Enzymes 2.4

Question 1

What is a cofactor?

Answer 1

A non-protein molecule or ion that has to be present to ensure that an enzyme catalysed reaction takes place at the appropriate rate.

Question 2

What are the 3 types of cofactors?

Answer 2

• activators
  -coenzymes
  -prosthetic groups

Question 3

What is a prosthetic group?

Answer 3

-a cofactor that is PERMANENTLY bound by covalent bonds to an enzyme molecule.

Question 4

What is an example of a prosthetic group?

Answer 4

-haemoglobin contains a prosthetic haem group which contains iron, permanently bound to the molecule, this serves as a means of binding oxygen

Question 5

What is a coenzyme?

Answer 5

-organic cofactors that BIND TEMPORARILY to the active site of enzyme molecules, either just before or at the same time that the substrate binds.
-THEY FACILITATE THE BINDING OF SUBSTRATE TO ENZYME
-the coenzymes are chemically changed during the reaction and need to be recycled back to their original state, sometimes by a different enzyme

Question 6

What are coenzymes derived from?

Answer 6

-vitamins are the source of coenzymes

Question 7

What are activators?

Answer 7

-activators are INORGANIC METAL IONS which TEMPORARILY binds to the enzyme and alters its active site
-making the reaction more feasible

Question 8

What is a cofactor for the amylase enzyme?

Answer 8

-amylase digests starch to maltose
-chlorine ions act as a cofactor for amylase

Question 9

What is the temperature coefficient, Q10 equation?

Answer 9

Q10= R2
———-
R1

R2= rate of reaction at (T+10) °C
R1= rate of reaction at T °C

Question 10

What is an inhibitor?

Answer 10

A substance that reduces or stops a reaction.

Question 11

What is a competitive inhibitor and what effect do they have on the reaction rate?

Answer 11

Competitive inhibitors are similar in structure to the substrate molecule therefore they bind to the active site of the enzyme, decreasing its activity as they compete with substrate for the enzyme. The amount of product formed remains the same, however the rate at which product formation occurs decreases. The higher the concentration of competitive inhibitor the lower the reaction rate. Increasing the substrate reverses the effect of competitive inhibitors by outcompeting them.

Question 12

What is the name of a competitive inhibitor that binds irreversibly to the enzyme’s active site?

Answer 12

An inactivator

Question 13

What is a non-competitive inhibitor and what is the effect of increasing the concentration of the substrate?

Answer 13

Non-competitive inhibitor does not bind to the active site; it binds at another site on the enzyme known as the allosteric site. Binding of the non-competitive inhibitors changes the shape of the active site therefore preventing the binding of the substrate. Increasing the concentration of substrate has no effect on non-competitive inhibition.

Question 14

What do reversible inhibitors do?

Answer 14

Reversible inhibitors bind to the active site through hydrogen bonds and weak ionic interactions therefore they do not bind permanently. Reversible inhibitors can either be competitive or non-competitive.

Question 15

What do irreversible inhibitors do?

Answer 15

They cause the disulphide bonds within the protein structure to break this causes the shape of the active site to change therefore affecting protein activity

Question 16

What is end-product inhibition an example of?

Answer 16

Negative feedback

Question 17

What does end-product inhibition do?

Answer 17

It regulates enzyme-catalysed reactions

Question 18

What are the steps in end-product inhibition?

Answer 18

-the product of one enzyme -catalysed reaction becomes the substrate for the next enzyme catalysed reaction in the metabolic pathway
-to not accumulate too much end product ,the product of the last enzyme catalysed reaction in the metabolic pathway may attach to part of the first enzyme in the pathway, but not at its active site
-the binding changes the shape of the enzyme 1’s active site preventing the pathway from running .This in non-competitive inhibition, that is reversible
-when the concentration of this product within the cell falls those molecules will detach from enzyme 1 and allow its active site to resume its normal shape . Therefore the metabolic pathway can run again.

Question 19

What is an example of an enzyme that catalyses intracellular reactions?

Answer 19

Catalase

Question 20

What is an example of an enzyme that catalyses extra cellular reactions?

Answer 20

Amylase

Question 21

What is a buffer and how are they used in laboratory investigations?

Answer 21

-something that resists changes to pH
-in laboratory investigations a buffer solution is used to maintain the desired pH for investigating enzyme action at different pH values or to keep the pH constant while investigating another factor

Question 22

How do changes in pH affect bonds within enzymes?

Answer 22

-excess hydrogen ions will interfere with the hydrogen bonds and ionic forces holding the tertiary structure of the enzyme together and so the active site of the molecule will change shape. If the substrate molecule does not fit well into the active site then the rate of reaction that the enzyme catalyses will be lowered
-as well as this increasing the concentration of hydrogen ions will also alter the charges on the active site of enzyme molecules as more protons will cluster around negatively charged groups in the active site. This interferes with the binding of the substrate molecule to the active site.

Question 23

What happens to an enzyme over a range of pH’s?

Answer 23

-small changes of pH either side of the optimum pH slow the rate of reaction because the shape off the active site is disrupted
-however, if the normal optimum pH is restored the hydrogen bonds can reform and the active site’s shape is restored
-at extremes of pH the enzyme’s active site may be permanently changed . When the enzyme is denatured it cannot catalyse the reaction

Question 24

What is the lock and key model hypothesis?

Answer 24

-the enzymes active site is complementary to the substrates
-they are a precise fit , no changes to the active site are needed
-the active site of the enzyme is a rigid fixed structure

Question 25

What is the induced fit model?

Answer 25

-when the substrate molecule fits into the the enzymes active site it changes shape slightly to give a precise fit
-this shape change is caused by hydrogen bonds, ionic interactions and hydrophobic interactions.
-when the product molecules have been formed they detach from the active site as they have a slightly different shape to the substrate molecules

Question 26

Describe how an enzyme such as pepsin breaks down a substrate

Answer 26

-substrate shape is complementary to active site
-substrate enters into the enzyme’s active site
-the enzyme’s active site changes shape slightly to give a precise fit due to interactions such as hydrogen bonds, ionic interactions,hydrophobic and hydrophilic interactions
-this forms the enzyme-substrate complex
-there is a destabilising of bonds in substrate,this then forms enzyme-product complex
-product leaves the enzymes active site