2.9 - Protein Structure

Question 1

What is a protein?

Answer 1

Are made up of chains of amino acids.

Question 2

What is 1 amino acid?

Answer 2

A monomer

Question 3

What are 2 amino acids?

Answer 3

A dipeptide

Question 4

What are 3 amino acids?

Answer 4

A polypeptide (polymer)

Question 5

What is one or more folded polypeptide?

Answer 5

Protein

Question 6

How are amino acids joined together?

Answer 6

Condensation reaction

Question 7

When amino acids join together in a condensation reaction what is formed?

Answer 7

Dipeptide and water

Question 8

What are the four protein structures?

Answer 8

• Primary structure
• Secondary structure
• Tertiary structure
• Quaternary structure

Question 9

What is primary structure?

Answer 9

One long polypeptide chain
The order of amino acids in a polypeptide chain
As little as one amino acid change in the sequence can alter the type of primary protein.

Question 10

What is secondary structure?

Answer 10

Folding of polypeptide chains.
→ Alpha helix (shown by coil)
→ Beta pleated sheet (shown as ribbon or arrow)
Held by hydrogen bond
H bonds are easily broken by high temperatures and pH changes.

Question 11

What is tertiary structure?

Answer 11

→ 3D shape
The structure is held by four bonds:
1. Hydrogen bonds
2. Disulfide bonds
3. Ionic bonds
4. Weak hydrophobic interactions.
→ Folds into a specific shape
→ R group help to determine the shape;
Polar R groups are hydrophilic so move towards the edge of a protein
Non-polar R groups are hydrophobic so move towards the centre of the protein

Question 12

What is quaternary structure?

Answer 12

→ only some proteins have a quaternary structure
→ They are made of more than one polypeptide chain
→ 3D shape
→ Same 4 bonds as tertiary structure

Question 13

What is a globular protein?

Answer 13

Can be tertiary or quaternary
→ Protein molecules curl up into a ball shape
→ Ex: haemoglobin and myoglobin, enzymes
→ Curl up so their non polar heads, hydrophobic R group, points into the centre of the molecule, away from watery surroundings
→ The hydrophilic R group remain on the outside of a molecule
→ Usually soluble.

Question 14

What is a fibrous protein?

Answer 14

→ Quaternary protein
→ Form long strands
→ Not usually soluble in water
→ Have structural roles e.g. keratin forms hair, nails, and outer skin layers.
→ Are waterproof
→ Another example is collagen

Question 15

What is haemoglobin?

Answer 15

→ The O2 carrying pigment found in red blood cells (RBC)
→ A globular protein; nearly spherical in shape
→ Made of four polypeptide chains = quaternary structure
Each chain contains a haem group which contains an iron molecule O2 can bind with the iron group
Therefore haemoglobin can carry four molecules of O2 (8 O atoms) at a time
The haem group gives haemoglobin its colour; red with O2, purple without O2
When haemoglobin is combined with O2, it is referred to as oxyhaemoglobin.