General Properties Of Proteins (3.1.4.1)

Question 1

What are proteins?

Answer 1

• The polymers of amino acids

Question 2

What elements are present in proteins?

Answer 2

• Carbon
• Hydrogen
• Oxygen
• Nitrogen
• Sometimes sulfur

Question 3

What is the general structure of all amino acids?

Answer 3

• Amine group, NH₂
• Carboxylic acid group, COOH
• Hydrogen atom, H
• Variable group, R

Question 4

How is a peptide bond formed?

Answer 4

• Through a condensation reaction between the amine group of one amino acid and the carboxyl group of another, with the elimination of a water molecule

Question 5

How is a dipeptide formed?

Answer 5

• When two amino acids join together in a condensation reaction

Question 6

How is a polypeptide formed?

Answer 6

• When more than two amino acids join together in a condensation reaction

Question 7

What is the primary structure?

Answer 7

• Refers to the sequence of amino acids in the polypeptide chain

Question 8

Why is the primary structure important?

Answer 8

• This specific sequence of amino acids is what determines where the hydrogen, ionic and disulfide bonds form in a tertiary structure and where these bonds form determines the unique 3D shape

Question 9

Why may a change to the amino acid sequence occur?

Answer 9

• Mutation

Question 10

What is the secondary structure?

Answer 10

• Represents the folding or coiling of the polypeptide chain as a result of the hydrogen bonding between amino acids
• Secondary structures that exist include the alpha helix and beta pleated sheet

Question 11

What is the tertiary structure?

Answer 11

• The further folding and coiling of the secondary structure due to the hydrogen, ionic and disulfide bonds and so creating a unique 3D shape

Question 12

Why is the tertiary structure important in enzymes?

Answer 12

• It determines the shape of the enzyme’s active site, determining its function

Question 13

What is the quaternary structure?

Answer 13

• When proteins consist of more than one polypeptide chain
• The polypeptide chains are held together by hydrogen bonds, ionic bonds and disulfide bonds

Question 14

What is denaturation of a protein?

Answer 14

• An alteration in the tertiary structure of a protein
• The loss of 3D shape of the protein causes the protein to be no longer functional

Question 15

How are proteins denatured?

Answer 15

• High temperatures above the optimum temperature
• Extreme changes in pH
• Heavy metals

Question 16

Describe the biuret test and positive result for proteins

Answer 16

• Add biuret reagent
• A purple or lilac colour