Lecture 31 - Coordinating Metabolism: Insulin and Glucose Transport

Question 1

What is metabolic homeostasis

Answer 1

The body’s ability to maintain various metabolic processes to ensure molecules essential for life are kept at an optimal level

Question 2

What is the preferred fuel type for the brain?

Answer 2

Glucose but can use ketone bodies as well

Question 3

What is the preferred fuel type for resting skeletal muscle?

Answer 3

Fatty acids

Question 4

What does resting skeletal muscle store?

Answer 4

Glycogen

Question 5

What is the preferred fuel type for exercising skeletal muscle?

Answer 5

All; glucose, fatty acids, branch-chain amino acids

Question 6

What fuels are exported from exercising skeletal muscle?

Answer 6

Lactate and alanine

Question 7

What is the preferred fuel type for cardiac muscle?

Answer 7

Fatty acids

Question 8

What is the preferred fuel type for the adipose tissue?

Answer 8

Fatty acids

Question 9

What fuel is stored in adipose tissue?

Answer 9

Triacylglycerols

Question 10

What fuel is exported from adipose tissue?

Answer 10

Fatty acids and glycerol

Question 11

What is the preferred fuel type for the liver?

Answer 11

Amino acids, glucose and fatty acids

Question 12

What fuel is stored in the liver?

Answer 12

Glycogen

Question 13

What fuels are exported from the liver?

Answer 13

Triacylglycerols, glucose, ketone bodies

Question 14

What is the prefered fuel for RBCs?

Answer 14

Glucose

Question 15

What fuel is exported from RBCs?

Answer 15

Lactate

Question 16

Why can the brain not use FAs?

Answer 16

They cannot cross the blood-brain barrier

Question 17

What can the RBCs not use FAs?

Answer 17

They lack mitochondria

Question 18

What is insulin?

Answer 18

A peptide hormone synthesised in the pancreas by the beta cells

Question 19

When is insulin secreted?

Answer 19

In response to high glucose levels

Question 20

What does insulin do?

Answer 20

Acts on the liver, muscle and adipose tissues to promote glucose transport and use

Question 21

What happens to the body without insulin?

Answer 21

It starves

Question 22

What is type 1 diabetes?

Answer 22

An early onset form of diabetes, diagnosed by symptoms, blood glucose and glycated haemoglobin

Question 23

What are common symptoms of diabetes?

Answer 23

Glycosuria (glucose in urine) and the presence of ketones in the blood

Question 24

What causes type 1 diabetes?

Answer 24

An autoimmune condition leading to the loss of pancreatic beta cells and therefore no insulin secretion

Question 25

What is preproinsulin?

Answer 25

Initial form of insulin synthesised from transcription and translation - in the ER

Question 26

What does preproinsulin contain?

Answer 26

An A-chain, B-chain, C-peptide, and a signal sequence

Question 27

What is the signal sequence?

Answer 27

A chain that helps direct the protein into the ER but is removed by signal peptidase, leaving proinsulin

Question 28

What is proinsulin?

Answer 28

The A-chain, B-chain, and C-peptide of insulin. It moves to the Golgi and is packaged into secretory granules. Proprotein convertase enzymes in the granules cleave proinsulin to release active insulin (A-chain and B-chain) and C-peptide.

Question 29

What is the C-peptide?

Answer 29

A chain released during the cleavage of proinsulin along with insulin, has a longer half-life than insulin and can be used as a marker of insulin secretion

Question 30

What is the c-peptide important for?

Answer 30

Distinguishing between endogenous insulin and exogenous insulin

Question 31

How does glucose stimulate insulin secretion?

Answer 31

GLUT1 transports glucose into pancreatic beta cells, glucose is metabolised via glycolysis and the CAC to increase ATP levels. Increased ATP:ADP ratio inhibits ATP-gated K+ channels triggering membrane depolarisation and the opening of voltage-gated Ca2+ channels. The calcium influx induces exocytosis of insulin-containing secretory vesicles

Question 32

When are glucose levels the highest?

Answer 32

About an hour after eating

Question 33

When are insulin levels the highest?

Answer 33

About two hours after eating

Question 34

What is the incretin effect?

Answer 34

The phenomenon where oral glucose intake stimulates a greater insulin response compared to an equivalent amount of glucose administered intravenously

Question 35

Why does oral glucose stimulate insulin better?

Answer 35

Due to the action of gut-derived hormones; GLP-1

Question 36

Why does insulin have to be taken intravenously?

Answer 36

Gets broken down in GI tract

Question 37

What is GLP-1 in the L-cells of the intestine an example of?

Answer 37

A different way of processing the same protein (similar to insulin)

Question 38

What is GLP-1?

Answer 38

A peptide hormone synthesised in the intestine in response to nutrients

Question 39

What is GLP-1 made from?

Answer 39

Glucagon via convertase enzyme

Question 40

What does GLP-1 do?

Answer 40

Acts through its receptor to stimulate insulin secretion

Question 41

How is GLP-1 used to treat type 2 diabetes?

Answer 41

Agonists are developed

Question 42

How does GLP-1 promote weight loss?

Answer 42

Slows gastric emptying and reduces appetite

Question 43

What is GLUT4?

Answer 43

An insulin-regulated glucose transporter

Question 44

Where is GLUT4 found in muscle and adipose cells?

Answer 44

Intracellular storage vesicles

Question 45

What happen when insulin binds to its receptor?

Answer 45

A phosphorylation cascade is activated that regulates the trafficking of GLUT4 vesicles to the plasma membrane by regulating vesicle trafficking proteins

Question 46

What is GSV?

Answer 46

The GLUT4 storage vesicle

Question 47

What does AS160 do?

Answer 47

Regulates a GTPase protein Rab10 which is involved in the trafficking of vesicles

Question 48

What is IRS?

Answer 48

Insulin receptor substrate

Question 49

What is PIP2 and PIP3?

Answer 49

Membrane phospholipids

Question 50

What is the insulin receptor an example of?

Answer 50

A tyrosine kinase receptor