1 Biological Molecules- Proteins & enzymes

Question 1

What are amino acids?

Answer 1

The monomers from which proteins are made

Question 2

What is the general structure of an amino acid?

Answer 2

H2N (amine group), COOH (carboxyl group), an R group (side chain, how amino acids differ) a H and a central C

Question 3

How is a peptide bond formed?

Answer 3

Through a condensation reaction between 2 amino acids

Question 4

How are dipeptides formed?

Answer 4

The condensation of 2 amino acid, peptide bond

Question 5

How are polypeptides formed?

Answer 5

The condensation of many amino acids, peptide bonds

Question 6

What does a functional protein contain?

Answer 6

One or more polypeptides

Question 7

What are some functions of proteins?

Answer 7

Structural proteins- long,strong polypeptide chains with cross-links,making the chains parallel (e.g. keratin, collagen)
Transport proteins- e.g. channel proteins, which transport molecules across the cell membrane, ones which are too large to diffuse freely or ones with a charge
Enzymes- biological catalysts, increase rate of reaction without being used up. Usually tightly folded, complex, soluble proteins
Antibodies- diverse proteins, made up of polypeptide chains that are used in the immune response

Question 8

What is the primary structure of a protein? + importance

Answer 8

The unique sequence of amino acids, determined by the gene encoding the protein

A change in the nucleotide sequence of the gene’s coding region may lead to a different amino acid being added to the polypeptide chain, which could change the protein’s structure and function

Question 9

What is the secondary structure of a protein? + explain

Answer 9

The folding of the primary polypeptide chain
Amino acids in the chain can form hydrogen bonds between each other, causing the protein to fold into specific structures; like alpha helices and beta-pleated sheets

The secondary structure is stable- individual hydrogen bonds are weak, but there are many, leading to an overall stability. This can be decreased by environmental factors weakening the bonds, like PH

Question 10

What is the tertiary structure of a protein? + importance

Answer 10

The further folding of the secondary polypeptide to form a tertiary, 3D chain
Interactions between R groups creates the tertiary structure, usually coiled or folded
Many weak and strong interactions, like ionic bonds, hydrogen bonds and disulphide bridges determine the final 3D shape of the protein

When the protein loses its 3D shape, it may no longer be functional.

Question 11

What is the quaternary structure of a protein? + examples

Answer 11

Multiple 3D polypeptide chains coming together
e.g. collagen (fibrous), insulin (globular), haemoglobin

Question 12

What is the test for proteins?

Answer 12

Add biuret’s solution to a sample and mix. A positive result is a lilac colour

Question 13

What are enzymes?

Answer 13

Biological catalysts and proteins, which lower the activation energy of each reaction they catalyse (breaking bonds when substrate binds, easier to react)

Question 14

How are enzyme-substrate complexes formed?

Answer 14

The active site has a specific shape for each enzyme. Substrates with a complementary shape to the active site can bind to form an enzyme-substrate complex.

Question 15

How is the shape of an active site determined?

Answer 15

The tertiary structure of the polypeptide

Question 16

What is the induced fit model?

Answer 16

As an enzyme and substrate come together, their interaction causes a small shift in the enzyme’s active site structure. Then, an enzyme-substrate complex can be formed and catalyse a reaction

Question 16

How does pH affect an enzyme?

Answer 16

Changing pH changes the number of hydroxide ions and hydrogen ions surrounding the enzyme (which interact with charges on the amino acids) The hydrogen and ionic bonds are affected, changing the tertiary structure and active site- denaturing the enzyme if its out of optimum range

Question 17

How does temperature affect an enzyme?

Answer 17

Increasing temperature increases kinetic energy of the molecules so there’s a higher chance of collision between the enzyme and substrate- rate of reaction is faster. Increasing/decreasing temperature outside of an optimum range can affect the chemical bonds (tertiary structure) within the active site, denaturing it

Question 18

How does enzyme concentration affect the rate of reaction?

Answer 18

Increasing enzyme concentration in a solution= more enzyme molecules available to catalyse the substrate in a given amount of time

Question 19

How does substrate concentration affect the rate of reaction?

Answer 19

Increasing substrate concentration = more substrate molecules can form enzyme-substrate complexes at any one time.Increases initial rate but when all enzyme molecules are occupied the rate will plateau as the enzyme is saturated

Question 20

What is a competitive inhibitor?

Answer 20

Chemical that slows down/stops the reaction, enzyme-substrates cannot be formed or are formed at a much lower rate. They’re similar in shape to the substrate and bind to the active site, blocking the formation of an enzyme-substrate complex. They don’t make permanent damage to the active site

Question 21

What is a non-competitive inhibitor?

Answer 21

Chemical that slows down/stops reaction. Affect another part of the enzyme, change shape of active site. So, it’s no longer complementary to the substrate. Some have reversible effects, but others are irreversible and denature the enzyme