Pentose Phosphate shunt and Gluconeogenesis - CB Flashcards
Where are the enzymes found for the pentose P shunt?
Cytosol
What are the products of the Pentose P shunt?
NADPH and ribose-5-phosphate (R5P)
R5P is converted to fructose 6 Phosphate and glyceraldehyde-3-phosphate during the nonoxidative steps
What phase of the pentose P shunt are irreversible?
Oxidative phase: first 3 reactions
enzymes: 1. G6P dehydrogenase
2. 6-phospho-glucono-lactonase
3. 6-phospho-gluconate dehydrogenase
what reactions produce NADPH in the pentose P shunt?
Oxidative phase: reactions 1 and 3
G6P dehydrogenase
6-phospho-gluconate dehydrogenase
Are the nonoxidative steps of the pentose P shunt reversible?
yes
What prosthetic group is in transketolase?
TPP
What is the purpose of the nonoxidative reactions of the pentose P shunt?
To convert Ribulose-5-Phosphate into intermediates of the glycolytic pathway
how many NADPH are produced per glucose in the pentose phosphate shunt?
2
Are enzymes specific to NAD+ or NADP+?
Yes, many are specific to only one
What tissues use the pentose phosphate pathway? functions?
Adrenal gland: steroid syn
Testes/ovaries: steroid syn
Liver: cholesterol and fatty acid syn
adipose tissue: fatty acid syn
mammary gland: fatty acid syn
Sm intestine: detoxify xenobiotics (cytochrome P450)
RBC: detoxify reactive oxygen species (glutathione reductase)
Main uses of NADPH (general)?
biosynthesis and detoxification?
what are the consequences of a glucose-6-phosphate dehydrogenase (G6PDH) deficiency?
Favism (hemolytic anemia)
however, advantage against malaria
What happens if we only need more ribose-5-phosphate and not NADPH
nonoxidative pathway in reverse: fructose-6-P (F6P) + gylceraldehyde phosphate (GAP)»> ribose-5-phosphate
what are the biosynthetic uses of ribose?
RNA/DNA NTPs NADH/FADH CoA In general: information storage, energy transfer, oxidation/reduction reactions, and enzyme catalysis
Where is glucose-6-phosphatase located and what is it used for?
Liver and a small amount in the kidney
gluconeogenesis
What is the primary fuel in the brain and RBCs?
Glucose
Where is glycogen broken down during fasting and why?
Liver, to maintain blood glucose
What system/process takes over when glycogen is depleted to maintain blood glucose?
gluconeogenesis
what are the substrates of gluconeogenesis?
lactate, pyruvate, CAC intermediates, amino acids (except Leu and Lys)
What reactions of glycolysis are irreverable and must be bypassed in gluconeogenesis?
THIS INFO IS SHITTY BUT PROLLY IMPORTANT:
Glucose->Glucose6P (via hexokinase) bypassed (bypass 3)) in opposite direction with glucose-6-phosphatase
Fructose-6P->Fructose-1,6-BP (via phosphofructokinase (PFK)) bypassed (bypass2) in opposite direction with fructose bis-phosphatase
phosphoenolpyruvate (PEP) -> pyruvate (via pyruvate kinase bypassed (bypass1) by 2 reactions:
pyrvate -> (via pyruvate carboxylase)-> oxaloacetate ->(via PEPcarboxykinase)-> PEP
where is the only place pyruvate carboxylase (gluconeo) is found? what does it do? what is the cofactor? any energy spent?
Mitochondria, adds COO to CH3 of pyruvate (making oxaloacetate), biotin, 1 ATP per rxn used 1CO2
What are the subsrates and products for PEPcarboxykinase (gluconeo)?
Substrates: oxaloacetate, GTP
Products: GDP, PEP (phosphoenolpyruvate), CO2
Only Amino acids not capable to contributing to gluconeogenesis?
Leu and lys
Can acetyl-CoA contributing to gluconeogenesis?
NOPE
Where does gluconeo start?
mitochondria ( minor exception: glycerol is converted to DHAP in cytosol)
Is Figure 20-13 Important?
No clue seems like BS to me
Is there a transport system for oxaloacetate?
Nope, but can use Mal/Asp shuttle in reverse
Is there a transport system for PEP?
Yep oddly named the PEP transporter
energy costs of gluconeogenesis?
6 ATP (really 4ATP and 2GTP) per molecule of glucose made
Bypass 1 (pyruvate carboxylase and PEPCK): 2ATP and 2 GTP respectively
Phosphoglycerate kinase reaction used 2 ATP in gluconeo (produced 2 in glycolysis)
The balance between liver and muscle glucose, glycogen, and lactate levels is called the _______ cycle.
Cori
What is the “Oxygen Debt”?
the amount of O2 consumed in liver during its replenishing of the muscle glycogen supply
Enzymes used in both glycolysis and gluconeogenesis? enzymes unique to each?
BOTH: enolase, phosphoglycerate mutate, phsphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, Triose phosphate isomerase, aldolase, phosphoglucose isomerase
ONLY glycolysis: pyruvate kinase, phosphofructokinase, or hexokinase
ONLY gluconeogenesis: pyruvate carboxylase PEPcarboxykinase, fructose bis-phosphatase, glucose-6-phosphatase
Oxidative Phase if Pentose P shunt enzymes and the type of reaction they catalyze?
Glucose-6P dehydrogenase: oxidation (Produces NADPH)
6-phosphoglucono lactonase: hydrolysis
6-phosphogluconate dehydrogenase: oxidation/decarboxylation (produced NADPH)
Non Oxidative Phase if Pentose P shunt enzymes and the type of reaction they catalyze?
Ribulose-5-P isomerase: isomerization
Ribulose-5-p epimerase: epimerization
Transketolase (3 rxns): intermolecular transfer of a C2 unit (dihydroxyethyl) then intermolecular transfer of a C3 unit (dihydroxyacetone) than another intermolecular transfer of a C2 unit (dihydroxyethyl)
Stare at Figure 15-23 (pg 105 of PDF) for 5 min
Throw something at Itamar if he’s within range
Stare at Figure 14-30 (pg 94 of PDF) for 5 min
Watch the “CHEETO Schiedo” Video
