy for this reaction:

• Heat the H₂O₂

_- Or can add an enzyme called catalase

Question 11

State the name of the 2 hypotheses that describe how enzymes work

Answer 11

Lock and key hypothesis

Induced fit hypothesis

Question 12

Lock and key hypothesis

What is it and how it works?

Answer 12

• Enzyme is a protein, tertiary structure of the protein results in the active site of the enzyme having a specific shape.
• Substrate fits the active site and an enzyme-substrate complex is formed.
• Reaction takes place and product is released.

Question 13

Induced fit hypothesis

What is it and how does it work?

Answer 13

• Similar to lock and key hypothesis.
• Difference = The active site moulds round the substrate (like a glove on a hand)

This is a better idea of how enzymes work compared to the lock and key hypothesis.

Question 14

What is the difference between intracellular and extracellular enzymes?

Answer 14

Intracellular enzymes = Work inside the cell

Extracellular enzymes = Are secreted and act outside the cell

Question 15

Intracellular enzymes

Example?

Answer 15

H₂O₂ is a toxic product of many metabolic pathways.

Catalase is an intracellular enzyme which breaks down H₂O₂ to oxygen and water.

Catalase acts extremely rapidly prevently the accumulation of the H₂O₂ in both plants and animal tissues.

Question 16

Purpose of extracellular enzymes?

Answer 16

Reactions in cells need a constant supply of raw materials to make products needed by the organism. These are called nutrients (i.e. materials needed for survival + growth.)

Nutrients is often in the form of macromolecules which are too large to enter the cell surface membrane directly so they need to be hydrolysed first.

Enzymes need to be secreted from cells to break down the macromolecules into smaller molecules - this is called digestion

Enzymes in the digestive system are extracellular enzymes such as TRYPSIN AND AMYLASE

Question 17

Example of extracellular enzymes?

Answer 17

Enzymes in the digestive system are usually extracellular.

E.G

In mammals starch is hydrolysed in a 2 step process involving 2 different enzymes (amylase then maltase).

Amylase = produced by salivary glands and pancreas.

Maltase molecules are a part of the cell surface membrane of the epithelial cells lining in the small intestine.

Question 18

Differences in the extracellular enzymes in:

• Single celled organisms
• Multicellular organisms

Answer 18

Single celled organisms = E.G Bacteria and yeast, release enzymes into their immediate surroundings. These enzymes break down macromolecules into smaller molecules which are then absorbed by the organism.

Multicellular organisms = Development of a specialised digestive system

Question 19

How is protein broken down in mammals?

Answer 19

It’s broken down by proteases which include pepsin in the stomach and trypsin in the small intestine.

Question 20

How are these formed?

Enzyme-substrate complex

Enzyme-product complex

4 Step process on how this works

Answer 20

Enzyme-substrate complex = Enzyme + Substrate → Enzyme-substrate complex

Enzyme-product complex = Enzyme + Product → Enzyme-product complex

1 - Enzyme + Substrate → Enzyme-substrate complex.

2 - Active site changes to convert the substrate into products. this is now the enzyme-product complex.

3 - Products are no longer complementary to active site so they’re released.

4 - Active site is now free for another substrate.

Question 21

How are enzyme controlled reactions represented as?

Answer 21

Enzyme + substrate ⇔ enzyme-substrate complex ⇔ enzyme-product complex ⇔ enzyme + product

E + S ⇔ ES ⇔ EP ⇔ E + P

Question 22

List the factors that affect enzyme activity (4)

Answer 22

Temperature

pH

Substrate concentration

Inhibitors

Question 23

How does temperature affect enzyme activity?

Answer 23

Increasing temperature will

• Increase the KE of the reacting molecules, move faster.
• Increase chance of collision between substrate and enzyme.
• More collisions in a given time, the faster the rate of reaction.
• But above the optimum temperature the enzymes thart to denature and enzyme subsrate complexes can’t form as the active site and substrate are no longer complementary.*

Question 24

Temperature coefficient (Q₁₀)

What is it and give the equation to work it out.

Answer 24

Temperature coefficient (Q₁₀) = A measure of how much the rate of a reaction increases with a 10ºC rise in temperature.

At temperatures between 0ºC and approx 40ºC most enzyme controlled reactions is 2.

For every 10ºC rise in temperature it’ll will cause the rate of an enzyme controlled reaction to double.

Question 25

Enzymes and adaptation: What are **thermophiles**? Why are the enzymes of these organisms more stable?

Answer 25

Organisms that have adapted to survive in very hot environments such as hot springs and deep sea hydothermal vents. *Enzymes in these organisms are more stable than other enzymes due to an increased number of bonds to maintain their working tertiary structure.* Similarly there are organisms that are adapted to surviving in cold environments which will have enzymes that are adapted to operate at very low temperatures.

