Proteins and Enzymes

Question 1

What are proteins (polymer) made up of?

Answer 1

Monomer = Amino Acids

Question 2

What is the general formula of an amino acid?

Answer 2

Amine group (N-H2) left. Carbon bonded to H and ‘R’ Group (variable). Carboxyl Group (C=O-OH) right.

Question 3

How many types of amino acids are there?

Answer 3

20

Question 4

How do you form a dipeptide?

Answer 4

Condensation reaction between two amino acids forms a peptide bond (OH from carboxyl, H from amine) to release a dipeptide and water.

Question 5

How do you form a polypeptide?

Answer 5

Condensation reactions join multiple amino acids (min. 3) with peptide bonds.

Question 6

What are the two types of proteins?

Answer 6

1. Globular proteins (enzymes, hormones, immunoglobulins, transport).
2. Fibrous proteins (long, used to make fibres for protection, support, form, shape)

Question 7

What is the primary structure of a protein?

Answer 7

The order and number of amino acids in a protein. The sequence of amino acids determines the protein’s function.

Question 8

What is the secondary structure of a protein ?

Answer 8

Lots of weak hydrogen bonds form to make an alpha helix or beta pleated sheets shape.

Question 9

What is the tertiary structure of a protein?

Answer 9

3D shape of protein due to formation of disulfide bridges, ionic and more hydrogen bonds.

Question 10

What is the quartenary structure of proteins?

Answer 10

More than 1 polypetide.

Question 11

Compare the 3 types of bonds in the tertiary structure of proteins.

Answer 11

Disulfide bridges are strongest (hard to break) form between sulfur atoms in ‘R’ group of amino acids.
Ionic bonds form between opposite carboxyl and amine groups, weaker than disulfide bridges and broken by changing pH.
Hydrogen bonds are numerous but weak and easily broken.

Question 12

How do you test for proteins?

Answer 12

Biuret’s Test.

Question 13

Describe the Biuret’s test for proteins.

Answer 13

• Add water and Biuret’s reagent to food sample in test tube.
• If proteins present, turns from blue to purple solution (tests for presence of more than 1 peptide bond).
  Control = test with denatured protein, solution remains blue.

Question 14

What is an enzyme?

Answer 14

A biological catalyst that speeds up a chemical reaction without being used up. Lowers activation energy.

Question 15

Describe the induced fit model.

Answer 15

Active site of enzyme is complementary to the substrate. Substrate enters the active site and it changes shape to fit around substrate. Reaction occurs and and products detach.

Question 16

What determines the complementary shape of the active site of enzymes?

Answer 16

The tertiary structure and the bonds formed (hydrogen, ionic, disulfide bridges) form the deppression in the 3D structure.

Question 17

How does enzyme concentration affect enzyme-controlled reactions?

Answer 17

As enzyme concentration increases, the rate of the reaction increases. More active sites to bind to. Beyond certain point, more active sites than substrate, no longer limiting factor so no effect on rate of reaction.

Question 18

How does substrate concentration affect enzyme-controlled reactions?

Answer 18

As substrate concentration increases, the rate of reaction increases. More enzyme-substrate complexes form. Beyond certain point, more substrate than active sites, no longer limiting factor so no effect on rate of reaction.

Question 19

How does concentration of competitive inhibitors affect enzyme-controlled reactions?

Answer 19

As concentration of competitive inhibitors increases, the rate of reaction decreases. Active sites are temporarily blocked by inhibitors so substrates cannot bind to them. Can be reversed by increasing substrate concentration.

Question 20

How does concentration of non-competitive inhibitors affect enzyme-controlled reactions?

Answer 20

As concentration of non-competitive inhibitors increases, the rate of reaction decreases. Binding to allosteric site, shape of enzyme is altered and no longer complementary to substrate. Cannot be reversed by adding more substrate.

Question 21

How does pH affect enzyme-controlled reactions?

Answer 21

Depending on the enzyme’s optimum, too low or high pH affects shape of enzyme by disrupting bonds in tertiary structure (hydrogen+ionic).

Question 22

How does temperature affect enzyme-controlled reactions?

Answer 22

As temperature increases, the rate of reaction increases. Kinetic energy of the enzyme increases. Just above the optimum temperature, the rate ofreaction plummets as the kinetic energy breaks the bonds and enzyme denatures.