Enzymes

Question 1

What are enzymes/ why are they important?

Answer 1

They are globular proteins that act as biological catalysts, they react with the substrate quickly without the need for a harsh environment.

Question 2

define substrate

Answer 2

The substance used or acted on by another process or substance - the enzyme - substrate reaction

Question 3

what is an anabolic reaction?

Answer 3

‘building up’ reactions - used for growth, different components are synthesized and assembled to form cell then tissue etc…

Question 4

what is a catabolic reaction?

Answer 4

‘breaking down’ reactions - energy, needed for living processes, is released from large organic organisms like glucose in metabolic pathways (involving catabolic reactions)

Question 5

What is metabolism?

Answer 5

sum of all the different reactions and reaction pathways happening in a cell or organism, enabled by the control of enzymes

Question 6

What is the specificity of an enzyme

Answer 6

each enzyme catalyzes one biological reaction - in which there and many within the cell so a living organism will produce many enzymes.

Question 7

difference between intracellular and extracellular enzymes

Answer 7

Intracellular are found within the cell and are used for biological reactions that happen within the cell. catalase
Extracellular enzymes are found outside of the cell for external chemical reactions. e.g. digestive enzymes - amylase.

Question 8

3 examples - name the substrate and products formed

Answer 8

catalase - decomposition of hydrogen peroxide to water and oxygen
amylase - starch to sugars - maltose
trypsin - proteins into amino acids

Question 9

Role of digestion enzymes

Answer 9

Nutrients in the form of polymers like proteins and polysaccharides can’t enter the cell directly so digestive enzymes break them down into smaller molecules which are able to then be absorbed by the cell.

Question 10

What is the active site

Answer 10

the area of an enzyme which is complimentary to a specific substrate allowing the enzyme to bind with specify to the substrate.

Question 11

what are the steps involved in an enzyme-controlled reaction

Answer 11

1. the substrate binds to the active site of the enzyme
2. the enzyme- substrate complex is formed
3. after they react the products are formed in what’s called the enzyme - product complex
4. the products are released

Question 12

describe the lock and key hypothesis

Answer 12

in a similar way only a key will fit into a lock only one substrate will fit into the active site of the enzyme

Question 13

describe the induced fit hypothesis

Answer 13

the active site of the enzyme actually changes shape slightly when the substrate enters
initial interaction is weak but induce change into the tertiary structure of the enzyme putting strain on the bonds in the substrate - lowering the activation energy.

Question 14

how are the R- groups of an amino acid are involved in catalyzing reactions

Answer 14

interactions between R groups cause the shape of the active site which must be complimentary, they may also be charged which also has to be complimentary

Question 15

what is activation energy

Answer 15

the energy required to initiate a reaction

Question 16

what is rate of reaction

Answer 16

the speed at which reactants are converted into products

Question 17

what does the presence of an enzyme do to activation energy

Answer 17

the presence of an enzyme lowers the activation action making it easier to take place so therefore it happens faster

Question 18

5 factors that affect rate of an enzyme controlled reaction

Answer 18

temperature
pH
enzyme concentration
substrate concentration
inhibitors

Question 19

why does increasing temp towards optimum increase rate

Answer 19

increasing temp increases the kinetic energy of the molecules which mean more successful collisions between enzyme and substrate so rate increases

Question 20

define ‘temperature coefficient of Q10’ and state it’s usual value

Answer 20

measure of how much the rate increases with a 10 degree temp rise
for enzymes rate doubles (so 2)

Question 21

why does increasing temp above optimum decrease rate drastically

Answer 21

enzymes denature so substrate can no longer fit therefore rate decreases

Question 22

explain why Siamese cats are white with black tails ears paws and face

Answer 22

mutation in enzyme that catalyzes melanin production where it denatures at boy temp. extremes such as end of the tail are cooler so melanin can produce the black fur

Question 23

explain why a pH away from the optimum decreases rate of reaction

Answer 23

enzyme structure depends on interaction of R groups as pH changes it changes charges and therefore these interactions between R groups so enzyme denatures and substrate can no longer fit

Question 24

define “Vmax”

Answer 24

maximum initial velocity or rate of an enzyme controlled reactions

Question 25

explain how increasing substrate concentration affects initial rate of reaction

Answer 25

as substrate concentration increases the free enzymes can combine with the extra substrate molecules but when saturation point is reached there are no longer any more free enzymes so rate stays steady even with increase in substrate

Question 26

describe how to investigate a factor affecting rate of an enzyme controlled reaction

Answer 26

using catalase and measure the rate by measuring volume of oxygen produced in a certain amount of time change conditions by using a pH buffer or different temperature water baths etc..

