Module 2 Section 4 - Enzymes

Question 1

intracellular

Answer 1

inside cells

Question 2

extracellular

Answer 2

outside of cells

Question 3

Why does increasing the substrate concentration initially increase the rate of reaction?

Answer 3

More substrate is available

this isn’t a full answer, but something else I can add to my explanation

Question 4

Give two examples of extracellular enzymes.

Answer 4

trypsin and amylase

Question 5

Give one examples of an intracellular enzyme.

Answer 5

catalase

Question 6

How does catalase work?

Answer 6

It breaks down toxic hydrogen peroxide (H₂O₂ - produced from many cellular processes) into harmless oxygen and water.

Question 7

How does trypsin work?

Answer 7

It catalyses the hydrolysis of peptide bonds to break down bigger polypeptides into smaller ones.

Question 8

How does amylase work?

Answer 8

It catalyses the hydrolysis of starch into maltose in the mouth.

Question 9

Where is trypsin produced?

Answer 9

Pancreatic cells

Question 10

Where is trypsin secreted?

Answer 10

Into the small intestine

Question 11

What organ system do amylase and trypsin work in?

Answer 11

The digestive system

Question 12

According to the induced fit model, how does an enzyme catalyse a reaction?

Answer 12

An enzyme’s active site changes shape slightly to better facilitate the reaction, allowing the substrate(s) to bind more tightly

Question 13

Describe two ways that the formation of enzyme-substrate complexes lowers the activation energy of chemical reactions.

Answer 13

• The enzyme’s active site holds two substrates closer together, reducing repulsion so they can bond more easily.
• The enzyme’s active site strains the bonds holding a substrate together, so the substrate molecules can be broken down more easily.

Question 14

Explain why enzymes denature due to high temperatures.

Answer 14

Enzymes vibrate more at higher temperatures. This breaks bonds between the amino acids in the enzyme protein, disrupting the enzyme’s tertiary structure (changing the shape of the active site).

This is only part of an explanation

Question 15

Explain why enzymes denature due to extreme pHs.

in terms of an exam question answer

Answer 15

As the pH changes from the optimum pH, there are fewer/more H⁺ and OH^- ions surrounding the enzyme. These interact with the charges on the enzyme’s amino acids, breaking ionic and hydrogen bonds within the tertiary structure of the enzyme, including the active site.

Question 16

Enzyme denaturation due to high temperature is ____.

Answer 16

irreversible

Question 17

Enzyme denaturation due to changes in pH is ____.

Answer 17

reversible for small variations but irreversible for large variations

Question 18

temperature coefficient

Answer 18

How much the rate of reaction changes when the temperature increases by 10°C.

Question 19

temperature coefficient symbol

Answer 19

Q₁₀

Question 20

temperature coefficient formula

Answer 20

Q₁₀ = rate at higher temperature / rate at lower temperature

Question 21

Q₁₀ of 3 = ?

Answer 21

rate of reaction triples (is multiplied by 3) for an increase in 10°C

Question 22

How can you calculate the rate of reaction from a graph of e.g. volume of gas produced against time?

Answer 22

Find the gradient - you will likely have to draw a tangent

Question 23

How can you calculate the initial rate of reaction?

Answer 23

Draw a tangent that passes through time = 0. Calculate the gradient of this line and include the units (y / x)

Question 24

V_max

Answer 24

The maximum velocity/rate of reaction with an enzyme - this is where the graph plateaus.

Question 25

inorganic - in terms of cofactors

Answer 25

Carbon isn’t bound to hydrogen

Question 26

cofactor

Answer 26

A non-protein **inorganic** substance that enables some enzymes to function

Question 27

How do cofactors help enzymes to function properly?

Answer 27

They help the enzyme & substrate bind together **without being directly involved in the reaction** (e.g. not directly in the enzyme's active site but does change the active site's shape) so they **aren’t used up/changed** in the reaction

Question 28

example of a cofactor

Answer 28

chloride ions for amylase

Question 29

coenzyme

Answer 29

A non-protein **organic** substance that enables some enzymes to function.

Question 30

How do coenzymes help enzymes to function properly?

Answer 30

They DO participate in the reactions so **are changed** by the reaction (e.g. they are carriers, moving chemical groups between different enzymes)

Question 31

If coenzymes are changed in a reaction, how do we not run out of them?

Answer 31

They are constantly recycled (for example, the coenzyme bounces between enzyme A which changes it into one form and enzyme B which changes it back into its initial form)

Question 32

prosthetic group

Answer 32

A cofactor that is tightly bound to the enzyme

Question 33

Give an example of a prosthetic group and how it helps an enzyme.

