12. Monosaccharide catabolism, amino acid catabolism, ketogenesis

Question 1

ME dietary protein =

Answer 1

17 kj/gr

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

Question 2

Is the fructose pathway similar tot he glucose pathway?

Answer 2

No, completely different pathway from glucose with other enzymes

Question 3

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

Answer 3

Small intestine.

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

What other monosaccharide cannot use PFK1?

Answer 6

Galactose

Question 7

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

Answer 7

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

Question 8

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

Answer 8

All 3 -> DHAP + GA3P

Question 9

What part of the triglyceride is hydrophilic?

Answer 9

Glycerol

Question 10

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?

Answer 10

-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.

Question 11

What is the ATP yield of glycerol upon complete oxidation?

Answer 11

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

total = 16.5

Question 12

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

Answer 12

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.

Question 13

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

Answer 13

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

AMP stimulates PFK1

Question 14

Which of the following pathways produce/consume glucose?

Glycogenesis
Glucogenolysis
Gluconeogenesis
Glycolysis

Answer 14

Produce:
gluconeogenesis
glucogenolysis (breakdown glycogen into glucose)

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

Question 15

By what molecule are ketone bodies made?

Answer 15

Acetyl-CoA

Question 16

When are ketone bodies produced?

Answer 16

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

Question 17

Which amino acid is purely ketogenic?

Answer 17

Lysine (can only make acetyl-CoA)

Question 18

Why are ketone bodies used? Is ketogenesis reversible?

Answer 18

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

Yes it is reversible

Question 19

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

Answer 19

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.

Question 20

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

Answer 20

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)

Question 21

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

Answer 21

Only - 2.5 to make Beta-hydroxybutyrate

Question 22

Why will the liver not consume ketone bodies itself?

Answer 22

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.

Question 23

Utilization of ketone bodies happens in what kind of tissues?

Answer 23

extra-hepatic tissues (outside the liver)

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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)

Question 26

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

Answer 26

Ketone body reaction: will yield 2x acetyl-CoA = 20 ATP TCA cycle: less ATP. Choice based on need of the cells.

Question 27

Highest energy yield of ketone bodies in descending order?

Answer 27

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

Question 28

What is the difference in ATP-yield after complete oxidation between glutamate and.. Aspartate (yielding OAA) Alanine (They all have one NH2)

Answer 28

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

Question 29

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

Answer 29

False

Question 30

Is every essential amino acid limiting?

Answer 30

No, depends on dietary intake

Question 31

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

Answer 31

True

Question 32

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

Answer 32

Citrulline Ornithine (arginine)

Question 33

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

Answer 33

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

Question 34

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

Answer 34

2.5 ATP

Question 35

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

Answer 35

False, substrate level phosphorylation requires 1 ATP.

Question 36

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

Answer 36

Heat ATP ROS (water)

Question 37

 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

Answer 37

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

Question 38

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

Answer 38

A+B

Question 39

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

Answer 39

b

Question 40

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

Answer 40

5 all of above

Question 41

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

Answer 41

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

Question 42

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

Answer 42

Alanine