Biochemistry - Insulin and Glucagon

Question 1

Blood glucose, insulin and glucagon levels after a high carbohydrate meal

Answer 1

• Glucose levels begin low and quickly increase and then will slowly drop back down
• Insulin level will begin low and spike again before dropping
• Glucagon levels will start high and drop rapidly before increases after around 180 mins

Question 2

Glucagon

Answer 2

• Secreted in endocrine pancreatic Alpha cells
• Produced in response to low blood sugar levels
• 29aa polypeptide
• Stops glycogen synthesis
• Stimulates glycogen breakdown in liver to glucose which can go into the blood

Question 3

Isuliun

Answer 3

• Secreted in endocrine pancreatic Beta cells
• Produced in response to high blood sugar levels
• 51 aa polypeptide
• Stimulates all body cells except brain cells to take up glucose and begin glycogen synthesis
• Insulin is a growth hormone, promotes fat deposition

Question 4

Glucose transporters

Answer 4

• GLUT1 is highly conceived and has high affinity for glucose
• GLUT2 is found in beta-cells, liver and gut and has a low affinity for glucose

Question 5

How does glucose trigger insulin release?

Answer 5

• Glucose binds to a glucose transporter and enters the cell beginning respiration
• ATP is produced
• ATP binds to a ATP sensitive K+ channel depolarising the cell (Ca2+ influx)
• This stimulates vesicles containing insulin to burst and move into the blood
• Arginine also triggers this pathway

Question 6

Glycogenolysis

Answer 6

Glycogen breakdown is regulated by the hormone Glucagon

Question 7

Glyconeogenesis

Answer 7

Formation of glycogen is regulated by the hormone insulin

Question 8

Insulin mediated glucose uptake

Answer 8

• Insulin binds to the insulin receptor on the outside of the cell membrane
• PI-3K and IRS1 bind to the insulin receptor on the inside of the cell membrane
• This stimulates the movement of the Glucose Transporter to the cell membrane
• Glucose can now move through this transporter into the cell

Question 9

Diabetes Mellitus

Answer 9

Typically hyperglycaemic- excess glucose in blood appears in urine.

• Fasting glucose is >11mM
• Capillaries and veins get damaged and most diabetic die from heart failure
• Nephropathy (kidney failure)

Question 10

Diabetes Mellitus

Answer 10

Typically hyperglycaemic- excess glucose in blood appears in urine.

• Fasting glucose is >11mM
• Capillaries and veins get damaged and most diabetic die from heart failure
• Nephropathy (kidney failure)
• Retinopathy
• Bad peripheral circulation
• Elevated glucose results in uncontrolled uptake in epithelial cells and blood vessels

Question 11

HbA1c

Answer 11

• Alpha chain of haemoglobin will bind glucose

- Can follow amount and see if people are monitoring glucose correctly

Question 12

Type 1 Diabetes

Answer 12

• Insulin dependants
• Common in juveniles - autoimmune disorder
• Viral infection can trigger in adults
• Loss of beta cells so cannot produce insulin
• Treat with insulin injections

Question 13

Type 2 Diabetes

Answer 13

• Non-insulin dependant, insulin insensitive i.e. cells do not respond to insulin
• Common in older people (90%) along with obesity and stress
• Variable insulin levels, start high and then drop
• After a while will stop producing insulin

Question 14

What can prevent uptake of glucose into cells

Answer 14

• High fat content of the blood may alter signalling/glucose metabolism
• Need more and more insulin in insulin insensitive people - body cannot keep with demand
• If mitochondria are overactive they will produce free radicals which in turn will shut off the glucose transporter
• Thus blood glucose levels rise
• Mitochondrial DNA mutations can also impair glucose uptake

Question 15

Fuel Choice During Starvation

Answer 15

1. Glucose in the blood
2. Glycogen stores
3. Use proteins for gluconeogenesis (from 2 days)
   - Creates large amounts of ketone bodies acidifying the blood

Question 16

Ketone Bodies

Answer 16

• brain cannot use fats
• from 3 days of starvation, 30% of the brains energy is from ketone bodies
• After 40 days it is 70%
• Use results in ketoacidosis

Question 17

Ketoacidosis

Answer 17

• Untreated type 1 diabetics
• Starving
• Binge drinking alcoholics

Question 18

ATP use in muscles

Answer 18

• When ATP is used it is replaces almost immediately through creatine phosphate
• If ATP stores declined cells dies by necrosis

Question 19

Fuel Use During Exercise

Answer 19

1. Muscle glycogen
2. Blood borne glucose
3. Blood borne fatty acids

Question 20

Fuel Sources for Muscle Contraction

Answer 20

• Creatine phosphate has the fastest rate of ATP production but produces little
• Fatty acids (adipose) have the slowest rate of ATP production but produce a lot of it