8. Carbohydrate metabolism 2 Flashcards
TCA cycle needs/does not need oxygen to work
does not
Glucose -> pyruvate: last step is irreversible (PEP -> pyruvate). What if you want to convert pyruvate into glucose? How is this process called?
Pyruvate can be converted into oxaloacetate into PEP with the help of the enzymes pyruvate carboxylase and PEP carboxykinase. = Gluconeogenesis
OAA occurs both in the cytoplasm and mitochondrion, but cannot pass te mitochondrial membrane. What needs to be done? ATP cost?
OAA is converted to malate (-2.5 ATP), transported outside of the membrane and then converted into OAA again (+1.5 ATP)
Cost = 1 ATP
How many TCA cycles before citrate is fully oxidated?
Two, because in one cycle two carbons are released and citrate is a C4 molecule.
How do you fully oxidize citrate?
Citrate 6C -> TCA cycle until malate 4C > outside membrane OAA 4C > 3C PEP > 3C pyruvate> 2C acetyl-CoA > TCA cycle
What is the ATP yield when you fully oxidize citrate?
21.5 ATP
Why is citrate ATP yield less efficient (21.5) than glucose (30 ATP)?
Citric acid is related to glucose (C6 both). Nevertheless it only yields 21.5 ATP instead of 30, because citrate does not enter glycolysis and misses all ATP production there
What is the difference in ATP yield between oxaloacetate (OAA) and citrate upon complete oxidation?
21.5 - 11.5 = 10 ATP
What is propionic acid?
volatile fatty acid (VFA). One of the SCFA’s. Fermentation in large intestine.
> produced by bacteria as waste product. Our bodies can use it.
Conversion of propionic acid to succinyl-CoA via two steps costs .. ATP
3 ATP
(first ATP -> AMP)
(then ATP -> ADP)
Where does propionic acid enter the cycle?
Succinyl-CoA
What is the ATP yield of propionic acid/propionate: complete oxidation?
13.5 ATP
Storage of glucose/other nutrients: Tell me about these organs
- Brain
- Muscle
- Adipose tissue
- Blood
Brain only uses glucose, or ketone bodies in fasting conditions. It has only a small amount of glucose stored.
Muscle has a lot of glucose and protein stored and some triacylglycerols
Adipose tissue: lot of triacylglycerols, some glucose and proteins
Blood: very constant amount of 250 kj glucose
What can only the liver do and why?
Liver can only convert glucose-6-ph into glucose because it has the glucose-6-phosphatase enzyme
Glucose homeostasis in blood plasma:
Constant, always 3-5 mM (1 gr/l)
With 2.5 liter plasma, only 2.5 gr circulates
How is glucose homeostasis maintained in fed/fasted state?
Fed state: good regulation by condensation to liver and muscle glycogen
Fasted state: release from liver, not muscle, into circulation
Changes in blood levels only reflect difference in … but is a poor indicator of …
Changes in blood levels only reflect difference between input – output.
Blood level is a poor indicator of total flux (throughput)
How does the glucose tolerance test work?
Fasting condition, give drink, check blood glucose levels.
Glucose from the diet can be stored as glycogen. First, the gluose molecule has to be …. , which takes …. ATP
2 ATP
(glucose -> gl-6-p = 1 ATP)
(gl-6-p -> gl-1-p = 0 ATP)
(gl-1-p -> UDP tag = 1 UDP = 1 ATP)
By UDP tagging (attaching to the gl-1-p)
Then, the molecule can be added to the linear glucose molecule by ..
release of UDP. STILL, 2 ATP used
Direct glycolysis = ?
Indirect glycolysis = ?
Indirect = from diet you obtain glucose > g-6-p -> g-1-p -> glycogen 2 ATP cost
Direct = glucose -> g-6-p = 1 ATP cost
Energy costs for storage and mobilisation of blood glucose via hepatic (=lever) glycogen = x ATP
2 ATP (indirect)
(glucose -> glycogen -> glucose)
ATP yield of (blood) glucose in leg muscle after direct oxidation = ?
30 ATP
ATP yield of (blood) glucose in leg muscle after indirect oxidation (via leg muscle glycogen) = ?
29 ATP (invest one more than direct)
ATP yield of (blood) glucose in leg muscle after indirect oxidation (via arm muscle glycogen):
0 (arm cannot give glucose to leg)
ATP yield of (blood) glucose in leg muscle after indirect oxidation (via liver):
28 ATP. Liver glucose > G-6-P > glycogen > glu = 2 ATP. It is released as glucose.
Then, in the leg muscle, glucose -> oxidation , so glucose -> g-6-p = 1 ATP ‘extra’
ATP yield of (blood) glucose in leg muscle after indirect oxidation (after 5 glycogenolysis/glycogen synthesis cycles in the leg muscle)?
glycogen > gl-6-p > glycogen (1 ATP)
x 5 = 5 ATP
30 - 5 = 25 ATP
Regulation of storage or glycolysis of gl-6-p is done by..
PFK phosphofructokinase
What does PFK usually help with in glycolysis?
fr-6-p to fr-1,6-p
It decides the faith of gl-6-p
PFK is inhibited by citrate. But what kind?
Not the citrate of the mitochondria.
From the cytosol, which is also coming from fatty acid synthesis. Lot of citrate in cytosol = lot of energy.
What is the pasteur effect?
Switch from slow to fast glucose use
How was the pasteur effect discovered?
Discovered by Pasteur, that yeast fermented at a lower speed in the presence of oxygen.
Oxidative phosphorylation is …. in low oxygen conditions
Blocked
What happens in the glycolysis when there is low oxygen?
Normally, glucose > pyruvate, ATP + NADH produced. NADH needs to be oxidated back to NAD+ so the glycolysis can continue. Happens in the mitochondria (shuttle).
> However, with low oxygen, no regeneration of NAD+.
What is a solution for low oxygen which inhibits NAD regeneration? Does this cost energy?
Regeneration of NADH to NAD+ by cytoplasmic conversion of pyruvate to lactate (No ATP!)
Pyruvate + NADH > lactate + NAD+
Normally, under aerobic conditions, glucose is oxidized which yields 30 ATP, 6 CO2 and 6 H2O. What is yielded with anaerobic conditions?
Glucose in anaerobic conditions yields 2 ATP and 2 lactate
Pasteur effect increases/decreases glucose utilisation by …
increases, 15x
Energy efficiency of glucose aerobic oxidation was 35%. For lactate, it is …
75%
GE glucose = 2816 kj/mol
GE lactate = 1364 kj/mol
ATP = 33 kj/mol
2 * 1264 = 2728 kj
2816 - 2728 = 88 kj lost
trapped 2 ATP = 66 kj
66/88 = 75%
