Enzymes 2.4

Question 1

What is an enzyme?

Answer 1

A biological catalyst

Question 2

What do enzymes do?

Answer 2

They reduce the activation energy for biochemical reactions

Question 3

What is activation energy?

Answer 3

The energy needed to break the bonds to start the reactions

Question 4

What is an intracellular enzyme?

Answer 4

An enzyme that works inside cells

Question 5

What are the 2 examples of intracellular enzymes?

Answer 5

• catalase which breaks down hydrogen peroxide into water and oxygen
• lysozyme which is found in lysosomes and digests old organelles and foreign bodies

Question 6

What is an extracellular enzyme?

Answer 6

An enzyme that works outside cells

Question 7

What are the 2 examples of extracellular enzymes?

Answer 7

• amylase which is found in saliva to catalyse the hydrolysis of starch into maltose
• trypsine which is produced by the pancrease and released into the small intestine to catalyse the hydrolysis opeptide bonds of large polypeptides into smaller ones which are then turned into amino acids by other enzymes

Question 8

What are the two enzymes which catalyse protein hydrolysis?

Answer 8

• trypsin turns proteins into amino acids from the pancrease
• pepsine turns proteins into amino acids from the stomach
• difference in PH causes a need for different enzymes

Question 9

What are the two mechanisms of enzyme action?

Answer 9

• lock and key model
• induced fit model

Question 10

What is the lock and key model?

Answer 10

Where the substrate is complimentary to the specific active site of the enzyme and it slots int the active site to form an enzyme substrate complex where it is then broken down into the products

Question 11

What is the induced fit model?

Answer 11

When a substrate fits into the active site of an enzyme as they have an aproximate complimentary shape and once an enzyme substrate complex has formed the enzyme slightly changes shape to fit the substrate better and to apply pressure on the bonds of the substrate, breaking or making the substrate to then form an enzyme product complex where the the products are released

Question 12

What is a catalyst?

Answer 12

A substance that speeds up chemical reactions by lowering the activation energy without being used up

Question 13

Why is the induced fit model considered better?

Answer 13

• it shows how other molecules can affect enzyme activity
• it shows how the activation energy is lowered

Question 14

What are the factors affecting enzyme activity?

Answer 14

• PH
• temperature
• conc. of enzymes
• conc. of substrate
• inhibitors ( competitive and non)

Question 15

What happenes to enzymes if the temperatures too hot?

Answer 15

The enzymes vibrate too much due to an increase in kinetic energy causing the bonds between the R groups to break, changing the tertiary structure therefore causing the enzymes to denature

Question 16

What happenes to enzymes if the temperatures too cold?

Answer 16

The kinetic energy of the enzymes decreases so much that they no longer have enogh energy to have any successful collisions meaning that no reaction can happen as they can not reach the activation energy

Question 17

What does Q10 stand for?

Answer 17

• temperature coefficient
• it shows how much the rate of reaction changes when the temperature is increased by 10 degrees celcius

Question 18

What does a Q10 of 2 mean?

Answer 18

If you increase the temperature by 10 degrees celcius, the rate of reaction doubles

Question 19

How does PH affect enzymes?

Answer 19

H+ ions and OH- ions found in acids and alkalis break the ionic and hydrogen bonds that hold the enzymes tertiary structure in place

Question 20

How does enzyme and substrate conc. affect rate of reaction?

Answer 20

It causes the rate of reaction to increase until it plateaus at the point of saturation where all the enzyme active sites have been filled as much as they can and there is another limiting factor stopping the rate of reaction from increasing any more

Question 21

What do these represent in an enzyme/ substrate, rate of reaction graph?
- steeper line
- flat line
- 2 lines levelling out at the same point
- 2 lines levelling out at different points
- 1st line to level off first

Answer 21

• faster rate of reaction
• reaction has stopped
• all of the reactants have been used up
• they made a different mass of product so there was a different limiting factor
• enzymes have denatured

Question 22

What does a competitive inhibitor do?

Answer 22

It has a similar shape to the substrate so it binds to the active site but no reaction takes place so the active site is blocked temporarily

Question 23

What does a non competitive inhibitor do?

Answer 23

It binds to an allosteric site which causes the enzymes active site to change shape so that the substrate molecule no longer fits

Question 24

What is reversible inhibition?

Answer 24

When the inhibitor binds with weaker bonds like hydrogen or ionic, so the inhibitor can be removed and the substrate can bind as normal

Question 25

What is a non reversible inhibitor?

Answer 25

When the inhibitor binds with stronger covalent bonds so the inhibitor can not be removed easily

Question 26

What are the differences in the inhibitor graphs?

Answer 26

• the line of the competitive inhibitor is not as steep as the one with no inhibitor meaning that it causes a slower rate of reaction but it eventually plateaus at the same point as the line with no inhibitors
• the line of the non competitive inhibitir is significantly less steep than the one with no inhibitor and plateaus much quicker and lower than the line with no inhibitors

Question 27

What is a cofactor?

Answer 27

A molecule that is not made of protein that will bind to and enzyme to help it work better; some enzymes will only work if there is another non protein substance bound to them

Question 28

What is a prosthetic group?

Answer 28

A cofactor that is tightly bound to an enzyme to the point where it is basically permanent

Question 29

What do inorganic cofactors do?

Answer 29

They help the enzyme and substrate bind together but do not directly participate in the reaction and they are not used up or changed in any way

Question 30

What is an example of an inorganic cofactor?

Answer 30

Chloride ions (Cl-) are cofactors for the enzyme amylase which is involved in the breakdown of carbohydrates

Question 31

What do organic cofactors (coenzymes) do?

Answer 31

They often act as carriers moving chemical groups between enzymes and participate in the reaction and are changed so the are continually recycled during the process

Question 32

What is a source for coenzymes?

Answer 32

Vitamines
Eg/ NDA = from vitamine B3

Question 33

What is an example of a prosthetic group that aids enzymes?

Answer 33

Zinc ions (Zn+2) is a prosthetic group for carbonic anhydrase where the ions are permanently bound to the enzymes active site (carbonic anhydrase is in RBCs and catalyses the reaction of carbonic acid into carbon dioxide and water)

Question 34

What are examples of inhibitor poisons?

Answer 34

• cyanide inhibits respiration enzyme (non competitive)
• snake venom enzymes involved with neuro transmitters

Question 35

What are exapmles of medicinal inhibitors?

Answer 35

• HIV protease inhibitors
• ethanol as an antifreeze poisoning treatment