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Molecular Biology 2 > Early Starvation > Flashcards

Early Starvation Flashcards

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1
Q

Starvation begins at the end of the ______ period. What does this mean?

A

Postabsorptive period. All the food is digested and no substances are coming in from the gut.

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2
Q

During starvation, the body becomes reliant on ____ and _____.

A

Blood and stored fuels.

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3
Q

What do we store a lot of energy as but not use as a source of energy in starvation? Why?

A

Protein. There is a limit to how much of it we can break down before we die.

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4
Q

Keep blood glucose at ____mM. Known as ______.

A

5mM. Euglycemia.

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5
Q

The brain can only use what as fuel under normal circumstances? How much does it use?

A

Glucose. 120g a day.

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6
Q

Why cant the brain use FA?

A

Cant cross the blood-brain barrier

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7
Q

How is the main energy source of the brain transported in?

A

GLUT-1 transporters.

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8
Q

We store most of our energy as _____. But it cant be converted into _______. Why?

A

Fat. Carbohydrates. Pyruvate to acetyl CoA is irreversible and Acetyl CoA cant be made in glucogenic precursors.

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9
Q

Which parts of the body can exclusively use glucose?

A

Kidney, Skin and RBC

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10
Q

Which parts of the body can switch to FA as an alternate fuel during starvation?

A

Other tissues (not brain) ie muscle.

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11
Q

What is the general strategy in the early stages of starvation?

A

Glucose conservation
Glucose recycling - don’t fully oxidise it - regenerate from lactate
De novo glucose formation (make it from other things).

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12
Q

What happens during the first few hours of starvation?

A

All the tissues are using glucose. Blood glucose concentration falls

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13
Q

How is hypoglycemia prevented in early starvation?

A

The liver releases glucose into the bloodstream.

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14
Q

What is glycogenolysis?

A

Catalyses an equilibrium across the liver cell membrane so glucose concentration in liver cells and blood the same (Through GLUT 2 transporters)

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15
Q

What does an equilibrium across the liver cell membrane and blood signal to the liver cells?

A

Glucose release comes from glycogen stored in the liver (glycogenolysis - breakdown of the molecule glycogen to glucose)

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16
Q

What is the enzyme that breaks down glycogen in glycogenolysis? How does this occur?

A

Phosphorylase (rate-limiting step). Phsosphoylase cleaves terminal glycogen molecules to make glucose-1-phosphate which phosphorylates to G-6 - phosphatase.

17
Q

What happens in glycogenolysis after G-6-Phosphatase is formed?

A

It is trapped in the cell (too big to leave) so it is transformed into glucose so it can be released by the GLUT-2 transporter into the bloodstream.

18
Q

Which part of the glycogen molecule is attacked by the enzyme in glycogenolysis?

A

The end terminal units - the glyosidic link.

19
Q

How is phosphorylase regulated?

A

By reversible phosphorylation - only active when phosphorylated by phosphorylase kinase.

20
Q

What is the chain of events for the regulation of enzymes after phosphorylase?

A

Card 13

21
Q

Why is the process of glycogenolysis so complex?

A

Amplifies signal

More control

22
Q

What are branch points?

A

Points in a metabolic pathway in which a compound can be used as a substrate in two or more reactions. The cell must decide which of the pathways to direct the molecule to.

23
Q

What does a debranching enzyme do to glucose at the branching point? Why?

A

Releases 10% of the glucose residues as neat glucose instead of G-6-Phosphate. Branching occurs every 10 residues.

24
Q

Does muscle contribute to euglycemia?

A

Muscle does not break down glycogen much in starvation because it has no glucagon receptors and no glucose-6-phosphatase (cant release glucose into the blood).

25
Q

Some glucose residues are able to be released from muscle ______ as _______. Why might this not get to the blood?

A

Glycogen released as neat glucose - due to the debranching enzyme. The muscle might just use this for itself.

26
Q

How can muscle contribute to blood glucose levels?

A

If PDH is inhibited the G^P will go to lactate - to the liver.

27
Q

How much glycogen is stored in the liver? What does that mean for glycogen depletion?

A

110g. This is inadequate and the brain will use this in 24 hrs. Need to persuade other tissues to use fat rather than glucose well before liver glycogen is depleted.

28
Q

What is the purpose of white adipose tissue lipolysis?

A

Accessing the large reserved of fat in WAT.

29
Q

What are the steps of WAT lipolysis?

A

Card 14

30
Q

What is the key enzyme in WAT lipolysis?

A

Hydrolyses triglyceride and releases fatty acids - Hormone sensitive lipase.

31
Q

Where is hormone-sensitive lipase released into?

A

Into boundary between lipid droplet and cytoplasm and chews away at fat.

32
Q

High levels of ______ stimulate PDH kinase which converts _____ into inactive phosphorylated form.
Hormone sensitive lipase activates _____ which was deactivated by ______.

A

Acetyl CoA…..PDH kinase. PDH…..phosphorylation.

33
Q

In starvation we want PDH to be _____. Why?

A

Off. Prevents wasteful oxidation of pyruvate. Pyruvate can be made into lactate.

34
Q

How is glucose oxidation stopped during starvation?

A

Oxidation of FA switched PDH off by producing a lot of acetyl CoA ( PDH kinase phosphorylates and so it’s inactive). Glucose oxidation cant go ahead without PDH.

35
Q

Why can’t glucose oxidation occur without PDH?

A

Pyruvate cant be oxidised to acetyl CoA

36
Q

When PDH is off what happens to lactate from pyruvate in the muscle?

A

It is taken in by the liver and remade into glucose by gluconeogenesis. (Cori-cycle)

37
Q

How much glucose per day can be made from glycerol?

A

30g

Molecular Biology 2 (13 decks)

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