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4 MEH Flashcards

(80 cards)

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1
Q

Which tissues have an absolute requirement for glucose as an energy source? (4)

A
  1. Red blood cells (no mitochondria)
  2. Neutrophils
  3. Innermost cells of kidney medulla
  4. Lens of the eye
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2
Q

Arounf which value is plasma glucose maintained?

A

5 mmol/L

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3
Q

At which concentration does confusion due to hypoglycaemia appear ?

A

2.8 mmol/L

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4
Q

At which concentration of plasma glucose does brain damage and potentially death occur?

A

0.6 mmol/L

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5
Q

to enable blood glucose to be kept at required levels, a store of glucose is required, this is called?

A

glycogen

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6
Q

Which form (appearance) does glycogen have under electron microscopy?

A

granules

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7
Q

Which 2 organs can stock glycogen?

A
  1. Liver 100g

2. Muscle 300g

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8
Q

What is glycogen, ie what is it amde of?

A

glycogen is a stocked form of glucose, it is a polymer consisting of chains of glucose residues.

  • chains are organized like branches on a tree originating form a dimer of the protein glycogenin.
  • glucose residues linked by a-1-4 glycosidic bonds with a1-6 glycosidic bonds forming branch point every 8-10 residues
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9
Q

Which element of cellulse structure explains why we can’t break it down?

A

Cellulose has b-1-4 glycosidic bonds and we dont have the enzymes necessary for that breakdown (our glycogen is a-1-4 glycosidic bonded).

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10
Q

What is glycogen synthesis called?

A

glycogenesis

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11
Q

The first reaction of glycogenesis is the same as the first reaction of…?

A

glycolysis:
glucose + ATP => glucose 6-phosphate
BY HEXOKINASE (glucokinase in the liver)

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12
Q

Does the synthesis of glycogen require energy?

A

yes! reactions 1 and 3

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13
Q

Which enzyme is responsible for the formation of branch point bonds (a-1-6 glycosidic)?

A

Branching enzyme forms a1-6 glycosidic bonds in glycogen synthesis

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14
Q

Which enzyme is responsible for the glycosidic bonds linking glucose residues in glycogenesis?

A

glycogen synthase

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15
Q

If we need glucose released from glycogen we need enzymes to break the gylcosidic bonds.
Which enzyme breaks a-1-6 glycosidic bonds?

A

de-branching enzyme

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16
Q

Which enzyme breaks a-1-4 glycosidic bonds?

A

glycogen phosphorylase

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17
Q

Is glycogenolysis the reverse of glycogenesis?

A

No! Because not all the reactions of glycogenesis are reversible.
Different enzymes allow for simultaneous inhibition of one pathway and stimulation of another

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18
Q

What function do glycogen stores serves in the muscle?

A

Muscle glycogen is exclusively reserved for the muscle’s own energy production.

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19
Q

What function do glycogen stored in the liver serve?

A

liver glycogen will be converted into glucose and exported to the blood compartment where is will buffer blood glucose levels.

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20
Q

Why can the glycogen stores of the muscle not join the blood to be used by the body?

A

Because muscle cells dont have glucose-6-phosphatase need to convert glucose-6P into glucose.

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21
Q

Which are the 2 enzymes responsible for glycogen degradation?

A
  1. Glycogen phosphorylase

2. De-branching enzyme

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22
Q

Which is the rate limiting enzyme of glycogen synthesis?

A

glycogen synthase

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23
Q

Which is the rate limiting enzyme of glycogen degradation?

A

Glycogen phosphorylase

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24
Q

LIVER: What effect does glucagon have on glycogen synthase?