Answer 33

Zinc is a permanent prosthetic group for **carbon anhydrase** (an enzyme in red blood cells) which catalyses the reaction water + carbon dioxide -> carbonic acid

Question 34

What does it mean if a molecule is a permanent prosthetic group? Give an example of one that you need to know.

Answer 34

They are a permanent part of the enzyme's active site. Zinc ions

Question 35

Give a source of many coenzymes.

Answer 35

vitamins

Question 36

competitive inhibitor

Answer 36

A molecule with a **similar shape** to the substrate molecule, that **fills the enzyme’s active sites** so the substrate is blocked from binding to them; they compete for the active sites

Question 37

non-competitive inhibitor

Answer 37

A molecule that binds to any place on the enzyme apart from the active site, but that causes the active site to change shape so the substrate molecules can no longer bind to them

Question 38

allosteric site

Answer 38

The place on an enzyme where a non-competitive inhibitor binds to (anywhere apart from the active site)

Question 39

What do competitive inhibitor rate of reaction graphs look like, compared to the normal graph?

Answer 39

The gradient is less steep. The competitive inhibitor means that it takes longer to reach V_max

Question 40

What do non-competitive inhibitor rate of reaction graphs look like, compared to the normal graph?

Answer 40

The gradient is less steep and the graph doesn't reach as high a V_max

Question 41

Competitive and non-competitive inhibitors can be ____ or ____.

Answer 41

reversible irreversible

Question 42

What makes an inhibitor reversible or irreversible?

Answer 42

Thre strength of the bonds between the enzyme and the inhibitor

Question 43

What sort of bonds form between a reversible inhibitor and an enzyme?

Answer 43

Weak hydrogen or ionic bonds

Question 44

What sort of bonds form between an irreversible inhibitor and an enzyme?

Answer 44

Strong covalent bonds

Question 45

How can antiviral drugs use enzyme inhibitors?

Answer 45

Inhibitor of **reverse transcriptase**, so it can't catalyse the replication of the viral DNA. This prevents the virus from replicating which keeps the virus level low

Question 46

How can antibiotics use enzyme inhibitors?

Answer 46

Penicillin is an inhibitor of **transpeptidase** so bacteria **can't catalyse the formation of their cell walls**. This weakens the cell wall and can lead to the cell bursting and the bacterium being killed

Question 47

Give two examples of metabolic poisons.

Answer 47

Arsenic (chosen one to learn) and cyanide

Question 48

Give an example of how one metabolic poison example works

Answer 48

Arsenic – non-competitive inhibitor of **pyruvate dehydrogenase** an enzyme that catalyses respiration reactions. Arsenic therefore reduces respiration - cells that can’t respire die

Question 49

end-product inhibition

Answer 49

A metabolic pathway where the final product of the series of reactions inhibits one of the enzymes in the process

Question 50

Give an example of end-product inhibition.

Answer 50

phosphofructokinase is one of the enzymes in the metabolic pathway that breaks down glucose to make ATP ATP inhibits the action of phosphofructokinase, so if there’s a high level of ATP, the production of ATP is stopped temporarily

Question 51

inactive precursor

Answer 51

An inactive form of an enzyme (one that cannot function properly)

Question 52

Why are some enzymes synthesised as inactive precursors? Give examples of some enzymes which are produced this way.

Answer 52

To prevent them from causing damage to the cell e.g. proteases or lysosomal enzymes (found in lysosomes) contain digestive enzymes. These would start breaking down the enzymes which made them or other proteins inside the cell.

Question 53

How do inactive precursors become active?

Answer 53

Part of the precursor molecule inhibits the enzyme’s action – this is removed via a chemical reaction when the enzyme is needed.

Question 54

What does amylase break starch down into?

Answer 54

Maltose

Question 55

What is the approximate temperature coefficient of an enzyme-controlled reaction?

Answer 55

2

Question 56

Which one of the following conditions is least likely to denature an enzyme? **A** a high temperature **B** an extreme pH **C** heavy metal ions **D** a low temperature

Answer 56

It's obviously C or D Heavy metal **ions** can affect the pH? They can form strong bonds with the enzyme due to the charges, distorting its structure and leading to denaturation Therefore the answer is D (enzymes just work very slowly at low temperatures).

Question 57

Order these bonds in order of least strong to most strong: disulfide ionic peptide hydrogen

Answer 57

hydrogen, ionic, disulfide, peptide

Question 58

Do enzymes denature at low temperatures?

Answer 58

No - they tend to just work really *really* slowly without causing permanent structural damage