paper 1: Proteins and Enzymes

Question 1

what is the definition of an amino acid

Answer 1

the monomers from which proteins are made

Question 2

what is the definition of a dipeptide

Answer 2

two amino acids joined together by condensation

Question 3

what is the definition of a polypeptide

Answer 3

many amino acids formed together by condensation

Question 4

what is the definition of a peptide bond

Answer 4

forms during a condensation reaction between the amine group of one amino acid and the carboxyl group of another amino acid

Question 5

define the primary structure of a protein

Answer 5

the sequence of amino acids in a polypeptide chain. it determines the rest of the structure

Question 6

define the secondary structure of a protein

Answer 6

the folding of the polypeptide chain into an alpha helix or beta plated sheet because of hydrogen bonding between NH group of one amino acid and the C=O group of another

Question 7

define the tertiary structure of a protein

Answer 7

the foldingof he polypeptide chain into a specific 3D shape held together by hydrogen bonds, ionic bonds and disulfide bridges between R groups of different amino acids

Question 8

define the quaternary structure of a protein

Answer 8

the arrangement of more than one polypeptide chain

Question 9

define an alpha helix

Answer 9

polypeptide chain is wound round to form a helix and is held together by many hydrogen bonds making it a very stable and strong structure

Question 10

define a beta pleated sheet

Answer 10

the poltpeptide chain zig-zags back and forth forming a sheet of antiparallel strands held together by many hydrogen bonds

Question 11

what is the Biuret Test

Answer 11

• the test for proteins
• add biuret solution to sample
• there will be a colour change from blue to lilac if protein is present

Question 12

define an enzyme

Answer 12

biological catalysts that speed up the rate of reaction by decreasing the activation energy needed for a chemical reaction

Question 13

define activation energy

Answer 13

the minimum amount of energy required for a chemical reaction to occur

Question 14

define the active site of an enzyme

Answer 14

the region of an enzyme with a specific 3D tertiary structure that is complimentary to a specific substrate molecule

Question 15

define enzyme-substrate complex

Answer 15

forms when a specific substrate binds to the active site of an enzyme

Question 16

define complimentary

Answer 16

fits into

Question 17

explain how enzymes are highly specific

Answer 17

• enzyme combines with only one specific substrate
• as enzyme has specific tertiary structure and so the active site has a specific shape which is only complementary to one type of substrate
• substrate binds to active site to form an enzyme substrate complex

Question 18

what is the basic structure of an amino acid

Answer 18

Question 19

draw a diagram showing the condensation of 2 amino acids:

Answer 19

Question 20

describe the induced fit hypothesis

Answer 20

• before the reaction the active site is not fully complimentary to the substrate.
• when substrate binds, this causes the tertiary structure of the enzyme to change which causes the active site to change shape so that it becomes complimentary to the substrate.
• an enzyme substrate complex forms which causes the bonds in the substrate to bend so that they break more easily which reduces activation energy

Question 21

how do enzymes lower the activation energy

Answer 21

the shape of the active site alters as substrate binds to it. This stresses the bonds which cause them to break more easily.

Question 22

draw the graph representing the effect of temperature on enzyme activity

Answer 22

Question 23

describe and explain the effect of temperature on enzyme activity

Answer 23

1. initially the rate of enzyme action increases as temperature increases because the substrate and enzymes are given more kinetic energy so there are more likely to be more successful collisions which form more enzyme-substrate complexes
2. beyond the optimum temperature, rate of enzyme action decreases because the enzymes denature as hydrogen bonds break, changing the 3D tertiary structure of the active site so it is no longer complimentary to the substrate. no enzyme-substrate complexes can form

Question 24

why is the rate of enzyme action slow at 0 degrees but not 0?

Answer 24

the enzyme and substrate molecules have some kinetic energy so some enzyme-substrate complexes can still form.

Question 25

draw a graph to show the effect of pH on enzyme action

Answer 25

Question 26

describe and explain the effects of pH on enzyme action

Answer 26

below or above the optimum pH the rate of reaction decreases because the enzyme hydrogen bonds break changing the 3D tertiary structure of the active site so it is no longer complimentary complimentary to the substrate therefor less enzyme-substrate complexes form

Question 27

why does pH effect the rate of enzyme action

Answer 27

the change in pH changes the amount of hydrogen ions present

Question 28

draw a graph showing the effect of substrate concentration on enzyme action

Answer 28

Question 29

describe and explain the effects of substrate concentration on the rate of enzyme action

Answer 29

initially the rate of enzyme action increases as the concentration increases because more enzyme-substrate complexes form. the concentration is the limiting factor

the rate of reaction plateaus as at a high substrate concentration there are no free active sites and the maximum number of enzyme-substrate complexes are formed. the enzyme is now the limiting factor.

Question 30

draw a graph showing the effect of enzyme concentration on the rate of enzyme action

Answer 30

Question 31

describe and explain the effects of enzyme concentration on the rate of enzyme action

Answer 31

initially the rate of enzyme action increases as the concentration increases because more enzyme-substrate complexes form. the enzyme is the limiting factor

the rate of reaction plateaus as at a high substrate concentration there are no more substrates free to bind to the active sites and the maximum number of enzyme-substrate complexes are formed. the substrate is now the limiting factor.

Question 32

what is a competitive inhibitor

Answer 32

they are substances similar in shape to the real substrate. they enter into the enzymes active site and prevent the substrate from binding but are not permanently bound.

Question 33

explain how the competitive inhibitor reduces the rate of reaction of an enzyme

Answer 33

1. the inhibitor is a similar shape to the substrate
2. the competitive inhibitor enters the active site of the enzyme
3. the specific substrates cannot bind the the complimentary active sites
4. therefore reducing the number of enzyme-substrate complexes forming

Question 34

draw a graph showing the effect of a competitive inhibitor on enzyme action

Answer 34

Question 35

explain why a maximum rate of reaction can still be reached with a high concentration in the presence of a competitive inhibitor

Answer 35

1. competitive inhibitors only temporarily bind so the substrate will be able to bind
2. the high concentration of substrate means there is a higher chance of the substrate binding to the enzyme active site instead of the inhibitor.

Question 36

what is a non-competitive inhibitor

Answer 36

• these bind to the enzyme not at the active site
• they change the 3D tertiary structure and shape of the active site
• the substrate cannot bind
• enzyme substrate complexes cannot form

Question 37

draw a graph showing the effect of a non-competitive inhibitor on the rate of enzyme action

Answer 37

Question 38

explain why by adding more substrate you cannot reduce the effect of the non-competitive inhibitor

Answer 38

• the enzyme active site has been changed permanently, reducing the concentration of functioning enzymes
• you cannot reach the maximum number of enzyme-substrate complexes as without the imhibitor.

Question 39

how are protiens denatured

Answer 39

• when hydrogen bonds in protein break, the tertiary structure changes and the protien become non-funcional