3. 1. 4. 1 Properties of Proteins

Question 1

What are amino acids?

Answer 1

Amino acids are the monomers from which proteins are made.

Question 2

What are the different groups in the genrral structure of an amino acid?

Answer 2

• Amine group (NH2) basic
• Carboxyl group (COOH) acidic
• Side chain (R)
• Hydrogen atom

Question 3

What do the 20 amino acids that are common in all organisms differ by?

Answer 3

Their side group

Question 4

What does a condensation reaction between two amino acids form?

Answer 4

A peptide bond

Question 5

How is a dipeptide formed?

Answer 5

By the condensation of two amino acids. The two amino acids become linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other.

Question 6

How are polypeptides formed

Answer 6

By the condensation of many amino acids

Question 7

What may a functional protein contain?

Answer 7

One or more polypeptide

Question 8

What is the role of ionic bonds in the structure of proteins?

Answer 8

Tertiary structure: More bonds form between different parts of the polypeptide chain, including hydrogen and ionic bonds in the further coiling or folding of the chain.

Question 9

What is the role of disulfide bridges in the structure of proteins?

Answer 9

Disulfide bridges form whenever two molecules of the amino acids cysteine come close together - the sulfur atom in one cysteine bonds to the sulfur atom in the other.

Question 10

What is the primary structure of a protein?

Answer 10

Chain of amino acids joined by polymerisation. Lots of condensation reactions and peptide bonds. Known as polypeptide chain.

Question 11

What does the primary structure determine?

Answer 11

Determines properties of protein through type and sequence of amino acids. Controlled by DNA (protein synthesis).

Question 12

What is the secondary structure of a protein?

Answer 12

Secondary structure: Hydrogen bonds form between the amino acids in the polypeptide chain, causing it to be twisted into a 3D shape such as a coil (alpha helix) or fold (beta pleated sheet).

Question 13

What is the tertiary structure of a protein?

Answer 13

Further bending or folding of secondary structure forming a 3D globular shape - shape is precise and specific to the function fo the polypeptide.

Question 14

What is the quaternary structure of a protein?

Answer 14

Folding together more than one polypeptide chain.

Question 15

What does the ‘R’ group of an amino acid determine?

Answer 15

How it bends and what bonds are formed. There are 3 types of side chain interactions:
- Hydrogen bonds
- Disulfide bonds
- Ionic bonds

Question 16

Describe the biuret test for proteins.

Answer 16

1) Add food sample to test tube.
2) Add 2ml NaOH and 5-6 drops of CuSO4 solution.
3) Shake gently
4) Allow mixture to stand for 4-5 minutes.
5) Bluiesh/violet colour indicates presence of protien.

Question 17

What are the 4 different types of amino acids?

Answer 17

• Nonpolar (hydrophobic) with hydrocarbon side chains
• Polar (hydrophilic) with polar or ionic side chains
• Acidic (hydrophilic) with acidic side chains
• Basic (hydrophilic) with NH2 side chains

Question 18

Describe the structure of an amino acid.

Answer 18

Amino acids are the basic monomer units which combine to make up a polymer called polypeptide.
Polypeptides can be combined to form proteins.

Question 19

What bonds are involved in the tertiary structure of proteins?

Answer 19

• Disulfide bridges which are fairly strong
• Ionic bonds which form between any carboxylate and amino group not involved in forming peptide bonds these are weaker than disulfide bridges.
• Hydrogen bonds, lots but easily broken