Enzymes

Question 1

what are enzymes and what do they do?

Answer 1

they are biological catalysts

it speeds up the rate of reaction without being used up itself

Question 2

what is an intracellular enzyme? give an example

Answer 2

its an enzyme that works inside cells

e.g. catalase catalyses the breakdown of hydrogen peroxide into oxygen and water

Question 3

what is an extracellular enzyme? give an example

Answer 3

its an enzyme that works outside cells
e.g. amylase, found in the saliva catalyses the hydrolysis of starch into maltose
trypsin catalyses the hydrolysis of peptide bonds

Question 4

what is the structure of an enzyme?

Answer 4

globular proteins
they have an active site- where the substrate molecule binds to
active site has a specific shape which is determined by the enzymes tertiary structure

Question 5

how do enzymes work?

Answer 5

the substrate has to be complimentary to the active site- if not, the reaction won’t be catalysed

Question 6

what is formed when the substrate binds to an enzyme?

Answer 6

an enzyme-substrate complex

Question 7

how do enzymes speed up reactions?

Answer 7

activation energy (often heat) needs to be supplied before the reaction starts 
enzymes reduce the amount of Ea needed i.e happens at a lower temp than without an enzyme

Question 8

why does Ea lower when an enzyme-substrate complex is formed?

Answer 8

if 2 substrate molecules need to be joined, attaching to the enzyme holds them close together, reducing any repulsion- they bond more easily
when the enzyme is catalysing a breakdown reaction, fitting into active site puts a strain on the bond in substrate- molecules break more easily

Question 9

how does the lock and key model work?

Answer 9

active site has a particular shape- It is specific to the substrate
the substrate is complementary to the active site
it creates an enzyme substrate complex
the product is released

Question 10

how does the induced fit model work?

Answer 10

the substrate makes the active site change in the right way
the active site changes shape to facilitate the reaction
when the reaction is over the product is released

Question 11

how does temperature affect enzyme activity?

Answer 11

when temperature increases the rate of enzyme controlled reaction increases
means more kinetic energy so molecules move faster
molecules more likely to collide with enzyme active site
energy of collisions also increases- collision is more likely to result in a reaction

Question 12

what is optimum temperature?

Answer 12

temp continues to increase until enzyme reaches optimum temperature
the rate of enzyme controlled reaction is at it’s fastest
if temperature goes too high the reaction stops increasing
molecules vibrate more- this break the bonds
active site changes shape, substrate no longer fits
enzyme is denatured

Question 13

What is temperature coefficient?

Answer 13

the value that shows how much the rate of reaction changes when temperature is raised by 10 degrees
Before optimum temperature is reached coefficient is in effect (Q10)

Question 14

how does pH affect enzyme activity?

Answer 14

all enzymes have optimum pH that they work best at
e.g. pepsin work best at acidic pH 2 which is useful because it’s found in the stomach
H+ and OH- ions break Ionic and hydrogen bonds between molecules that hold tertiary structure enzyme denatures

Question 15

how does enzyme concentration affect enzyme activity?

Answer 15

more enzymes mean more collisions
higher rates of reaction
If substrate becomes limited Vmax is reached

Question 16

what is Vmax?

Answer 16

]the maximum rate of reaction when enzymes are fully saturated by substrate

Question 17

how does substrate concentration affect enzyme activity?

Answer 17

more substrate means more collisions
the saturation point is the point at which there are more substrate molecules than enzyme molecules
after that, there are more substrate molecules enzymes have than they can cope with
adding more makes no difference- enzyme concentration becomes a limiting factor
Vmax is reached at this point

Question 18

how do you estimate the initial rate of reaction?

Answer 18

draw a tangent to the curve at t = 0
using a ruler estimate where the curve would continue if it carried on below 0
draw a line along the ruler
calculate the gradient of the tangent (gradient = change and y-axis/change in x axis)
work out units of the rate- units of the y-axis/units of the x-axis (which should always be time)

Question 19

what are inorganic cofactors?

Answer 19

inorganic molecules
often are ions
are not directly involved in the reaction
not altered during the reaction
allow substrate and enzyme to bind together
chloride ions are required for amylase function

Question 20

what are organic cofactors?

Answer 20

participate in the reaction and ARE changed
they are constantly recycled
they often act as carriers
e.g. B3 is used to make NAD which is a coenzyme for alcohol dehydrase

Question 21

what are prosthetic groups?

Answer 21

these are cofactors tightly bound to the enzyme
they can become a permanent part of the enzyme
e.g. zinc ions are added to carbonic anhydrase, the zinc ions are a permanent part of the enzymes active site

Question 22

what are competitive inhibitors?

Answer 22

similar shape to substrate molecules
compete with the substrate molecules to bind to the active site but no reaction takes place
they block the active site so no substrate molecules can fit in
high concentration of inhibitor: take up nearly all the active site and hardly any substrate will get to the enzyme
high concentration of substrate: the substrate chances of getting into an active site before the inhibitor increases therefore increasing substrate increases rate of reaction

Question 23

what are non competitive inhibitors?

Answer 23

bind to the enzyme away from its active site (known as allosteric site)
causes the active site to change shape so substrate molecules can no longer bind to it
don’t ‘compete’ with the substrate molecules to bind to the active site because they’re a different shape
increasing the concentration of the substrate won’t make any difference - enzyme activity still inhibited

Question 24

what is reversible and non reversible inhibition?

Answer 24

reversible- not bind permanently to an enzyme
non-reversible- bind permanently to an enzyme
which one they are depends on the strength of the bond between enzyme and inhibitor:
strong- (covalent bonds) the inhibitor can’t be removed easily and the inhibition is irreversible weak- (hydrogen bonds & weaker ionic bonds) the inhibitor can be removed and inhibition is reversible

Question 25

state examples of medical drugs that are enzyme inhibitors?

Answer 25

some antiviral drugs e.g. reverse transcriptase inhibitors are a class of antiviral developed treat HIV they inhibit the enzyme reverse transcriptase which catalyses the replication of viral DNA
this prevents the virus from replicating
some antibiotics e.g. penicillin inhibits the enzyme transpeptidedase which catalyses the formation of protein in bacterial cells
prevents the bacterium from regulating osmotic pressure- the cell bursts

Question 26

what are metabolic poisons and give examples?

Answer 26

interfere with metabolic reactions causing damage, illness, or death.
cyanide is a non-competitive reversible inhibitor of cytochrome C oxidase
malonate is a competitive inhibitor
arsenic is a non-competitive inhibitor
they all catalyse respiration reactions

Question 27

what is product inhibition?

Answer 27

metabolic pathways are regulated by end-product inhibition
a metabolic pathway is a series of connected metabolic reactions
product of first reaction takes part in second reaction etc
each reaction is catalysed by different enzyme
enzymes are inhibited by product of reaction they catalysed (product inhibition)
end product inhibition is when final product in metabolic pathway inhibits enzymes that act earlier on in the pathway
i.e regulating the pathway and controlling the amount of end product that gets made

Question 28

how does enzyme inhibition protect cells?

Answer 28

sometimes synthesized as inactive precursors in metabolic pathways to prevent causing damage to cells
part of molecule inhibit its action as an enzyme
once removed the enzyme becomes active
e.g. protease are synthesized as inactive precursors to stop them damaging proteins in the cell in which they are made