Energy Storage - Glycogen And Fat Flashcards
What tissues have an absolute requirement for glucose as an energy source ?
1) red blood cells
2) neutrophils
3) inner most kidney medulla
4) lens of the eye
What is the normal concentration of plasma glucose ?
5mM
Can the brain utilise ketone bodies during extreme periods of stress ?
Yes
When blood plasma levels of glucose drops below 0.6mmol/L what are the consequences ?
Brain damage or death . This is because the blood brain barrier utilises GLUT1 transporter for the transport of glucose. The GLUT1 transporter has a km of 0.6 so if it drops below that level , can no longer transport glucose to the brain
What occurs when the blood glucose levels drops below 2.8mm/L ?
Confusion
What occurs when the blood glucose levels drops below 1.7mm/L ?
Weakness , nausea
What occurs when the blood glucose levels drops below 1.1 mm/L?
Muscle cramps
How is glycogen stored ?
As granules in skeletal muscle and the liver
Roughly how many grams of glycogen is stored in skeletal muscle ?
300 g
Roughly how many grams of g,glycogen is stored in the liver ?
100 g
Describe the structure of glycogen
- polymer consisting of chains of glucose residues
- chains are organised like branches originating from a dimer of the protein glycogenin
- glucose residues are linked by 1,4 and 1,6 glycosidic bonds forming branch points at every 8-10 residues
How is the structure of glycogen related to its function ?
1) branches which allows enzymes to react at many points , this increased the speed at which energy is released.
2) glycogen is insoluble so it does not have no osmotic effect on other cells
3) it is a compact molecule so can store a lot of energy in a small space
Define glycogenesis
Glycogen synthesis from glucose
Does the synthesis of glycogen require energy?
Yes
Outline the steps of glycogenesis
1) glucose is converted into glucose-6-phosphate by hexokinase. This in turn converts ATP into ADP.
2) glucose 6 phosphate is converted into glucose 1-phosphate by phosphoglucomutase.
3) glucose 1 phosphate is then converted into UDP-glucose by G1P uridylytransferase. Glucose -1-phosphate + UDP + H20 = UDP glucose + 2PPi
4) glycogen ( n residues ) is combined with UDP glucose which adds additional glucose residues to the chain. This releases UDP. Glycogen synthase is used to make the 1,4 bonds and branching enzyme is used to make 1,6 bonds
Define glycogenolysis
Pbreakdown of glycogen
Outline the steps of glycogenolysis
1) Gkycogen(n residues) +Pi = glucose 1 phosphate +glycogen (n-1 residues). This is with the aid of glycogen phosphorylase or Debranching enzyme.
2) glucose -1- phosphate is converted into glucose -6-phosphate by phosphoglucomutase.
3) glucose 6-phosphate is then used by muscle for energy production , but released by liver into blood for other tissues.
What occurs to glucose-6 - phosphate in the liver ?
Glucose 6 phosphate is converted back into glucose by glucose -6-phosphatase.
- the glucose is then expected to blood.
What occurs to glucose 6 phosphate in the muscle ?
Glucose 6phpshaye will enter glycolysis in the muscle and produce energy. REMAINS IN THE MUSCLE
What energy store of glycogen is used as a buffer for blood glucose levels ?
Glycogen storage in the liver
How comes the g,Yvonne in muscle is only used for muscle cells and not for other tissues around the body ?
Because muscle does not contain the enzyme glucose -6- phosphatase to convert glucose -6-phosphate into glucose. So it remains trapped in the muscle cells.
Under what regulation is liver glycogen metabolism under?
Hormonal regulation
What are the two rate limiting enzymes in glycogen metabolism ?
1) glycogen synthase ( glycogen synthesis )
2) glycogen phosphorylase ( glycogen degradation)
If glucagon and adrenaline is produced , wat are the effects of glycogen synthase and glycogen phosphorylase ?
- glycogen synthase activity would decrease , whereas glycogen phosphorylase activity would increase
If insulin is produced , what are the effects of glycogen synthase and glycogen phosphorylase ?
Glycogen synthase activity would increase , whereas glycogen phosphorylase activity would decrease
Do glucagon levels have an effect on muscle glycogen ?
No
Give an example of an allosteric activator of muscle glycogen phosphorylase ?
AMP ( low energy signal ) which mobilises glycogen to produce more glucose
McArdle disease
Muscle glycogen phosphorylase deficiency
Vin Gierke’s disease
Glucose-6-phosphatase deficiency in liver
When would gluconeogensis s occur ?
