Biochem Chapt 16

Front 1

Cellular respiration

Back 1

Process in which cells consume O and produce CO2

Provides more E (ATP) from glucose than glycolysis

Front 2

3 major stages

Back 2

Acetyl CoA production

Acetyl CoA oxidation

e- transfer and oxidative phosphorylation

Front 3

Respiration stage 1: Acetyl-CoA production

Back 3

Generates some ATP, NADH, FADH2

Carbs release 1/3 of total potential CO2 during stage 1

Front 4

Respiration stage 2: Acetyl-CoA oxidation

Back 4

Generates more NADH FADH2 and one GTP

Remaining C atoms from carbohydrates, amino acids, and fatty acids are released during this stage

Front 5

Respiration stage 3: oxidative phosphorylation

Back 5

Generates the vast majority of ATP during catabolism

Front 6

In eukaryotes stages 2 & 3 are localized to mitochondria

Back 6

Glycolysis occurs in cytoplasm

Citric acid cycle occurs in mitochondrial matrix

Oxidative phosphorylation occurs in the inner membrane

Front 7

Conversion of pyruvate to Acetyl CoA

Back 7

Catalyze by the pyruvate dehydrogenase complex

Requires 5 coenzymes

TPP, lipoate, FAD, NAD+, CoA-SH

Front 8

Structure of lipoate

Back 8

Prosthetic groups are strongly bound to the protein

Lipoic acid is covalently linked to the enzyme via a lysine residue

Front 9

Pyruvate dehydrogenase complex (PDC)

Back 9

A large multienzyme complex includes:

Pyruvate dehydrogenase, dihydrolipoyl transacetylase, dihydrolipoyl dehydrogenase

Front 10

Advantages of multienzyme complexes

Back 10

The short distance btw catalytic sites allows channeling of substrates from one catalytic site to another

Channeling minimizes side rxn

Regulation of activity of one subunit affects the entire complex

Front 11

Sequence of events in oxidative decarboxylation of pyruvate

Back 11

Enzyme 1:

Step1-decarboxylation of pyruvate to an aldehyde

Step 2- oxidation of aldehyde to a carboxylic acid

Enzyme 2:

Step 3- formation of Acetyl-CoA (product 1)

Enzyme 4-

Step4- reoxidation of the lipoamide cofactor

Step 5- regeneration of oxidized FAD cofactor (forming NADH product 2)

Front 12

Citric acid cycle

Back 12

8 steps summarized

1. Make citrate

2. Isomerization

3-4. Produce 2 NADH

5. GTP which converts to ATP

6. FADH2

7. Hydration

8. NADH

Front 13

Step 1 citrate synthesis

Back 13

Condensation of Acetyl CoA and oxaloacetate

The only rxn with a C-C bond formation

An acid/base catalysis

Rate limiting step and activity largely depends on oxaloacetate

Highly favorable/irreversible

Regulated by substrate availability and product inhibition

Front 14

Induced for in citrate synthase

Back 14

Conformational change after binding of oxaloacetate allows CoA to bind

Front 15

Step 2:aconitase isomerization by dehydration/rehydration

Back 15

Elimination of H2O from citrate gives a cis C=C bond (lyase)

Citrate (3 degree OH) is poor for oxidation so rearrange to get Ioscitrate (2 degree OH) is good substrate for oxidation

Front 16

Aconitase

Back 16

Contains iron sulfur center

Stereospecific

Front 17

Step 3: isocitrate dehydrogenase-oxidative decarboxylation

Back 17

Specific for NADP (cytosolic) or NAD+ (mitochondria)

1. Isotrate is oxidized to NADH or NADPH

2. Decarboxylation is facilitated by e- withdrawal (carbonyl and Mn). Releases CO2!

3. Rearrangement of the enol intermediate creates alpha-ketoglutarate

Highly favorable/irreversible and regulated by ATP

Front 18

Step 4: alpha-ketoglutarate dehydrogenase: final oxidative decarboxylation

Back 18

Last oxidative decarboxylation

Succhinyl CoA is another high thioester bond

Highly favorable/irreversible

Front 19

Alpha-ketoglutarate dehydrogenase

Back 19

Complex similar to pyruvate dehydrogenase

Same coenzymes, identical mechanisms

Active sites differ to accommodate different-size substrates

Front 20

Step 5: succinyl CoA synthestase

Back 20

Substrate level phosphorylation

Goes through a phospho-enzyme intermediate

Produced GTP (converts to ATP)

Slightly favorable and reversible

Front 21

Step 6: succinate dehydrogenase: oxidation of all and to alkene

Back 21

Bound to mitochondrial inner membrane

Reduction of the alkane to alkene requires FADH2 ( too low for NADH)

Near equilibrium/ reversible

Front 22

Step 7: fumurase hydration across a dble bond

Back 22

Water addition is always trans and forms L-Malate

OH- adds to fumerate then H+ adds to carbanion

Either C can gain OH-

Front 23

Step 8: malate dehydrogenase:oxidation of OH tons ketone and regeneration of oxaloacetate

Back 23

Final step

Regenerates oxaloacetate for citrate synthase

Highly unfavorable/ reversible

Front 24

Summary of citric acid cycle

Back 24

Back (Definition)

Front 25

Net results

Back 25

Added:

2 C from Acetyl CoA, 3 NAD+, FAD, GDP, Pi, 2 H2O

Got:

2 CO2, 3 NADH, FADH2, GTP, CoA, 3H+

Front 26

Total ATP made from glycolysis and the citric acid cycle

Back 26

30-32

Front 27

Anaplerotic rxn

Back 27

Intermediates in CAC can be used in biosynthetic pathways (removed from cycle)

Most important is pyruvate carboxylase reversed to form oxaloacetate

Front 28

Biotin (pyruvate carboxylase)

Back 28

CO2 carrier so important

Front 29

Regulation of CAC

Back 29

Regulated at highly favorable/ irreversible steps by:

Activated substrate availability

Inhibition by product accumulation

Overall products of the pathway are NADH and ATP which can inhibit or activate if high levels of NAD+ and AMP

Front 30

Also regulation is pyruvate dehydrogenase

Back 30

See pic