enzymes 2.1.4

Question 1

how can you speed up a chemical reaction in a lab ?

Answer 1

raising the temperature
increasing the pressure
thermal energy is transferred to the particles, move more rapidly, more collisions, more frequent reactions

Question 2

what are enzymes ?

Answer 2

biological catalysts that speed up metabolic reactions in living organisms
a small amount of catalyst can catalyse the conversion of a large amount of substrate in products
they remain unchanged and can be reused

Question 3

what is the turnover number ?

Answer 3

the number of reactions that an enzyme can catalyse per second

Question 4

why are enzymes important ?

Answer 4

to sustain life , chemical reactions must occur rapidly, without them they would happen to slowly

Question 5

what type of protein is an enzyme ?

Answer 5

globular proteins that are soluble in water because of the hydrophilic nature of the side groups of amino acids

Question 6

what are anabolic reactions ?

Answer 6

small molecules are assembled into large ones , energy is required + enzymes
build up large polymers
eg. cellulose, long proteins for muscle contraction filaments

Question 7

what are catabolic reactions ?

Answer 7

large molecules are broken down into small ones , energy is released
they break down large organic molecules
eg. digestion of starch–> glucose, release of energy from glucose in reoperation

Question 8

where so enzymes function ?

Answer 8

intracellularly - DNA replication
extracellularly - digestion
inside membranes - synthesis of ATP

Question 9

name some extracellular enzymes

Answer 9

protease - proteins into amino acids
carbohydrase - starch into glucose
lipase - lipids into fatty acids and glycerol
cellulase - cellulose

Question 10

name a intracellular enzyme

Answer 10

catalase - protects cells from damage by hydrogen peroxide to water and oxygen
it consists of 4 polypeptide chains and a haem group
it has the highest turnover number of 6 million per second
white blood cells use catalase to kill microbes

Question 11

what is a metabolic pathway ?

Answer 11

a series of consecutive reactions with each step being catalysed by a different enzyme, specific for the substrate produced
if one enzyme cannot function the whole pathway cannot
eg, photosynthesis and respiration

Question 12

what is a metabolite ?

Answer 12

can be a reactant, intermediate or product in a metabolic pathway

Question 13

what is the classification of enzymes ?

Answer 13

oxidoreductases : enzymes that catalase the transfer of electrons during oxidation + reduction reactions
transferases : the transfer of a functional group from one molecules to another
hydrolases : catalyses the hydrolysis of bonds , addition of water
lyases : the splitting of bond other than oxidation and hydrolysis
isomerases : the rearranging of a molecule ( same type and number of atoms at different arrangement )
ligases: joining of to molecules by formation of covalent bonds

Question 14

what is enzyme specificity ?

Answer 14

the substrate fits into the complementary active site , they are highly specific for their function

Question 15

what is the general equation for an enzyme-controlled reaction ?

Answer 15

enzyme + substrate –> enzyme-substrate complex + enzyme-product complex –>enzyme + product

Question 16

what is activation energy ?

Answer 16

the amount of energy need to start a reaction ,
enzymes lower this

Question 17

how do enzymes increase the rate of reaction ?

Answer 17

an enzyme lowers the activation energy by creating a transition state between the enzyme and the substrate that is more stable( had less energy )

Question 18

why does forming the enzyme-substrate complex help to lower the activation energy ?

Answer 18

if a substrate molecules need to be join , attaching the enzyme holds them close together so they can bond easier
if an substrate needs to breakdown fitting the enzyme into the active site puts a strain on the bonds in the substrate allowing the molecules to break more easily

Question 19

explain the energy graphs for an anabolic reaction

Answer 19

reactants lower than the products as it is an endothermic reaction which gains energy

Question 20

explain the energy graphs for a catabolic reaction

Answer 20

reactants higher than the products as it is an exothermic reaction which loses energy

Question 21

what is the structure of an enzyme ?

Answer 21

very large molecules but only a small part is the active site the rest is amino acids which maintain the precise shape of the enzyme and active site

Question 22

how could a mutation affect an enzyme ?

Answer 22

a gene holding a mutation will mean the sequence of amino acids is altered and the enzymes made at the tertiary level will be changed which may prevent it from functioning

Question 23

an what is the active site on an enzyme ?

Answer 23

an indentation on the surface of the molecule
made of 6 - 10 amino acids
its shape is complimentary to the shape of the substrate
changes in temperature and pH can affect the shape of it , because the bonds that hold proteins in their tertiary structure

Question 24

what is the lock and key hypothesis ?

Answer 24

the substrate molecule exactly fits into the active site
and it held there by bonds to form the enzyme substrate complex
the strain on bonds to break them or bringing the substrate close together to facilitate formation of bonds
after the enzyme substrate complex, the products are formed and creates an enzyme product complex and the products are released

Question 25

what is the induced fit hypothesis ?

Answer 25

the active site is initially not an exact fir for the substrate molecule - as the substrate moves into the active site forced between them distort the enzyme and its active site so that it tightly envelopes the substrate, to make the ES complex

Question 26

what are cofactors (as an umbrella term) ?

Answer 26

a small non protein molecule that attaches to the enzyme to allow it to work to types ; cofactors and coenzymes

Question 27

what is the difference between cofactors and coenzymes ?

Answer 27

cofactors ; small inorganic groups that bind permanently (prosthetic group) or temporarily eg. copper, zinc, iron coenzymes ; large organic molecules that bind temporarily to the enzyme , transferring a chemical group that is necessary for the reaction

Question 28

what is an example of a cofactor ?