Beyond 6 Horus of fasting because liver glycogen stores have started to deplete and an alternative source of glucose is required
Define gluconeogenesis
Production of new glucose
Where does gluconeogensis occur ?
In the liver and to lesser extent in kidney cortex
What are the three major precursors for glucose ?
1) amino acids ( mainly alanine)
2) glycerol ( released from adipose tissue from breakdown of TAGS)
3) lactate ( from anaerobic glucoses In exercising muscle and RBC)
What is the cori cycle
Metabolic pathway in which lactate Produced in the muscles is moved to the liver , and converted into glucose. Glucose then moves into the muscle and is converted back into lactate again during anaerobic respiration.
What are the three key enzymes in gluconeogensis?
1) PEPCK ( phosphoenolpyruvate carboxykinase) ( important 1)
2) fructose 1,6 -bisphosphate ( important 1)
3) glucose 6 phosphate
What is the role of PEPCK?
Converts oxaloacetate into phosphoenolooyruvate
What is the role of fructose 1,6 bisphosphate?
Converts fructose 1,6 bisphosphate into fructose 6 phosphate
When glucagon and cortisol levels are high , what are the effects on PEPCK and fructose 1,6 bisphosphate?
Increased activity of PEPCK and fructose 1,6 bisphosphate because more glucose is required.
What are the effects of insulin levels being high ?
PEPCK and fructose 1,6 bisphosphate activity would decrease because less glucose is required in the blood so gluconeogenesis is inhibited
What comes first : glycogenolysis or gluconeogensis?
Glycogenolysis occurs first , the. Gluconeogensis
When are TAGS used ?
During extreme periods of stress , eg pregnancy, starvation and prolonged exercise
Where are TAGSstored ?
Adipose tissue
Describe the structure of white adipocytes ?
They have a large lipid droplet at the centre of the cell. Nucleus and cytoplasm is squeezed to one side of the cell.
What occurs to adipocytes in obese people ?
Adipocytes increase in size about four fold on weight gain. Then they divide and increase in total number of fat cells
Why when obese lose weight , they can easily put on weight after ?
Because they still have the same number of adipocytes, just many empty adipocytes without fat.
Define lipogenesis
Fatty acid synthesis
Where does fatty acid synthesis occur ?
In liver
Does fatty acid synthesis require ATP and NADPH ?
Yes
Outline the process of fatty acid synthesis
1) glucose in the cytoplasm is converted into Pyruvate . This is called glycolysis.
2) Pyruvate then Enters the mitochondria and forms acetyl co A and oxaloacetate. These combine to form citrate.
3 ) citrate enters the cytoplasm and is cleaved back into acetyl-coA and OAA.
4) acetyl coA (2C) is then converted into malonyl coA (3C) by Acetyl coA carboxylase. ATP converted into ADP. And then co2 is removed.
5) then fatty acid synthase complex builds fatty acids by sequential addition of 2 carbon units provided by malonyl coA.
Why can’t the acetyl coA produced in the mitochondria simply be used directly to make fatty acids ?
Use there is no transporter in the mitochondria to take acetyl Co A in the mitochondria into the cytoplasm
What is the key regulatory enzyme in lipogenesis ?
Acetyl-coA carboxylase
Outline a few differences between fatty acid synthesis and fatty acid oxidation
Fatty acid synthesis occurs in the cytoplasm , whereas fatty acid oxidation occurs in mitochondria
2) fatty acid oxidation produces NADH and FADH2 ( oxidative ) , whereas fatty acid synthesis requires NADPH.( reductive)
3) fatty acid oxidation produces acetyl coA , whereas fatty acid synthesis consumes acetyl co A
4) fatty acid oxidation removes 2C whereas fatty acid synthesis add 2C
5) insulin inhibits fatty acid oxidation , whereas insulin stimulates fatty acid synthesis
What is hormone sensitive lipase ?
An amphiphillic enzyme in adipose tissue which determines the rate of hydrolysis of stored TAGs and thereby produces fatty acids and releases them into circulation
What hormone would activate hormone sensitive lipase ?
Glucagon and adrenaline - which leads to activation of HSL and phosphorylation
What hormone would inhibit hormone sensitive lipase ?
Insulin - which leads to de-phosphorylation and inhibition of HSL
In a 70kg man , what is the energy content of TAGS?
600,000KJ
In a 135kg obese man , what is the nerdy content ?
3,000,000 KJ
