Energy Storage Flashcards
Which tissue have an absolute requirement for glucose?
Red blood cells
Neutrophils
Kidney medulla
Lens of eye
What glucose stored as?
Glycogen
What is glycogen stored as?
Granules
What are the two types of structure on a glycogen molecule?
At what bond?
Branch points A-16
Chains A-14
What does glycogen originate from?
A dimer of the protein glycogenin
What is the process of glycogen production?
Glycogenesis
What is the process of glycogen breakdown?
Glycogenolysis
What is the importance of the structure of glycogen?
Multiple points where enzymes can release glucose monomers
What are the key enzymes in glycogenesis?
Hexokinase - glucokinase in liver
Glycogen synthase
Branching enzyme
What does hexokinase catalyse?
Glucose to glucose 6 phosphate
What are the functions of glycogen synthase and branching enzyme?
Synthase - extends the chain
Branching - makes it branched
What are the two key enzymes in glycogenolysis that break down glycogen into glucose 1 phosphate?
Glycogen phosphorylase
De-branching enzyme
What do different enzymes in glycogen synthesis and degradation allow?
Simultaneous inhibition
What happens to glucose 6 phosphate in muscle cells?
Why?
Used in glycolysis
They lack g6phosphatase - so it cannot be broken down into glucose
What happens to glucose 6 phosphate in liver cells?
Broken down by g6phosphatase into glucose
Glucose is transported in the blood to other tissues
What does glycogen act as in liver cells?
Buffer of blood glucose levels
What are the two rate limiting enzymes in glycogen metabolism - in the liver?
In which recess are they in?
Glycogen synthase - synthesis
Glycogen phosphorylase - degradation
What hormones regulate liver glycogen metabolism?
Glucagon, adrenaline
Insulin
Describe the effect of glucagon and adrenaline on glycogen metabolism
Synthase - decreases
Phosphorylase - increases
Describe the effect of insulin on glycogen metabolism
Synthase - increases
Phosphorylase - decreases
What is the difference between the regulation of glycogen metabolism in muscle and liver cells?
Glucagon has no effect in muscle cells
AMP is an allosteric activator of glycogen phosphorylase
How do glycogen storage diseases arise?
Deficiency or dysfunction of enzymes of glycogen metabolism
Describe the effects of excess and diminished glycogen storage
Excess - tissue damage
Diminshed - hypoglycaemia and poor exercise tolerance
Explain two key examples of glycogen storage diseases
Von gierke - g6phosphatase deficiency
McArdle - muscle glycogen phosphorylase deficiency
What word describes the synthesis of glucose
Gluconeogenesis
When does gluconeogenesis occur?
Where?
Beyond 8 hours of fasting
Liver and to a lesser extent in the kidneys
What are the three main precursors of gluconeogenesis?
Lactate
Glycerol - from adipose tissue from the breakdown of triglycerides
Amino acids
What are the three key enzymes in gluconeogenesis?
G6Phosphatase
F16biphosphatase
PEPCK
What are the two regulatory enzymes in gluconeogenesis?
What are they in response to? (3)
Fructose16bisphosphatase
PEPCK
Starvation, prolonged exercise, stress
What are the two hormones that effect gluconeogenesis?
Glucagon, cortisol
Insulin
Describe the effect of insulin on gluconeogenesis
PEPCK and F16BP decreases
Inhibits
Describe the effect of glucagon and cortisol on gluconeogenesis
PEPCK and F16BP increases
Stimulated
What is the three step timeline of glucose utilisation?
Glucose consumed from food
Glycogenolysis
Gluconeogenesis
What is excess ‘energy’ stored as?
Where?
Triacylglycerol
Adipose tissue
Why is triacylglycerol stored in adipose tissue?
Hydrophobic
So stored in anhydrous form
What is the storage of triacylglycerols controlled by?
When are they mobilised?
Hormone
Prolonged excercise, starvation, pregnancy
What is a key feature of adipocytes?
Organelles pushed to the edge
Where does fatty acid oxidation not occur?
Cells lacking mitochondria
Brain - do not pass blood brain barrier
What is the process of fatty acid synthesis?
Where does it occur?
Lipogenesis
Liver
What are the 5 steps of lipogenesis?
- Glycolysis - glucose to pyruvate
- Pyruvate enters mitochondria and forms acteylCoA and oxaloacetate
- AcetylCoA and oxaloacetate condense to form citrate
- Citrate enters cytoplasm and is broken into oxaloacetate and acetylCoA
- AcetylCoA is converted to malonly CoA by AcetylCoA carboxylase
- Fatty acid synthase complex aids the addition of 2C units provided by malonylCoA
What two things does lipogenesis require?
ATP
NADPH
What is the key regulatory enzyme in liver lipogenesis?
What hormones control it?
AcetylCoA carboxylase
Insulin + citrate - increase
Glucagon and adrenaline + AMP - decrease
What 4 differences between fatty acid oxidation and synthesis?
O - removes C2 S - add C2
O - in mitochondria S - in cytoplasm
O - insulin inhibits S - insulin stimulates
O - oxidative (produces NADH, FAD2H) S - reductive (requires NADPH)
What is the process of triacylglycerols being broken down?
Into what?
Lipolysis
Glycerol
Fatty acids
What happens to glycerol during lipolysis?
Travels to liver
Source of C for gluconeogenesis
What happens to fatty acids during lipolysis?
Travels complexed with albumin
To muscle and tissues
For B oxidation
