Glycogenesis And Glycogenolysis Flashcards
Why is glycogen called a homopolysaccharide
Consistent glucose sugars polymerised
Explain the structure of glycogen
High branched a glucose with 1,4 a bonds on backbone
1,6 a bond branches
What are 3 reasons glucose can’t be monosaccharides within cells stored
Renal loss (excretion from the blood in urine)
Osmotic pressure inside cell causes lysis
Glycogen mobilises fast release of free glucose(due to branches)
Why are branches needed for glucose supple
Allows degrading of glucose from multiple points at once increasing the rate
What are the differences between liver and muscle glycogen
Muscle glycogen contains glucose 6 phosphate which is then used for muscle supply ONLY
Liver glycogen removes glucose for use for all cells - it controls blood glucose conc
Which energy store out of fat protein and glucose/glycogen have most energy release
Fat
When does glycogenesis occur in liver and muscle cells
When glucose is high in conc eg when you’re eating a meal
What is the first step of glucose 6 phosphate conversion to glycogen
DIVERSION (away from glycolysis)
G 6 p is converted to G 1 P by
Phosphoglucomutase
Once glucose 1 phosphate is produced by phosphoMUTASE , what happens
Activation step
UTP (uridine triphopshate)
Converted to UMP (1 monophosphate ) by cleaving a pyrophosphate
UMP then joins glucose 1 phosphate forming UDP glucose
What converts UTP into UMP and then joins UMP to g1P to form UDP glucose
Pyrophosphate hydrolysis catalysed by pyrophosphorylase
Ump joined to glucose by UDP glucose pyrophosphorylase
What happens once UDP glucose forms
Glucose is split from UDP + P
Forming free glucose
Joined to end of glycogen by glycogen synthase enzyme (non reducing end)
What does glycogen synthase need to join free glucose to glycogen
Glycogenin- acts as a primer to start glycogen forming and prevents further glycogen depending on size
When does glycogen start to branch (glycogen synthase moves from 14 bonds to 1,6)
After 10 glucose residues
What happens to UDP + p when glucose is cleaved in polymerisation stage
It is recycled back into UTP for next glucose activation
Which enzyme is needed to convert 1,4 a bonds to 1,6 a bonds in branching (glycogen synthase)
Amylo 1-4 —-> 1,6 transglycosylase
What is glycogenolysis activated by and importent for
Activated by glucagon and epinephrine so that glucose can be released from liver cells to blood
What happens first in glycogenolysis
Erosion of chain ends
Glycogen phosphorylase catalyses the release of a glucose 1 phosphate by addition of a free phosphate to the end glucose
This releases it from glycogen
Which type of glycogen phosphorylase is active and inactive
A = active
B = inactive
Via allosteric control (a phosphate binds to enzyme to inactivate or activate it)
Why is there remaining 4 glucose on a branch after glycogen phosphorylase activity
AS only fits up to the last 4 on branch remain
Which enzyme removes the 3 glucose left by glycogen phosphorylase to add onto the other branch
Amylo 1-4 transferase enzyme
Which enzyme is needed to cleave the last glucose on the 1,6 branch left by both glycogen phosphorylase and a 1,4 transferase
Amylo 1-6 glucosidase
Hydrolyses the 1,6 bond
What happens to the free glucose 1 phosphate in glycogenolysis
It is converted into glucose 6 phosphate again by phosphoglucomutase
More useful eg for glycolysis
What happens in the liver with the remaining glucose 6 phosphate
It is cleaved to produce free glucose for blood homeostasis
By glucose 6 phosphatase (regenerates glucose by addition of h20
cleaved it via hydrolysis)
What is glycogen storage disease
Where enzymes that are in glycogenesis or glycogenolysis are disrupted
Causes muscle weakness and tiredness (no glucose in blood etc)
What is type O Glycogen storage disease
Glycogen synthase in the liver is deficient
Can’t attach glucose form UDP glucose into glycogen branches
Free glucose molecules if turned into glucose can = hyperglycaemia
If stay as glucose 1 phosphate = hypoglycaemia as this can’t be broken down
What is type 1 GSD
No glucose 6 phosphatase
G6P stays G6P and can’t be used as glucose in liver or blood
= hypoglycaemia
What is type III GSD
Amylo 1-6 glucosidase deficiency (debranching enzymes)
The last glucose on branch not cleaved
Debranching ineffective
Glycolysis of the glucose is blocked = hypoglycaemia
What is type IV GSD
Amylo both 1-4 and 1-6 glucosidase deficient
Left with long branches glycogen
Not efficient glycogenolysis
Hypoglycaemia
What is type V GSD
Muscle glycogen phosphorylase A deficient
= no glycogen breakdown
=
No glucose release
= muscle weakness
When does glycogenolysis not occur
Between meals- we use glycogen breakdown in emergencies only
