Enzymes

Question 1

define the term enzyme.

Answer 1

An enzyme is a type of protein specific to a certain substrate. it is a biological catalyst that speeds up the rate of reaction.

Question 2

define the term substrate.

Answer 2

the substance that is used up in an enzyme controlled reaction, leading to the formation of a product. it fits into the active site of an enzyme.

Question 3

define the term product.

Answer 3

the substance/molecule produced after an enzyme controlled reaction.

Question 4

explain why enzymes are necessary to life.

Answer 4

Without enzymes metabolic reactions in the body would be too slow and inefficient.

Question 5

define the term anabolic reaction.

Answer 5

when two substances are combined to create a more complex one

Question 6

define the term catabolic reaction.

Answer 6

when a substance is broken down into its component parts.

Question 7

define the term digestion.

Answer 7

the process of breaking down large molecules into their subunits. this requires the peptide, glycosidic or ester bonds to be broken down.

Question 8

define the term metabolism.

Answer 8

any biological reaction happening within the body, anabolism or catabolism all add up to the overall metabolism of the body.

Question 9

explain how enzymes affect both the structure and function of cells and whole organisms.

Answer 9

They do not affect the organism other than to make it more efficient at reactions.

Question 10

define the term intracellular enzyme.

Answer 10

an enzyme found within a cell. synthesized within the cell and found within the cytoplasm, nucleus, mithochondria and chloroplasts.

Question 11

define the term extracellular enzyme.

Answer 11

enzymes found outside of a cell but still within the body. synthesized within the cell but secreted out, usually found within the human digestive system.

Question 12

give an example of an intracellular enzyme.

Answer 12

catalase - catalysing the breakdown of hydrogen peroxide (h2o2) to water and oxygen.

Question 13

give two examples of extracellular enzymes.

Answer 13

• salivary amylase catalysing the hydrolysis of starch into maltose.
• pancreatic trypsin catalysing the hydrolysis of peptide bonds.

Question 14

state the substrate and product for catalase.

Answer 14

hydrogen peroxide to water and oxygen

Question 15

state the substrate and product for amylase

Answer 15

starch to maltose

Question 16

state the substrate and product for trypsin

Answer 16

protein into amino acids

Question 17

explain the role of extracellular enzymes in general.

Answer 17

extracellular enzymes are secreted from cells into the digestive system where they breakdown large molecules such as starch.

Question 18

define the term active site.

Answer 18

a group of catalytic amino acids that cluster together to form a specific shape into which a substrate will fit and bind onto.

Question 19

define the term complementary shape.

Answer 19

each enzyme has a specific shape that only one substrate fits into. the substrate and the shape of the active site are therefor complimentary.

Question 20

define the term specific.

Answer 20

each enzyme is specific to one substrate meaning that it only catalyses the breakdown of that one substrate.

Question 21

state the sequence of events in an enzyme controlled reaction.

Answer 21

the enzyme and the substrate bind together.
this is then called an enzyme-substrate complex
then the products are released from the enzyme

Question 22

describe the ‘lock and key’ model.

Answer 22

the substrate is the key and the enzyme is the lock. the substrate and enzyme are both rigid shapes to if the substrate is the wrong size or shape it cannot bind to the enzyme.

Question 23

describe the induced fit model

Answer 23

the model assumes that the substrate plays a role in shaping the active site and it’s actually pretty flexible. this explains why some substrates bind to an enzyme but do not react because the shape of the active site has been too distorted. only the proper substrate is capable of producing the correct alignment of the active site.

Question 24

suggest how the R groups of an amino acid are involved in catalysing reactions.

Answer 24

the R groups that form the active site are called catalytic amino acids, the way these react with each other and the substrate forms the shape of the enzyme.

Question 25

define the term activation energy.

Answer 25

the amount of energy needed to start a reaction. enzymes reduce the activation energy of a specific reaction so the substrate doesn’t need as much energy as when there was no enzyme.

Question 26

define the term rate of reaction.

Answer 26

how fast the reaction takes place. this can be measured either by how fast a product is formed or by how fast a substrate disappears depending on the reaction.

