OCR Biology Enzymes

What are metabolic reactions?

the sum of all reactions in the organism

What are anabolic reactions?

Building up larger molecules

What are catabolic reactions?

Breaking down molecules

What are enzymes?

Biological catalysts that speed up chemical reactions

Name the energy that is required to start a reaction.

Activation energy

What are enzymes' effect on the activation energy of a reaction?

Enzymes lower Ea

Name the area on the enzyme that binds to and reacts with the substrate.

Active site

The active site has a _____ shape to the substrate.

Complementary/Specific

Name the two models used to illustrate enzyme actions.

Lock-and-key + Induced fit

Name the structure where the enzyme and substrate are bound together.

Enzyme-substrate complex

What is the difference between the lock-and-key model and the induced fit model?

Lock-and-key: rigid, no movement; Induced fit: slight movement of active site to allow better binding to substrate

Name an intracellular enzyme.

Catalase

Name an extracellular enzyme.

Amylase/trypsin

Define the term 'denaturation'.

Loss of active site shape

Explain how an increase of temperature increases enzyme activity.

"- Increasing temperature increases particles' kinetic energy

-

Particles move faster and collide more often

-

More successful collisions (between active site and substrate)

Explain how high temperatures can denature enzymes.

"- High temperature leads to more vibrations

-

Too much vibration breaks the bonds that hold the protein together

What is the temperature coefficient (Q10)?

A measure of how much the reaction rate increases with a 10oC increase

How are the enzymes in organisms that live in cold environments adapted?

"- enzymes are more flexible, hence less stable

How are the enzymes in organisms that live in hot environments adapted?

"- enzymes are more stable (have more bonds in tertiary structure)

How does a change in pH affect enzyme structure?

"- A change in pH refers to a change in H+ concentration

-

H+ ions interact with polar and charged R groups in tertiary structures

-

This breaks the bonds/interactions between R groups, leading to loss of tertiary structure

Explain why an increase in substrate concentration increases rate of reaction.

"- Higher successful collision rate

-

Between active site and the substrate

-

Forming more enzyme-substrate complexes

What does it mean by a 'reversible' inhibitor?

The inhibitor can be released from the enzyme to resume the enzymes' function

Most competitive inhibitors are reversible or irreversible?

Reversible

Explain how Vmax of the enzyme can be unchanged in competitive inhibition.

"- By adding more substrates to outcompete inhibitors

-

More substrates leads to more successful collisions between enzymes and substrates, hence more ESC formed

-

Therefore less enzymes available for inhibitors to bind"

What types of inhibitor does aspirin belong to?

Irreversible, competitive

Explain the difference between competitive and non-competitive inhibition mechanisms.

"- Competitive: inhibitor binds to active site substrate can no longer bind to AS

-

Non-competitive: inhibitor binds to a location other than the active site (allosteric site) changes 3o structure, hence change AS shape

Explain how an increase in substrate concentration affects the rate of reaction in non-competitive inhibition.

"No change

State two examples of irreversible, non-competitive inhibitors for human use.

"- Organophosphates insecticides and herbicides (inhibits AChE)

-

Proton pump inhibitors (PPIs) treat long term indigestion

What is end-product inhibition?

The product of an enzyme-catalysed reaction acts as the inhibitor

How does ATP regulate its own production by end-product inhibition?

"- ATP binds to the allosteric site of PFK

-

Prevent second phosphorylation of glucose

-

Glucose is not broken down to produce more ATP

State the difference between cofactors and coenzymes.

"- Cofactors = a non-protein component to help enzymes carry out their functions

-

Coenzymes = organic cofactors

From which chemical are cofactors derived from?

Minerals

From which chemical are coenzymes derived from?

Vitamins

Name the cofactor found in amylase.

Chloride ion

Name the cofactor invovled in photosynthesis.

NADP

Name the cofactor invovled in respiration.

NAD + FAD

State the difference between cofactors and prosthetic groups.

"- Cofactors are temporarily bound to the enzyme

Name the prosthetic group in haemoglobin.

Iron ion in haem group

Name the prosthetic group in carbonic anhydrase.

Zn2+

What are the three ways that an enzyme can be activated by changing the tertiary structure?

"- Adding a cofactor

Why is it important that some enzymes are produced in its inactive form?

Otherwise it may damage the cell it was produced in

What is an apoenzyme?

Inactive form of enzyme

What is a holoenzyme?

Active form of enzyme