Proteins And Enzymes

Question 1

What is a protein?

Answer 1

Polymers made up from many amino acids joined by peptide bonds

Question 2

What is an amino acid?

Answer 2

The monomers from which proteins are made

Question 3

What is a peptide bond?

Answer 3

The bond between amino acids in the primary structure of all proteins

Question 4

What is the structure of an amino acid?

Answer 4

Carboxyl group (-COOH), amine group (-NH2), R group (variable region) ans a hydrogen all attached to a carbon atom

Question 5

types of proteins?

Answer 5

fibrous (simple rope like structure) and globular (complex tertiary structure)

Question 6

Proteins

Answer 6

The doing molecule
Their shape (tertiary/quaternary structure) determines their function
Their shape is controlled by their internal bonding (mostly between their R groups)
The order/sequence of amino acids (primary structure) controls their shape and therefore their function

Question 7

How are dipeptides and polypeptides formed?

Answer 7

Amino acids are linked by condensation reactions.
A molecule of water is released.
Bonds formed between amino acids = peptide bond.

Question 8

primary structure

Answer 8

The sequence of amino acids in the polypeptide chain

Question 9

secondary structure

Answer 9

The long chains of amino acids fold into regions (within the tertiary structure) with repeating patterns. Peptide bonds and hydrogen bonds

Question 10

tertiary structure

Answer 10

W The final 3D resting shape of the protein. Peptide bonds, hydrogen bonds, ionic bonds (between negative and positive charges on different parts of the molecule, R groups). Disulfide bridges (between 2 cystein amino acids)

Question 11

quaternary structure

Answer 11

The final 3D resting shape of the protein made from more than one polypeptide chain. Peptide bonds, hydrogen bonds, ionic bonds and disulfide bonds.

Question 12

The biuret test for proteins

Answer 12

1. Make the solution alkaline by adding a few drops of sodium hydroxide solution. Then add copper (II) sulfate solution. DONT HEAT.
2. If colour changed from pale blue to lilac then a protein is present.
   This is a qualitative test. To make it quantitative you could use a colorimeter.

Question 13

What are enzymes?

Answer 13

Biological catalysts that increase the rate of reaction by lowering the activation energy

Question 14

What is the active site?

Answer 14

The region of an enzyme where a complementary substance can bind to form an enzyme substrate complex

Question 15

What is a metabolic pathway?

Answer 15

Series of enzyme catalysed reactions where the product of one reaction is the reactant in the next reaction e.g respiration

Question 16

Why does an enzyme substrate complex lower the activation energy?

Answer 16

Two substrates need to be joined holding them together which reduces any repulsion between molecules so can bond easily
If enzyme is catalysing a breakdown reaction fitting into active site puts a strain on bonds in the substrate so break up more easily

Question 17

What is the lock and key model?

Answer 17

Past theory of enzyme action
Shape of the active site is fixed so does not change shape
Active site is complementary to the substrate before during and after it forms an enzyme substrate complex

Question 18

What is the induced fit model?

Answer 18

Modern theory of enzyme
Active site and substrate are not complementary before enzyme substrate complex is formed
Active site changes shape to fit more closely around the substrate to become complementary (induced fit)
Forming an enzyme substrate complex strains the bonds in the substrate causing them to form or break (activation energy is lowered)

Question 19

Notes on enzymes

Answer 19

All enzymes are proteins
Enzymes have a specific tertiary structure (their active site is only complementary to one substrate) e.g maltase only hydrolyses maltose
Control all intercellular and extra cellular reactions in organisms

Question 20

How does enzyme specificity work

Answer 20

The specific tertiary structure of the active site is complementary to the shape of one substrate forming an enzyme substrate complex

Question 21

When is an enzyme denatured

Answer 21

An increase in kinetic energy breaks the hydrogen and ionic bonds between the r groups changing the tertiary structure of the protein.

Question 22

When does mutation occur?

Answer 22

Change to the base sequence of DNA changes the base sequence of mRNA changing the primary structure of the protein- change to tertiary structure of protein

Question 23

How do mutation and denaturing lead to a non functional enzyme

Answer 23

Changes the shape of the active site. Substrate is no longer complementary so no enzyme substrate complex is formed

Question 24

What does denatured mean?

Answer 24

A permanent change to the active site which means no more E-S complexes are formed

Question 25

How can you measure the rate of reaction?

Answer 25

1. How fast the product is made (measure the amount of end product at different times during the experiment)
2. How fast the substrate is broken down (measure the amount of substrate molecules left at different times during the experiment)

Question 26

Factors affecting the rate of enzyme catalysed reactions.

Answer 26

1. Temperature
2. PH
3. Enzyme concentration
4. Substrate concentration
5. Inhibitors (competitive and non competitive)

Question 27

How does temperature affect the rate of enzyme catalysed reaction?

Answer 27

As temperature increased the molecules vibrate more so more collisions so a higher percentage of collisions have the activation energy so more ES complexes formed.
At the optimum temperature molecules vibrate and break internal bonds (ionic and disulphide bridges)
Changes the shape of the active site so doesn’t form ES complexes. Enzyme is denatured.

Question 28

How does pH affect enzyme activity?

Answer 28

enzymes have an optimal pH
If you increase or decrease the pH from the optimum enzyme activity (rate) will decrease
The OH- (alkali) or H+ (acid) ions will interact with/disrupt the hydrogen bonds or ionic bonds.
Changes the shape of the tertiary structure
Changes the shape of the active site
Fewer ES complexes formed
The enzyme is denatured

Question 29

How does enzyme concentration affect the rate of reaction/enzyme activity?

Answer 29

As the enzyme concentration increases the rate of reaction increases in a positive correlation because there are more successful collisions between the enzyme and substrate so more enzyme substrate complexes are formed.
If the substrate runs out adding more enzyme will make no difference to the rate of reaction

Question 30

What are competitive inhibitors?

Answer 30

Have a similar shape to the substrate so can also bind to the active site so stops the substrate forming an ES complex. The proportion of substrate to competitive inhibitor will affect how much the rate of reaction changes

Question 31

What are non-competitive inhibitors?

Answer 31

They bind to the enzyme but NOT at the active site but changes the shape of the active site.
No more ES complexes are formed so changing the concentration of substrate wont make any difference.