UNIT 1 (topic 4) proteins and enzymes

Question 1

what is a enzyme

Answer 1

• a biological catalyst that lowers the activation energy of a reaction to speed up reactions
• they are proteins, globular shaped

Question 2

define the active site

Answer 2

specific 3D shape because of the tertiary structure that binds to the substrate

Question 3

define the substrate

Answer 3

the reactants that are complementary to an enzyme

Question 4

what is the lock and key theory

Answer 4

• substrate and active site are complementary
• when they bind, E-S complex is formed
• reaction occurs and products are released from the active site
• active site is free to bind to other complementary substrate

Question 5

what is the induced fit theory

Answer 5

• the binding of substrate causes the active site to change shape
• active site becomes complementary forming E-S complexes
• places stress on the bonds within the substrate - lowering the active site
• forces a reaction to take place

Question 6

what are the factors effecting enzymes

Answer 6

• temperature
• pH
• concentration of enzymes
• concentration of substrate

Question 7

why does temperature increase enzyme rate

Answer 7

• increases kinetic energy of enzymes and substrate
• more collisions between substrate and active site
• more E-S complexes formed

Question 8

why does temperature decrease enzyme rate

Answer 8

• high temperature causes the H-bonds in the tertiary structure to break
• change shape of the active site meaning substrate no longer complementary
• E-S complexes no longer form

Question 9

how is rate affected at the optimum pH

Answer 9

more E-S complexes formed, increased rate

Question 10

what is the rate above and below the optimum pH

Answer 10

• changing pH affects concentration of H+ / OH-
• Disrupts H-bonds and ionic bonds in the tertiary structure
• changes shape of the active site
• no longer complementary so E-S complexes can’t be formed

Question 11

why does the rate increase as the concentration of enzyme/ substrate increases

Answer 11

• more substrate/ active sites so higher chance of collisions
• more E-S complexes formed

Question 12

why does the rate plateaus as the concentration increases

Answer 12

• enzyme/ substrate becomes the limiting factor
• all is occupied so rate cannot increase further

Question 13

define an enzyme inhibitor

Answer 13

substances that prevent the active site from binding to the substrate to prevent E-S complexes

Question 14

how does competitive inhibitors prevent E-S complexes

Answer 14

• inhibitor has similar shape to the substrate and bind to active site
• physically prevents the binding of substrate and active site

Question 15

how does the non- competitive inhibitors prevent E-S complexes

Answer 15

• the inhibitor binds to an allosteric site in the enzyme
• this alters the tertiary structure
• changes shape of the active site

Question 16

why does the non-competitive have decreased rate

Answer 16

• increasing substrate concentration has no effect
• inhibitor altered shape of the active site
• no longer complementary

Question 17

why does the competitive have an increased rate

Answer 17

• substrate and inhibitor are competing for the active site
• increased collision for substrate at high concentration

Question 18

explain the primary structure of a protein

Answer 18

• sequence of amino acids in a polypeptide chain
• peptide bonds between the carboxyl group and amino group

Question 19

explain the secondary structure of a protein

Answer 19

folding of the polar peptide bonds creating a-helices or b-pleated sheets
- hydrogen bonds between the peptide bonds

Question 20

explain the tertiary structure of a protein

Answer 20

more folding of the a-helices and b-pleated sheets
- ionic, hydrogen and disulphide bonds between the R-groups

Question 21

explain the quaternary structure in a protein

Answer 21

multiple polypeptide chains bonded together or a polypeptide chain bonded to a prosthetic group
- ionic, hydrogen and disulphide bonds between the chain’s R-groups

Question 22

what is a prosthetic group

Answer 22

a non protein e.g. iron

Question 23

how do you find the rate of reaction on a graph

Answer 23

Change in y (amount of product) /
Change in x (time)