Biology 1.3 Protein Structure and Enzymes

Question 1

Polypeptides

Answer 1

The polypeptide must fold into a protein with a specific shape to function correctly. Secondary interactions between amino acids in the polypeptide determine the three-dimensional shape of the protein. Therefore, amino acids sequence determines protein shape.

Question 2

Protein Structure - Primary

Answer 2

Determined by the amino acid sequence.

Question 3

Protein structure - secondary

Answer 3

Alpha helices and beta sheets. Determined by the secondary interactions between amino acids.

Question 4

Protein structure - tertiary

Answer 4

Results from interactions between the alpha helices and beta sheets to produce a three-dimensional protein shape.

Question 5

Protein Structure - quaternary

Answer 5

Fromed by groups of polypeptides. only occurs in some proteins.

Question 6

Protein shape is critical to function

Answer 6

The function of most proteins relies on molecular recgnition: they must be able to recognise and bind to other molecules. proteins must be folded in the correct shape. Proteins are critical for cell survival. They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs.

Question 7

Enzymes

Answer 7

Enzymes are globular proteins that function as catalysts to speed up chemical reactions in cells. They are highly specific and allow reactions to be regulated and controlled.

Question 8

Mutation to DNA

Answer 8

Mutations in the DNA may causes change in the amino acid sequence, and therfore the protein may be misfolded and either not functional at all, or function incorrectly. This may lead to disease.

Question 9

Induced Fit model

Answer 9

When a substrate binds to the active site of the enzyme, the enzyme-substrate complex is formed. the enzyme changes shape slightly so that it fits the substrate more exactly. This is called the induced fit model of enzyme binding.

Question 10

Enzyme reactions

Answer 10

there are two types of enzyme reactions:
1. breakdown reactions: energy released.
2. synthesis reactions: energy taken in.

Question 11

Enzyme in reactions

Answer 11

1. Lowering the activation energy of a biological reaction.
2. Bringin substrate molecules together in the correct orientation for a reaction to occur.
3. Putting stress on the chemical bonds of the substrate molecules, causing the bonds to break and reform with less energy input.

Question 12

Enzyme activity

Answer 12

enzyme activitt is influenced by specific conditions including:
- temperature
- pH
- inhibitor presence

Question 13

enzyme activity temperature

Answer 13

enzymes work best at their optimum temperature. At optimum temperature, the enzyme maintains its shape and has the greatest number of successful substrate collisions.

if the temperature of a reaction is too low:
- kinetic energy in the enzyme and substrate molecules is low.
- fewer successful collisions occur in the correct orientation for a reaction to occur.

As temperature increases, reaction rate increases due to greater kinetic energy.

if the temperature of a reaction is too high:
- the enzyme will denature.
- when an enzyme loses its tertiary shape, it can no longer recognise and bind to its substrate.
- without enzyme binding, the reaction rate slows down.

Question 14

enzyme activity pH

Answer 14

the shape of an enzyme is affected by pH, and different enzymes function in different ph conditions. the optimum pH produces the highest rate of enzyme activity.

if the pH of a reaction is lower or higher:
- the enzyme will denature. (results in a loss shape and decrease in reaction rate.)

Question 15

enzyme activity inhibitor presence

Answer 15

some chemicals can inhibit the activity of enzymes.

1. Competitive inhibitors
   - have a similar shape to the substrate.
   - bind to the enzyme’s active site.
   - compete with the substrate for binding.
   - the effect of a competitive inhibitor can be overcome by increasing the concentration of the substrate.
   - this increases the chance that the substrate will bind ot the enzyme instead of the inhibitor.
2. non-competitive inhibitors
   - have a diffrent shape to the susbtrate.
   - bind to a part of the enzyme (allosteric site) but not the active site.
   - dont compete with the substrate for binding.
   - a non competitive inhibitor distorts the enzyme’s shape so that the active site is no longer complementary to the substrate.
   - the effect of a non-competitive inhibitor cannot be overcome by increaseing the substrate concentration.

Question 16

reaction rates

Answer 16

the rate of enzyme-controlled reactions is affected by: concentrations of reactants, concentration of the enzyme.

Question 17

Concentration of reactants

Answer 17

• the rate of biological reaction can be increased by increasing the concentration of the substrate.
• a maximum rate of reaction is reached when all the enzyme’s active sites are occupied by substrate.
• at this point, adding more substrate will not increase the reaction rate, and the graph of reaction rate plateaus.
• the only way to increase the reaction rate further is to add more enzymes.

Question 18

Concentration of the enzyme

Answer 18

• the rate if biological reaction can be increased by increasing the concentration of the enzyme.
• a maximum rate of reaction is reached when the substrate concentration becomes the limiting factor.