Energy Storage Flashcards
(84 cards)
Why is it good that glycogen is branched?
There’s lots of laces for the enzymes to work so can be broken down and mobilise glucose quicker.
Which cells have an absolute requirement of glucose?
Kidney medulla
Brain
Lens and cornea of eye
Which are the three main energy stores in humans and which one contains the most energy?
Triacylglycerol (the most)
Glycogen
Muscle protein
Which out of glycogenesis and glycogen breakdown I’d catabolic and anabolic?
Glycogenesis is anabolic
Glycogen breakdown is catabolic
What is the process of glycogenesis?
Glucose + ATP makes glucose 6-phosphate and ADP. Catalyses by Hexokinase in most cells and glucokinase in the liver.
Glucose 6-phosphate to glucose 1-phosphate catalysed by phosphoglucomutase
Glucose 1-phosphate + UTP + H2O to UDP-glucose and 2Pi.
Glycogen(n residues) +UDP-glucose to glycogen(n+1 residues) +UDP. irreversible and catalysed by glycogen synthase (alpha 1,4 bonds) and branching enzyme (alpha 1,6 bonds)
What is UTP and what is its role in glycogen synthesis?
It is a molecule structurally similar and energetically equivalent to ATP. UDP- glucose is a highly activated form of glucose that allows it to be joined to the glycogen chain.
What is glycogen broken down in response to in the muscle and liver?
Skeletal muscle - response to exercise
Liver - in response to fasting or from stress response.
What does glycogen breakdown not being a complete reversal of glycogen synthesis mean?
Different enzymes in each pathway allow for the simultaneous stimulation of one pathway and inhibition of the other.
Is glycogen ever degraded fully?
No, small amount of primer is always conserved so that the chain can reform when needed.
What is the process of glycogen breakdown?
Glycogen(n residues) + Pi to glucose 1-phosphate + glycogen(n-1 residues). Catalysed by glycogen phosphorylase that attacks the alpha 1,4 bonds and debranching enzyme that attacks the alpha 1,6 bonds. Glucose 1-phosphate to glucose 6-phosphate catalysed by phosphoglucomutase. In the muscles this enters glycolysis to generate ATP for the exercising muscle cell. In the liver the glucose 6-phosphate is converted to glucose catalysed by glucose 6-phosphotase. The glucose is released into the bloodstream via glucose transporter and transported to other tissues.
What is the difference between glycogen breakdown in muscle and liver cells?
In liver cells there is the enzyme glucose 6-phosphotase that catalyses the reaction that converts glucose 6-phosphate into glucose. This can travel in the blood stream and so the liver is a glucose store for all tissues of the body.
This enzyme is absent in muscle cells and so the glucose 6-phosphate enters glycolysis to produce energy for the muscle cell only. Therefore the muscle cells are a glucose 6-phosphate store and the liver is a glucose store.
What affects the muscle and liver in glycogen breakdown and what doesn’t?
Muscle - glucagon has no effect and AMP is an allosteric activator
Liver - AMP is not an allosteric activator and is activated by glucagon.
What do glycogen metabolism storage diseases result from and which enzymes can lead to glycogen storage diseases (+egs of 2 of them)?
Glycogen phosphorylase - McArdel disease (muscle deficiency)
Phosphoglucomutase
Glucose 6-phosphotase (in the liver) - Von Gierkes disease
Why would you never see hypoglycaemia in a normal healthy person?
The bodys system can maintain the levels in other ways.
What may glycogen diseases cause?
Increased/decreased amounts of glycogen
- tissue damage is excessive storage
- fasting hypoglycaemia (low blood glucose)
- poor exercise tolerance
Glycogen structure may be abnormal
-usually liver and/or muscle are affected
What does gluconeogenesis allow and what is it for?
Production of glucose when carbs are absent.
Glucose dependent tissues eg CNS
How long can glycogen stores last?
8-10 hrs
Where is the main site for gluconeogenesis?
The liver
What are the possible substrates for gluconeogenesis?
Pyruvate, lactate and glycerol, essential and non essential aas whose metabolism involves pyruvate (can be converted to alanine) or intermediates of the TCA cycle.
How is glucose produced from pyruvate?
Using some of the steps from glycolysis (the reversible steps) and the irreversible steps are bypassed.
Which steps of glycolysis are bypassed in the gluconeogenesis from pyruvate? What are the bypass reactions called? What are they catalysed by?
Step 10 - bypassed by 2 reactions that are driven by GTP and ATP hydrolysis.
- Pyruvate + CO2 + ATP + H2O to oxaloacetate + ADP + 2Pi + 2H+. Catalysed by pyruvate carboxylate (added CO2)
- Oxaloacetate + GTP + 2H+ to phosphoenolpyruvate + GDP + CO2. Catalysed by PEPCK and pyruvate and oxaloacetate can be provided from Glucogenic aas (intermediates in TCA cycle)
Steps 1+3 - bypassed by thermodynamically spontaneous reactions catalysed by phosphotases.
- Fructose 1,6-bisphosphate + H2O to fructose 6-phosphate + Pi. Catalysed by fructose 1,6-bisphosphatase (removes a phosphate)
- Glucose 6-phosphate +H2O to glucose + Pi. Catalysed by glucose 6-phosphatase (removes a phosphate).
What mainly controls gluconeogenesis?
Hormones
Where are the main control sites in gluconeogenesis?
PEPCK and fructose 1,6-bisphosphatase
What are the effects of glucagon, insulin and cortisol on PEPCK activity?
Glucagon, cortisol - increase
Insulin - decrease