Question 27

define “cofactor” and “coenzyme” and two possible roles

Answer 27

cofactor - non protein component of an enzyme that is essential for the function of the enzyme
coenzyme - if the cofactor is organic then it is a cofactor
may form part of the active site or transfer molecules from one reaction to another in a multi step pathway

Question 28

describe similarities and differences between cofactors, coenzymes and prosthetic groups

Answer 28

cofactors are inorganic and not permanently combined to the enzyme
coenzymes are organic and not permanently bound to the enzyme
prosthetic groups are permanently bound to the enzyme

Question 29

explain why the chloride ion in the active site in amylase is a cofactor

Answer 29

it is inorganic and not permanently bound to the enzyme

Question 30

explain why the zinc ion in the structure of carbonic anhydrase is a prosthetic group

Answer 30

it is an inorganic ion permanently bound to the enzyme

Question 31

give two examples of coenzymes that are synthesized from vitamins in our diet

Answer 31

NAD s synthesized from vitamin B3 and is involved in respiration to transfer hydrogen
coenzyme A from vitamin B5 used in breakdown of fatty acids and carbohydrates in respiration

Question 32

4 ways in which multi step pathways are regulated by cells

Answer 32

competitive and non competitive inhibitors
end product inhibitors
inactive precursor enzymes

Question 33

define “enzyme inhibitor” “competitive inhibitor” “non competitive inhibitor” “reversible inhibitor” “irreversible inhibitor” “allosteric site”

Answer 33

enzyme inhibitor - factor effecting rate of enzyme catalyzed reactions
competitive inhibitor - competes with substrate to bind to active site of enzyme
non competitive inhibitor - inhibitor that binds to allosteric site of an enzyme
reversible inhibitor - inhibitor that can temporarily bind to enzyme but also dissociate so enzyme can return to normal functions
irreversible inhibitor - inhibitor that one bound to the enzyme can’t dissociate and stops enzyme function permanently
allosteric site - place on an enzyme where a molecule which is not the substrate can bind changing the shape of the enzyme and it’s ability to be active

Question 34

explain how a competitive inhibitor affects the rate of reaction of an enzyme

Answer 34

have a similar shape to substrate so bind with active site of the enzyme preventing the enzyme substrate complex forming reducing rate of reaction

Question 35

name two competitive inhibitors

Answer 35

statins- affect enzyme that produces cholesterol prescribed to reduce cholesterol
aspirins - inhibit production of chemicals responsible for pain

Question 36

explain how a non competitive inhibitor works

Answer 36

bind to allosteric site of enzyme which alters the tertiary structure of the enzyme reduces the rate as the substrate can no longer fit.

Question 37

name two non competitive inhibitors

Answer 37

organophosphates - used in insecticides inhibit enzyme used in nerve transmission causing paralysis
proton pump inhibitors - block enzymes releasing hydrogen ions reducing build up of acid in stomach which could cause ulcers

Question 38

explain the effect of competitive and non competitive enzymes on Vmax

Answer 38

competitive inhibitors do not reduce Vmax but instead slow down the rate to reach it because once substrate conc increased effect is reduce and will bind rather than inhibitor
non competitive inhibitors reduce Vmax as they take a certain number of enzymes out of action regardless on substrate conc

Question 39

describe what “end product inhibition” is and it’s usefulness in metabolic pathways

Answer 39

negative feedback controls rate. If there is little product then there is little inhibition so more is made and if there is a lot of product then a lot of inhibition so rate slows drastically and less is made

Question 40

describe how ATP is involved in end product inhibition of the enzyme phosphofructokinase

Answer 40

first step of breakdown of glucose involves addition of 2 phosphate molecules second catalyzed by PFK which is competitively inhibited by ATP so regulates own product

Question 41

define the term “inactive precursor enzyme” and why enzymes may be produced in this form

Answer 41

an inactive enzyme which can be turned on by post translational modification some enzymes can cause damage to some cells so only want to be activate in certain conditions

Question 42

describe 3 ways inactive precursor enzymes may be activated

Answer 42

addition of cofactor
changes in condition (e.g. pH)
action of another enzyme

Question 43

define “apoenzyme” “haloenzyme” “zymogen” and “proenzyme”

Answer 43

apoenzyme - inactive enzyme activated by addition of a cofactor
haloenzyme - enzyme with it’s required coenzyme
zymogen/ proenzyme - inactive substance converted into enzyme when activated by another enzyme

Question 44

give 4 examples of inactive precursor enzymes and how they are activated

Answer 44

During blood clotting factor X is released by platelets which catalyses prothrombin into thrombin which is a protease which catalyses fibrinogen into fibrin - this series of activations is called the coagulation cascade

Pepsinogen released into stomach becomes pepsin due to pH - this protects body tissues from digestive action of pepsin