Metabolic Stores COPY Flashcards

1
Q

Where is glucose mainly stored as glycogen ?

A

In liver and muscle

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2
Q

How much moderate exercise does the glycogen supply in the liver and muscle allow for ?

A

3-5 hours

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3
Q

How is glycogen broken down and used as fuel ? Does any of the processed used to break it down use ATP ?

A

Most (90%) Wis converted directly to glucose-6-P without consuming ATP
This is only possible if the glucose-6-P is to be in the cell in which it is formed (NO ATP, phosphorylation process)
If glucose is required elsewhere in the body, glycogen converted to glucose (through hydrolysis), and then it is phosphorylated when it has been transported to its destination (x1 ATP used)

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4
Q

What are the major form in which fuel is stored ?

A

Lipids

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5
Q

How much more energy can lipids produce relative to glycogen, weight-for weight ?

A

Triglycerides* (= triacylglycerols*) can produce about six times as much energy as glycogen

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6
Q

Which reaction produces esters ?

A

Alcohol with an organic acid

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7
Q

What is the difference between a diacyl glycerol and a triacyl glyerol ?

A

One of the alcohol groups of glycerol is not esterified

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8
Q

Describe the process of lipolysis, and state where each step occurs. Which step(s) are responsible for ATP production ?

A
  1. Lipase digests triglycerides into glycerol and 3 FAs

CYTOSOL:

  1. FAs combined with CoA, becoming fatty acyl CoA
  2. Transporter takes fatty acyl coA into mitochondria
  3. Glycerol becomes a glycolysis substrate, forming pyruvate

MITOCHONDRIA

  1. Beta oxidation chops 2-carbon acyl units off the FAs
  2. Acyl units become acetyl coA and can be used in the citric acid cycle (along with the pyruvate formed from glycerol)

Electrons removed during fatty acid oxidation are passed along the respiratory chain, so indirectly producing ATP

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9
Q

Where are the fatty acids and glycerol released by adipose tissue mainly metabolized ?

A

In the liver

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10
Q

When do ketone bodies form ?

A

Under conditions when other fuels are not available, breakdown of fatty acids leads to the formation of ketone bodies (STARVATION)

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11
Q

What are the main ketone bodies ?

A

Acetoacetate, 3-hydroxybutyrate and acetone

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12
Q

Why are ketone bodies produced when other fuels are not available (starvation) ?

A

Because acetyl-CoA formed in the breakdown of fatty acids cannot enter the citric acid cycle since oxaloacetate becomes depleted because the liver converts it to pyruvate to produce glucose (gluconeogenesis).
As a result, Acetyl CoA is converted to ketone bodies

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13
Q

What is the distinctive smell of ketone bodies ? You could smell it in the breath of which type of person ?

A

Fruity

Someone fasting

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14
Q

What are the different ways in which proteins broken down and stored or used as fuel ?

A
  • Dietary proteins broken down into AAs
  • Either incorporated into new proteins, converted to carbohydrates (storage) or used as metabolic fuel (used)
  • If used, then: some deaminated, yielding NH4 + a keto acid (intermediates of the glycolytic pathway or of the citric acid cycle)
  • Others cannot be deaminated so pass their amino group to a keto acid (mainly α-ketoglutarate) = TRANSAMINATION. Resulting keto acid fed into glycolysis or citric acid cycle (as pyruvate, acetyl-CoA, α-ketoglutarate or oxaloacetate), while resulting AA deaminated and used similarly
  • NH4+ formed (through direct deamination or transamination followed by deamination) v toxic so rapidly converted to urea (less toxic, passed through the blood to the kidney, then excreted in urine)
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15
Q

What is anabolism ?

A

Synthesis of more complex molecules (requires ATP)

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16
Q

What is gluconogenesis ?

A

Formation of glucose from non-carbohydrate sources

17
Q

Are gluconogenesis and glycolysis the same but in reverse ?

A

No, similar to glycolysis in reverse, but some enzymes different

18
Q

Where does the bulk of gluconogenesis occur ?

