topic three - enzymes - mr hedditch

Question 1

define an enzyme?

Answer 1

enzymes are biological catalysts. They speed up

chemical reactions without being used up. They are globular proteins with a specific tertiary structure

Question 2

what are the two types of metabolic reactions?

Answer 2

breaking large molecules into smaller molecules (catabolic)

building smaller molecules up into larger molecules (anabolic)

Question 3

what’s an enzyme made up of and what structure does it have?

Answer 3

enzymes are proteins with a tertiary structure

Question 4

define activation energy?

Answer 4

the level of energy required to enable a reaction to
take place

enzymes reduce the amount of energy required to allow a reaction to take place (means that reactions can proceed at lower temperatures)

Question 5

what would happen to the chemical reactions if there were no enzymes?

Answer 5

many chemical reactions would proceed too slowly to sustain life

Question 6

define intracellular?

Answer 6

describes an enzyme that remains active only within the cell in which it is formed

Question 7

define extracellular?

Answer 7

describes an enzyme (such as a digestive enzyme) that functions outside the cell from which it originates

Question 8

what does catalyse break down?

Answer 8

it catalyses the breakdown of hydrogen peroxide into
water and oxygen :
H2O2 H2O + O2

Question 9

two examples of extracellular enzymes?

Answer 9

amylase & trypsin

Question 10

where is amylase produced and what does it do to your mouth?

Answer 10

salivary amylase is produced in the salivary glands and hydrolyses starch to maltose in the mouth

the pancreas also produces amylase, which acts in the small intestine

Question 11

where is trypsin made and what does it breakdown?

Answer 11

Made in the pancreas and acts
made in the small intestine

breaks peptide bonds and hydrolyses proteins into
smaller polypeptides, ready for other enzymes to break the polypeptides into amino acid

Question 12

what type of protein is enzyme?

Answer 12

globular proteins

Question 13

what are the medicinal drugs reduce enzyme activity?

Answer 13

enzyme inhibitors

Question 14

what are the two different models of enzyme action?

Answer 14

the lock-and-key model and induced-fit model

Question 15

state the stages of the lock-and-key model?

Answer 15

enzymes are specific to particular substrates

the active site has a shape complementary to the shape of the substrate

the substrate binds to the enzyme to form an enzyme substrate complex

the products are released (no longer fit
the active site)

Question 16

state the stages of induced-fit model?

Answer 16

shape of the active site does not match the shape of the substrate exactly

active site moulds itself around the substrate

a close fit is needed before the reaction can take place

an enzyme-product complex forms

the products are released (no longer fit the active site)

the enzyme reverts to its original shape

Question 17

what are the effects on temperature on enzyme action?

Answer 17

heat increases the kinetic energy of molecules, making them collide more frequently and with more force

increasing the temperature initially increases the rate of reaction

if the temperature is increased further then ionic and hydrogen bonds holding the enzyme’s tertiary structure in place are broken (peptide bonds are unaffected)

Question 18

review the temperature coefficient?

Answer 18

in book

Question 19

effect of PH on enzyme action?

Answer 19

pH is a measure of the concentration of hydrogen ions (H+)
the more H+ ions in a solution, the lower the pH
HCl > H+ + Cl-

H+ ions are attracted towards negatively-charged ions and molecules they can interfere with the hydrogen and ionic bonds holding the enzyme’s tertiary structure in place by affecting the charges
on the amino acid side chains

Question 20

what does the optimum PH of an enzyme depend on what enzymes work best where?

Answer 20

where it is found, enzymes from the stomach work best in strongly acidic
conditions (e.g. pepsin – optimum pH 2)

enzymes from the small intestine work best in slightly alkaline conditions (e.g. trypsin – optimum pH 7-8)

Question 21

effect of enzyme concentration?

Answer 21

as soon as the product(s) leave an enzyme’s active site it is free to accept more substrate and continue catalysis

so long as temperature and pH are suitable and there is not a shortage of substrate, the rate of reaction is directly
proportional to the enzyme concentration

Question 22

define an enzymes turnover number?

