enzymes

Question 1

what is an enzyme?

Answer 1

a biological catalyst

Question 2

what is the difference between an intracellular enzyme and extracellular enzyme?

Answer 2

intracellular enzymes are found inside cells and extracellular enzymes are found outside cells.

Question 3

give an example of an intracellular enzyme and describe what it does

Answer 3

Catalase, it binds to hydrogen peroxide which is a toxic molecule and speeds up its breakdown to the harmless molecules, water and oxygen.

Question 4

give two examples of extracellular enzymes and describe what it does

Answer 4

-amylase, its produced in the pancreas and released in the small intestine. It catalyses the breakdown of starch into maltose. Maltose is broken down by other enzymes to produce glucose which is absorbed in the bloodstream.
-trypsin, its produced in the pancreas and is released into the digestive system. It catalyses the breakdown of protein molecules into peptides. Other enzymes breakdown peptides into amino acids which is absorbed into the bloodstream.

Question 5

what type of proteins are enzymes?

Answer 5

globular proteins

Question 6

why are enzymes soluble in water?

Answer 6

because there are hydrophilic amino acids on the surface but hydrophobic amino acids within the centre.

Question 7

how is the enzyme-substrate complex formed?

Answer 7

the tertiary structure of the active site is complementary to the structure of the substrate. They are specific.

Question 8

what happens when the enzyme-substrate complex is formed?

Answer 8

amino acids on the surface of the active site forms temporary bonds with the substrate molecule. Enzyme catalyses reaction to form enzyme product complex, then products are released.

Question 9

how do enzymes increase rate of reaction?

Answer 9

by lowering activation energy

Question 10

Describe the lock and key theory?

Answer 10

the tertiary structure of the enzyme is fixed and doesn’t change shape so the substrate molecule and active site fit perfectly.

Question 11

Describe the induced fit model?

Answer 11

as the substrate starts to form bonds with amino acids in the active site, the tertiary structure adjusts and moulds itself around the substrate. Molecules which aren’t the correct substrate, can’t form the correct bonds to the amino acids on the active site, so the tertiary structure doesn’t change.

Question 12

what is the difference between catabolic and anabolic reactions?

Answer 12

catabolic reaction is breaking down, anabolic is building up.

Question 13

what is metabolism?

Answer 13

the sum of all different reactions and reaction pathways happening in a cell or an organism.

Question 14

why does the rate of reaction decrease when temperature goes past its optimum?

Answer 14

enzymes vibrate more rapidly causing hydrogen bonds to break. The tertiary structure of the enzyme begins to change, its no longer complementary to the substrate and denatured.

Question 15

when describing the Trend in graphs discuss…

Answer 15

-frequency of successful collisions
-the rate of reaction change
-optimum temp is the max frequency of successful collisions

Question 16

what is the temperature coefficient (Q10) formula?

Answer 16

(rate of reaction at temperature x + 10 degrees) divided by rate of reaction at temperature x

Question 17

what is value is Q10 usually around?

Answer 17

2 as when temp is increased by 10, the rate usually doubles. However it doesn’t occur after the optimum temp as the enzyme denatures

Question 18

pH is dependant on what?

Answer 18

hydrogen ions, lower pHs have a higher conc of H+ ions and higher pHs have lower conc of H+ ions

Question 19

every enzyme has different specific optimum pHs, dependent on what?

Answer 19

their environment. Acidic? neutral?

Question 20

why does rate of reaction decrease when passing the optimum pH?

Answer 20

hydrogen ions can bond with the R group of the amino acids in the active site which affects R group bonding with the substrate. Bonding from the H+ ions can also break the bonds holding the tertiary structure in place which may cause it to become denatured.

Question 21

increasing substrate concentration, increases rate of reaction. However at a point, the rate stops increasing why?

Answer 21

At that point it is working its fastest and it is called V max. The active site of the enzymes become the limiting reactant as there aren’t enough free active sites.

Question 22

increasing enzyme concentration, increases rate of reaction. However at a point, the rate stops increasing why?

Answer 22

the substrate molecules become a limiting reactant.

Question 23

Describe the affect of a competitive inhibitor

Answer 23

competitive inhibitors have a similar shape of the substrate, it binds to the active site but no reaction happens this prevents the substrate from binding with the active site, reducing the frequency of successful collisions.

Question 24

How can we reduce the effect of a competitive inhibitor?

Answer 24

by increasing substrate concentration.

Question 25

Many drugs are examples of competitive inhibitors, describe some

Answer 25

-Methotrexate is used to treat certain cancers. It binds reversibly
-Penicillin is used to treat bacterial infections by acting as a competitive inhibitor for the enzyme involved in the synthesis of bacterial cell walls. It binds irreversibly so increasing substrate concentration, doesn’t affect it.

Question 26

Describe non-competitive inhibitors

Answer 26

they bind to the allosteric site of the enzyme causing the enzyme’s tertiary structure to change therefore it isn’t complementary to the substrate and an enzyme-substrate complex cannot form, the rate decreases. The effect of a non-competitive inhibitor cannot be overcome.

Question 27

what is a cofactor?

Answer 27

a non-protein chemical compound(co-enzymes), ion or prosthetic group required for the enzymes role as a catalyst. They usually come from vitamins.

Question 28

are prosthetic groups a permanent part of the enzymes structure?

Answer 28

yes

Question 29

cofactor of amylase?

Answer 29

Cl-

Question 30

explain why enzymes are essential to all organisms? (2 marks)

Answer 30

enzymes are biological catalysts which lower activation energy