A

In the liver

19
Q

What examples of molecules can be fed into gluconogenesis ?

A

Glycerol (from triglycerides) and the carbon backbone of amino acids can fed into this pathway

20
Q

Briefly identify the main steps in lipid synthesis.

A

1 .Glycerol made from glucose through glycolysis

  1. 2-C acyl units from Acetyl CoA linked together by FA synthase to form FAs
  2. One glycerol + 3 FAs = 1 triglyceride
21
Q

Where are FAs incorporated into triglycerides ?

A

In adipose tissue

22
Q

Where is the bulk of triglycerides stored ? Where else is it stored ?

A

In adipose tissue

In liver and muscles

23
Q

Why is it that our energy production cannot be as high when we are using lipids as fuel rather than carbohydrate ?

A

Because fats are not used as effectively as fuel as carbohydrate.

24
Q

How are the AA not in the diet formed ?

A

Made by transferring amino groups to keto acids

25
Q

What is the largest source of protein that can be broken down for fuel in times of need ?

A

Muscle

26
Q

Explain the metabolic characteristics of brain (sources of energy).

A
  • Normally: Uses only glucose. CANNOT store glucose or glycogen so requires constant supply in blood. Also cannot convert glucose-6-P to to glucose, so cannot export glucose.
  • STARVATION: May use ketone bodies (mainly acetoacetate and 3-hydroxybutyrate) formed in other tissues
27
Q

How much of the body consumption of glucose does the brain account for ? How many g of glucose is that per day ?

A

60%

120 g per day

28
Q

Why can’t the brain use FAs as fuel ?

A

Because of BBB, protecting the brain from other potentially dangerous chemicals

29
Q

Explain the metabolic characteristics of skeletal muscle (sources of energy).

A
  • Can use glucose, FAs, ketone bodies
  • Resting state: Mainly uses FAs but can also use glucose (has glycogen reserves so converts glycogen to glucose-6-P, cannot convert this to glucose, so cannot export glucose)
  • Active state: rate of glycolysis&raquo_space; citric acid cycle, so pyruvate must be converted to lactate. Lactate then passes into the blood and to the liver, where it is converted back to glucose
30
Q

How much of body glycogen is stored in muscle ?

A

3⁄4 of body glycogen

31
Q

How does the liver takes some of the metabolic burden away from muscle ?

A
  • Under conditions when muscle protein is being broken down, many amino acids pass their amino group to pyruvate (transamination) to form alanine. Alanine enters the blood and in the liver can be converted to back to pyruvate, which is used to synthesize glucose
  • Pyruvate also converted to lactate which passes into the blood and to the liver, where it is converted back to Pyruvate then into glucose.
32
Q

What are fat cells called ? What is the main function of these cells ?

A

Adipocytes

Synthesize and store triglycerides (=triacylglycerols) and release fatty acids and glycerol in times of need

33
Q

Which factor determines the rate at which fatty acids are esterified ?
Which factor influences the activity of the lipase that hydrolyses triglycerides into FAs and glycerol ?

A

Availability of glucose

Hormones (the lipase is hormone-sensitive)

34
Q

Explain the metabolic characteristics of the liver.

A

-Normal: Can readily store and release GLUCOSE and can make new GLUCOSE (gluconeogenesis) from LACTATE, ALANINE and GLYCEROL in the diet or released by other tissues
When available, synthesizes FAs, esterifies them and then secretes them into the blood as very low density lipoprotein (VLDL)

-Fasting: liver generates ketone bodies for use in other tissues

35
Q

Which attribute of the liver ensures that the liver has ready access to nutrients absorbed by the gut ?

A

Hepatic Portal System

36
Q

How are tryglcerides mobilised and utilised when body is in fasting state ?

A

Acetyl-CoA formed in the breakdown of fatty acids cannot enter the citric acid cycle since oxaloacetate becomes depleted because the liver converts it to pyruvate to produce glucose (gluconeogenesis).
As a result, Acetyl CoA (produced as a result of lipolysis) is converted to ketone bodies (instead of going through citric acid cycle, because it cannot do the latter).