M2, C4 Enzymes

Question 1

define enzyme

Answer 1

biological catalyst that interact with substrate molecules to facilitate chemical reactions

Question 2

what are enzymes made of

Answer 2

globular proteins

Question 3

define anabolic

Answer 3

reactions of metabolism that construct molecules from smaller units
they require energy from the hydrolysis of ATP

Question 4

define active site

Answer 4

area of an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind a substrate with specificity

Question 5

define activation energy

Answer 5

the energy required to initiate a reaction

Question 6

define catabolic

Answer 6

reactions of metabolism that break molecules down into smaller units
these release energy

Question 7

define substrate

Answer 7

a substance used, or acted on, by another process or substrate
eg. a reactant in an enzyme catalysed reaction

Question 8

how does an enzyme speed up a reaction

Answer 8

it lowers the activation energy

this means it takes less energy to initiate a reaction hence speeding the reaction up

Question 9

what is the lock and key hypothesis

Answer 9

• an enzyme has a specific active site which is complementary to the shape of the substrate
• when the substrate is bound to the active site and enzyme-substrate complex is formed
• the substrates then react forming an enzyme-product complex
• the products are released leaving the enzyme unchanged
• temporary bonds are also formed when the R groups of the enzymes interact with the substrate which helps the reaction along

Question 10

what is the induced fit hypothesis

Answer 10

• modified version of the lock and key hypothesis
• the active site of the enzyme actually changes shape slightly as the substrate enters
• the initial reaction between the enzyme and substrate is relatively weak
• the enzyme’s tertiary structure changes which strengthens binding and putting strain on the substrate molecules
• this lowers the activation energy for the reaction

Question 11

how would you work out metabolism

Answer 11

catabolic reactions + anabolic reactions

Question 12

how is starch digested

Answer 12

starch polymers are broken down into maltose by amylase
amylase is produced by the salivary glands and pancreas and released in the saliva and pancreatic juice in the small intestine

maltose is then broken down into glucose by maltase
maltase is present in the small intestine

glucose is then absorbed into the bloodstream

Question 13

how is protein digested

give an example of protease

Answer 13

trypsin is a protease
it catalases proteins into smaller peptides
peptides are broken into amino acids
trypsin are produced in the pancreas and released in the pancreatic juice in the small intestine
amino acids are absorbed by cells lining the digestive system and go into the bloodstream

Question 14

As temperature increases how does enzyme activity change?

What’s the optimum temp in humans?

Answer 14

Increasing temp, increases kinetic energy in particles. The particles collide more frequently. This would mean more successful collisions between the substrate and the enzyme which increases the rate of reaction.
The rate of reaction doubles with a 10 degree Celsius temp rise.
Optimum temperature in humans is 37

Question 15

Why do enzymes denature at a too high temp?

Answer 15

As temperature gets high the bonds between proteins vibrate more. Bonds will then strain and break. This changes the shape of the tertiary structure of the protein.
The active site changes shape so won’t fit with the substrate so the enzyme can no longer act as a catalyst.

Question 16

What does the graph look like of temperature against rate of reaction

Answer 16

Slow increase up to the optimum temp and then a rapid decrease

Question 17

What adaptions do enzymes have which are in the cold and in the hot?

Answer 17

More flexible structures making them less stable

Enzymes at high temp have more bonds so are more stable and are more resistant to change

Question 18

What is pH and what is its relation to hydrogen ions

Answer 18

It’s the measure of hydrogen ion concentration

The lower the pH, the more hydrogen ions are (more acidic)

Question 19

How does pH affect enzyme reactions

Answer 19

Hydrogen ions are attracted to negatively charged areas. Different amino acids have different charges and hydrogen ionic bonds holds amino acids in a very precise shape.
Hydrogen ions interfere with these bonds and thus change the structure of the enzyme and its active site.

Question 20

What is the optimum pH for amylase? For pepsin?

Answer 20

Amylase - pH 7.8

Pepsin - pH 1.8

Question 21

How does substrate concentration affect the rate of reaction

Answer 21

More concentration increases the rate of reaction because there is a higher collision rate.
However eventually all the active sites are used up and the rate of reaction can no longer increase. This is the V max.