Answer 22

an enzyme’s turnover number is the number of substrate molecules that an enzyme can turn into products in one minute

turnover number varies considerably between different enzymes

Question 23

review the practical on the effect of substrate concentration on the rate of an enzyme-controlled reaction

Answer 23

olc

Question 24

what is standard deviation + formula?

Answer 24

The standard deviation is a statistical device that tells
you how tightly the data are scattered around the mean

a low standard deviation means that the data are tightly clustered; a high standard deviation means that they are widely scattered

formula in book

Question 25

define a cofactor?

Answer 25

any non-protein molecule that must be present to ensure that enzyme-controlled reactions
take place

some enzymes will only work if a particular
cofactor is present

Question 26

types of cofactors?

Answer 26

inorganic cofactors
organic cofactors
prosthetic groups

Question 27

what are cofactors?

Answer 27

some cofactors are permanently bound to the
enzyme (prosthetic groups)

others affect the enzyme on a temporary basis -
coenzymes and inorganic ions

cofactors remain unchanged or are regenerated or recycled at the end of the reaction

Question 28

what are inorganic cofactors?

Answer 28

cofactors can be inorganic molecules or ions. They work by helping the enzyme and its substrate to bind together to form an
enzyme-substrate complex
Inorganic cofactors are not changed or used up during the reaction – they do not directly participate in the reaction

E.g. chloride ions (Cl-) act as cofactors for the enzyme amylase

Question 29

what are organic cofactors?

Answer 29

some cofactors are organic molecules – we call these coenzymes.

coenzymes participate in the reaction and are altered in some way

often they act as carriers, moving chemical groups between different molecules.

in this way they are continually recycled

E.g. in respiration coenzyme A (CoA) temporarily binds to a molecule of acetate to become acetyl CoA. The coenzyme carries the acetate molecule to the next stage of respiration,
where they decouple. The regenerated CoA then returns to collect more acetate (acting as a shuttle)

Question 30

what is a prosthetic group?

Answer 30

Prosthetic cofactors are non-protein molecules that
are permanently bound to the enzyme (as opposed to
inorganic cofactors and coenzymes which only bind
temporarily)
E.g. zinc ions (Zn2+) form
part of the active site for
the enzyme carbonic
anhydrase

Question 31

give two differences between organic and inorganic cofactors [2]

Answer 31

inorganic cofactors do not participate directly in the
reaction but organic cofactors do

inorganic cofactors are not changed or used up
during the reaction but organic cofactors are
changed/recycled/regenerated

Question 32

define inhibition?

Answer 32

an enzyme inhibitor
is any substance or molecule that slows down the rate of an
enzyme-controlled reaction by affecting the enzyme molecule

Question 33

state the two types of inhibitors?

Answer 33

competitive inhibitors

non-competitive inhibitors

Question 34

what are competitive inhibition?

Answer 34

competitive inhibitor
molecules have a shape
complementary to the shape
of the enzyme’s active site

they bind to the active site
instead of the enzyme’s
normal substrate. An enzyme inhibitor complex is formed, but no products are released

Question 35

what does high concentrations of the inhibitors causes in competitive inhibitions?

Answer 35

make collisions between the inhibitor and the active site more likely/frequent

Question 36

what does high concentrations of substrate cause inhibitions?

Answer 36

dilutes the effects of the

inhibitor

Question 37

what are competitive inhibition?

Answer 37

non-competitive inhibitor
molecules bind to the
enzyme in an area that is
NOT the active site.

this area is called the allosteric site

this changes the shape of
the active site by
interfering with the
enzyme’s tertiary structure

this prevents the substrate
from binding, so the
reaction is not catalysed

Question 38

what will changing the substrate concentration do in non competition inhibition?

Answer 38

nothing it will NOT affect

reaction rate with this type of inhibitor

Question 39

what is a metabolic pathway?

Answer 39

a metabolic pathway is a series of enzyme-controlled biochemical reactions in which one substance is built up or broken down into
another

e.g. respiration and photosynthesis

Question 40

examples of inhibitors that are used for good?

Answer 40

penicillin
aspirin
protease inhibitors

Question 41

examples of inhibitors that are used for bad?

Answer 41

potassium cyanide

snake venom