MEH - Energy Storage (Glycogen And Fat) Flashcards
Which tissues/cells have an absolute requirement for glucose?
- red blood cells
- neutrophils
- innermost cells of kidney medulla
- lens of the eye
At what level should blood glucose be maintained?
Roughly 5 mmol/L
What happens when blood glucose falls below 2.8 mmol/L?
Confusion
What happens when blood glucose falls below 1.7 mmol/L?
Weakness, nausea
What happens when blood glucose falls below 1.1 mmol/L?
Muscle cramps
What happens when blood glucose falls below 0.6 mmol/L?
Brain damage, death
Where is glycogen stored in the body?
In muscles (to supply muscle) and in liver (to replenish plasma glucose conc.)
How does glycogen appear on imaging?
Small black granules
How is glycogen structured?
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
How is glycogen synthesised?
- 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
How is glycogen degraded?
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.
What happens to glycogen stores in the liver?
G6P converted to glucose and exported to blood. Liver glycogen in a buffer of blood glucose levels.
What happens to glycogen stores in the muscle?
Muscle lacks the enzyme glucose-6-phosphatase. G6P enters glycolysis for energy production
What is the rate limiting enzyme of glycogen synthesis?
Glycogen synthase
What is the rate limiting enzyme of glycogen degradation?
Glycogen phosphorylase
What effect does glucagon have on muscle glycogen stores?
None
What effect does AMP have on muscle glycogen phosphorylase?
It is an allosteric activator, but does not work on liver form of enzyme
What are glycogen storage diseases?
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.
What are the consequences of incorrect levels of glycogen storage?
Excess glycogen storage can lead to tissue damage, diminished glycogen storage can lead to hypoglycaemia and poor exercise tolerance
What is deficient in von Gierke’s disease?
Glucose-6-phosphatase
What is deficient in McArdle disease?
Muscle glycogen phosphorylase deficiency
Where does gluconeogenesis occur?
In liver and in kidney cortex
What are the main precursors of gluconeogenesis?
- Lactate (from anaerobic glycolysis in exercising muscle)
- glycerol (released from adipose tissue due to breakdown of triglycerides)
- amino acids (mainly alanine)
What are the three key enzymes involved with gluconeogenesis?
1) PEPCK
2) fructose 1,6-bisphosphatase
3) glucose-6-phosphatase
What effect does glucagon/cortisol have on gluconeogenesis?
- increases amount of PEPCK and fructose-1,6-bisphosphatase
- stimulates gluconeogenesis
What effect does insulin have on gluconeogenesis?
- decreases amount of PEPCK and fructose-1,6-bisphosphatase
- inhibits gluconeogenesis
At what point after eating does gluconeogenesis occur?
After a fast of 8-10 hours onwards
How is excess energy stored in the body?
As triacylglycerol in adipose tissue
True or false - adipocytes are a constant/unchanging size?
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.
How do triacylglycerides get from intestinal epithelia cells to the blood?
Via the lymph fluid
Where does fatty acid synthesis mainly occur?
In the liver
How does lipgloss occur?
Hormone sensitive lipase (stimulated by gluconeogenesis/adrenaline, inhibited by insulin) causes break down of triacylglycerol into glycerol and free fatty acids in the blood
Outline fatty acid synthesis
- 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.
