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Metabolism > Energy Storage > Flashcards

Energy Storage Flashcards

0
Q

For how many hours do glycogen stores last?

A

-8-12 hrs

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1
Q

What is glycogen and why is it needed?

A
  • A storage form of glucose

- For those tissues which need a continual supply of glucose

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2
Q

What results from abnormal storage of glucose? (umberalla term)

A

-Glycogen storage diseases

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3
Q

What is the structure of glycogen?

A
  • Highly branched polymer of glucose
  • a1-4 and a1-6 glycosidic links
  • Large
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4
Q

What is the benefit of glycogen being a large molecule and what limits its size?

A
  • Large which means it can be stored with minimal osmotic effects
  • It size is limited as it is a very polar molecule so it will attract water
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5
Q

Where is glycogen stored?

A

-As granules in skeletal muscle and liver

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6
Q

What is the benefit of glycogen being highly branched?

A

-Rapid synthesis and degredation

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7
Q

What 4 enzymes are used in glycogen synthesis?

A
  • Hexokinae
  • Phosphoglucomutase
  • Glycogen synthase
  • Branching enzyme
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8
Q

What is the difference between glycogen synthase and branching enzyme?

A
  • Glycogen synthase adds glucose by a1-4 links

- Branching enzyme adds glucose by a1-6 links

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9
Q

What 2 high energy of phosphorylation molecules are used in glycogen synthesis?

A
  • 1ATP

- 1UTP

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10
Q

What is the function of phosphoglucomutase?

A

-To rearrange phosphate molecules on glucose

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11
Q

Which step is the same in glycogen synthesis and glycolysis?

A
  • Step 1

- Glucose->Glucose-6-P by hexokinase with a molecule of ATP

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12
Q

What is the name for glycogen degradation?

A

-Glycogenolysis

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13
Q

What are the steps of glycogenolysis?

A
  • Glycogen->Glucose-1-P
  • Glucose-1-P -> Glucose-6-P
  • Glucose-6-P -> Glucose
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14
Q

What 3 enzymes are involved in glycogenolysis?

A
  • Glycogen phosphorylase
  • Debranching enzyme
  • Phosphoglucomutase
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15
Q

What is the difference between glycogen phosphorylase and debranching enzyme?

A
  • Glycogen phospharylase degrade glycosidic a1-4 links and produces G-1-P
  • Debranching enzyme degrades glycosidic a1-6 links and produces free glucose
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16
Q

Is glycogen completely degraded?

A

-No, small primer is always reserved

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17
Q

Describe glycogenolysis in skeletal muscle

A
  • Degraded in response to exercise
  • Stops at G-6-P and enters glycolysis
  • Can only be used by the muscle
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18
Q

Describe glycogenolysis in the liver

A
  • Degraded in response to fasting/stress
  • Commits to making free glucose which is released into tissues
  • Can be used as a source of glucose in all tissues
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19
Q

By which enzymes is glycogen metabolism regulated?

A
  • Glycogen synthase

- Glycogen phosphorylase

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20
Q

Under what mechanisms of control are the regulating enzymes of glycogen metabolism?

A
  • Allosteric activation

- Covalent modifiction

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21
Q

What is an allosteric activator of glycogen phosphorylase?

A

-AMP

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22
Q

What is meant by the enzymes of glycogen metabolism being under reciprocal control?

A

-The mechanism of activation of one enzyme is the mechanism of inhibition of the other

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23
Q

What happens when both regulating enzymes in glycogen metabolism are phosphorylated? What is the result of this?

A
  • Glycogen synthase is inhibited
  • Glycogen phosphorylase is activated
  • Glycogenolysis occurs
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24
Q

What happens to the regulating enzymes in glycogen metabolism when they are dephosphorylated? What is the result of this?

A
  • Glycogen synthase is activated
  • Glycogen phosphorylase is inhibited
  • Glycogen synthesis occurs
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25
Q

What controls the covalent modification of the regulating enzymes of glycogen metabolism?

A

-Changes in hormone levels in the blood

26
Q

Which hormones cause phosphorylation of the regulating enzymes of glycogen metabolism, thus promoting glycogenolysis?

A
  • Glucagon

- Adrenaline

27
Q

Which hormone causes dephosphorylation of the regulating enzymes of glycogen metabolism, and thus stimulates glycogen synthesis?

A

-Insulin

28
Q

What causes a rise in insulin levels and why would glycogen synthesis become activated?

A
  • High glucose

- Glycogen synthesis activated in order to reduce blood sugar levels and store the exracellular glucose as glycogen

29
Q

What causes glycogen storage diseases?

A

-Inherited disorders of various enzymes involved in glycogen metabolism whose severity is dependant on the enzymes and tissues effected

30
Q

What is an example of excessive glycogen storage disease and what enzyme in involved?

A
  • Von Gierke’s

- Glucose-6-Phosphatase -> glucose6p cannot be converted to free glucose so is stored as glycogen

31
Q

What are the symptoms of decreased glycogen storage?