Question 22

what are intracellular enzymes

Answer 22

enzymes that act within the cells

eg. hydrogen peroxide which is broken down by catalase

Question 23

what are extracellular enzymes

Answer 23

enzymes that break down substances outside of cells
for example nutrients and proteins which need to be transported from cell to cell may be too big to get into the cell so enzymes can break them down so they can fit.
they can make smaller molecules for digestion.

Question 24

what are enzyme inhibitors

Answer 24

molecules that prevent enzymes from carrying out their normal function of catalysis
two types - competitive and non-competitive

Question 25

what is competitive inhibition

Answer 25

A molecule that has a similar shape to the substrate of an enzyme fits into the active site of that enzyme.
It blocks the substrate from entering the active site, preventing the enzyme catalysing the reaction.
The enzyme is said to be inhibited.
The number of substrates binding with active sites reduces, hence slowing down the rate of reaction.
The inhibitor only binds temporarily for most cases.

Question 26

what are some examples of competitive inhibition

Answer 26

Statins - inhibits the enzyme that synthesises cholesterol to stop high cholesterol levels

Aspirin - irreversibly inhibits enzymes that synthesise prostaglandins and thromboxane which produce pain and fever

Question 27

what is non-competitive inhibition

Answer 27

The inhibitor binds to the enzyme at a location other than the active site - this is called the allosteric site.
This causes the tertiary structure of the enzyme to change which changes the shape of the active site.
The substrate therefore can no longer bind with the enzyme and is said to be inhibited.
Active sites therefore become unavailable hence decreasing the rate of reaction.
Can be reversible or irreversible

Question 28

what are some examples of irreversible non-competitive inhibitors

Answer 28

Organophosphates - insecticides which stop the nerve impulse transmission which leads to paralysis

Proton pump inhibitors - treat long term indigestion by stopping the production of excess acid

Question 29

what is end-product inhibition

Answer 29

When a product of a reaction then acts as an inhibitor to the enzyme that produces it.
Serves as a negative feedback control mechanism.
Stops excess products being made and stops resources being wasted.
It is non-competitive reversible inhibition.

Question 30

How does respiration involve end-product inhibition

Answer 30

• Breaking down a glucose molecule involves the enzyme PFK (phosphofructokinase).
• This enzyme is competitively inhibited by ATP. It therefore regulates its own production.
• When ATP levels are high, more ATP binds to PFK which stops glucose being broken down.
• As ATP is used up less binds to PFK so the enzyme can catalyse more so respiration resumes leading to the production of more ATP.

Question 31

define cofactor

Answer 31

non-protein components necessary for the effective functioning of an enzyme

Question 32

define prosthetic group

Answer 32

non-protein component of a conjugated protein

Question 33

what is a coenzyme

Answer 33

an organic cofactor

Question 34

where are inorganic cofactors obtained from

Answer 34

the diet as minerals

eg. iron, calcium, chloride and zinc

Question 35

what cofactor is in amylase

Answer 35

chloride ion

Question 36

where are coenzymes derived from

Answer 36

vitamins in the diet

Question 37

whats the difference between cofactors and prosthetic groups

Answer 37

cofactors are temporary and prosthetic groups are tightly bound to the enzyme and can be permanent

Question 38

what are precursor enzymes

Answer 38

inactive enzymes which are produced like that

Question 39

why is it important that some enzymes are precursor

Answer 39

so they don’t cause damage

so they can be controlled and activated only under certain conditions

Question 40

how are precursor enzymes activated

Answer 40

they need to undergo a change in shape to the tertiary structure
this is done by adding a cofactor

Question 41

what is an apoenzyme

Answer 41

a precursor enzyme before a cofactor is added

Question 42

what is a holoenzyme

Answer 42

when a cofactor is added to a precursor enzyme so it is activated

Question 43

In blood clotting describe the enzyme activation process / the coagulation cascade

Answer 43

when platelets touch the collagen of the skin, they become aggregated and release factor X
It is activated by the cofactor vitamin K
When it is activated it converts prothrombin to thrombin by changing the structure
Thrombin is a protease which converts soluble fibrinogen to insoluble fibrin fibres
Fibrin forms the blood clot