3.1.4.2 Many proteins are enzymes

Question 1

EQ: how the drug lowers the rate of reaction- competitive inhibitor

Answer 1

• the drug is a similar shape to the substrate
• so it fits the active site as it is a complimentary shape
• so less substrate binds to form enzyme-substrate complexes

Question 2

EQ: Methotrexate only affects the rate of the reaction controlled by folate reductase. Explain why this drug does not affect other enzymes

Answer 2

-the drug is a similar shape to the substrate so only fits into that particular active site

Question 3

What are enzymes made up of?

Answer 3

Enzymes are proteins, long chain of amino acids made up from the elements carbon, oxygen, hydrogen and nitrogen.

Question 4

What is a catalyst?

Answer 4

A substance that speed up chemical reactions without being used up in the reaction itself.

Question 5

How enzymes catalyse reactions

Answer 5

Decrease activation energy
(bind to a molecule or substrate and modify it to lower the activation energy)
By putting stress on bonds within a molecule
Holding bonds close together
Increasing likelihood of reaction
Decreasing activation energy

Question 6

What are enzymes and what do they do?

Answer 6

Enzymes are biological catalysts: they lower the activation energy by providing an alternative pathway, often allowing reactions to occur at much lower temperature. This speeds up the rate of reaction.

Question 7

Why does the formation of enzyme-substate complexes lower activation energy?

Answer 7

1. If two substrate molecules are being joined in a reaction, being both attached to the enzyme holds them closer together overcoming repulsion and making it easier to bond.
2. If the enzyme is catalysing a breakdown reaction, fitting into the active site with an induced fit strings the substrate bonds making breakdown easier.

Question 8

Activation energy (Ea) definition

Answer 8

The minimum energy required to start a reaction

Question 9

Types of enzymes

Answer 9

Catabolic
└breaks
Anabolic
└makes

Question 10

Enzyme active site

Answer 10

Determined by tertiary structure/ 3D shape

Question 11

What do biological catalysts catalyse?

Answer 11

Metabolic reaction: both at cellular level such as respiration and for the organism as a whole such as digestion.

Question 12

What are the two enzyme models?

Answer 12

1. Lock and key model (early scientists)

2. Induced Fit model (more Modern)

Question 13

Lock and key model of enzyme action

Answer 13

Shape of enzymes active site is exactly complimentary to shape of the substrate
└enzyme-substrate complex
└enzyme-product complex
Enzymes can catalyse a reverse reaction

Question 14

Induced-fit model of enzyme action

Answer 14

enzyme changes shape slightly so substrates fit
└enzyme and substrate are not exactly complimentary so change shape to become complimentary
Substrate changes shape slightly
└=bonds break more easily
└=lowers activation energy

Question 15

Specificity of enzymes

Answer 15

└enzymes are specific
└substrates are different shapes
└active site of enzyme and substrate are complementary
└so substrate fits= enzyme-substrate complex
└induced fit/lock and key
└any other substrate will not fit

Question 16

What does enzymes being so specific result with?

Answer 16

They typically only catalyse one reaction e.g. maltase enzyme only breaks down maltose.

Question 17

What results as a change in tertiary structure?

Answer 17

If the tertiary structure of an enzyme is altered, the shape of the active site will change, and enzyme-substrate complexes cannot form so the enzyme is denatured as it cannot function.

Question 18

What can denaturation be caused by?

Answer 18

This can be caused by pH and temperature.

Question 19

How can primary structure changing result with a change in tertiary structure?

Answer 19

The primary structure, the order of amino acids in a chain is determined by a gene. If a mutation occurs in that gene, it could change the tertiary structure produced.

Question 20

What factors can effect the rate of enzyme controlled reactions

Answer 20

enzyme concentration
substrate concentration
concentration of competitive inhibitors
concentration of noncompetitive inhibitors
pH 
temperature

Question 21

The effects of the following factors on the rate of enzyme controlled reactions
enzyme concentration

Answer 21

Increase enzyme concentration= increase rate of reaction
└more active sites available as long as there are enough substrates to occupy
└as reaction progresses, rate decreases as substrate is used up

Question 22

The effects of the following factors on the rate of enzyme controlled reactions
substrate concentration

Answer 22

Increase substrate concentration= increase rate of reaction
└more molecules available to enter active site
└more enzyme-substrate complexes
└once all enzymes filled- rate of reaction plateaus

Question 23

The effects of the following factors on the rate of enzyme controlled reactions
concentration of competitive inhibitors

Answer 23

inhibitor has a similar shape to the substrate
=can fit into the active site (as the shape is complimentary to the active site)for a short time
= This prevents the substrate from entering the active site
rate is determined by relative concentrations and the rate is little reduced if substrate concentration is larger than inhibitor concentration
The effects of this inhibitor can be reversed by increasing the substrate concentration

Question 24

The effects of the following factors on the rate of enzyme controlled reactions
concentration of non-competitive inhibitors

Answer 24

reduces rate as it fits into a site other than the active site (an allosteric site)
alters the shape/charge of the active site =substrate cannot bind to the active site
=no enzyme substrate complex
=reaction will not reach Vmax.
Increasing substrate concentration will have no effect on the rate.

Question 25

The effects of the following factors on the rate of enzyme controlled reactions
pH

Answer 25

└pH altered= loss of 3D structure= enzyme denatured
└charge distribution on enzyme changes causing hydrogen/ionic bonds to be affected
└=changes active site
└no enzyme-substrate complexes
└decrease enzyme activity

Question 26

The effects of the following factors on the rate of enzyme controlled reactions
Temperature

Answer 26

Optimum temperature:
└kinetic energy=collisions= enzyme-substrate complexes
└max rate of reaction achieved
Higher temperature
└increase kinetic energy=collisions more frequent, more energy= vibrate too much
└=breaks hydrogen bonds- alters 3D shape of enzymes active site
└=enzyme denatured-loses specific and complimentary shape
└substrate molecules don’t fit in active site
└no enzyme-substrate complexes formed
└rate of reaction decrease/stop

Question 27

An example of non-competitive inhibition?

Answer 27

Cyanide ions (CN⁻) bind to a site other that the active site (allosteric site) on cytochrome oxide preventing respiration.

Question 28

EQ: Describe the induced fit model of enzyme action

Answer 28

• active site of enzyme is not complimentary
• but is flexible
• and changes shape so the substrate can fit and an E-S complex can form

Question 29

EQ: way that the lock and key model is different from the induced fit model

Answer 29

-active site does not change shape and is complementary before binding

Question 30

EQ: the monomers that make up the active site of the enzyme

Answer 30

-amino acids

Question 31

EQ: Enzyme inhibition- how aspirin prevents substrate molecules being converted to product molecules

Answer 31

• it blocks the active site

- so the substrate does not bind

Question 32

EQ: Non-competitive inhibitors- now imatinib stops uncontrolled cell division in leukaemia

Answer 32

• imatinb is a non competitive inhibitor as it binds to a site other than the active site (allosteric site)
• this means that the active site is now the wrong shape and no e-s complex is formed
• so the uncontrolled cell division is now controlled

Question 33

EQ: Enzyme specificity- why the enzyme only breaks down a specific lipid

Answer 33

• the active site
• has a complimentary and specific shape
• so does not bind with other lipids
• to form e-s complexes

Question 34

EQ: Suggest why they cannot give the missing enzyme as a tablet that is swallowed

Answer 34

-enzymes are proteins
-and are digested by enzymes
OR
-enzymes are too large
-to enter the blood stream