A
  • Poor tolerance to exercise

- Fasting hypoglycaemia

32
Q

What is gluconeogenesis?

A

-The synthesis of glucose from a non-carbohydrate source

33
Q

What are substrates of gluconeogenesis?

A
  • Glycerol
  • Glucogenic a’a
  • Lactate
  • fructose
  • Galactose
34
Q

Why is gluconoegenesis important?

A

-Specific tissues (kidney medulla, lens of the eye, RBCs, CNS) need a constant supply of glucose and glycogen stores are depleted after 8-12 hours

35
Q

Where does gluconeogenesis occur?

A

-Primarily liver but can occur in kidney cortex

36
Q

What are the two important enzymes in gluconeogeesis?

A
  • Fructose-1-6-Bisphosphatase

- PEPCK

37
Q

Can acetylcoA be used in gluconeogenesis?

A

-No, Pyruvate Dehydrogenase is irreversible

38
Q

Is glycolysis the reverse of gluconeogenesis?

A

-Nearly, the three irreversible steps are bypassed

39
Q

How is step 1 of glycolysis (step 10 in gluconeogenesis) bypassed?

A

-Glucose-6-P -> Glucose via Glucose-6-Phosphatase

40
Q

How is step 3 of glycolysis (step 7 in gluconeogenesis) bypassed?

A

-Fructose-1-6-Bisphosphate->Fructose-6-Phosphate by Fructose-1-6-bisphosphatase

41
Q

What enzymes are involved in bypassing step 10 of glycolysis(step 1 in gluconeogenesis)?

A
  • Pyruvate carboxylase

- PEPCK

42
Q

What is required for step 1 in gluconeogenesis?

A
  • Oxaloacetate
  • ATP
  • GTP
  • PEPCK
  • Pyruvate carboxylase
43
Q

When is gluconeogenesis activated?

A

-In response to stress such as fasting or prolonged exercise

44
Q

What type of regulation controls gluconeogenesis?

A

-Hormonal control

45
Q

What are the two main control sites of gluconeogenesis?

A
  • Fructose-1-6-Bisphosphatase

- PEPCK

46
Q

Which hormones activate PEPCK and F16BP?

A
  • Glucagon activates both

- Cortisol activates PEPCK

47
Q

What effect does insulin have on gluconeogenesis?

A

-Inhibits gluconeogenesis by decreasing the activity of PEPCK and F16BP

48
Q

How is gluconeogenesis linked to diabetes?

A
  • In diabetes there is a reduction in insulin
  • The reduction in insulin means that gluconeogenesis is not inhibited
  • This contributes to hyperglycaemia
49
Q

What makes triacylglycerols efficient storage molecules?

A
  • Stored in bulk
  • Anhydrous
  • High energy content
  • Can be used during exercise/stress/pregnancy
  • Under hormonal control
50
Q

What is lipogenesis?

A

-The synthesis of TAGs

51
Q

Where does lipogenesis occur?

A

-In the cytoplasm of hepatocytes (liver)

52
Q

How are dietary TAGs stored?

A
  • Hydrolysis in small intestine by pancreatic lipase
  • Transported across membranes as FA and glycerol
  • Recombined and transported in chylomicrons to adipose tissue
53
Q

What is the substrate for lipogenesis?

A

-Acetyl CoA

54
Q

Is lipogenesis oxidative/reductive and exogonic/endergonic?

A
  • Reductive (uses NADPH)

- Endergonic (requires ATP)

55
Q

How is acetylcoA shuttled from the mitochondrial matrix to the cytoplasm?

A

-Combined with oxaloacetate to make citrate which can cross the membrane and then reversed back to acetyl coA and oxaloacetate

56
Q

What happens to AcetylcoA to synthesise TAG?

A
  • AcetylCoA->MalonylCoA via Acetyl carboxylase

- MalonylCoA added to FA chain, growth in a C2 stepwise fashion

57
Q

What is linked to FA in the cytoplasm?

A

-acyl carrier protein as FA is lipid soluble

58
Q

By what enzyme is lipogenesis controlled and through what mechanisms?

A
  • Acetyl carboxylase
  • Allosteric inhibition by AMP and citrate
  • Covalent modification
59
Q

What covalent modification of acetyl carboxylase activates it?

A

-dephosphorylation

60
Q

What covalent modification inhibits acetyl carboxylase?

A

-phosphorylation

61
Q

What hormones control acetyl carboxylase and in what manner?

A
  • Glucagon/adrenaline inhibits acetyl carboxylase

- Insulin activates acetyl carboxylase

62
Q

What enzyme is a control site of lipolysis?

A

-Hormone-sensitive lipase

63
Q

Which hormones activate and inhibit lipase in lipolysis?

A
  • Glucagon/adrenaline activate lipolysis

- Insulin inhibits lipolysis

Metabolism (14 decks)

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