Enzymes

Question 1

What type of protein are enzymes?

Answer 1

Globular

Question 2

What structure do enzymes have?

Answer 2

Tertiary - complex 3D shape held together by bond (ionic, hydrogen, disulphide bridges, hydrophobic interactions) determines shape of active site

Question 3

What are enzymes?

Answer 3

Globular proteins which act as biological catalysts

Question 4

What’s a biological catalyst?

Answer 4

Something made of living cells which helps speed up the rate of chemical reactions

Question 5

What two types of metabolic reactions do enzymes control?

Answer 5

Anabolic
Catabolic

Question 6

What’s an anabolic reaction?

Answer 6

Building up molecules (eg. Protein synthesis)

Question 7

What’s a catabolic reaction?

Answer 7

Breaking down molecules (eg. Digestion )

Question 8

When a substrate binds to an enzyme what forms?

Answer 8

Enzyme-substrate complex

Question 9

What does complimentary shape mean?

Answer 9

Enzymes are specific to their substrate

Question 10

How does an enzyme act on a substrate?

Answer 10

It makes temporary bonds at the active site forming an enzyme substrate complex

Question 11

What does each enzyme do?

Answer 11

It catalyses one SPECIFIC reaction

Question 12

Why do enzymes only catalyse one Specific reaction?

Answer 12

They have a specific 3D tertiary structure (active site is only specific to one substrate)

Question 13

Why does Maltase only catalyse maltose in digestion? (3marks)

Answer 13

Maltase only catalyses maltose in a hydrolysis reaction because it has a specific 3D structure.
Therefore the active site will have a specific shape so only maltose (substrate) which has a complimentary shape will bind to the active site to form an enzyme substrate complex

Question 14

How do reactions occur between enzymes and substrates?

Answer 14

Reactions occur due to collisions which have to be the right orientation and force

Question 15

Where are enzymes made and where do they act?

Answer 15

Intracellular (inside cells)
Extracellular ( secreted outside cells)

Question 16

What are the two different theories of how enzyme substrate complexes form?

Answer 16

Lock and Key Model
Induced Fit Model

Question 17

What does the lock and key model suggest about E-S complexes?

Answer 17

It’s an earlier model which suggests enzyme active sites are rigid and permanent

Question 18

Explain the lock and key model?

Answer 18

The active site of the enzyme acts as the specific lock whilst the substrate acts as the key due to its complimentary shape. When the substrate binds to the active site an anabolic or catabolic reaction occurs to achieve the products.

Question 19

Explain the induce fit model?

Answer 19

Before the reaction, the active site is NOT complimentary to the substrate
As the substrate binds the active site changes shape to better fit/become complimentary to the substrate to form an enzyme-substrate complex
This stresses and distorts the bonds in the substrate causing the reaction to occur and products to be released

Question 20

What do enzymes do to cause a high rate of reaction?

Answer 20

Lower activation energy

Question 21

How is activation energy lowered and why is it useful?

Answer 21

The stress/ distorting of bonds in the substrate causes the activation energy to be lower
It reduces the minimum energy required to start a reaction

Question 22

What needs to happen for a successful collision and what does it cause ?

Answer 22

It causes a reaction:
- collide with enough energy
- collide with suitable orientation
- substrate must be complimentary to active site
- come into physical contact with a substrate

Question 23

Explain how the active site of an enzyme causes a high rate of reaction?

Answer 23

• Lowers activation energy
• Induced Fit = active site changes so E-S complex forms causing bonds to be stressed/distorted

Question 24

What is an exergonic reaction?

Answer 24

Where energy is released

Question 25

What is an endergonic reaction.?

Answer 25

Where energy is absorbed

Question 26

What are the 5 factors affecting enzyme action?

Answer 26

Temperature pH Enzyme Concentration Substrate Concentration Inhibition

Question 27

What is a buffer?

Answer 27

An aqueos solution that has a highly stable pH

Question 28

What is the purpose of a buffer solution?

Answer 28

Resists changes in pH

Question 29

How do you measure pH of a solution?

Answer 29

pH = - Log10 [H+]

Question 30

How does substrate concentration affect enzyme action?

