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Medical Biochemistry > 1- Biosynthesis of carbohydrates > Flashcards

1- Biosynthesis of carbohydrates Flashcards

1
Q

How much glucose does the human metabolism consumes ?

A

20 ± 160 grams

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2
Q

How much free glucose can the body fluids carry ?

A

20 grams

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3
Q

How much glucose can glycogen stores normally provide ?

A

180 to 200 grams

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4
Q

If glucose is not obtained in the diet, where does the body produce new glucose from?

A

Non-carbohydrate precursors

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5
Q

What does the term Glycogenesis mean?

A

Generation of new glucose

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6
Q

What are the 4 tissues that mainly depend on glucose for energy metabolism?

A

Brain, erythrocytes ( Red blood cells ), testis, mammary ( human breast )

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7
Q

What uses glucose as the only fuel molecule?

A

Erythrocytes

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8
Q

In addition to dietary glucose, what also provides glucose?

A

Glycogenesis

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9
Q

What are the four type of non-carbohydrate precursors of glucose?

A
  1. lactate from muscles that form pyruvate
  2. TCA cycle intermediates
  3. Propionate from breakdown of TG and amino acids.
  4. Glycerol from certain lipids
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10
Q

What cannot convert fatty acids to glucose ?

A

Mammals

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11
Q

Is the pyruvate dehydrogenase reactions reversible ?

A

No they are irreversible

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12
Q

What dose plants, yeast and many bacteria have to make glucose from acetyl-CoA ?

A

Glyoxylate pathway

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13
Q

What are the three by-pass reactions in gluconeogenesis ?

A

1- formation of phosphoenolpyruvate from pyruvate
2- formation of 6-phosphate from fructose 1,6-bisphosphatas.
3- formation of glucose from glucose 6- phosphate

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14
Q

In the first by-pass reaction how is oxaloacetate is reduced to malate ?

A

By using mitochondrial malate dehydrogenase

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15
Q

What is the formula for the conversion of pyruvate to phosphoenolpyruvate ?

A

Pyruvate + ATP + GTP + HCO3- (to) PEP + ADP +GDP + Pi + CO2

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16
Q

What is found on the endoplasmic reticulum of the hepatocytes ( liver ), renal cells and epithelial cells of small intestine.

A

Glucose 6-phosphatase

17
Q

What is the cori cycle ?

A

It is a metabolic pathway in which lactate is transported to the liver from the muscle and converted to glucose and then transported back to the muscle to be used .

18
Q

What is the glucose alanine cycle ?

A

It is the series of the reactions in which amino groups and carbons from muscles are transported to the liver

19
Q

Why is glycolysis and gluconeogenesis regulated ?

A

To prevent wasteful operation of both pathways at the same time .

20
Q

How are glycolysis and Glucogenesis are hormonally regulated ?

A

By fructose 2,6-biophosphate

21
Q

What is the allosteric activator of Pirate carboxylase

A

Acetyl-CoA

22
Q

Where dose the first bypass reaction happen ?

A

In the mitochondrion

23
Q

What are the two reactions in the bypass of pyruvate?

A
  1. Pyruvate carboxylase catalyzes the atp. 2. Biotin-dependent conversion of pyruvate to oxaloacetate .
24
Q

Where dose the oxaloacetate must move from to be used for gluconeogenesis ?

A

It has to move out of the mitochondrion to the cytosol.

25
Q

Dose the mitochondrial membrane have an effective transporter for oxaloacetate ?

A

No

26
Q

oxaloacetate is reduced by mitochondrial malate dehydrogenase
to malate which is transported to the cytosol by the exchange of what ?

A

Orthophosphate and then reoxidized by cytosolic malate dehydrogenase

26
Q

What is the product of oxaloacetate acted on by phosphoenolpyruvate carboxykinase ?

A

Phosphoenolpyruvate

27
Q

In the second bypass reaction why is the reaction of glycolysis is essentially irreversible ?

A

Because it is driven by phosphate transfer from atp .

28
Q

In the third bypass reaction why is the glucose -6- phosphate cannot be converted to glucose by the reverse action of the hexokinase or gluockinase ?

A

Because of the high (delta) G-initial of the reaction

29
Q

How is glucose stored in animals ?

A

It is stored as glycogen mainly in the liver and the muscles

30
Q

How dose plants make starch and cellulose ?

A

Through photosynthesis

31
Q

What is the role of digestion when animals and humans eat plant materials and products ?

A

the starch is broken into the various monosaccharides

32
Q

What is glucose used for ?

A

To make energy

33
Q

When excess glucose is converted in the liver and muscles into glycogen for storage. Any glucose in excess of the needs for energy and storage as glycogen is converted to what ?

A

Fat

34
Q
A

Medical Biochemistry (5 decks)

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