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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
What happens to the regulating enzymes in glycogen metabolism when they are dephosphorylated? What is the result of this?
- Glycogen synthase is activated - Glycogen phosphorylase is inhibited - Glycogen synthesis occurs
25
What controls the covalent modification of the regulating enzymes of glycogen metabolism?
-Changes in hormone levels in the blood
26
Which hormones cause phosphorylation of the regulating enzymes of glycogen metabolism, thus promoting glycogenolysis?
- Glucagon | - Adrenaline
27
Which hormone causes dephosphorylation of the regulating enzymes of glycogen metabolism, and thus stimulates glycogen synthesis?
-Insulin
28
What causes a rise in insulin levels and why would glycogen synthesis become activated?
- High glucose | - Glycogen synthesis activated in order to reduce blood sugar levels and store the exracellular glucose as glycogen
29
What causes glycogen storage diseases?
-Inherited disorders of various enzymes involved in glycogen metabolism whose severity is dependant on the enzymes and tissues effected
30
What is an example of excessive glycogen storage disease and what enzyme in involved?
- Von Gierke's | - Glucose-6-Phosphatase -> glucose6p cannot be converted to free glucose so is stored as glycogen
31
What are the symptoms of decreased glycogen storage?
- Poor tolerance to exercise | - Fasting hypoglycaemia
32
What is gluconeogenesis?
-The synthesis of glucose from a non-carbohydrate source
33
What are substrates of gluconeogenesis?
- Glycerol - Glucogenic a'a - Lactate - fructose - Galactose
34
Why is gluconoegenesis important?
-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
Where does gluconeogenesis occur?
-Primarily liver but can occur in kidney cortex
36
What are the two important enzymes in gluconeogeesis?
- Fructose-1-6-Bisphosphatase | - PEPCK
37
Can acetylcoA be used in gluconeogenesis?
-No, Pyruvate Dehydrogenase is irreversible
38
Is glycolysis the reverse of gluconeogenesis?
-Nearly, the three irreversible steps are bypassed
39
How is step 1 of glycolysis (step 10 in gluconeogenesis) bypassed?
-Glucose-6-P -> Glucose via Glucose-6-Phosphatase
40
How is step 3 of glycolysis (step 7 in gluconeogenesis) bypassed?
-Fructose-1-6-Bisphosphate->Fructose-6-Phosphate by Fructose-1-6-bisphosphatase
41
What enzymes are involved in bypassing step 10 of glycolysis(step 1 in gluconeogenesis)?
- Pyruvate carboxylase | - PEPCK
42
What is required for step 1 in gluconeogenesis?
- Oxaloacetate - ATP - GTP - PEPCK - Pyruvate carboxylase
43
When is gluconeogenesis activated?
-In response to stress such as fasting or prolonged exercise
44
What type of regulation controls gluconeogenesis?
-Hormonal control
45
What are the two main control sites of gluconeogenesis?
- Fructose-1-6-Bisphosphatase | - PEPCK
46
Which hormones activate PEPCK and F16BP?
- Glucagon activates both | - Cortisol activates PEPCK
47
What effect does insulin have on gluconeogenesis?
-Inhibits gluconeogenesis by decreasing the activity of PEPCK and F16BP
48
How is gluconeogenesis linked to diabetes?
- In diabetes there is a reduction in insulin - The reduction in insulin means that gluconeogenesis is not inhibited - This contributes to hyperglycaemia
49
What makes triacylglycerols efficient storage molecules?
- Stored in bulk - Anhydrous - High energy content - Can be used during exercise/stress/pregnancy - Under hormonal control
50
What is lipogenesis?
-The synthesis of TAGs
51
Where does lipogenesis occur?
-In the cytoplasm of hepatocytes (liver)
52
How are dietary TAGs stored?
- Hydrolysis in small intestine by pancreatic lipase - Transported across membranes as FA and glycerol - Recombined and transported in chylomicrons to adipose tissue
53
What is the substrate for lipogenesis?
-Acetyl CoA
54
Is lipogenesis oxidative/reductive and exogonic/endergonic?
- Reductive (uses NADPH) | - Endergonic (requires ATP)
55
How is acetylcoA shuttled from the mitochondrial matrix to the cytoplasm?
-Combined with oxaloacetate to make citrate which can cross the membrane and then reversed back to acetyl coA and oxaloacetate
56
What happens to AcetylcoA to synthesise TAG?
- AcetylCoA->MalonylCoA via Acetyl carboxylase | - MalonylCoA added to FA chain, growth in a C2 stepwise fashion
57
What is linked to FA in the cytoplasm?
-acyl carrier protein as FA is lipid soluble
58
By what enzyme is lipogenesis controlled and through what mechanisms?
- Acetyl carboxylase - Allosteric inhibition by AMP and citrate - Covalent modification
59
What covalent modification of acetyl carboxylase activates it?
-dephosphorylation
60
What covalent modification inhibits acetyl carboxylase?
-phosphorylation
61
What hormones control acetyl carboxylase and in what manner?
- Glucagon/adrenaline inhibits acetyl carboxylase | - Insulin activates acetyl carboxylase
62
What enzyme is a control site of lipolysis?
-Hormone-sensitive lipase
63
Which hormones activate and inhibit lipase in lipolysis?
- Glucagon/adrenaline activate lipolysis | - Insulin inhibits lipolysis

Metabolism (14 decks)

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