2.4. Protein Structure

Question 1

Primary structure

Answer 1

Sequence of amino acids as determined by mRNA codons

- contains peptide bonds

Question 2

Secondary structure

Answer 2

1. Two regular folding patterns (alpha helix and beta pleated sheet) are formed as dictated by amino acids in primary sequence (secondary structure)
   - results from hydrogen-bonding between between N-H & C=O groups in the polypeptide backbone

Question 3

Alpha helix (secondary structure)

Answer 3

1. Single polypeptide chain twists to form a rigid cylinder

2. Hydrogen bonds within polypeptide chain spaced 4 amino acids apart

Question 4

Beta pleated sheet (secondary structure)

Answer 4

1. Rigid planar structures with hydrogen bonds between amino acids in adjacent strands
2. Can form from parallel chains or anti parallel chains

Question 5

Parallel chains

Answer 5

Neighboring polypeptide chains that run in the same orientation

Question 6

Antiparallel chain

Answer 6

1. Polypeptide chain that folds back and forth upon itself, with each section of the chain running in the direction opposite to that of its immediate neighbours

Question 7

Tertiary structure

Answer 7

3D structure of polypeptide chain

1. Disulphide bonds
2. Hydrogen bonds
3. Ionic bonds
4. Hydrophobic interactions
5. van der waals forces
   - formed by secondary structures folding with each other
   - highest level of organization in monomeric proteins

Question 8

Quaternary structure

Answer 8

1. describes the number and relative positions of subunits in multimeric proteins

Question 9

Dynamic

Answer 9

Modify proteins & elicit changes in cellular function

Question 10

PTM

Answer 10

Post translational modifications

Question 11

Proportion

Answer 11

Form protein translated as before being activated by removal of amino terminal amino acids

Question 12

Phosphorylation

Answer 12

1. Addition of a phosphate molecule

Question 13

Protein kinases

Answer 13

Enzymes that facilitate transfer of phosphate

Question 14

Phosphorylases

Answer 14

Help to remove phosphate

Question 15

Methylation

Answer 15

Addition of methyl (CH3)

Question 16

Acetylation

Answer 16

Addition of acetyl (COCH3)

Question 17

Polyubiquinated

Answer 17

1. Addition of many ubiquitins (a 76 amino acid polypeptide) which regulates degradation in the proteosome

Question 18

Ubiquitin

Answer 18

Attached to lysin residue of target proteins

Question 19

Mono-ubiquitinated

Answer 19

Regulates protein sorting

Question 20

Glycosylation

Answer 20

Addition of saccharides (sugars) to proteins to produce proteoglycans in ER, golgi or cytoplasm
E.g. ABO blood group proteins on red blood cells, gp120 of HIV