Protein Structure

Question 1

What are all proteins made up of?

Answer 1

Polymers of amino acids

Question 2

How many types of amino acids are there?

Answer 2

20 different amino acids

Question 3

How many different amino acids can plants make?

Answer 3

Plants can make all 20 types of amino acids whereas animals can only make some. They obtain others through their diet.

Question 4

What is the general structure of an amino acid?

Answer 4

Amine group -NH2
Carboxylic acid group -COOH
Hydrogen -H
Residual group

Question 5

How is a dipeptide formed?

Answer 5

Two amino acids monomers undergo a condensation reaction. A peptide bond forms between the two units producing a dipeptide and a water molecule.

Question 6

What is the primary structure of a protein?

Answer 6

Many amino acid molecules are joined together by peptide bonds during condensation reactions.
This creates a long chain of amino acids called a polypeptide chain.
A protein is made up of one or more polypeptide chains.

Question 7

What reaction can break the peptide bond?

Answer 7

Hydrolysis reaction

Water reacts with the joined amino acids.

Question 8

Functions of proteins

Answer 8

Hormones
Enzymes
Antibodies
Components of cell membranes

Question 9

What are the two structures made in the secondary structure of a protein?

Answer 9

Alpha Helix
Beta pleated sheet
One protein may contain both structures or one.

Question 10

What bonds are formed in a alpha helix structure?

Where do they form?

Answer 10

Hydrogen bonds form between the NH (amine group) and the C=O (carboxylic acid.
The H bonds stabilise the helix shape.

Question 11

What bonds are formed in a beta pleated sheet structure? Where do they form?

Answer 11

Hydrogen bonds hold parallel chains between several polypeptide chains.

Question 12

The type of bonding in the tertiary structure of the protein is dependent on…

Answer 12

The r-groups within the polypeptide chains

Question 13

What chemical bonding occurs in the tertiary structure?

Answer 13

Disulphide bridging - Sulphur R groups
Ionic bonding - Between ionised R groups
Hydrogen bonding- alpha helix and beta pleated sheet

Question 14

The chemical bonding in the tertiary structure work to..

Answer 14

Polypeptide chains bend and fold to give a precise 3D shape.

Question 15

What maintains the final tertiary structure of the protein?

Answer 15

Chemical bonds and the hydrophobic interactions between the R groups

Question 16

Characteristics of a polar R-group

Answer 16

• e- not shared evenly through molecule
• Attracted to other polar molecules e.g. water
• Hydrophilic

Question 17

Characteristics of non-polar R group

Answer 17

• Hydrophobic
• Repel water
• Non-polar R-groups arranged to face the inside of the protein to exclude water from the centre of molecule

Question 18

What proteins have a quaternary structure?

Answer 18

A protein made up of several polypeptide chains.

Single chain proteins stop at the tertiary structure.

Question 19

Examples of proteins with a quaternary structure

Answer 19

Haemoglobin; 4 polypeptide chains held tightly together

Question 20

Why is the primary structure important?

Answer 20

The amino acids join together in a chain
The order determines the position of the bonds, the folding of the protein into its 3D structure and its properties, in the tertiary structure.

Question 21

What is a conjugated protein?

Answer 21

.

Question 22

What are the two groups of proteins?

Answer 22

Globular

Fibrous

Question 23

What shape do globular proteins fold into?

Answer 23

Polypeptide chains fold into a compact spherical shape.

Soluble

Question 24

Globular proteins are soluble/insoluble? Why?

Answer 24

Soluble

Hydrophilic side chains project out of the molecule, attracting water molecules. - important for metabolic reactions

Question 25

Examples of globular proteins

Answer 25

Transport proteins; haemoglobin, myoglobin (oxygen store in muscles)
Antibodies: precise active site for microorganisms
Enzymes: catalyse reactions

Question 26

How does the structure of a globular protein relate to their function?

Answer 26

The three dimensional structure of the globular protein is crucial to their roles of binding to other substances.
The specific shape is formed to create an active site allowing specific substrate molecules to attach.
Important to form enzyme substrate complexes and to catalyse reactions in cells.

Question 27

What is the shape of a fibrous protein?

Answer 27

Polypeptide chains remain as long chains to be used as structural molecules.
Several polypeptide chains can be cross linked for extra strength. (H bonds)

Question 28

Are fibrous proteins soluble or non-soluble?

Answer 28

Insoluble

Question 29

Examples of fibrous proteins

Answer 29

Keratin - hair and skin

Collagen (3 chains, H cross links) - blood vessel walls, skin, tendons

Question 30

How does the structure of fibrous proteins relate to their function?

Answer 30

Several chains joined by strong H bonds create strength required to create blood vessels and hair

Question 31

How does the primary structure of a protein affect the tertiary structure? [4 marks]

Answer 31

The primary structure determines the order of amino acids and their r-groups in the polypeptide chain.
This order determines the type of bonding which occurs, causing the protein to fold into a specific shape.
The types of bonding which may form; H, ionic and di-sulphide bridging