Answer 28

amylase can only digest starch to maltose is chloride ions are present - the binding of Cl ions causes a conformational change in the enzyme which allows it to bind to starch

Question 29

what is precursor activation ?

Answer 29

inactive enzymes are known as inactive precursor enzymes, they often undergo a change in shape to become active ( done by a cofactor ) before the cofactor is added they are apoenzymes and after they are called haloenzymes

Question 30

what factors affect enzymes ?

Answer 30

temperature pH concentration of enzyme concentration of substrate

Question 31

how does temperature effect the rate of chemical reactions ?

Answer 31

if the temperature is increased molecules gain kinetic energy and this increases the rate of reaction between molecules and the reaction occurs more rapidly

Question 32

how does increasing the temperature effect reactions with enzymes ?

Answer 32

both the enzyme and substrate will gain kinetic energy and move faster this will increase the rate of collisions this will mean more ES complexes form and a higher rate of reaction

Question 33

how do you measure initial rate of reaction ?

Answer 33

draw a tangent at the start of the graph initial rate = product formed divided by time

Question 34

why is the initial rate of reaction the fastest ?

Answer 34

at the beginning of the reaction the enzyme and substrate molecules have a greater chance of successfully colliding as the reaction continues the substrate is used up and the frequency pf collisions decreases

Question 35

what is the temperature coefficient ?

Answer 35

the change in the rate of reaction for every 10 degrees C also called Q10 it is normally about 2 the rate doubles every 10 degrees C

Question 36

how do you calculate the Q10 ?

Answer 36

rate of reaction at ( T + 10 ) degrees C ------------------------------------------------------ rate of reaction at T degrees C

Question 37

what happens to temperature is too high ?

Answer 37

- the enzyme vibrates - hydrogen and ionic bonds holding the tertiary structure break - the active site changes and the substrate cant fit - more heat cause an irreversible change and the enzyme is denatured

Question 38

which organisms can survive in harsh temperature environments ?

Answer 38

thermophilic bacteria live in hot springs at very high temperatures there enzymes are stable as they have more disulphide bonds psychrophilic bacteria lives in cool temperatures

Question 39

what is pH ?

Answer 39

power of hydrogen measure of concertation of hydrogen ions

Question 40

how do changes in pH affect enzymes ?

Answer 40

excess H+ will interfere with hydrogen and ionic bonds in the tertiary structure if the shape of the active site hanged the substrate will not fit and the rate of reaction will decrease if the pH is too extreme then the active site can be permanently changed

Question 41

what is a buffer ?

Answer 41

resists change in pH by donating or accepting H+ ions

Question 42

what will happen to the rate of reaction as the substrate concentration increases ?

Answer 42

1. the rate increases 2. more enzyme substrate complexes can form 3. therefore more EP complexes 4. more product is formed 5. substrate concentration is the limiting factor

Question 43

what will happen to the rate of reaction as the enzyme concentration increases ?

Answer 43

1. the rate increases 2. this is because more active sites become available 3. more ES complexes and EP complexes 4. more product molecules are formed 5. enzyme concentration is the limiting factor as all the active sites are in use ( active site saturation )

Question 44

what is v max ?

Answer 44

shows the maximum rate of rection when all active sites are occupied the reaction has not stopped but the rate cant increase

Question 45

why should this metabolic pathway not be allowed to continue to run without stopping ?

Answer 45

( it is allowed to stop because ... ) 1. build up of excess product 2. inefficient in terms of energy usage

Question 46

what are inhibitors ?

Answer 46

molecules that prevent enzymes form carrying out their normal function or slow them down

Question 47

how do competitive inhibitors work ?

Answer 47

they compete with the substrate for binding at the enzymes active site as their shape closely resembles the substrates the competitive inhibitor binds to the active sit and forms a enzyme-inhibitor complex which physically blocks the substrate binding this type of inhibitor can be overcome if the concentration of the substrate is much greater

Question 48

how does a non competitive inhibitor work?

Answer 48

they bind to the allosteric site on the enzyme , this causes a change in conformation ( shape ) in the active site so that the substrate cannot bind

Question 49

are inhibitors irreversible or reversable ?

Answer 49

both competitive and non competitive inhibitors can be reversible or irreversible and this depends on the strength of the bonds hydrogen and ionic bonds are weak and will break easily allowing the inhibitor to leave the active site covalent bonds are strong and cannot be removed so its irreversible

Question 50

what are examples of medical inhibitors ?

Answer 50

statins aspirin protein pump inhibitors reverse transcriptase inhibitor (HIV)

Question 51

how do competitive inhibitors effect the rate of reaction ?

Answer 51

the rate of reaction is initially lower (than without the inhibitor) but the substrate will eventually overwhelm the inhibitors and will reach the the same v max as the reaction would without the inhibitor

Question 52

how do non competitive inhibitors effect the rate of reaction ?

Answer 52

the v max reached will be much lower than when an inhibitor isn't used as the active sites are occupied increasing the amount o substrate will have no effect of the inhibitors ability to bind to the allosteric site

Question 53

what are examples of natural metabolic inhibitors ?

Answer 53

inhibitors in toxins or venoms can irreversible block enzymes that can cause paralysis or death heavy metals like mercury and cadmium are irreversible non competitive inhibitors blocking a range of metabolic reactions

Question 54

what is end product inhibition?

Answer 54

the final product made in a metabolic pathway binds non competitively to an enzyme in the pathway blocking more production of itself when the amount of the final product falls the inhibition ends and the pathway restarts