Proteins and Enzymes

Question 1

What is a protein?

Answer 1

A polymer built up of one or more amino acids.

Question 2

What is an amino acid?

Answer 2

The monomer that make up proteins.

Question 3

What is a peptide bond?

Answer 3

The bond between amino acids in all proteins.

Question 4

What are some types of proteins?

Answer 4

Enzymes, antibodies, transport and structural.

Question 5

What letters represent the amine group in an amino acid?

Answer 5

NH

Question 6

What letters represent the carboxyl group in an amino acid?

Answer 6

COOH

Question 7

What letter represents a side chain in an amino acid?

Answer 7

R

Question 8

What is the only part of the amino acid that changes?

Answer 8

The side (R) group.

Question 9

How is a dipeptide formed?

Answer 9

Condensation of two amino acids.

Question 10

How is a polypeptide formed?

Answer 10

Condensation of many amino acids.

Question 11

What is the name for the test for proteins?

Answer 11

The Biuret test.

Question 12

How do we conduct the Biuret test for proteins?

Answer 12

1) Add biuret reagent (copper sulphate and sodium hydroxide)

2) if protein is present, colour turns purple.

Question 13

What is the primary structure of proteins?

Answer 13

The sequence of amino acids.

Question 14

What bonds are present in the primary structure of proteins?

Answer 14

Peptide bonds.

Question 15

What is the secondary structure of proteins?

Answer 15

The long chains of amino acids fold into regions with repeating patterns (alpha helix and beta pleated sheet).

Question 16

What bonds are present in the secondary structure of proteins?

Answer 16

• Peptide bonds.

- Hydrogen bonds.

Question 17

What is the tertiary structure of proteins?

Answer 17

The final 3D resting shape of the protein.

Question 18

What bonds are present in the tertiary structure of proteins?

Answer 18

• Peptide bonds.
• Hydrogen bonds.
• Ionic bonds.
• Disulphide bridges.

Question 19

What is the quaternary structure of proteins?

Answer 19

Proteins made of more than one polypeptide chain (e.g. haemoglobin).

Question 20

What bonds are present in the quaternary structure of proteins?

Answer 20

• Peptide bonds.
• Hydrogen bonds.
• Ionic bonds.
• Disulphide bridges.

Question 21

What is the ideal answer to a protein shape question (enzymes/antibodies)?

Answer 21

The tertiary structure of the active site is complementary to the shape of the substrate and so forms an enzyme-substrate complex/ antibody-enzyme complex.

Question 22

How can a mutation cause a protein to become non-functional?

Answer 22

Changes the primary structure and therefore the tertiary structure. This changes the active site shape so substrate is no longer complementary. this means no enzyme-substrate complex can be formed.

Question 23

How can denaturation lead to a non-functional protein?

Answer 23

Changes ionic bonds so changes tertiary structure. This changes the shape of the active site so the substrate is no longer complimentary. This means no enzyme-substrate complex can be formed.

Question 24

What is an enzyme?

Answer 24

A biological catalyst that lowers the activation energy of the reaction is catalyses.

Question 25

What type of protein are enzymes?

Answer 25

Globular proteins.

Question 26

What is the lock and key hypothesis of enzyme action?

Answer 26

It states that the shape of the active sites of enzymes are exactly complementary to the shape of the substrate. This means that when a substrate molecule collides with it complementary enzyme, the substrate will fit into the active site and an enzyme-substrate complex will form.

Question 27

What is the induced fit hypothesis of enzyme action?

Answer 27

It states that the shape of the active sites are not exactly complimentary, but change shape in the presence of a specific substrate to become complementary. When a substrate molecule collides with an enzyme, if its composition is specifically correct, the shape of the enzyme’s active site will change so that the substrate fits into it and an enzyme-substrate complex can form.

Question 28

What factors can affect the rate of enzyme catalysed reactions?

Answer 28

• Temperature.
• pH.
• Enzyme concentration.
• Substrate concentration.
• Inhibitors.

Question 29

What is meant by the term denatured?

Answer 29

A permanent change to the active site which means no more enzyme-substrate complexes are formed.

Question 30

What effect does temperature have on enzyme action?

Answer 30

As the temperature increases the molecules vibrate more so more collisions and more E_S complexes are formed (lower activation energy). This continues until optimum temperature.
If temperature gets too high, internal bonds break and the shape of the active site changes. this means no E-S complexes can be formed; the enzyme is denatured.

Question 31

What effect does pH have on enzyme action?

Answer 31

Enzymes have an optimum pH. If you increase or decrease the pH away from the optimum, the enzyme activity will decrease.

Question 32

Why does the pH level effect enzyme action?

Answer 32

The OH- (alkali) or H+ (acid) will interact with the hydrogen bonds or ionic bonds. This changes the shape of the tertiary structure and therefore the active site of the enzyme. Fewer/no E-S complexes are formed. The enzyme is denatured.

Question 33

How does enzyme concentration affect enzyme activity?

Answer 33

As you increase the enzyme concentration, the rate of reaction increases because there are more collisions and more E-S complexes formed. Once the substrate runs out, adding more enzymes will make no difference to the rate of reaction.

Question 34

How does substrate concentration affect enzyme activity?

Answer 34

As you increase substrate concentration, the rate of reaction increases because there are more collisions and more E-S complexes formed. This continues until all active sites are occupied, then the enzyme concentration is the limiting factor (adding more substrate will make no difference).

Question 35

What affect do competitive inhibitors have on enzyme action?

Answer 35

Competitive inhibitors have a similar shape to the substrate. They can also bind to the active site and prevent the E-S complex forming. The proportion of substrate to competitive inhibitor will affect how much the rate of reaction changes.

Question 36

What affect do non-competitive inhibitors have on enzyme action?

Answer 36

Non-competitive inhibitors bind to the enzyme but not at the active site. This changes the shape of the active site so no more E-S complexes can form. Changing the concentration of substrate won’t make any difference.