3.6 Structure of Proteins

Question 1

What is a polypeptide?

Answer 1

Polymer of amino acids

Question 2

What is an amino acid?

Answer 2

Monomer used to build polypeptides & proteins

Question 3

Draw the general structure of an amino acid:

Answer 3

(Carbon attached to amine group, carboxyl group & random group)

Question 4

How many different naturally occuring amino acids are there?

Answer 4

20

Question 5

Describe the reaction in which a polypeptide is formed from amino acids:

Answer 5

Condensation

peptide bond formed

catalysed by peptidyl transferase

Question 6

State the different levels of protein structure:

Answer 6

• PRIMARY STRUCTURE
  
  • sequence of amino acids
• SECONDARY STRUCTURE
  
  • alpha helix/beta pleated sheet
• TERTIARY STRUCTURE
  
  • Coiling/Folding into subunit
• QUATERNARY STRUCTURE
  
  • Association of multiple subunits

Question 7

Describe the primary structure of proteins:

Answer 7

Sequence of amino acids

Peptide bonds between amino acids

(order of amino acids determines folding of polypeptide later on)

Question 8

Describe the secondary structure of amino acids:

Answer 8

Hydrogen bonds form between H + N/O

Forms alpha helix or beta pleated sheet

Question 9

Describe the tertiary structure of proteins:

Answer 9

R-group interactions cause coiling/folding of secondary structure into subunit:

• IONIC BONDS
  
  • stronger than H bonds
  • occurs between oppositely charged ions on R groups
• HYDROGEN BONDS
• HYDROPHOBIC/HYDROPHILIC INTERACTIONS
  
  • Weak interactions between polar & non-polar R-groups
• DISULFIDE BRIDGES
  
  • Strongest bond present
  • Only occurs between R-groups with sulfur

Question 10

Describe the quarternary structure of proteins:

Answer 10

Association of many subunits

contains same type of bonds as tertiary, but between subunits

Question 10

Describe the quarternary structure of proteins:

Answer 10

Association of many subunits

contains same type of bonds as tertiary, but between subunits

Question 11

3.6 Structure of Proteins

What type of bonds are present in:

a. primary structure
b. secondary structure
c. tertiary structure
d. quaternary structure

Answer 11

a. peptide
b. peptide, hydrogen
c. peptide, hydrogen, ionic, hydrophobic/hydrophilic interactions, disulphide bridges
d. same as c, but between subunits

Question 12

Describe the reaction which breaks down polypeptides into smaller peptides/amino acids:

Answer 12

Hydrolysis of peptide bonds

catalysed by proteases