p1: 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 condemsation

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 sheets 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 folding of 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. \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

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 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

what is the basic structure of an amino acid

Answer 17

Question 18

draw a diagram showing the condensation of 2 amino acids:

Answer 18

Question 19

describe the induced fit hypothesis

Answer 19

the substrate enters the enzymes active site. The binding of the substrate molecule alters the 3D tertiary structure of the active site. This stresses the bonds which causes them to break more easily. This explains how enzymes lower activation energy. When substrate leaves the active site it returns to its previous shape allowing it to bind to other substrates.

Question 20

how do enzymes lower the activation energy

Answer 20

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

Question 21

draw the graph representing the effect of temperature on enzyme activity

Answer 21

Question 22

describe and explain the effect of temperature on enzyme activity

Answer 22

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 23

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

Answer 23

the rate of reaction is slow because there is not enough kinetic energy for many collisions to occur. even at 0degrees the enzyme and substrate molecules have some kinetic energy so some enzyme-substrate complexes can still form.

Question 24

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

Answer 24

Question 25

describe and explain the effects of pH on enzyme action

Answer 25

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 26

why does pH effect the rate of enzyme action

Answer 26

the change in pH changes the amount of hydrogen ions present

Question 27

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

Answer 27

Question 28

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

Answer 28

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 29

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

Answer 29

Question 30

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

Answer 30

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 31

what is a competitive inhibitor

Answer 31

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 32

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

Answer 32

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 33

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

Answer 33

Question 34

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

Answer 34

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 35

what is a non-competitive inhibitor

Answer 35

• 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 36

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

Answer 36

Question 37

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

Answer 37

• 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.