Proteins

Question 1

What are proteins

Answer 1

Contain the relents C,H,O,N and sometimes Sulphur
They are polymers of the monomer amino acids (20 different amino acids)

Question 2

Structure of an amino acid

Answer 2

Amine Group - NH2
Carboxylic acid group - COOH
R group - The rest (anything from a hydrogen atom to a more complex ring structure)
General Structure :
R
I
H2N-C-COOH
I
H

Question 3

R Groups

Answer 3

R groups have different properties:
- Acidic (-ve charge)
- Basic (+ve charge)
- Polar (attracted to H2O)
- Non polar (hydrophobic/repel water)

Question 4

Charged R groups

Answer 4

+ve and -ve side chains can be attracted to each other

Question 5

Polar R groups

Answer 5

Polar side attract water

Question 6

Hydrophobic R Groups

Answer 6

Hydrophobic attract eachother and repel water

Question 7

How do amino acids join together?

Answer 7

Amino Acid + Amino Acid —> Dipeptide + H2O
-CONH- = peptide bond

Question 8

Peptide Bond Formation

Answer 8

Between the OH on the carboxylate group and the H on the amine group

Condensation reaction
H2O as a product alongside dipeptide
Amine group on one amino acid and Carboxyl group on another amino acid react to form a peptide bond

Question 9

What is primary structure

Answer 9

Refers to the sequence of amino acids in the polypeptide chain and the precise order of them
The sequence determines the specific shape and function of the protein

Question 10

What is secondary structure?

Answer 10

Represents the folding or coiling of the polypeptide chain as a result of hydrogen bonding between the amino acids
Twisted to make an alpha helix
Folded/Bent to make a beta pleated sheet
The structures are held together in place by hydrogen bonds l

Question 11

Where do the hydrogen bonds form?

Answer 11

Between th C=O groups of the carboxyl (COOH) group of one amino acid and the H in the amine (NH2) group of another amino acid

Question 12

What is tertiary structure?

Answer 12

Further twisting and folding of the secondary structure
Caused by:
Hydrogen bonds (weak)
Ionic bonds
Disuphide bridges/bonds (S-S) - strong
so some amino acids must contain sulphur
Tertiary structures are specific and form a unique 3D shape

Question 13

Tertiary structures : Hydrogen Bonds

Answer 13

Can form between the R groups of polar amino acids
Form between O and OH

Question 14

Tertiary Structure : Ionic Bonds

Answer 14

Form between a positive and negatively charged side chain of basic and acidic amino acids
Basically, form between oppositely charged R groups

Question 15

Tertiary Structure : Disulphide bonds

Answer 15

Form as a result of an oxidation reaction between sulphur atoms (e.g 2 cysteines)
Only sometimes occur as there must be a sulphur in the R groups for this bind to occur

Question 16

Tertiary structure : Hydrophobic regions

Answer 16

Form as hydrophobic R groups side chain tend to exclude water and are attracted to each other

Question 17

What is Quarternary structure?

Answer 17

A protein made up of more than 1 polypeptide chain, each with a tertiary structure combined to form a larger protein complex
Held together by hydrogen bonds,ionic bonds and disulphide bonds/bridges
Can have non protein groups called prosthetic groups

Question 18

Summary of Primary, Secondary, Tertiary and Quaternary structure

Answer 18

Primary :
Amino Acur sequence/order
Peptide Bonds
Sequence determined specific shape and function of the protein

Secondary:
Hydrogen Bonds
Alpha Helix
Beta pleated sheet

Tertiary:
Further folding and twisting
Hydrogen, Ionic and Disulphide bonds

Quarternary:
More than 1 polypeptide chain

Question 19

Denaturation of Proteins

Answer 19

• An alteration of tertiary structure and loss of 3D shape which is often irreversible so the protein cannot function

Question 20

Causes of protein denaturation

Answer 20

High temp=hydrogen bonds break
Changes in pH = Ionic bonds disrupted
Heavy metals = Bind to sites on protein
Detergents = Disrupt hydrophobic interaction
Reducing agents = Break disulphide bonds/bridges

Question 21

How can a small change in primary structure lead to a non functional protein?

Answer 21

Change in sequence of amino acids (primary structure)
Hydrogen bonds form in diffent places —> alters secondary structure
Further hydrogen, ionic and disulphide bonds form in different places —> different tertiary structure

Question 22

What if the protein is an enzyme

Answer 22

Shape of active site is altered —> no longer complementary to substrate —> cannot catalyse reaction

Question 23

Biuret test for proteins

Answer 23

1) Add biuret reagent
2) A purple or lilac colour indicates protein is present
3) If the solution remains blue (copper sulfate colour) then no protein is present