Proteins and Enzymes

Question 1

Structure of Amino Acid

Answer 1

Central carbon, Amine (NH2) group, Carboxyl (COOH), Side Chain (R), Hydrogen.

Question 2

Bond between Amino Acids

Answer 2

Peptide Bonds

Question 3

Primary Structure

Answer 3

Sequence of amino acids in polypeptide chain bonded with peptide bonds

Question 4

Secondary Structure

Answer 4

Hydrogen bonds form between the amino acids in the polypeptide chan. This results in:
-an alpha helix
-a beta plated sheet

Question 5

Tertiary Structure

Answer 5

Ionic bonds, more hydrogen bonds and disulphide bridges cause the polypeptide chain to fold again into a tertiary structure

Question 6

Quaternary Structure

Answer 6

Proteins with more than one polypeptide chain have a quaternary structure

Question 7

Test for Proteins

Answer 7

Biuret Test
Add biuret, positive: colour change blue to purple

Question 8

Globular

Answer 8

Compact, roughly spherical in shape and soluble in water
Can be easily transported around organisms and be involved in metabolic reactions
Folding of the protein due to the interactions between the R groups results in globular proteins having specific shapes
Enzymes and antibodies are globular

Question 9

Fibrous

Answer 9

Long strands of polypeptide chains
Have cross-linkages due to hydrogen bonds
No tertiary structure
Insoluble in water
Have a limited number of amino acids with the sequence usually being highly repetitive
Largely has structural roles
Examples: keratin, collagen

Question 10

Enzyme

Answer 10

Globular protein with a tertiary structure.
Biological catalyst, increases the rate of reaction of biological reactions.
Specific to substrates and can only catalyse specific reactions.
The sequence and tertiary structure of the polypeptide chain in the active site causes it to be specific to a substrate.

Question 11

How do enzymes increase the rate of reaction

Answer 11

Enzymes lower the activation energy of the reaction.
Binds to the substrate and ensure it has the correct orientation.
Puts strain on the bonds in the substrate so they break more easily and require less energy to react.

Question 12

Induced Fit Model

Answer 12

Active Site of Enzyme and Substrate are complementary to each other, however as they bind to form a enzyme-substrate complex, the active site undergoes a conformational change and slightly changes shape.

Question 13

Effect of Enzyme Concentration

Answer 13

Increasing the concentration of enzyme, more enzyme molecules available, more enzyme substrate complexes formed, increased rate.
Levels off as it is limited by substrate concentration.

Question 14

Effect of Substrate Concentration

Answer 14

Increasing the concentration of the substrate increases the numbers of substrate molecules, increases the no. of enzyme-substrate complexes.
Levels off as it is limited by the enzyme concentration

Question 15

Effect of Temperature

Answer 15

Increase temperature, increased kinetic energy of particles.
This increases the frequency of collisions between enzymes and substrates.
More enzyme-substrate complexes formed.
Increasing the temperature by 10oC will double the rate of reaction.

Question 16

Effect of pH

Answer 16

Changing the pH changes the number of hydroxide ions and hydrogen ions (OH− and H+).
These interact with the hydrogen and ionic bonding in the enzyme and thus the tertiary structure of the enzymes.
(Can cause the enzyme to temporarily denature)

Question 17

Competitive Inhibitors

Answer 17

Similar shape to the substrate, bind with the enzymes at active site, preventing the formation of enzyme substrate complexes reducing the enzymes ability to increase rate of reaction.

As substrate concentration increases, no. of substrate molecules increases so they can outcompete inhibitors so gradual, linear increase in rate of reaction, eventually levels off as enzyme concentration becomes limiting factor

Question 18

Non-competitive Inhibitors

Answer 18

Have a shape complementary to the allosteric site of the enzyme. Bind to enzyme, alters the shape of the enzyme’s active site. Substrate no longer complementary, enzyme substrate complexes not formed.

As substrate concentration increases, rate of reaction increases very small and only initially as only some enzymes unaffected by inhibitor. Levels off quickly as most enzymes disabled already