Term
| How long can liver glycogen meet the needs of glucose to the body? |
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Definition
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Term
| Precursors for glucose during a prolonged fast |
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Definition
Lactate, pyruvate, glycerol
alpha ketoacids |
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Term
| What substrates directly enter gluconeogenesis? |
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Definition
| pyruvate and oxaloacetate |
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Term
| name two ketogenic amino acids |
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Definition
Leucine and Lysine
These break into acetoacetate |
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Term
| Can glucose be formed by reverse glycolysis? |
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Definition
| No, because the equilibrium of glycolysis STRONGLY favors the formation of pyruvate. |
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Term
Organ that plays main role in overnight fasting?
In emergencies? |
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Definition
Liver for overnight, 90% contribution while kidney only contributes 10%
In emergencies- kidneys will help 40%
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Term
Hydrolysis of TGs:
yields what?
where does it happen?
where does the product go? |
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Definition
Yields glycerol!
Happens in adipose tissue
Delivered to liver by blood |
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Term
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Definition
Blood bourne glucose is converted into lactate in sk muscle
muscle then releases lactate into the blood
lactate diffuses into liver and is reconverted into glucose |
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Term
| Major glucose source for fasting |
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Definition
| Amino acids from hydrolysis of tissue proteins (proteins are usually a last source for this process) |
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Term
| Indirect substrates for gluconeogenesis |
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Definition
| lactate, glycerol, glucogenics amino acids |
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Term
| In gluconeogenesis, Pyruvate needs to be converted to what? |
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Definition
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Term
| Describe the first 4 reactions of gluconeogenesis |
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Definition
First 2 rxns in mitochondria, then converts to malate to travel via the malate shuffle. travels into cytoplasm for remaining reactions .
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Term
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Definition
| pyruvate is carboxylated by pyruvate carboxylase to OAA, then converted to PEP by the action of PEP-carboxykinase |
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Term
| What purposes does OAA serve in the mitochondria of liver and kidneys? |
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Definition
provides substrate for gluconeogenesis
OAA can replenish TCA cycle (muscles use OAA for this purpose) |
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Term
| How is pyruvate carboxylase activated? |
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Definition
| It is allosterically activated by binding of acetyl CoA |
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Term
| What happens to malate once it is transported from mitochondria to cytosol? |
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Definition
| Malate must be reoxidized to OAA by cytosolic malate dehydrogenase |
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Term
| Role of NADH in transfer of OAA across mitochondria |
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Definition
| NADH is oxidized to NAD+ to convert OAA to malate so it can cross mitochondria via malate shuttle to cytosol |
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Term
| What happens to malate once it is in the cytosol? |
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Definition
Malate will be reozidized into OAA.
OAA is converted to phosphoenolpyruvate by PEP carboxykinase |
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Term
PEP will be acted on by reverse glycolysis until what step?
What happens when this step is reached? |
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Definition
Until F 1,6 BP
Which will be hydrolzyed by F 1,6 BPase. Irreversible dephosphorylation by BFPK-1 will form F6P |
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Term
| Can muscle glycogen maintain blood glucose levels |
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Definition
| No- muscle lacks G6P, which is the final enzyme that is converted into glucose. Therefore, muscle recieves energy frm glycolysis and NOT from gluconeogenesis |
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Term
| 3 irreversible steps of glycolysis |
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Definition
1. glucose is converted to G6P by hexokinase
2. Fructose-6-phosphate is converted to Fructose 1,6 BP by PFK-1
3. Phosphoenolpyruvate converts to pyruvate by pyruvate kinase |
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Term
| Gluconeogenesis leads to the formation of what 3 things? |
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Definition
GLUCOSE!
PEP
F6P
Comes at the cost of 6 ATP and 2 NADH for every glucose |
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Term
| Direct activators of gluconeogenesis |
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Definition
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Term
| Indirect activators of gluconeogenesis |
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Definition
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Term
| Steps of gluconeogenesis (irreversible) |
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Definition
1. using PEP carboxylase to convert oxaloacetate to PEP
2. Using F6BPase to form Fructose-6-P from F1,6-BP
3. Using G6Pase to form glucose from G6P |
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Term
| 3 mechanisms by which glucagon stimulates gluconeogenesis |
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Definition
1. Lowers F2,6BP, activates F1,6Pase, inhibits PFK
2. increases cAMP, activates PKA, phosphorylates pyruvate kinase, degrades PEP to pyruvate
3. increases transcription of PEP carboxykinase |
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Term
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Definition
activates pyuvate decarboxylase during fasting.
Excessive lypolysis will increase levels of AcCoA
it also inhibits pyruvate dehydrogenase, which diverts pyruvate towards gluconeogenesis |
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Term
| Result of low insulin levels |
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Definition
| AAs are mobilized from skeletal muscle to provide glucogenic carbon skeletons |
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Term
| Why can't glucose be formed by reversal of glycolysis? |
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Definition
equilibrium favors pyruvate formation, using mit and cystolic enzymes.
overnight fast is 90% gluconeogenisis in liver, 10% in kidneys.
prolonged fasting is 40% kidneys (only in emergency) |
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Term
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Definition
| phosphorylated & become substrate in glycolytic path after TG is broken down |
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Term
Carboxylation of pyruvate
(first road block of gluconeogenesis) |
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Definition
pyruvate carboxylated by pyruv carboxylase (activated by acetyl CoA) to OAA > PEP (by PEP carboxykinase)
Biotin bound to lysine. ATP hydrolyzes to carboxy pyruvate to ALSO make oaa.
OAA (substrate for gluconeogenesis, replenish TCA) |
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Term
Transport of OAA to cytosol
(part two of gluconeogenesis) |
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Definition
converts to PEP (which is in both mit & cytosol)
Mit PEP goes to cytosol via transporter
Cytosol PEP is the transporter, but OAA reduced to malate first. (by malate dehydrogenase)
reoxidized to OAA by cyt malate dehydrogenase once in cytosol. |
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Term
Decarboxylation of cyt OAA & dephosphorylation of F1,6BP
(step 2/3 gluconeogenesis) |
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Definition
OAA > PEP in cytosol (by PEP carboxykinase..needing GTP)
PEP > F1,6 BP via reverse rxn > hydrolyzed by F16BPase > F6P (phosphotase removes phosphate to become F6P) |
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