Lecture 8: Metabolic Redox Reactions

Question 1

reduction potentials are a measure of

Answer 1

electron affinity

E

Question 2

electrons flow…

Answer 2

from reductants to oxidants

toward compinds with higher (more pos) E values

Question 3

Pyruvate dehydrogenase (PDH)

Answer 3

converts pyruvate to acetyl-CoA

Question 4

acetyl-CoA is used for…

Answer 4

1. complete oxidation by citrate cycle

2. fatty acid synthesis

Question 5

how is energy avalible from ReDox reactions?

Answer 5

based on nrg avalible from redox reactions

due to differences in electron affinity of 2 compounds

Question 6

coupled reactions

Answer 6

2 half reactions

oxidation reaction and reduction rxn

Question 7

oxidant

Answer 7

will accept electrons

are REDUCED

Question 8

reductants

Answer 8

donate electrons

are OXIDES

Question 9

Fe-Cu redox reaction

Answer 9

occurs in cytochrome c oxidase

in electron transport system

Question 10

aerobic resiration transfer…

Answer 10

electrons from GLUCOSE to O2 (oxygen)

to form CO2 and H2O

Question 11

see slide 5

Answer 11

see slide 5

Question 12

who owns the electrons in a CH bond?

Answer 12

Hydrogen is less electronegative than carbon!

so carbon owns the electrons

Question 13

Who owns electrons in an OH bond

Answer 13

oxygen is more electronegative than carbon!

Oxygen owns the electrons

Question 14

NAD+ and NADH

Answer 14

reduction of NAD+ to NADH

transfer of hydride ion (:H-)
-contains 2e- and 1 H+
and release of proton (H+)

NAD+ + 2e- + 2H+ NADH+ H+

electrons added as a pair associated with a hydride ion (proton gets lost)

Question 15

FAD and FADH2

Answer 15

FAD reduced by SEQUENTIAL ADDITION of one Hydrogen (1e- and 1 H+) at a time to get fully reduced FADH2

differs from NADH b/c e- can be added one at a time

FAD + 1e- +1H+ FADH +1e- + H+FADH2

Question 16

hydrogen half reaction

Answer 16

0 value

what we compare everything else to

Question 17

electron affinity measured by…

Answer 17

comparing it to hydrogen half reaction

Question 18

E^0’

Answer 18

Standard

under same standard conditions as deltaG^0’

Question 19

review how to read table on slide 9!

Answer 19

review how to read table on slide 9!

hydrogen half reaction is in middle!

Question 20

table is read…

Answer 20

standard reduction potentials are written in the direction of reduction reaction

Question 21

facts about E^0’

Answer 21

subtract reduction potential of donor from acceptor
proportional to standard free energy change
A CONSTANT
(it is favorable when value is POSITIVE)

Question 22

n in G^0’ / e^0’ equation means…

Answer 22

NUMBER OF ELECTRONS

Question 23

tip for doing reduction potential reactions

Answer 23

keep everything as reduction (don’t flip signs) and SUBTRACT donor from acceptor
(can flip reaction to show oxidation and change sign of E^0’, but that’s harder)

Question 24

review/ listen to slide 11

Answer 24

review/ listen to slide 11

Question 25

if you know ACTUAL CONCENTRATIONS of oxidants and reductants, use....

Answer 25

Nernst equation

Question 26

Pyruvate converted to acetyl-CoA by...

Answer 26

Pyruvate dehydrogenase complex (PDH)

Question 27

acetyl-CoA and the citrate cycle

Answer 27

metabolized to convert redox nrg to ATP | Oxidative phosphorylation

Question 28

acetyl-CoA used as a form of stored energy

Answer 28

conversion to fatty acids | go to adipocytes as triglycerides

Question 29

pyruvate dehydrogenase complex

Answer 29

made up of 3 subunits E1 (22 of them) E2 (60) and E3(6) lots of active sites (60) so 1 enzyme can do this reaction a bunch of times simulatneously

Question 30

PDH coenzymes

Answer 30

TPP attached to E1 lipoamide attached to E2 FAD covalently bound to E3

Question 31

see slide 16 for how PDH works

Answer 31

see slide 16 for how PDH works

Question 32

PDH step 1

Answer 32

E1 loses CO2, attach acetyl group of pyruvate to E1

Question 33

PDH step 2

Answer 33

in PDH subunit, theres a lipoamide group with a disulfide bond acetyllipoamide made when disulfide bond reduced that makes acetyl Co-A b/c acetyl groupd transfered onto left with oxidized molec

Question 34

transfer of the acetyl group in PDH

Answer 34

take it off pyruvate transfer on to TPP transfer onto lipoamide put onto Co-a to make acetyl CoA

Question 35

PDH step 3

Answer 35

``` regenerating for turnover use FAD that is attached to E3 oxidized molec left from 2 reduce FAD, redoxidzes the thing left from 2 use NAD to reoxidze FAD we get reduced NADH ```

Question 36

REVIEW SLIDE 17

Answer 36

REVIEW SLIDE 17 | reaction and red questions

Question 37

what comes out of the PDH reaction

Answer 37

pyruvate + CoA + NAD+-----> Acetyl CoA + CO2 + NADH

Question 38

is the PDH reaction reversible?

Answer 38

NO

Question 39

what does the PDH complex do?

Answer 39

catalyzes oxidative decarboylation of pyruvate to make CO2 and acetyl-CoA

Question 40

Arsenite

Answer 40

inhibitor of lipoamide ingestion can lead to death b/c it irreversibly blocks ability of lipoamide-containing enzymes like PDH found in arsenic

Question 41

REVIEW SLIDE 19

Answer 41

REVIEW SLIDE 19

Question 42

NAD+

Answer 42

redox transfer of hydride ion from B3

Question 43

FAD

Answer 43

``` redox transfer of electrons (2) (H) from B2 (riboflavin) ```

Question 44

CoA

Answer 44

acetyl group transfer from B5 (panthothenic acid) carrier molec for acetate units to make acetyl-CoA

Question 45

TPP

Answer 45

``` aldehyde transfer from B1 (thiamine) ```

Question 46

lipoamide

Answer 46

acetyl group transfer | not a vitamn

Question 47

biocytin

Answer 47

carboxyl group transfer | from Biotin

Question 48

Catabolic redox reactions

Answer 48

use redox pair NAD+/NADH

Question 49

the "+" in NADH

Answer 49

does NOT refer for charge of NAD moelc | only refers to charge on ring nitrogen in oxidized state

Question 50

anabolic redox reactions use

Answer 50

NADP+/NADPH

Question 51

Acetate

Answer 51

covalently attached to CoA through activated thiosester bond requires high deltaG^0' values