Protein structure and function 2

Question 1

Quaternary structure

Answer 1

number and arrangement of multiple folded protein subunits in a multi-subunit complex
can be simple dimers to oligomers

Question 2

Bonds between subunits in quaternary structure

Answer 2

normally interact non-covalently, can have disulfide bonds

contain closely packed non-polar side chains, H bonds between backbones and side chains

Question 3

Spatial arrangement of quaternary structure

Answer 3

polypeptide subunits associate with specific geometry

Question 4

Types of proteins

Answer 4

fibrous and globular

Question 5

Fibrous proteins

Answer 5

normally display one type of secondary struture

Question 6

Globular proteins

Answer 6

exhibit regular secondary structure interspaced with stretches devoid of recognisable structure

Question 7

Example of globular protein

Answer 7

haemoglobin

Question 8

Haemoglobin structure

Answer 8

4 globin subunits
adult: 2α and 2β subunits
fetal: 2α and 2γ subunits
one haem group per subunit binds to O2
deoxyHB subunits held together by salt bridges and H bonds

Question 9

How does O2 binding affect the structure of Hb?

Answer 9

conformational change, subunit-subunit salt bridges break, H-bonding changes, weaker interaction between αβ dimers

Question 10

Co-operativity of haemoglobin

Answer 10

deoxyhaemoglobin has relatively low affinity for O2, but when one O2 molecule binds to one haem group, affinity for 2nd O2 to bind is increased

Question 11

Structure of transmembrane proteins

Answer 11

span membrane with a stretch of hydrophobic amino acids

Question 12

Role of protein modifications

Answer 12

regulation of protein activity: phosphorylation, methylation, acetylation
regulation of destination: lipidation, glycosylation

Question 13

Glycosylation

Answer 13

attachment of carbohydrates
particularly for extracellular and cell-surface proteins
in euks: aids folding of protein, role in cell-to-cell recognition (aid in targeting and trafficking of newly synthesised protein to its destination)

Question 14

How do some diseases/disorders arise in relation to proteins

Answer 14

misfolding: can act as seeds for aggregation

Question 15

Example of disease

Answer 15

prion diseases
result from misfolding and aggregation of Celluar Prion Protein
early symptom of toxicity: activation of immune response causing inflammation