pyruvate and citric acid cycle quiz

regeneration of NAD+

• glycolysis makes NADH but needs NAD+ to run

• NADH must be turned back into NAD+

• if NAD+ runs out, glycolysis stops → no atp

fermentation

• turns NADH → NAD+

• happens when there’s no oxygen to keep glycolysis running

• its the backup system to restore NAD+

• pyruvate → ethanol

enzyme involved in fermentation

alcohol dehydrogenase

redox balance In alcoholic fermentation

keeps NAD+/NADH balanced

• restores NAD+ by making ethanol

alternative pathway for regenerating NAD+

• lactate fermentation

• pyruvate → lactate

• happens in muscles when oxygen is low

enzyme in lactic acid fermentation

lactate dehydrogenase

Entry points in glycolysis for galactose and fructose

galactose (G-6P) and fructose (F-6P) adipose tissue

enzymes that control glycolysis

• hexokinase

• PFK

• pyruvate kinase

control sites

irreversible steps in glycolysis

regulation of glycolysis In muscle

muscles adjust glycolysis based on energy needs

long slow run (glycolysis slows down)

• co2 and h2o is made from pyruvate

• oxygen is more abundant

sprint (glycolysis speeds up)

• lactate is made to regenerate NAD+ to keep glycolysis running

• oxygen is not abundant you need more

PFK (phosphofructokinase)

• most important enzyme in glycolysis

• inhibited by: ATP (high energy) stop

• activated by: AMP (low energy) go

• has 2 ATP binding sites: active site and regulatory site

the allosteric regulation of PFK

when atp is low, more PFK is made at a faster rate. when atp is high, PFK is able to generate and accumulate less and slower

fructose 2,6-BP

• strong activator of PFK

• pushes glycolysis forward even if ATP is present/high

pyruvate dehydrogenase

• enters mitochondria under aerobic conditions (oxygen present)

• gets turned into Acetyl CoA (irreversible)

• enzyme: pyruvate dehydrogenase complex

acetyl CoA

fuel for citric acid cycle

the link between glycolysis and the citric acid cycle

aka pyruvate processing (pyruvate → acetyl coa)

mitochondria

• where pyruvate processing happens

• citric acid cycle happens in the matrix

E1

oxidative decarboxylation of pyruvate

E2

transfer of acetyl group to CoA

E3

regeneration of the oxidized form of lipoamide

3 enzymes involved in the synthesis of acetyl coa from pyruvate

E1, E2, E3

5 coenzymes involved in the synthesis of acetyl coa from pyruvate

• TPP

• lipoamide

• CoA

• FAD

• NAD+

  • memory trick: TLC Friday Night

3 steps for pyruvate → acetyl coa

1. decarboxylation

2. oxidation

3. transfer to coa

coenzyme A

the activated carrier for acyl groups

• activated carrier: universal, reusable currency that can do different reactions

decarboxylation (step 1)

• E1 catalyzes decarboxylation (CO2 removed)

• uses TPP coenzyme to combine with pyruvate

oxidation (step 2)

• electrons transferred

• forms acetyllipoamide on E2

• catalyzed by E1

formation of acetyl coa (step 3)

• acetyl group transferred to coa

• transfer is catalyzed by E2

to participate in another reaction cycle of pyruvate processing

• dihydrolipoamide must be re-oxidized

• reaction is catalyzed by E3

• FAD → FADH2

• NAD+ → NADH

big picture pf pyruvate processing

pyruvate → Acetyl CoA + CO2 + NADH

Pyruvate dehydrogenase complex is regulated by two mechanisms

1. pyruvate → acetyl coa is IRREVERSIBLE

2. Acetyl coa can either be metabolized in the citric acid cycle OR made into fatty acids

Response of the pyruvate dehydrogenase complex to the energy charge

• high energy charge (atp, nah) → inhibit PDH (slow down)

• low energy charge → activate PDH (speed up)

what 2 enzymes regulate the pyruvate dehydrogenase complex

PDH kinase and PDH phosphatase

how does PDH kinase regulate the pyruvate dehydrogenase complex

turns off PDH (phosphorylation)

how does PDH phosphatase regulate the pyruvate dehydrogenase complex

turns on PDH (dephosphorylation)