Lecture 1

Question 1

Is glucose a reducing or non-reducing sugar and why?

Answer 1

Glucose is a reducing sugar because it has a free aldehyde group that can act as a reducing agent and become oxidised itself

Question 2

Give one reason why glucose being a reducing sugar may cause oxidative cellular damage?

Answer 2

Increase in reactive oxygen species due to increased polyol pathway flux

Question 3

Why does increased polyol pathway flux cause oxidative cellular damage?

Answer 3

The aldose reductase enzyme that oxidises the glucose intracellularly to its respective alcohol using NADPH as a cofactor leads to reduction in available NADH.

NADH is used to regenerate glutathione (GSH) which is an important scavenger of ROS

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2996922/

Question 4

In which tissues is aldose reductase found?

Answer 4

nerve, retina, lens, glomerulus and vascular cells

Question 5

Why are tissues such as nerve, retina, lens, glomerulus and vascular cells more at risk of damage from hyperglycaemia?

Answer 5

The GLUT transporters that move glucose intracellularly from the blood are insulin-independent so moves straight into cell and accumulates.

Question 6

What are the three main types of diabetes mellitus and what are the main features of each type?

Answer 6

Type 1 - autoimmune destruction of pancreatic islets of Langerhans beta cells so insulin not produced

Type 2 - acquired insulin resistance

Gestational diabetes - first detected in pregnancy

Question 7

Which cells secrete insulin?

Answer 7

Beta cells of islets of langerhans in pancreas

Question 8

Which cells perceive insulin?

Answer 8

muscle cells and hepatocytes (liver)

Question 9

What is the overall effect of insulin?

Answer 9

decreases blood glucose level

Question 10

Which cells produce glucagon?

Answer 10

alpha cells of islets of langerhans in pancreas

Question 11

Which cells perceive glucagon?

Answer 11

most hepatocytes (liver)

Question 12

What is the overall effect of glucagon?

Answer 12

Increase blood glucose level

Question 13

Describe the structure of the Sarcoma Homology 2 (SH2) domain

Answer 13

antiparallel beta-sheet flanked by two alpha helices

Question 14

What feature is recognised by SH2 domains?

Answer 14

pY (phosphotyrosine residue)

Question 15

How do modular binding domains convey specificity?

Answer 15

All proteins in the same domain family recognise the same feature but each individual domain only recognises this feature in a given motif.

Question 16

Name four modular binding domain families

Answer 16

1. Sarcoma Homology 2 (SH2)
2. Sarcoma Homology 3 (SH3)
3. Phosphotyrosine Binding (PTB) domain
4. Pleckstrin Homology (PH) domain

Question 17

Give the definition of a protein domain

Answer 17

a conserved part of a given protein sequence that forms a compact three-dimensional structure that is independently stable and folded, and may evolve, function, and exist independently.

Question 18

What is the amino acid sequence of the SH2 domain that binds the pY residue and why is it important?

Answer 18

FLVR
- the positively charged R (arginine) will be able to coordinate the negatively charged pY

Question 19

Which part of the SH2 domain affects specificity?

Answer 19

The C-terminal flanking sequence (variability in the primary sequence of the substrate)

Question 20

What feature is recognised by SH3 domains?

Answer 20

Proline rich PXXP cores (aromatic proline residues)

Question 21

Why do SH3 domains exhibit avidity?

Answer 21

binds with a weaker affinity so multiple SH3 domains bind to increase the association constant

Question 22

What feature is recognised by PH domains?

Answer 22

PIPs (phospholipids) - binds phosphate of phosphoinositides

Question 23

What is the structure of the SH3 domain?

Answer 23

5 anti-parallel beta strands in two perpendicular beta sheets

Question 24

What feature is recognised by the PTB domains?

Answer 24

pY (Phosphotyrosine)

Question 25

What is the motif recognised by PTB domains?

Answer 25

NPXpY

Question 26

What increases binding affinity and specificity of the PTB domains?

Answer 26

N-terminal sequences flanking the recognised motif and pY

Question 27

What is the structure of the PTB domain?

Answer 27

2 orthogonal beta-sheets with a c-terminal amiphipathic alpha-helix capping one end of the beta sandwich

Question 28

Why are the N-terminal flanking sequences of the PTB binding peptide important?

Answer 28

increases binding affinity and specificity

forms an additional anti-parallel beta-strand to the second beta sheet of the domain

Question 29

What controls the specificity of recognition of different phosphoinositide’s by the PH domains?

Answer 29

The location of the phosphate and the number of phosphates

Question 30

What is the structure of the PH domain?

Answer 30

Beta-barrel of two antiparallel beta-sheets and amphipathic alpha-helix