MEH - Energy Storage (Glycogen And Fat)

Question 1

Which tissues/cells have an absolute requirement for glucose?

Answer 1

• red blood cells
• neutrophils
• innermost cells of kidney medulla
• lens of the eye

Question 2

At what level should blood glucose be maintained?

Answer 2

Roughly 5 mmol/L

Question 3

What happens when blood glucose falls below 2.8 mmol/L?

Answer 3

Confusion

Question 4

What happens when blood glucose falls below 1.7 mmol/L?

Answer 4

Weakness, nausea

Question 5

What happens when blood glucose falls below 1.1 mmol/L?

Answer 5

Muscle cramps

Question 6

What happens when blood glucose falls below 0.6 mmol/L?

Answer 6

Brain damage, death

Question 7

Where is glycogen stored in the body?

Answer 7

In muscles (to supply muscle) and in liver (to replenish plasma glucose conc.)

Question 8

How does glycogen appear on imaging?

Answer 8

Small black granules

Question 9

How is glycogen structured?

Answer 9

Glucose residues linked by alpha 1-4 glycosidic bonds (joining chains) and alpha 1.6 glycosidic bonds (forming branch points every 8-10 residues), surrounding a central protein called glycogenin

Question 10

How is glycogen synthesised?

Answer 10

• glucose and ATP concreted to G6P and ADP by hexokinase
• G6P converted to G1P by phosphoglucomutase
• G1P converted to UDP-glucose by G1P uridylyltransferase
• UDP glucose converted to glycogen by glycogen synthase/branching enzyme

Question 11

How is glycogen degraded?

Answer 11

Glycogen phosphorylase and phosphoglucomutase break down glycogen into G6P, so it can be used in glycolysis or be released by the liver into the blood.

Question 12

What happens to glycogen stores in the liver?

Answer 12

G6P converted to glucose and exported to blood. Liver glycogen in a buffer of blood glucose levels.

Question 13

What happens to glycogen stores in the muscle?

Answer 13

Muscle lacks the enzyme glucose-6-phosphatase. G6P enters glycolysis for energy production

Question 14

What is the rate limiting enzyme of glycogen synthesis?

Answer 14

Glycogen synthase

Question 15

What is the rate limiting enzyme of glycogen degradation?

Answer 15

Glycogen phosphorylase

Question 16

What effect does glucagon have on muscle glycogen stores?

Answer 16

None

Question 17

What effect does AMP have on muscle glycogen phosphorylase?

Answer 17

It is an allosteric activator, but does not work on liver form of enzyme

Question 18

What are glycogen storage diseases?

Answer 18

Inborn errors of metabolism - inherited. They arise from deficiency/dysfunction of enzymes of glycogen metabolism. There are 11 types. Liver and/or muscle can be affected.

Question 19

What are the consequences of incorrect levels of glycogen storage?

Answer 19

Excess glycogen storage can lead to tissue damage, diminished glycogen storage can lead to hypoglycaemia and poor exercise tolerance

Question 20

What is deficient in von Gierke’s disease?

Answer 20

Glucose-6-phosphatase

Question 21

What is deficient in McArdle disease?

Answer 21

Muscle glycogen phosphorylase deficiency

Question 22

Where does gluconeogenesis occur?

Answer 22

In liver and in kidney cortex

Question 23

What are the main precursors of gluconeogenesis?

Answer 23

• Lactate (from anaerobic glycolysis in exercising muscle)
• glycerol (released from adipose tissue due to breakdown of triglycerides)
• amino acids (mainly alanine)

Question 24

What are the three key enzymes involved with gluconeogenesis?

Answer 24

1) PEPCK
2) fructose 1,6-bisphosphatase
3) glucose-6-phosphatase

Question 25

What effect does glucagon/cortisol have on gluconeogenesis?

Answer 25

• increases amount of PEPCK and fructose-1,6-bisphosphatase

- stimulates gluconeogenesis

Question 26

What effect does insulin have on gluconeogenesis?

Answer 26

• decreases amount of PEPCK and fructose-1,6-bisphosphatase

- inhibits gluconeogenesis

Question 27

At what point after eating does gluconeogenesis occur?

Answer 27

After a fast of 8-10 hours onwards

Question 28

How is excess energy stored in the body?

Answer 28

As triacylglycerol in adipose tissue

Question 29

True or false - adipocytes are a constant/unchanging size?

Answer 29

False - they expand as more fat is added. Can increase in size by about four times on weight gain before dividing and increasing total number of fat cells.

Question 30

How do triacylglycerides get from intestinal epithelia cells to the blood?

Answer 30

Via the lymph fluid

Question 31

Where does fatty acid synthesis mainly occur?

Answer 31

In the liver

Question 32

How does lipgloss occur?

Answer 32

Hormone sensitive lipase (stimulated by gluconeogenesis/adrenaline, inhibited by insulin) causes break down of triacylglycerol into glycerol and free fatty acids in the blood

Question 33

Outline fatty acid synthesis

Answer 33

• Pyruvate enters mitochondria and forms acetyl-CoA & OAA which then condense to form citrate
• Citrate enters cytoplasm and cleaved back to Acetyl-CoA & OAA
• Acetyl-CoA carboxylase (key regulator) produces
  malonyl-CoA from Acetyl-CoA.
• Fatty acid synthase complex builds fatty acids by sequential addition of 2 carbon units provided by malonyl-CoA.