Answer 30

The higher the substrate concentration the faster the rate or reaction (due to more successful collisions) because more E-S complexes form. This is true until ‘saturation’ when all available active sites of complimentary enzymes are filled

Question 31

When the substrate concentration has reached ‘saturation’ what does this mean’?

Answer 31

All available active sites are full so an increase in substrate concentration will have no further effect nd the rate of reaction plateaus.

Question 32

How does enzyme concentration affect rate of reaction?

Answer 32

The more enzyme molecules there are the more likely a substrate molecule will collide and form a enzyme-substrate complex. Increasing enzyme concentration will increase the rate of reaction as more active sites are available.

Question 33

What is the limiting factor when increasing substrate concentration has no further effect on rate of reaction?

Answer 33

Enzyme concentration

Question 34

If the amount of substrates is limited what happens to the rate of reaction?

Answer 34

Enough enzyme molecules to deal with available substrate so adding more enzymes will have no further effect on rate of reaction

Question 35

How does temperature effect enzyme activity?

Answer 35

Increase rate of reaction to provide enough kinetic energy for a successful collision

Question 36

What happens if the temperature is too low (enzymes)?

Answer 36

There is not enough kinetic energy for a successful collision (to form an enzyme-substrate complex)

Question 37

If the temperature is too high what happens to the enzyme?

Answer 37

The enzyme denatures - active site irreversibly changes - so enzyme substrate complexes don’t form

Question 38

Why do enzymes denature at high temperature?

Answer 38

The energy (high temperatures) breaks the weak hydrogen bonds between nearby peptide bonds so alters tertiary structure and consequently active site

Question 39

What is it called when enzymes reach there maximal rate of reaction?

Answer 39

Optimum

Question 40

What do all enzymes have?

Answer 40

A unique optimum pH value

Question 41

What happens if the pH is too high or low?

Answer 41

The OH- ions or H+ ions interfere with the charges in the peptide chains and disrupt the ionic/hydrogen bonds holding the tertiary structure together so active site is altered and less E-S complexes form

Question 42

What are enzyme inhibitors?

Answer 42

Substances that directly or indirectly affect the functioning of the active site of a specific enzyme, and therefore prevent the substrate binding, preventing the formation of an enzyme substrate complex which leads to a decrease in the rate of reaction

Question 43

What are the two types of enzyme inhibitors?

Answer 43

* Competitive * Non-Competitive

Question 44

What sort of structure do competitive inhibitors have?

Answer 44

Have a similar structure/shape to substrates so they can bind to occupy the active site of an enzyme

Question 45

What do you competitive inhibitors do?

Answer 45

They compete with substrate for the active site

Question 46

How do you reverse the binding of competitive inhibitors active sites?

Answer 46

Increase substrate concentration, which will overcome competitive inhibition as it is a reversible reaction

Question 47

Where do competitive inhibitors bind?

Answer 47

On active site of an enzyme

Question 48

What are competitive inhibitors.?

Answer 48

- Substances with a similar shape/structure to substrate so bond to and occupy active site of enzyme - Compete with substrate - Binding to active site is reversible and can be overcome by increasing substrate concentration

Question 49

What a non-competitive inhibitors?

Answer 49

- Bind to enzyme at allosteric site - Causes a change in the tertiary structure or enzyme so alters shape of active site - Active site is no longer complimentary to the substrate so E-S complex can’t form - Occurs permanently and can’t be overcome by increasing substrate concentration

Question 50

Where do Noncompetitive inhibitor bind?

Answer 50

Allosteric site (other site than active site)

Question 51

What do non-competitive inhibitors cause?

Answer 51

Cause a change in the tertiary structure of an enzyme therefore also change the shape of the active site

Question 52

Can non-competitive inhibition be overcome?

Answer 52

No bind permanently changing the shape of the specific active site

Question 53

Cells don’t want to make more or less product than required so use what?

Answer 53

End - Product Inhibition to control reaction pathways in negative feedback loop

Question 54

What do inhibitors do?

Answer 54

Reduce binding of enzyme to substrate to form enzyme substrate complexes