Proteins

Question 1

What are proteins formed from?

Answer 1

Amino acids.

Question 2

How many bases code for one amino acid?

Answer 2

Three.

Question 3

What is the bond formed between amino acids in a condensation reaction?

Answer 3

A peptide bond.

Question 4

What is the primary structure of a protein?

Answer 4

The sequence and number of amino acids in a polypeptide chain.

Question 5

What is the secondary structure of a protein?

Answer 5

The way the polypeptide chain twists into 3d shapes like alpha helices and beta pleated sheets due to weak hydrogen bonds forming between the N-H and C=O on amino acids.

Question 6

What is the tertiary structure of a protein?

Answer 6

The way the protein folds into its complex, unique, 3D structure due to hydrogen bonds, ionic bonds, disulphide bridges and hydrophobic interactions of the R group of the amino acids.

Question 7

What is the quaternary structure of a protein?

Answer 7

When a protein is made of 2 more polypeptide chains joined together. This sometimes involves a prosthetic group.

Question 8

What is an example of a quaternary structure?

Answer 8

Haemoglobin, which has 4 tertiary structures bonded together with a prosthetic group of iron in the middle.

Question 9

Which protein structure is only had by some proteins?

Answer 9

Quaternary structure.

Question 10

How do you test for protein and what is the positive result?

Answer 10

Add biuret, will turn purple if positive.

Question 11

What is activation energy?

Answer 11

The minimum amount of energy required for a chemical reaction to occur / the particles to collide.

Question 12

What is a substrate?

Answer 12

The molecule which is complementary to the enzyme’s active site.

Question 13

What is an active site?

Answer 13

Where the substrate binds to the enzyme.

Question 14

As a substrate approaches its complementary enzyme - what happens?

Answer 14

The proximity of the substrate causes a conformational change to the active site and tertiary structure of the entire enzyme (change of shape) which allows the active site to become functional and an enzyme-substrate complex to form.

Question 15

What factors affect rate of reaction?

Answer 15

• Temperature
• Concentration
• Non-competitive inhibition
• Competitive inhibition

Question 16

What happens to enzymes at high temperatures?

Answer 16

They will denature (a conformational change in tertiary structure due to breaking bonds).

Question 17

How does temperature affect rate of reaction?

Answer 17

At low temperatures, substances have less kinetic energy, therefore the enzyme and substrate will be less likely to collide and form an enzyme-substrate complex which means enzyme activity decreases.
As temperature increases, rate of reaction increases until the temperatures gets too high and enzymes denature, meaning their active site is no longer complementary to the substrate and cannot form an enzyme-substrate complex.

Question 18

How does pH affect enzymes?

Answer 18

• A change in pH alters the charges of the amino acids that make up the active site, which prevents an enzyme substrate-complex forming.
• A significant change in the pH can also cause the ionic and disulphide bridges to be disrupted.