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Nutritional physiology > 12. Monosaccharide catabolism, amino acid catabolism, ketogenesis > Flashcards

12. Monosaccharide catabolism, amino acid catabolism, ketogenesis Flashcards

1
Q

ME dietary protein =

A

17 kj/gr

Ch = 16 kj/gr
Fat = 39 kj/gr

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2
Q

Is the fructose pathway similar tot he glucose pathway?

A

No, completely different pathway from glucose with other enzymes

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3
Q

Fructose metabolism: what organ has the highest metabolic activity? (At least in mice)

A

Small intestine.

Low dose: Most fruc metabolized by intestine.
High dose: Excess fructose spills over to the liver and colonic microbiota.

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4
Q

Fructose metabolism: What is the same with glucose metabolism? Where do the pathways meet?

A

Fructose + ATP -> DHAP + GA3P
Fructose is entrapped, just as is the case with glucose.
Similar endproducts, different intermediary steps.

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5
Q

What is a big difference in terms of regulation of fructose/glucose?

A

Glucose: PFK1 is used, which is rate limiting in glycolysis. Other factors that stimulate or decrease PFK1, such as ATP, citrate, AMP.

Fructose: does not have regulation. Always enters metabolic pathway, oxidation. No control on this

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6
Q

What other monosaccharide cannot use PFK1?

A

Galactose

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7
Q

Galactose degradation pathway arrives at a common pathway with glucose way quicker than fructose. Explain.

A
  1. Entrap the galactose (-1 ATP) into galactose-1-p.
  2. Then, galactose-1-p forms glucose-6-P. = common product
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8
Q

So, what pathway do glucose, fructose and galactose have in common?

A

All 3 -> DHAP + GA3P

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9
Q

What part of the triglyceride is hydrophilic?

A

Glycerol

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10
Q

Degradation of glycerol: How much ATP for the first steps until dihydroxy-aceton-P? What enzyme is involved in this process and where else can you find it?

A

-1 + 1.5 = 0.5 ATP
Glycerol-3-P0dehydrogenase.
Seen before with the glycerol shuttle to bring the NADH from cytosol into mitochondria. Exists both in the cytoplasm and the mitochondria.

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11
Q

What is the ATP yield of glycerol upon complete oxidation?

A
  1. Glycerol > DHAP/GA3P = + 0.5
  2. GA3P > CO2 = 16

total = 16.5

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12
Q

What is important to always remember when you consider fatty acid catabolism?

A

Do not only consider fatty acid part which leads to a certain number of Acetyl-CoA’s depending on the carbons. But also the glycerol molecule, which will always lead to 16.5 ATP when you break it down.

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13
Q

The rate of glycolysis is controlled at the level of the conversion of …. to …. (by PFK1) What again stimulates PFK1?

A

fr-6-ph to fr-1,6-biph

AMP stimulates PFK1

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14
Q

Which of the following pathways produce/consume glucose?

Glycogenesis
Glucogenolysis
Gluconeogenesis
Glycolysis

A

Produce:
gluconeogenesis
glucogenolysis (breakdown glycogen into glucose)

Consume:
Glycolysis
Glycogenesis (formation of glycogen, consuming glucose)

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15
Q

By what molecule are ketone bodies made?

A

Acetyl-CoA

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16
Q

When are ketone bodies produced?

A

Ketone bodies are usually produced when on a very low carbohydrate diet. On a late starvation phase from protein (muscle).

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17
Q

Which amino acid is purely ketogenic?

A

Lysine (can only make acetyl-CoA)

18
Q

Why are ketone bodies used? Is ketogenesis reversible?

A

Glucose levels drop, brain relies on glucose. Ketones are needed for other organs as glucose is spared for the brain.

Yes it is reversible

19
Q

Where are ketone bodies formed? How does this go very broadly?

A

Mitochondria of the liver.

FFA are coming from adipose tissue in a fasting state bound to albumin. FA’s enter the beta oxidation where they are converted into acetyl-CoA with stepwise removal of 2C. They are then converted into ketone bodies by the liver.

20
Q

Formation of ketone bodies in detail: use metabolic map. Which 3 ketone bodies are formed?

A
  1. Condensation of 2x acetyl-CoA. Result: 4C molecule with acetyl-CoA (acetoacetyl CoA)
  2. Enzyme adds acetyl-CoA which is then removed again to create acetoacetate. So 3x acetyl-CoA is used until now. Carbon in acetoacetate is from 2 acetyl-CoA only.
  3. 1 Carbon is released: aceton can be released. Expelled outside via lungs. Bad breath. Losing energy. Not nice.
  4. Another compound is made (beta-hydroxybutyrate) (-2.5 ATP).
     So, three ketone bodies are made: 1. Acetone 2. Acetoacetate 3. Beta-hydroxybutyrate (mostly this one. It is stored and when needed NADHm will be released)
21
Q

How much ATP is used for this ketone formation (starting from acetyl-CoA)?

