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Metabolism > Session 4: Energy Storage - Carbohydrates & Lipids > Flashcards

Session 4: Energy Storage - Carbohydrates & Lipids Flashcards

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1
Q

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

A

Erythrocytes and leukocytes, Testes, Kidney medulla, Lens and cornea of the eye

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2
Q

Stable blood glucose levels are absolutely essential for normal ____ function

A

brain function

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3
Q

What is the most severe outcome of SEVERE hypoglycaemia (~0.6mmol/L)?

A

Brain damage, death

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4
Q

How is glucose granules stored in the liver and muscle?

A

Glycogen

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5
Q

Describe the structure of glycogen

A
  • Polymer of glucose (polysaccharide)
  • Highly branched originating from dimer glycogenin
  • Chains linked by α-1-4 glycosidic bonds
  • Branch points = α-1-6 glycosidic bonds
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6
Q

What types of bonds can be found in glycogen?

A

The α-1-6 glycosidic bonds = form branching points
The α-1-4 glycosidic bonds = join the chains

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7
Q

What is glycogenin?

A

Glycogenin is a core protein that glycogen uses as its core and starting synthesis point.

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8
Q

What is glycogenesis and where does it occur?

A

The conversion of glucose to the storage form of glycogen

It occurs in the muscle and liver

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9
Q

What is the first reaction in glycogenesis?

A

Glucose converted to glucose-6-phosphate
Catalysed by hexokinase (most cells) or glucokinase (in liver)

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10
Q

What is the second reaction in glycogenesis?

A

Glucose-6-phosphate is converted to glucose-1-phosphate
Catalysed by phosphoglucomutase

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11
Q

Different enzymes allow for catalysis of glycogen in glycogenolysis - what are these enzymes?

A

Glycogen phosphorylase = alpha-1-4 glycosidic bonds
De-branching enzyme = alpha-1-6 glycosidic bonds

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12
Q

What is the third reaction in glycogenesis?

A

Glucose-1-phosphate is converted to UDP-glucose
Catalysed by uridyl transferase

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13
Q

What is the fourth and final step in glycogenesis?

A

Glycogen (n residues) + UDP-glucose produces = glycogen (n+1 residues) + UDP

Two enzymes are involved…
Glycogen synthase = formation of α-1-4 glycosidic bonds
Branching enzyme = formation of α-1-6 glycosidic bonds

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14
Q

What enzyme catalyses the conversion of glucose-1-phosphate to glucose-6-phosphate in glycogenolysis?

A

Phosphoglucomutase

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15
Q

Why can’t glucose-6-phosphate from glycogenolysis be broken down into free glucose in the muscle?

A

The muscle lacks the glucose-6-phosphatase enzymes - so the glucose-6-phosphate must enter glycolysis to produce ATP

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16
Q

What are the rate-limiting enzymes in glycogen synthesis (glycogenesis)?

A

Glycogen synthase

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17
Q

What are the rate-limiting enzymes in glycogen degradation (glycogenolysis)?

A

Glycogen phosphorylase

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18
Q

Hormones that regulate glycogen metabolism

A

Glucagon, adrenaline, insulin

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19
Q

Major precursors of gluconeogenesis

A

1) Lactate = cori cycle via **lactate dehydrogenase **
2) Glycerol
3) Pyruvate
4) Glucogenic amino acids = alanine
5) Galactose
6) Fructose

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20
Q

Triacylglycerols are hydrophobic and therefore stored in an anhydrous form in specialised tissue known as _______.

A

white adipose tissue.

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21
Q

In what organ does fatty acid synthesis mainly occur?

A

liver

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22
Q

Glucose is stored in the body as…

A

Glycogen

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23
Q

Name two processes which lead to increased availability of glucose in the body

A
  1. Glycogenolysis
  2. Gluconeogenesis
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24
Q