Question 27

state what the presence of an enzyme does to the activation energy and how this increases rate of reaction.

Answer 27

the enzyme lowers the activation energy. this increases the rate of reaction as the substrate requires less energy throughout the reaction.

Question 28

state 5 factors that affect the rate of an enzyme controlled reaction.

Answer 28

• PH
• temperature
• enzyme concentration
• substrate concentration
• presence of cofacters/inhibitors

Question 29

define the term ‘initial rate of reaction’ and describe it’s significance.

Answer 29

the initial rate of reaction is the rate of reaction at the very beginning of the reaction. the rate of reaction is fastest the closer you get to 0. when investigating rate of reaction you take it from the tangent of the initial rate.

Question 30

explain why increasing the temperature from below the optimum up towards the optimum increases the rate of reaction.

Answer 30

the particles gain more kinetic energy as you increase the temperature so more collisions with the enzyme are more likely. when you reach the optimum it is the point at which the particles have the most energy before the enzyme denatures.

Question 31

define the term ‘temperature coefficient Q10’ and state it’s usual value for an enzyme controlled reaction.

Answer 31

the temperature coefficient measures how much the rate of reaction increases with a 10 degrees C rise in temperature. in most enzyme controlled reactions this is 2

Question 32

explain why increasing the temperature above the optimum deceases the rate of reaction rapidly.

Answer 32

above the optimum temperature the enzymes begin to denature which means no substrate can bind to the enzyme anymore, as more and more enzymes begin to denature in quick succession the rate of reaction decreases rapidly.

Question 33

explain why a PH change away from the optimum would decrease the rate of reaction.

Answer 33

increasing or decreasing the concentration of hydrogen ions (changing the PH) can disrupt ionic and hydrogen bonds that hold together the tertiary structure of the enzyme, changing the active site so the substrate no longer fits.

Question 34

define the term ‘Vmax’

Answer 34

Vmax is the maximum rate, or velocity that an enzyme can catalyse the reaction. so Vmax is the point at which the rate of reaction is fastest.

Question 35

explain how increasing the substrate concentration affects the initial rate of an enzyme controlled reaction.

Answer 35

increasing the substrate concentration will increase the rate of reaction in direct proportion. this is because the more substrate there is the more likely a substrate molecule is to bind to the active site of an enzyme. however above a certain point the rate of reaction will become constant as all of the active sites are full.

Question 36

explain how increasing the enzyme concentration affects the initial rate of an enzyme controlled reaction.

Answer 36

the more enzymes that are present the more active sites will be available to form enzyme-substrate complexes so the rate of reaction will increase. however at a certain point the rate will become constant as there is no longer enough substrate to fill the active sites.

Question 37

define the term cofactor.

Answer 37

a cofactor is a non protein substance that causes some enzymes to catalyse a reaction (some cannot without a cofactor) cofactors can form part of the active site or transfer atoms/groups from one reaction to another in a multi-step pathway.

Question 38

define the term coenzyme.

Answer 38

a coenzyme is a type of organic cofactor. it is usually responsible for carrying chemical groups between enzymes and linking together reactions. they are changed in some way by the reaction but are recycled back to be used again

Question 39

describe the similarities and differences between cofactors, coenzymes and and prosthetic groups.

Answer 39

a cofactor is the overall term for a non protein substance that helps enzymes to catalyse reactions. a coenzyme is a cofactor that is organic and is responsible for carrying chemical groups between enzymes.
a prosthetic group is a permanent part of the enzyme and contribute to both it’s shape and charge.

Question 40

explain why the chloride ion necessary for the correct formation of the active site in amylase is called a cofactor not a coenzyme or prosthetic group.

Answer 40

because the amylase is not a permanent part of the enzyme and can bind to either substrate or enzyme so is not a prosthetic group. it is also not a coenzyme because it is an ion not an enzyme.

Question 41

explain why the zinc ion that forms an important part of the structure of carbonic anhydrase (an enzyme necessary for the metabolism of carbon dioxide) is called a prosthetic group not a cofacter or coenzyme.