A

Only - 2.5 to make Beta-hydroxybutyrate

22
Q

Why will the liver not consume ketone bodies itself?

A

Pivotal enzyme acetoacetate succinyl-CoA transferase is lacking in liver cells (it breaks down ketone bodies to make acetyl-CoA). Liver will not use it for own metabolism.

23
Q

Utilization of ketone bodies happens in what kind of tissues?

A

extra-hepatic tissues (outside the liver)

24
Q

Utilization (breakdown) of ketone bodies follows the reverse pathway of the build-up of ketone bodies.
True/false

A

False. Build up = in liver, utilization in exrta-hepatic tissues and other pathway. Not indicated in A3 map.

25
Q

What happens in detail + terms of energy with conversion of beta-hydroxybutyrate (ketone body) to acetyl-CoA?

A
  1. Beta-hydroxybutyrate -> acetoacetate (+NADHm = +2.5 ATP).
  2. Then -> acetoacetyl CoA with a subsequent conversion of succinyl-CoA to malate, which is not the same as in the TCA cycle.
  3. Acetoacetyl CoA > 2 acetyl-CoA (both 10 ATP)
26
Q

Why/when sacrifice succinyl-CoA for ketone body reactions instead of for the TCA cycle?

A

Ketone body reaction: will yield 2x acetyl-CoA = 20 ATP
TCA cycle: less ATP.

Choice based on need of the cells.

27
Q

Highest energy yield of ketone bodies in descending order?

A
  1. beta-hydroxybutyrate (-2.5 NADH)
  2. acetoacetate
  3. Acetone (least)
28
Q

What is the difference in ATP-yield after complete oxidation between glutamate and..
Aspartate (yielding OAA)
Alanine

(They all have one NH2)

A

Glutamate = 19 ATP

Difference aspartate + glutamate from OAA = 19-11.5 = 7.5 ATP
Difference alanine + glutamate = 19-12.5 = 6.5 ATP

They all have one NH2 so all is same amount of ATP difference

29
Q

All dietary energy can be converted into body fat
True/false

A

False

30
Q

Is every essential amino acid limiting?

A

No, depends on dietary intake

31
Q

A limiting amino acid is always an essential amino acid. Non-essentials are never limiting

True/false

A

True

32
Q

Which amino-acids are not used to synthesize protein but involved in the urea cycle? (look at map)

A

Citrulline
Ornithine
(arginine)

33
Q

Arginine has the highest N-content. What could be a reason for this?

A

It makes sense as it is a transporter in the urea cycle

34
Q

By oxidative phosphorylation in the mitochondira, one NADH provides how much ATP?

A

2.5 ATP

35
Q

By substrate level phosphorylation in the cytoplasm, NADH provides 1.5 ATP.
True/false

A

False, substrate level phosphorylation requires 1 ATP.

36
Q

What may the electron transport chain in the mito’s may produce?

A

Heat
ATP
ROS
(water)

37
Q

 For the carbohydrates X and X you expect the largest difference in gross energy (kj/gr)

Choose:

A glucose + saccharose
B amylose + cellulose
C amylose + amylopectin
D glycogen + cellulose

A

A

GE for polymers is about 17.5 kJ. For monomer/dimer: monomer is ~15 and dimer ~16.5.

38
Q

There are 2 iso-enzymes that catalyze th eformation of gl-6-p in the liver: hexokinase and glucokinase. Which statement is correct?

A. Hexokinase has a low Km and acts at its minimal rate under nearly all physiological conditions to cover the normal demands of liver metabolism

B. Glucokinase has a high Km and is only active after a meal, most of the gl-6-p formed is used for synthesis of glycogen.

A
B
A+B
None

A

A+B

39
Q

What is true about gl-6-p and ATP?

a. formation out of glucose does not require ATP
b. formation out of glycogen does not require ATP
c. hydrolysis tog lucose releases ATP
d. conversion to glucose 1-p requires ATP

A

b

40
Q

Glycerol can be converted to dihydroxy acetone-P. In the cytoplasm the glycerol is phosphorylated to alfa-glycerol-P (1 ATP used) which is subsequently dehydrogenated (1 NADH formed) to dihydroxy acetone-P.

What is correct?

  1. Glycerol = glucogenic component.
  2. Can be used to produce ATP by substrate level phosphorylation.
  3. Will yield 16.5 ATP upon complete oxidation.
  4. None of above
  5. All of above
A

5 all of above

41
Q

 The glucose -> fructose reaction in glycolysis consumes X ATP

A

2
(A3 map: until fr-1,6-biph)

42
Q

Pyruvate can be converted to different components. The conversion of pyruvate to X is NOT associated with the use/production of energy

Choose:
- Actyl-CoA
- Lactate
- OAA
- Alanine

A

Alanine

Nutritional physiology (26 decks)

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