Question 26

How does pH affect enzyme activity? Exmaple? (2)

Answer 26

Has a similar effect as temperature. Outside the small range the **H⁺ **and **OH**^- ions found in acids and bases will affect the ionic bonds. **Ionic bonds** help hold the tertiary structure together and if they are affected then the shape of the active site on the enzyme changes (denatured). E.G *_Amylase_ = optimum at pH 7* *_Pepsin_ = optimum at pH 2*

Question 27

How does substrate concentration affect enzyme activity? Look at the graph. What happens between A-B and then from B-C? When is the enzyme a limiting factor and when is the substrate concentration the limiting factor?

Answer 27

Graph shows: - Enzyme conc = fixed - Substrate conc = increasing Between **A - B**: - More substrate molecules = greater chance of collisions with enzyme molecules. - More collisions = more enzyme-substrate complexes formed. - **Substrate conc is limiting** Between **B - C**: As the substrate conc increases the rate of reaction remains constant at it's maximum. This is because: - Increasing the substrate conc makes no difference to the rate of reaction as all the enzyme's active sites are occupied. - Enzymes are working at the maximum turnover rate. - **Enzyme conc is limiting**

Question 28

What are enzyme inhibitors? State the 2 types of inhibitors

Answer 28

They slow down the rate of enzyme controlled reactions. - Competitive inhibitors - Non-competitive inhibitors

Question 29

What are **competitive inhibitors**? What do they do and their properties?

Answer 29

Have a **similar shape** to the enzyme's usual substrate (complementary). Can fit into active site and forms an **enzyme-inhibitor complex**. **Reversible competitive inhibitors** = Can leave the active site after being in it. **Non-reversible competitive inhibitors** = Can't get back out of the acative site once in. *Enzyme has no effect on the competitive inhibitor molecule. As long as the competitive inhibitor remains in the active site, no other molecule can enter; while it remains it prevents access for molecules of it's true substrate.*

Question 30

Competitive inhibitors and concentration?

Answer 30

The inhibitor and substrate _compete_ for the active sites of the enzyme, the molecule that is most likely to form a complex with the enzyme will be the one present in the highest concentration.

Question 31

What are non-competitive inhibitors? What do they do and their properties?

Answer 31

Has **no real structural similarity to the substrate** and will never fit into the active site. It's **irreversible**! *It attaches to a part of the enzyme which is not the active site. Alters the globular structure of the enzyme, shape of active site changes, active site is no longer complementary to substrate so no enzyme substrate complexes can form. Decreases the rate of reaction.*

Question 32

Summarise the differences between competitive and non-competitive inhibition. 1 - *Shape of inhibitor compared to substrate* (similar/different) 2 - *Shape of active site* (changed/unchanged) 3 - *Substrate can still fit active site* (y/n) 4 - *Enzyme substrate complexes can still be formed* (y/n) 5 - *Rate of reaction* (increase/decrease) 6 - *Effect of inhibitor* (reversible/irreversible)

Answer 32

Question 33

Inhibitors and metabolic pathways? Explain **end-product inhibition**

Answer 33

Inhibitors are very important in controlling metabolic pathways. **Metabolic pathway** = Series of enzyme-controlled reactions. Each step of the metabolic pathway is controlled by a different enzyme. **_End-product inhibition_**: - When enough of the end-product **D** is formed to meet the body's needs, no more is formed. - End-product **D** acts as a _non-competitive inhibitor_ for **enzyme E₁ **preventing the formation of any more **B**. - No more **D** is produced.

Question 34

What are coenzymes and prosthetic groups? What is their purpose and their properties? Example?

Answer 34

**Small organic molecules which bind temporarily to the active site along with the substrate.** *They take part in the reation and are altered, but unlike substrates they'll be recycled back to take part in a reaction again.* E.G. NAD is important in respiration Coenzymes that is a permanent part of a molecule is called a **prosthetic group**. Prosthetic groups are also found in other protein molecules: E.G. haemaglobin contains the heam group which contains the iron ions which allow it to function properly. Are vital to the function of the enzyme as they contribute to the structure and shape of the enzyme.

Question 35

What are **cofactors**?

Answer 35

A non-protein compound that must be present in order for the enzyme to work. This includes coenzymes and prosthetic groups.

Question 36

What are inorganic ion cofactors? Properties and purpose? Example?

Answer 36

In some enzyme controlled reactions the presence of certain ions can increase the reaction rate. _The presence of the ion makes the enzyme substrate complex form more easily._ E.G ***Amylase** catalyses the hydrolysis of **starch → maltose**. It'll only function properly if **Cl^- ions** are present.*

Question 37

Enzyme inhibitors and poisons? Exmaple?

Answer 37

Enzyme inhibitors may act as **metabolic poisons**. E.G. **_Potassium cyanide_ inhibits cell respiration. It acts as a _non-competitive inhibitor of a respiratory enzyme_ found in mitochondria called _cytochrome oxidase_**_._ Inhibition of this enzyme decreases the use of oxygen and so ATP can't be made. **100-200mg** of cyanide can kill an adult.

Question 38

Enzyme inhibitors and drugs?

Answer 38

Some medicinal drugs work by inhibiting the activity of anzymes. E.G. The **_antibiotic Penecilin_ inhibits a _bacterial enzyme_ involved in the production of cell walls.** This means the walls of growing bacteria are not made, so bacterial reproduction is halted.