Enzymes

Question 1

intracellular enzymes

Answer 1

enzymes that are produced and found inside the cell

Question 2

extracellular enzymes

Answer 2

Extracellular enzymes are produced inside the cell but are secreted by cell via exocytosis and catalyse reactions outside cells (eg. digestive enzymes in the gut)

Question 3

what is the structure of enzymes?

Answer 3

globular proteins making them soluble in water. The tertiary structure of the active site is complementary to the structure of substrate making the enzymes specific.

Question 4

how do enzymes increase the rate of reaction?

Answer 4

• enzymes lowers the activation energy barrier meaning more substrate molecules have enough energy to cross the activation barrier and react

Question 5

example of intracellular enzymes

Answer 5

catalase which hydrolysis toxic hydrogen peroxide into water and oxygen

Question 6

examples of extracellular reactions

Answer 6

• amylase which hydrolyses carbohydrates
• trypsin which hydrolyes proteins

Question 7

what is meant by turnover number of an enzyme?

Answer 7

the number of reactions than an enzyme molecule can catalyse per second

Question 8

why are enzymes called biological catalyst?

Answer 8

‘Biological’ because they function in living systems

‘Catalysts’ because they speed up the rate of chemical reactions without being used up or changed

Question 9

Induced fit model

Answer 9

• when the substrate molecule approaches the active site of the enzyme it starts to form temporary bonds with the amino acid in the active site, so the tertiary structure of the enzymes adjusts so that the active site moulds itself tightly around the substrate.

Question 10

Lock and key theory

Answer 10

-the substrate has a complentary shape to the active site on the enzyme
-binds forming a enzyme-substrate complex
-releasing the enzyme-product complex

Question 11

Catabolic reactions

Answer 11

The breakdown of complex molecules into simpler products. Happens when a single substrate is broken down into two or more molecules

Question 12

Examples of a catabolic reaction

Answer 12

Cellular respiration and hydrolysis reaction

Question 13

Anabolic reactions

Answer 13

Building of more complex from simpler ones. Drawing 2 or more substrates into the active sites, forming bonds between them and releasing a single product

Question 14

Example of anabolic reactions

Answer 14

Protein synthesis and photosynthesis

Question 15

the effect of temperature on enzyme activity?

Answer 15

as we increase the temperature the rate of reaction increases as the enzyme and substrate gain more kinetic energy so vibrate more which increases the number successful collisions between the enzyme and substarte molecule increases therefore more enzyme-substrate complexes are formed. past the optimum temperature the increase vibrations break the hydrogen and ionic bonds holding the tertiary structure of the active site causing it to change. Eventually it will be no longer complementary to the substrate molecule so the enzyme has denatured and fewer enzyme-substate complexes are formed

Question 16

why is the rate of reaction slow when temperature is low?

Answer 16

Molecules move relatively slowly as they have less kinetic energy
Less kinetic energy results in a lower frequency of successful collisions between substrate molecules and the active sites of the enzymes which leads to less frequent enzyme-substrate complex formation

Question 17

formula for temperature coefficient

Answer 17

temperature coefficient = (rate of reaction at (x + 10) °C) ÷ (rate of reaction at x °C)

Question 18

temperature coefficient when 10degrees is added

Answer 18

For most enzyme-catalysed reactions the rate of the reaction double.s for every 10 °C increase in temperature
The temperature coefficient (Q) for a reaction that follows this pattern is: Q₁₀ = 2

Question 19

effect of PH on enzyme activity

Answer 19

-at a low PH the hydrogen ions attract te negative R groups in the hydrogen and ionic bonds causing them to break . This changes the tertiary struvture of the enzyme therefore the active site to is no longer complemenatry meaning less enzyme-substrate complexes are formed.
-at high PH. The OH- groups also cause bonds to break=same explnation but attracts positive parts instead

Question 20

example of optimum PH’s of enzymes

Answer 20

• pepsin is found in the stomach, an acidic environment at pH 2,
• trypsin 8

Question 21

effect of substrate concentration on the rate of reaction

Answer 21

– At low concentrations of substrate molecules there is a low frequency of collisions between the substrate molecule and the active site so less enzyme-substrate complexes are formed so the rate of reaction is low. At high substrate concentrations the frequency of collisions increases. the substrate concentration is the limiting factor. Eventually the graph levels off as the active site becomes saturated therefore there a no free active sites for the substrate molecule to collide with.

Question 22

effect of enzyme concertation on the rate of reaction

Answer 22

As the enzyme
concentration increases there are more successful collisions between the active site and the substrate; there are more
enzyme-substrate
complexes formed; sidiconds all the substrate it used up; and the substrate concentration becomes the limiting factor;

Question 23

what are cofactors?

Answer 23

-ionorganic permenantly bound to an enzyme .
-produce specific shape of the enzyme active site but do not take part in the reaction

Question 24

what are coenzymes?

Answer 24

small organic non-protein molecules that bind temporarily to the active site of enzyme molecules. they chemically changed in a reaction. also derived from vitamins e.g (NAD)

-as volume/concentartion increases rate of raction increases

Question 25

what are prosthetic groups?

Answer 25

• a non-protrein molecule that is permanently attached to an enzyme molecule. e.g the enzyme carbonic anhydrase contains a zinc ion present. and amylase contains chloride ions

Question 26

the effect of competitive inhibitors on the rate of reaction

Answer 26

• competitive inhibitors are similar shape to the substrate molecule
  -Substrate competes with inhibitor;
  Both the substrate and the inhibitor have a complimentary, specific shape to the active site; there will be fewer enzyme-substrate complexes; more substrate reduces the chance of the inhibitor getting into the active site.

Question 27

examples of competive inhibitors

Answer 27

• penicillin which used to treat bacteria infections and binds irreversibly
• methotrexate which is used to treat certain cancers binds reversibly.

Question 28

effect of non-competitive inhibitors

Answer 28

they bind to a different part of the enzyme (allosteric site) which causes the tertiary structure of the enzyme to change so the shape of the enzyme changes and is no longer complementary to the substrate molecule, so an enzyme-substrate can no be formed reducing the rate of reaction. Increasing the substrate molecule cannot reduce the effect of non competitive inhibitors.

Question 29

what is end-product inhibition

Answer 29

a way of regulating a enzyme catalysed reaction when a product molecule remains tightly bound to the enzyme so the enzyme cannot form more of the product than the cell needs.

Question 30

how are metabolic sequences controlled?

Answer 30

the product of the last enzyme catalysed reaction attaches to a the allosteric site of the first enzyme in the pathway changing the tertiary structure of the enzyme. preventing the pathway from running acting as a non-competitive enzyme.

Question 31

Inactive precursor

Answer 31

• no biological activity until it’s metabolised by an enzyme into its active form