Lecture 3 - Energy Storage glycogen and fat Flashcards
what is hypoglycemia ?
low blood sugar levels
how and why do we store glucose within the body ?
some cells require glucose for energy - RBC’s, Neutrophils, lens of the eye
we need to be able to keep some glucose even during starvation - so we store it as glycogen - so these cells at minimum have glucose to function
how and where is glycogen stored ?
what does it look like in imaging ?
musclular glycogen - it is stuck within the muscle - only the muscle cells can use this
intermyofibrilar glycogen - edges of the sarcomeres
intramyofibirilar glycoen - within sarcomeres
both are still black granules
Liver glycoen - black granules of glycogen storage used to replenish bodys plasma glucose levels - within hepatoctyes
what is the structure of glycogen ?
why is it advantageous for storage ?
highly branched molecule - polymer of glucose residues
a1-6 form the branch points , a1-4 form the chain extension
its nature provides storage as a large macro molcule with no osmotic effects
highly branched - allows for lots of release of lots of glucose from many points simultaneously - allows for the rapid synthesis or breakdown of glycogen
outline the process of glycogenesis
glycogen synthesis
glucose —– to G-6-P with hexokinase (1st step of glycolysis) - uses ATP
G-6-P feed out of glycolysis to G-1-P
phosphoglucomutase
G-1-P + UTP + H2O —-> UDP glucose + 2Pi
Glycogen is then extended with UDP glucose by glycogen synthase (1-4 extension) or branching enzyme (1-6 branch) - this step is irreversible
outline the process of glycogenolysis
draw a outline of how glycogen use is different in the muscle and liver
glycogen degregation
glycogen + Pi ——> G-1-P + glycogen(-1n)
uses glycogen phosphorylase for (1-4 chain reduction)
and
De-branching enzyme (1-6 branch breakage)
G-1-P is converted to G-6-P with phospoglucomutase
in the muscles it can be used in glycolysis (as they lack g-6-P phosphotase)
in the liver G-6-P is converted to glucose and released into the blood for other tissues to use
why do we have both glycogenisis and glycogenolysis ?
so we have different enzymes allowing for simultaneous inhibition of one path and stimulation of the other path
draw a outline of glucose metabolism and check against lecture 3
do it
how is liver glycogen metabolism regulated ?
check lecture
glycogen synthesis - rate limiting enzyme is - glycogen synthase
glycogen degradation - rate limiting enzyme is - glycogen phosphorylase
glucagon/adrenaline - increase glycogen degradation via glycogen phosphrylase and decrease glycogen synthase activity - decrease glycogen sysnthesis
both are phosphorylated
insulin - dephosphorylation of both synthase and phosphorylase - will increase synthase / synthesis
will decrease - phosphorylase / storage
how does muscle metabolism differ to liver metabolism
glucagon has no effect
AMP is an allosteric activator of muscle glycogen phosphorylase
outline glycogen storage diseases
12 types
due to disfunction or deficieny of enzymes of glycogen metabolism
can affect liver and/or muscle
Excess glycogen storage can lead to tissue damage
• Diminished glycogen stores can lead to hypoglycaemia & poor exercise tolerance
Examples:
• von Gierke’s disease - glucose 6-phosphatase deficiency - hepatomegaly - caused by glycogen build up
• McArdle disease - muscle glycogen phosphorylase deficiency- severe fatigue in exercise
what is gluconeogenesis ?
8 hours past eating we deplete glycogen stores so we must synthesise new glucose
occurs mainly in the liver and abit in the kidney cortex
three pre cursors feed into gluconeogenesis
Lactate - cori cycle - anaerobic glycolysis in muscles and RBC’s produces lactate - transported to liver and converted to glucose for distribution - allows muscle to dispose of lactate
Glycerol released from adipose tissue via the breakdown of triglycerides
glucogenic amino acids such as alanine
what are the key enzyme steps in gluconeogenesis
glucose - 6- phosphotase - converts G-6-P to glucose
- Fructose 1,6-bisphosphatase converts Fructose 1,6-bisphosphate to fructose - 6 - phosphate
- Phosphoenolpyruvate carboxykinase (PEPCK)
uses GTP —-> GDP + CO2
to convert oxaloacetate to phospoenolypyruvate
1 + 2 are the major control points of the pathway
outline the regulation of gluconeogenesis with a table and the key enzmyes
check against lec 3 when done
what is the purpose of lipid storage ?
it is a high density energy storage
glycerol and fatty acids combine to make triacylglycerol
where we store our excess energy as fat - stored in adipose tissue - they are hydrophobic so stored in anhydrous adipose tissue
utilised in starvation, exercise ect
storage and mobilisation of TAG’s are under hormonal control
adipocytes are white single fat droplets - when we gain weight we divide to produce more fat cells, this explains why it is easier to put back on weight
