12. Monosaccharide catabolism, amino acid catabolism, ketogenesis Flashcards
ME dietary protein =
17 kj/gr
Ch = 16 kj/gr
Fat = 39 kj/gr
Is the fructose pathway similar tot he glucose pathway?
No, completely different pathway from glucose with other enzymes
Fructose metabolism: what organ has the highest metabolic activity? (At least in mice)
Small intestine.
Low dose: Most fruc metabolized by intestine.
High dose: Excess fructose spills over to the liver and colonic microbiota.
Fructose metabolism: What is the same with glucose metabolism? Where do the pathways meet?
Fructose + ATP -> DHAP + GA3P
Fructose is entrapped, just as is the case with glucose.
Similar endproducts, different intermediary steps.
What is a big difference in terms of regulation of fructose/glucose?
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
What other monosaccharide cannot use PFK1?
Galactose
Galactose degradation pathway arrives at a common pathway with glucose way quicker than fructose. Explain.
- Entrap the galactose (-1 ATP) into galactose-1-p.
- Then, galactose-1-p forms glucose-6-P. = common product
So, what pathway do glucose, fructose and galactose have in common?
All 3 -> DHAP + GA3P
What part of the triglyceride is hydrophilic?
Glycerol
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?
-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.
What is the ATP yield of glycerol upon complete oxidation?
- Glycerol > DHAP/GA3P = + 0.5
- GA3P > CO2 = 16
total = 16.5
What is important to always remember when you consider fatty acid catabolism?
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.
The rate of glycolysis is controlled at the level of the conversion of …. to …. (by PFK1) What again stimulates PFK1?
fr-6-ph to fr-1,6-biph
AMP stimulates PFK1
Which of the following pathways produce/consume glucose?
Glycogenesis
Glucogenolysis
Gluconeogenesis
Glycolysis
Produce:
gluconeogenesis
glucogenolysis (breakdown glycogen into glucose)
Consume:
Glycolysis
Glycogenesis (formation of glycogen, consuming glucose)
By what molecule are ketone bodies made?
Acetyl-CoA
When are ketone bodies produced?
Ketone bodies are usually produced when on a very low carbohydrate diet. On a late starvation phase from protein (muscle).
Which amino acid is purely ketogenic?
Lysine (can only make acetyl-CoA)
Why are ketone bodies used? Is ketogenesis reversible?
Glucose levels drop, brain relies on glucose. Ketones are needed for other organs as glucose is spared for the brain.
Yes it is reversible
Where are ketone bodies formed? How does this go very broadly?
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.
Formation of ketone bodies in detail: use metabolic map. Which 3 ketone bodies are formed?
- Condensation of 2x acetyl-CoA. Result: 4C molecule with acetyl-CoA (acetoacetyl CoA)
- 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.
- 1 Carbon is released: aceton can be released. Expelled outside via lungs. Bad breath. Losing energy. Not nice.
- 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)
How much ATP is used for this ketone formation (starting from acetyl-CoA)?
Only - 2.5 to make Beta-hydroxybutyrate
Why will the liver not consume ketone bodies itself?
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.
Utilization of ketone bodies happens in what kind of tissues?
extra-hepatic tissues (outside the liver)
Utilization (breakdown) of ketone bodies follows the reverse pathway of the build-up of ketone bodies.
True/false
False. Build up = in liver, utilization in exrta-hepatic tissues and other pathway. Not indicated in A3 map.
What happens in detail + terms of energy with conversion of beta-hydroxybutyrate (ketone body) to acetyl-CoA?
- Beta-hydroxybutyrate -> acetoacetate (+NADHm = +2.5 ATP).
- Then -> acetoacetyl CoA with a subsequent conversion of succinyl-CoA to malate, which is not the same as in the TCA cycle.
- Acetoacetyl CoA > 2 acetyl-CoA (both 10 ATP)
Why/when sacrifice succinyl-CoA for ketone body reactions instead of for the TCA cycle?
Ketone body reaction: will yield 2x acetyl-CoA = 20 ATP
TCA cycle: less ATP.
Choice based on need of the cells.
Highest energy yield of ketone bodies in descending order?
- beta-hydroxybutyrate (-2.5 NADH)
- acetoacetate
- Acetone (least)
What is the difference in ATP-yield after complete oxidation between glutamate and..
Aspartate (yielding OAA)
Alanine
(They all have one NH2)
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
All dietary energy can be converted into body fat
True/false
False
Is every essential amino acid limiting?
No, depends on dietary intake
A limiting amino acid is always an essential amino acid. Non-essentials are never limiting
True/false
True
Which amino-acids are not used to synthesize protein but involved in the urea cycle? (look at map)
Citrulline
Ornithine
(arginine)
Arginine has the highest N-content. What could be a reason for this?
It makes sense as it is a transporter in the urea cycle
By oxidative phosphorylation in the mitochondira, one NADH provides how much ATP?
2.5 ATP
By substrate level phosphorylation in the cytoplasm, NADH provides 1.5 ATP.
True/false
False, substrate level phosphorylation requires 1 ATP.
What may the electron transport chain in the mito’s may produce?
Heat
ATP
ROS
(water)
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
GE for polymers is about 17.5 kJ. For monomer/dimer: monomer is ~15 and dimer ~16.5.
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+B
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
b
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?
- Glycerol = glucogenic component.
- Can be used to produce ATP by substrate level phosphorylation.
- Will yield 16.5 ATP upon complete oxidation.
- None of above
- All of above
5 all of above
The glucose -> fructose reaction in glycolysis consumes X ATP
2
(A3 map: until fr-1,6-biph)
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
Alanine