Glycogen synthesis requires energy in a form of…

A

UTP and ATP

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25
What are two enzymes with key regulatory roles in gluconeogenesis?
* Fructose 1,6-bisphosphatase * Phosphoenolpyruvate carboxykinase (PEPCK)
26
Name the important enzyme in glycogen metabolism which catalyses this reversible reaction... Glucose 1-phosphate ⇔ Glucose-6-phosphate
Phosphoglucomutase
27
Name two rate-limiting enzymes which play key role in glycogen metabolism
Glycogen synthase Glycogen phosphorylase
28
Glycogen is stored in granules in myocytes and hepatocytes. There are more granules in the liver but muscles stores more glycogen molecules. True or false?
True
29
Glucose obtained from glycogenolysis is processed differently in liver and muscle because cells of one of these tissues do not have this enzyme...
Muscle does not have glucose-6-phosphatase
30
Glycerol is hydrophobic and fatty acid is hydrophilic. True or false?
False
31
Precursors for gluconeogenesis
Lactate Glucogenic amino acids (mainly alanine) Glycerol Galactose and Fructose
32
Insulin inhibits gluconeogenesis through inhibition of the amount and/or activity of PEPCK and fructose 1,6-bisphosphatase. True or false?
True
33
Name enzyme playing important role in the regulation of the fatty acid synthesis
Acetyl-CoA carboxylase
34
The lipid which may accumulate in the liver is...
Triglyceride
35
Fatty acids travel complexed with ___ to muscle and other tissues
albumin
36
What are the names of the hormones which influence hormone-sensitive lipase (HSL) and adipose triacylglycerol lipase (ATGL)?
Hormones that ACTIVATE HSL and ATGL (lipolysis) - Glucagon - Adrenaline Hormones which INHIBIT HSL and ATGL (lipolysis) Insulin = INHIBITS HSL and ATGL
37
Where does fatty acid synthesis occur?
Liver
38
Name of the process where fatty acids are catabolised?
Beta-oxidation
39
Triacylglycerols are hydrophobic and are stored in their anhydrous form in specialised tissues known as ____ tissue
white adipose tissue
40
What are the major precursors of gluconeogenesis?
Lactate Glycerol Pyruvate Glucogenic amino acids such as alanine Galactose Fructose
41
Give an example of a disorder which arises from excess glycogen storage (excess glycogenesis)
Von Gierke disease ## Footnote Glucose-6-phosphatase deficiency in liver
42
Give an example of a disorder which arises from insufficient glycogen degradation
McArdle disease ## Footnote Glycogen phosphorylase enzyme deficiency in muscle
43
What are the 'rate-limiting' enzymes involved in glycogen metabolism?
Glycogen synthesis = glycogen synthase ## Footnote Glycogen degradation = glycogen phosphorylase
44
Which enzyme is lacking in muscle that leads to substrate entering into glycolysis as free glucose is not readily produced?
Glucose-6-phosphatase lacking in the muscle
45
At what blood glucose plasma level (mmol/L) does hypoglycaemia lead to brain damage and death?
0.6 mmol/L
46
Symptoms of hypoglycaemia
Confusion, weakness, nausea, muscle cramping
47
Major difference between glycogen metabolism between liver and muscle
In the liver = Glucose-6-phosphatase enzyme present In the muscle = LACK of glucose-6-phosphatase enzyme means that glucose-6-phosphate is not turned into free glucose. Instead, glucose-6-phosphate enters glycolysis to produce ATP instead
48
Compare glycogen metabolism in liver and muscle
Glucagon has ___ effect on metabolism of glycogen in the muscle ## Footnote NO
49
Name two Glycogen Storage Diseases (GSDs)
Von Gierke disease McArdle disease
50
Von Gierke Disease (GSD)
Deficiency in liver glucose-6-phosphatase enzyme
51
McArdle Disease (GSD)
**Deficiency in muscle glycogen phosphorylase** enzyme
52
When does gluconeogenesis occur?
During 8-10 hours of fasting (liver glycogen stores are depleted at this point via glycogenolysis) and more glucose is now required
53
Where does gluconeogenesis occur?
Liver and kidney cortex (cytosol)
54
What two key enzymes regulate gluconeogenesis?
Phosphoenolpyruvate carboxykinase (PEPCK) Fructose 1,6-bisphosphatase
55
In what situations does gluconeogenesis occur?
- Starvation/fasting - Prolonged exercise - Stress (fight or flight)
56
What three hormones increase activity of enzymes (below) that regulate gluconeogenesis?
- Glucagon - Cortisol - Adrenaline
57
What hormone decreases the activity of enzymes (below) that regulate gluconeogenesis?
Insulin
58
TGs is a highly ___ energy store
efficient
59
Are TGs hydrophobic or hydrophilic?
hydrophobic
60
Triglyceride utilisation occurs during...
- Exercise - Stress - Starvation - Pregnancy
61
The energy content of triglycerides per gram is ___ that of carbohydrate or proteins
twice
62
Fat mobilisation is called
Lipolysis
63
What enzymes regulate fat mobilisation (lipolysis) in adipose tissue?
Hormone Sensitive Lipase (HSL) Adipose TAG Lipase (ATGL)
64
Hormones that stimulate LIPOLYSIS enzymes HSL + ATGL by phosphorylating them?
Glucagon Adrenaline ## Footnote leads to phosphorylation and activation of HSL/ATGL
65
Hormones that inhibit LIPOLYSIS enzymes HSL + ATGL by de-phosphorylating them?
Insulin ## Footnote leads to de-phosphorylation and inhibition of HSL/ATGL
66
Free fatty acids travel complexed to ___ to muscle and other tissues where they undergo B-oxidation
albumin
67
Glycerol travels to ___ and is utilised in gluconeogenesis
liver
68
The key regulatory enzyme in fatty acid synthesis in the liver
Acetyl-CoA carboxylase
69
Insulin and ___ increase the activity of Acetyl-CoA carboxylase (fatty acid synthesis regulating enzyme)
Citrate
70
Glucagon and ___ and AMP decrease the activity of Acetyl-CoA carboxylase (fatty acid synthesis regulating enzyme)
Adrenaline
71
Acetyl-CoA carboxylase (key regulator) produces ___ from acetyl-CoA in fatty acid synthesis
malonyl-CoA
72
Fatty acid synthase complex builds fatty acids by the sequential addition of 2 carbon units provided by ___ in fatty acid synthesis
malonyl-CoA
73
AMPK
AMP-activated protein kinase
74
What is AMPK activated by?
AMP ## Footnote Activates catabolic pathways, inhibits anabolic pathways
75
What tissues is AMPK expressed in?
liver, skeletal muscle
76
What does AMPK do?
1. Glucose uptake & glycolysis 2. Fatty acid oxidation 3. Decreases cholesterol synthesis
77
The average adult has ~30 billion fat cells weighing ___kg
15kg
78
White adipocytes can increase in size about ___ times during weight gain before dividing and increasing total number of fat cells
four
79
What enzyme can be found in small intestine that facilitates TG metabolism?
Pancreatic lipase
80
Lipoprotein lipase
an enzyme that sits on the outside of cells and breaks apart triglycerides (lipolysis), so that their fatty acids can be removed and taken up by the cell
81
Fatty acids do not easily pass the ___ barrier
blood-brain
82
Why is more glycogen stored in the muscles rather than liver?
In muscle = - Glycogen stored both intra-cellularly and inter-cellularly

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