Glycolysis and Krebs Cycle Review Flashcards
Preparatory Phase function
Pay-off Phase function
Carbon is activated via 2 phosphorylation events, expending ATP.
The ring is cleaved to form 2 trioses
Trioses are oxidized
Phosphoryl groups used to produce ATP via substrate level phosphorylation of ADP
4 ATP (2 net) produced and 2 pyruvate
Preparatory Phase of Glycolysis steps
1) Glucose —> Glucose-6-phosphate catalyzed by hexokinase (all cells) or glucokinase (liver)
- ATP consumed
2) Glucose-6-phosphate —> Fructose-6-phosphate catalyzed by phosphoglucose isomerase
3) Fructose-6-phosphate —> Fructose-1,6-bisphosphate catalyzed by phosphofructokinase-1
- ATP consumed
4) Fructose-1,6,-bisphosphate —> Glyceraldehyde-3-phosphate + Dihydroxyacetone phosphate catalyzed by aldolase
5) Dihydroxyacetone phosphate —> glyceraldehyde-3-phosphate catalyzed by triose phosphate isomerase
Pay-off phase of glycolysis steps (2x)
1) Glyceraldehyde-3-phosphate+ Pi —> 1,3-bisphosphoglycerate catalyzed by glyceraldehyde-3-phosphate dehydrogenase
- NADH + H+ produced
2) 1,3-bisphosphoglycerate —> 3-phosphoglycerate catalyzed by phosphoglycerate kinase
- ATP produced
3) 3-phosphoglycerate —> 2-phosphoglycerate catalyzed by phosphoglycerate mutase
- H2O produced
4) 2-phosphoglycerate + H2O —> phosphoenolpyruvate catalyzed by enolase
5) Phosphoenolpyruvate —> pyruvate catalyzed by pyruvate kinase
- ATP produced
Anaerobic conditions:
6) Pyruvate —> lactate catalyzed by lactate dehydrogenase
- NAD+ produced
Krebs Cycle
1) Acetyl coA + oxaloacetate –> Citrate + coA
Citrate synthase
2) Citrate –> Isocitrate
Aconitase
3) Isocitrate + NAD+ –> a-ketoglutarate + NADH + H+ + CO2
Isocitrate dehydrogenase
4) a-ketoglutarate + NAD+ + CoA –> succinyl coA + NADH + H+ + CO2
A-ketoglutarate dehydrogenase
5) succinyl-coA + GDP + Pi –> succinate + coA + GTP
succinate thiokinase
6) succinate + FAD –> fumarate + FADH2
succinate dehydrogenase
7) fumarate –> malate
fumarase
8) malate + NAD+ –> oxaloacetate + NADH + H+
malate dehydrogenase
Krebs cycle products per pyruvate
2 CO2
1 FADH2
1 GTP
3 NADH
3 H+
Oxidative decarboxylation of intermediates
Arsenic inhibits which enzymes?
Malonate?
Fluorocitrate?
Antimyacin?
Oligomyacin?
These inhibitors can be used in the lab to test efficacy of Krebs cycle efficiency
Arsenic inhibits: PDH and KGDH (a-ketglut)
Malonate: succinate dehydrogenase
Fluorocitrate: aconitase
These inhibitors can be used to measure mitochondrial respiration:
Antimyacin: inhibts complex III
Oligomyacin: inhibits complex V
Irreversible reactions in Krebs cycle
1, 3 and 4 are one way
Citrate synthase, isocitrate dehydrogenase and a-ketoglutarate dehydrogenase
Also pyruvate dehydrogenase
What is a keto acid dehydrogenase?
Example?
any enzyme using coA
ex. a-ketoglutarate dehydrogenase catalyzing a-ketoglutarate –> succinyl-coA
Nutrients required for cellular respiration
Minerals: Mn, Fe (Ca and Mg as activators)
Cofactors: Niacin (B3, NADH), Thiamine (B1, TPP), Pantothenic acid (B5), Biotin (B7), (ribo)Flavin (B2, FMN)
Glucose for adenosine production and AA for protein synthesis
Intermediates from Krebs cycle can be used to build:
- amino acids
- porphyrin rings/heme (succinyl coA)
- nucleotides (ribose-5-phosphate PPP)
- fatty acids (citrate)
- urea cycle (fumarate)
- glucose via gluconeogenesis
NADH inhibits which steps of the Krebs cycle?
PDH, citrate synthase, isocitrate dehydrogenase, a-ketoglutarate dehydrogenase, malate dehydrogenase
ATP inhibits which steps of Krebs cycle?
GTP?
ATP inhibits: PDH, citrate synthase, isocitrate dehydrogenase, a-ketoglutarate dehydrogenase
GTP inhibits: a-ketoglutarate dehydrogenase
Succinyl coA is an allosteric regulator for which enzyme(s) in Krebs cycle?
Succinyl-coA inhibits: Citrate synthase and a-ketoglutarate dehydrogenase
Ca2+ is an allosteric regulator for which enzyme(s) in Krebs cycle?
Mg2+?
Ca2+ activates: PDH, isocitrate dehydrogenase, a-ketoglutarate dehydrogenase
Mg2+ activates: PDH
Acetyl coA is an allosteric regulator for which enzyme(s) in Krebs cycle?
Acetyl CoA inhibits: PDH
Acetyl coA activates: citrate synthase
Citrate is an allosteric regulator for which enzyme(s) in Krebs cycle?
Citrate as a product inhibits citrate synthase