Answer 41

because the zinc is permanently attached to the active site of the enzyme.

Question 42

define the term enzyme inhibitor.

Answer 42

an enzyme inhibitor is a molecule that prevents an enzyme from carrying out its normal function.

Question 43

define the term competitive inhibitor.

Answer 43

a molecule of a similar shape to the substrate that fits into the active site and stops the substrate from being able to bind. most are temporary and reversible.

Question 44

define the term non-competitive inhibitor.

Answer 44

a molecule that binds to the enzyme, not at the active site but at another point called the allosteric site. they change the tertiary structure of the enzyme and change the shape of the active site. can be reversible or irreversible.

Question 45

define the term reversible inhibitor.

Answer 45

substances that do not permanently disable the enzyme. they are often less likely to be toxic due to this.

Question 46

define the term irreversible inhibitor.

Answer 46

a substance that permanently changes the shape or prevents an enzyme from functioning properly. more likely to be toxic in large enough quantities.

Question 47

define the term allosteric site.

Answer 47

the point on the enzyme at which a non competitive inhibitor binds to and disrupts the shape of the enzyme by doing so.

Question 48

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

Answer 48

the presence of the inhibitor will slow the rate of reaction, because the inhibitors block the active sites so there will be fewer available active sites to form enzyme-substrate complexes. however the effect of the inhibitor will be overcome by high concentrations of the substrate because the substrate will immediately fill the active sites.

Question 49

state two examples of competitive inhibitors and how they work.

Answer 49

Ethylene glycol is a chemical in antifreeze, when broken down by the liver after being ingested by the enzyme alcohol dehydrogenase it produces the toxic oxalic acid. alcohol competitively inhibits this enzyme so the treatment for ingesting antifreeze is to get drunk.
protease inhibitors are used for treatment of viral diseases like HIV because they inhibit the production of protein coats so decreases the number of viral particles in the body.

Question 50

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

Answer 50

the presence of a non competitive inhibitor will slow the rate of reaction significantly. increasing substrate concentration will have no effect on this but increasing inhibitor concentration will slow the rate further. this is because the inhibitor changes the shape of each active site so fewer are available for the substrate.

Question 51

state two examples of a non-competitive inhibitor and explain how they work.

Answer 51

penicillin inhibits an enzyme involved in the synthesis of bacterial cell walls. this puts holes in the daughter cell walls causing the bacteria to swell and burst.
cyanide is a metabolic inhibitor as it binds to an enzyme involved in respiration and inhibits the production of ATP.

Question 52

define the term ‘end product inhibition’ and describe why it can be useful.

Answer 52

this is a process that occurs when the product of an enzyme controlled reaction acts as the inhibitor to the enzyme that produced it. this is useful as it performs as a negative feedback loop to ensure that excess product is not formed.

Question 53

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

Answer 53

in the breakdown of glucose two phosphate molecules are added. the addition of the second phosphate is catalysed by PFK - which is competitively inhibited by ATP. when ATP levels are high the PFK cannot catalyse the reaction so less ATP is created. when the levels are lower the PFK can continue to catalyse the reaction so more ATP is produced.

Question 54

define the term ‘inactive precursor enzyme’ and explain why enzymes may be produced in this form.

Answer 54

an inactive precursor enzyme is an inactive enzyme that is activated by a number of factors including PH changes or the use of a cofactor. they are often produced in this form if they would be harmful to the inside of a cell for example some enzymes involved in digestion.

Question 55

describe three ways in which an inactive precursor enzyme could be activated.

Answer 55

• a cofactor can be added to change the shape of the active site.
• a change in the tertiary structure by another enzyme which cuts certain bonds or equivalent actions
• a change in temperature or PH that changes bonds within the enzyme.

Question 56

define the term apoenzyme.

Answer 56

an inactive precursor enzyme that is essentially a protein because it is it’s form before the addition of a cofactor.

Question 57

define the term holoenzyme.

Answer 57

a precursor enzyme after the addition of a cofactor to activate it.

Question 58

define the term zymogen/proenzyme.

Answer 58

types of precursor enzyme activated by changes in PH or temperature.