A

Inhibits by phosphorylation

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25
LIVER: What effect does glucagon have on glycogen phosphorylase?
activates by phosphorylation
26
What effect does insulin have on glycogen synthase?
Insulin stimulates glycogen synthase by dephosphorylation.
27
What effect does insulin exert on glycogen phosphorylase?
Insulin decreases glycogen phosphorylase activity by dephosphorylation.
28
Is glycogen synthase activated when dephosphorylated or phosphorylated?
Dephosphorylated
29
Is glycogen phosphorylase active when phosphorylated or dephosphorylated?
phosphorylated
30
In the MUSCLE, what effect does glucagon have on glycogen phosphorylase?
none! the msucle does not have receptors to glucagon, it would be useless as it can't release glucose into the blood stream anyway.
31
What is the allosteric activator of MUSCLE glycogen phosphorylase? (but not the lover glycogen phosphorylase)
AMP
32
Glycogen storage diseases that diminish glycogen stores can lead to ... (2)
1. Hypoglycaemia | 2. Poor exercise tolerance
33
What enzyme is deficient in von Gierke's disease?
glucose 6-phosphatase (ie, liver only)
34
Which enzyme of glycogen metabolism is deficient in McArdle disease?
muscle glycogen phosphorylase
35
What is gluconeogenesis?
the production of new glucose beyond 8 hours of fasting when glycogen stores are depleted.
36
Where does gluconeogenesis occur?
1. Liver ++ | 2. Kidney cortex
37
Which precursors can be used for gluconeogenesis? (3)
1. Lactate form anaerobic glycolysis in exercising muscle and red blood cells. 2. Glycerol released from adipose tissue breakdown of triglycrides 3. Amino acids, mainly alanine (and other glucogenic aas)
38
What is the Cori cycle?
It is the pathway for recycling lactate from anaerobic muscle activity to make glucose.
39
Is gluconeogenesis the reversal of glycolysis?
No, because some reactions of glycolysis are not reversible, the enzyme only works one way.
40
Which reactions of glycolysis are not reversable and must be bypassed in gluconeogenesis?
1, 3 and 10 of glycolysis
41
Which enzymes are rate limiting for gluconeogenesis?
They are the ones that bypass irreversible reactions of glycolysis: - PEPCK - Fructose 1,6-biphodphatase - Glucose 6-phosphatase
42
Which 2 key enzymes of gluconeogenesis are regulated by hormones?
- PEPCK | - fructose 1,6-biphosphatase
43
What action do glucagon and cortisol exert on gluconeogenesis?
Increase amount of rate limiting enzymes = stimulate gluconeogenesis
44
On which enzyme do glucagon and cortisol act to stimulate gluconeogenesis?
Glucagon and cortisol act on PEPCK and fructose 1,6-phosphatase. they increase amount of these enzymes.
45
What action does insulin exert on gluconeogenesis?
Insulin inhibits gluconeogenesis by decreasing amount of rate limiting enzymes PECK and fructose 1,6-biphosphatase
46
What sort of receptor does glucagon have?
GPCR
47
What sort of receptor does cortisol have?
Nuclear receptor
48
What sort of receptor does insulin have?
Tyrosine kinase rceptor
49
Which source of glucose is used for 2 hours post-meal?
glucose form food
50
from 1 to 10 hours after a meal, what is the source of glucose for the body?
glycogenolysis
51
8-10 hours after meal, what is the source of glucose for the body?
gluconeogenesis form lactate, amino acids and glycerol
52
How is excess energy stored in the body?
in the form of Triacylglycerols TAG
53
Which specialised tissue stocks TAGS's?
adipose
54
TAGs are hydrophobic and so stored without water, this is called
anhydrous
55
Recently, adipocytes have been discovered a function in the endocrinal system, what is it?
they secrete leptin
56
Can dietary fat be absorbed as it is into small intestine wall?
No, fat can only be absorbed under the form of fatty acids + glycerol
57
Which digestive enzyme is essential for fat absorbtion by the small intestine?
pancreatic lipase
58
What happens to TAGs in the intestinal epithelial cells?
they are packaged into chylomicrons
59
Do dietary lipids get absorbed straight into the blood stream like other nutrients?
no, they joins the lymph once packaged into chylomicrons
60
at which point will dietary lipids end up in the blood stream?
When the thoracic duct drains into the left subclavian veins.
61
The TAGs in the blood have 2 destinies, these are
1. Tissues for fatty acids oxidation to provide energy (NOT in cells lacking mitochondria or in the brain because FAs cant pass the blood-brain barrier) 2. Adipose for storage
62
TAGs of adipose tissue can be mobilised as a source of energy. What is released from the cells into the blood?
Fatty acids. | These will bind to albumin so as to be soluble in blood.
63
Which enzyme is able to mobilise the TAGs of adipose as an energy source?
Hormone sensitive lipase
64
What is hormone sensitive lipase?
Hormone sensitive liaose is the enzyme responsible for mobilising the TAG store in adipose. It breaks TAGs down and releases FAs into the blood stream.
65
What are the effects of glucagon and adrenaline on hormone sensitive lipase?
activates lipase
66
What action does insulin exert on hormone sensitive lipase?
inhibition
67
What is the main site for fatty acid synthesis?
liver
68
Which 2 substrates does lipogenesis require?
ATP | NADPH
69
For which processes is NADPH important?
1. Anabolic, lipogenesis | 2. Protection against oxidative stress, by contributing to glutathione production
70
Which enzyme is the key regulator of lipogenesis?
Acetyl-CoA carboxylase | converts acetyl-CoA into Malonyl-CoA
71
How does insulin act on acetyl-coA carboxylase (lipogenesis)
increases activity by dephosphorylation
72
How does citrate act on acetyl-CoA carboxylase (lipogenesis)?
allosterically stimulates
73
How do glucagon and adrenaline act on acetyl-CoA carboxylase?
decrease activity by phosphorylation
74
How does AMP regulate acetyl-CoA carboxylase?
allosterically inhibits
75
Where does fatty acid oxidation (b-oxydation) occur?
in the mitochondria
76
Where does fatty acid synthesis occur?
in the cytoplasm
77
Hormone sensitive lipase will degrade TAGs in adipose into fatty acids and glycerol. Where do these go now?
1. Glycerol travels to the liver in the blood and utilised as carbon source for gluconeogenesis 2. Free fatty acids travel in the blood complexed to albumin to muscle and other tissues for b-oxidation
78
Does the liver or the muscle have a bigger mass of glycogen?
The muscle does. - muscle 300g - liver 100g ... in 70kg male
79
Do a healthy 70kg man and an obese person 135kg have the same mass of glycogen?
yes
80
What type of store is increased in a 135kg obese man?
triacylglycerols!

MEH (4 decks)

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