Proteins

Question 1

What do amino acids consist of?

Answer 1

A hydrogen atom, an amino group, a carboxyl group and a variable R group

Question 2

What is the monomer for polypeptides?

Answer 2

Amino acids

Question 3

How do amino acids join?

Answer 3

Condensation reaction between carboxyl group (-COOH) and amino group (-NH) with removal of one water molecule, forming a peptide bond

Question 4

What is the bond between amino acids?

Answer 4

Peptide bonds

Question 5

How is a protein’s function determined?

Answer 5

It is determined by its conformation, which is dictated by its amino acid sequence

Question 6

What are the 4 levels of organisation in proteins?

Answer 6

Primary, Secondary, Tertiary and Quaternary structures

Question 7

What does primary structure refer to?

Answer 7

It refers to the unique and specific number, sequence and types of amino acids maintained by peptide bonds in a specific polypepetide

Question 8

What does secondary structure refer to?

Answer 8

It refers to the regular coiling or pleating of a single polypeptide chain. The structure is usually maintained by hydrogen groups between CO and NH groups of polypeptide backbone

Question 9

What are the 2 examples of secondary structures?

Answer 9

α-helix and β-pleated sheet

Question 10

What is the structure of α-helix secondary structure?

Answer 10

It is made up of a single polypeptide chain wound into a coiled/spiral structure with each turn linked by hydrogen bonds between CO and NH groups. There are 3.6 amino acid residues in every turn of the α-helix.

Question 11

What is the structure of a β-pleated sheet secondary structure?

Answer 11

It is formed by 2 or more regions of a single polypeptide chain lying side by side linked together by hydrogen bonds, formed between CO and NH groups of adjacent regions. Chains may run parallel or anti-parallel

Question 12

What does tertiary structure refer to?

Answer 12

it refers to the further extensive folding and bending of a single polypeptide chain, giving to specific conformation of a protein.

Question 13

What bonds maintains the tertiary structure?

Answer 13

Hydrophobic interactions, hydrogen bonds, ionic bonds and disulfide bonds formed between R groups of amino acid residues

Question 14

What does quaternary structure refer to?

Answer 14

It refers to the association between 2 or more polypeptide chains to form one functional protein molecule

Question 15

What bonds can maintain the quaternary structure?

Answer 15

Hydrophobic interactions, hydrogen bonds, ionic bonds and disulfide bonds formed between R groups of amino acid residues on different polypeptide chains

Question 16

What are the 2 kinds of proteins?

Answer 16

Fibrous and globular/spherical proteins

Question 17

What is the quaternary structure of haemoglobin?

Answer 17

4 polypeptide subunits, 2 α-globin subunites and β-globin subunits. Each subunit consist of a polypeptide component called globin and a prosthetic component called haem group

Question 18

How are the subunits of haemoglobin held together?

Answer 18

They are held together by ionic bonds, hydrogen bonds and hydrophobic interactions.

Question 19

How does the bonds between subunits in haemoglobin help with its functions?

Answer 19

Ionic bonds, hydrogen bonds and hydrophobic interactions allow subunits to move with respect with each other allowing a change in position that influences its affinity with oxygen. Hence, binding of one oxygen molecule induces a conformation change in remaining subunits so that affinity to oxygen increases.

Question 20

What is a collagen molecule?

Answer 20

It consists of 3 helical polypeptide chains wound around each other. It is said to have both a secondary and quaternary structure (no tertiary structure).

Question 21

What is the structure of each helical polypeptide chain in collagen?

Answer 21

It has a loose helix secondary structure that is stabilised by hydrogen bonds. The sequence is usually glycine-X-Y.

Question 22

What is the assembly of tropocollagen (molecule of collagen)?

Answer 22

• It can form a tight triple helix as almost every third amino acid is a glycine, the smallest amino acid, allowing it to fit into restricted space in triple helix
• Hydrogen bonds between adjacent polypeptide chains increases tensile strength and makes molecule insoluble

Question 23

What is the assembly to form fibrils in collagen?

Answer 23

Tropocollagen molecules crosslinks with neighbouring molecules running parallel to it. Cross-linking of adjacent tropocollagen molecules results in formation of fibrils, greatly increasing tensile strength.

Question 24

What is the assembly to form collagen fibre?

Answer 24

Many fibrils in turn assemble to form a fibre, increasing tensile strength of collagen

Question 25

What is the observation of a biuret test if protein is present?

Answer 25

A purple colour develops slowly.

Question 26

What organisational levels does haemoglobin have?

Answer 26

Primary, Secondary, Tertiary, Quaternary

Question 27

What organisational levels does collagen have?

Answer 27

Primary, Seconday, Quaternary

Question 28

How is each subunit of haemoglobin arranged?

Answer 28

Most of its hydrophilic amino acid side chains are on the external surface while most of its hydrophobic amino acid side chains are buried in the interior.