module 3: fermentation, gluconeogenesis, pyruvate oxidation, krebs cycle

After glycolysis what happens if O2 is present

cellular respiration

1. link rxn: 2 pyruvate → 2 acetyl CoA +2CO2

2. Krebs

3. ETC

4. Ox phos

(slow, generate 30 additional ATP)

After glycolysis what happens if O2 is not present

fermentation

• allows for regeneration of NAD+

• 2 lactate or 2 ethanol/2CO2

• 0 ATP

who does lactic acid fermentation

very active muscles and some bacteria do this in absence of O2 to regenerate NAD+

lactate dehydrogenase (LDH) rxn

pyruvate +NADH + H+ ←→ L-Lactate + NAD+

who does ethanol fermentation

some microbes (NOT MUSCLE)

ethanol fermentation rxn

pyruvate → acetaldehyde → ethanol

1st enzyme: pyruvate carboxylase

2nd enzyme: alcohol DH

2 CO2 made

2 NAD+ made

acetaldehyde is poison

warburg effect

cancer cells turn off respiration and do aerobic lactate production (fermentation)

why do cancer cells favor lactate production over cellular respiration

1. glycolysis is 100x times faster method of ATP production

2. glycolysis produces a lot of pyruvate (hub molecule)

gluconeogenesis net rxn

2 pyruvate → glucose

4 ATP → 4 ADP +4 Pi

2 GTP → 2 GDP + 2Pi

2 NADH +2 H+ → 2NAD+

which organ/tissue does a lot of gluconeogenesis

liver

what are the irreversible steps of gluconeogenesis

steps 1,2,9,11

what are steps 1&2 of gluconeogenesis

bypass steps of pyruvate kinase

step 1:

pyruvate +ATP → oxaloacetate

• enzyme: pyruvate carboxylase (also uses biotin as a cofactor)

• occurs in the mitochondrion

step 2:

GTP + OAA → GDP + PEP + CO2

• enzyme: phosphoenolpyruvate carboxykinase (PEPCK) (also uses Mg2+)

• occurs in the cytosol

step 9 of gluconeogenesis

fructose 1-6 BP → fructose 6P (enzyme: glucose-1,6-bisphosphatase)

enzyme is a hydrolase

step 11 of gluconeogenesis

glucose 6 P → glucose (enzyme: glucose 6 phosphatase)

enzyme is a hydrolase

to regenerate NAD+, the muscles use ________, instead of cellular respiration because oxygen might be limiting (called ____) and cellular respiration is slow. This causes a build up of ______.

lactate fermentation

hypoxia

lactate

where does the build up of lactate go?

the cori cycle

cori cycle

how the liver uses the lactate from muscle exercise to make glucose during recovery from exercise

can cells make glucose from things other than lactate or pyruvate?

yes; glycerol, amino acids, lactate and pyruvate can all be converted into glucose

regulation of gluconeogenesis

• much of regulation of gluconeogenesis is reciprocally regulated w glycolysis

• hormones

  • insulin= high glucose _> turn off gluconeogenesis

  • glucagon= low glucose → turn on gluconeogenesis

• [S] + [P]

what are the 3 stages of respiration

1. pyruvate oxidation (link rxn) (occurs in mito matrix)

2. Kreb’s (occurs in mito matrix)

3. ETC/Ox Phos (occurs in inner membrane and IMS)

pyruvate oxidation rxn

pyruvate + NAD+ + CoA-SH → Acetyl-CoA +NADH +CO2

• irreversible

• major point for regulation

where does pyruvate oxidation occur?

PDH complex (metabolon)

• contains 3 enzymes required for pyruvate oxid

what are the advantages of PDH forming a metabolon?

allows for “substrate channeling” to..

• ensure fast/efficient catalysis

• prevents unwanted side rxns

• keeps local [S] high

catalytic coenzymes

regenerated by the end of the reaction so it does not appear in the net final reaction

stoichiometric coenzymes

function much like substrates, and appear in net final reaction

5 coenzymes needed for pyruvate oxidation what are they, what vitamin are they derived from and what is the coenzyme type.

1. NAD+ , derived from Niacin (B3), stiochiometric

2. CoA-SH, derived from pantothenate (B5), stoichiometric

3. TPP, derived from thiamin (B1), catalytic

4. lipoamide, catalytic

5. FAD, derived from riboflavin (B2), catalytic

PDH step 1

pyruvate combines with the ionized form of TPP, releasing CO2

PDH step 2

lipoamide swings from E2 to E1

PDH step 3

lipoamide steals the acetyl from TPP and swings back to E2

the lipoamide S is now reduced to form -SH

PDH step 4

• formation of acetyl-CoA

• dihydrolipoamide swings to E3

PDH step 5

dihrdolipoamide donates 2e-/2H to FAD to regenerate lipoamide

FAD becomes FADH2

lipoamide returns to E2

PDH step 6

FADH2 donates 2e- to NAD+ to make NADH and regenerate FAD

how many electrons are extracted from pyruvate by PDH complex

2 (NAD+ accepts 2 electrons to become NADH)

what are the prosthetic groups in PDH complex

FAD, TPP, and lipomaide

positive regulators of pyruvate oxidation

insulin

ADP

pyruvate

Ca2+

negative regulators of pyruvate oxidation

acetyl-coA

NADH

ATP

pyruvate oxidation is primarily regulated by reversible covalent modification of the PDH complex. what is the most common form of reversible covalent modification?

phosphorylation

kinase

enzyme that adds a phosphate group to a substrate using ATP as the donor of the phosphate (aka trasnferase)

phosphatase

enzyme that removes a phosphate group from a substrate using hydolysis (aka hydrolase)

inactive PDH complex

phosphorylated by PDH kinase

active PDH complex

de-phosphorylated by PDH phosphatase

active form of PDH favored by

high Ca2+

high insulin

high pyruvate and ADP

inactive form of PDH favored by

high product (ATP, NADH, Acetyl-CoA)

8 enzymes of Kreb’s

1. Citrate Synthase

2. Aconitase

3. Isocitrate DH

4. Alpha-Ketoglutarate DH

5. Succinyl CoA Synthetase

6. Succinate DH

7. Fumarase

8. Malate DH