Lecture 8: Metabolic Redox Reactions Flashcards
reduction potentials are a measure of
electron affinity
E
electrons flow…
from reductants to oxidants
toward compinds with higher (more pos) E values
Pyruvate dehydrogenase (PDH)
converts pyruvate to acetyl-CoA
acetyl-CoA is used for…
- complete oxidation by citrate cycle
2. fatty acid synthesis
how is energy avalible from ReDox reactions?
based on nrg avalible from redox reactions
due to differences in electron affinity of 2 compounds
coupled reactions
2 half reactions
oxidation reaction and reduction rxn
oxidant
will accept electrons
are REDUCED
reductants
donate electrons
are OXIDES
Fe-Cu redox reaction
occurs in cytochrome c oxidase
in electron transport system
aerobic resiration transfer…
electrons from GLUCOSE to O2 (oxygen)
to form CO2 and H2O
see slide 5
see slide 5
who owns the electrons in a CH bond?
Hydrogen is less electronegative than carbon!
so carbon owns the electrons
Who owns electrons in an OH bond
oxygen is more electronegative than carbon!
Oxygen owns the electrons
NAD+ and NADH
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)
FAD and FADH2
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
hydrogen half reaction
0 value
what we compare everything else to
electron affinity measured by…
comparing it to hydrogen half reaction
E^0’
Standard
under same standard conditions as deltaG^0’
review how to read table on slide 9!
review how to read table on slide 9!
hydrogen half reaction is in middle!
table is read…
standard reduction potentials are written in the direction of reduction reaction
facts about E^0’
subtract reduction potential of donor from acceptor
proportional to standard free energy change
A CONSTANT
(it is favorable when value is POSITIVE)
n in G^0’ / e^0’ equation means…
NUMBER OF ELECTRONS
tip for doing reduction potential reactions
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)
review/ listen to slide 11
review/ listen to slide 11
if you know ACTUAL CONCENTRATIONS of oxidants and reductants, use….
Nernst equation
Pyruvate converted to acetyl-CoA by…
Pyruvate dehydrogenase complex (PDH)
acetyl-CoA and the citrate cycle
metabolized to convert redox nrg to ATP
Oxidative phosphorylation
acetyl-CoA used as a form of stored energy
conversion to fatty acids
go to adipocytes as triglycerides
pyruvate dehydrogenase complex
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
PDH coenzymes
TPP attached to E1
lipoamide attached to E2
FAD covalently bound to E3
see slide 16 for how PDH works
see slide 16 for how PDH works
PDH step 1
E1 loses CO2, attach acetyl group of pyruvate to E1
PDH step 2
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
transfer of the acetyl group in PDH
take it off pyruvate
transfer on to TPP
transfer onto lipoamide
put onto Co-a to make acetyl CoA
PDH step 3
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
REVIEW SLIDE 17
REVIEW SLIDE 17
reaction and red questions
what comes out of the PDH reaction
pyruvate + CoA + NAD+—–> Acetyl CoA + CO2 + NADH
is the PDH reaction reversible?
NO
what does the PDH complex do?
catalyzes oxidative decarboylation of pyruvate to make CO2 and acetyl-CoA
Arsenite
inhibitor of lipoamide
ingestion can lead to death b/c it irreversibly blocks ability of lipoamide-containing enzymes like PDH
found in arsenic
REVIEW SLIDE 19
REVIEW SLIDE 19
NAD+
redox
transfer of hydride ion
from B3
FAD
redox transfer of electrons (2) (H) from B2 (riboflavin)
CoA
acetyl group transfer
from B5 (panthothenic acid)
carrier molec for acetate units to make acetyl-CoA
TPP
aldehyde transfer from B1 (thiamine)
lipoamide
acetyl group transfer
not a vitamn
biocytin
carboxyl group transfer
from Biotin
Catabolic redox reactions
use redox pair NAD+/NADH
the “+” in NADH
does NOT refer for charge of NAD moelc
only refers to charge on ring nitrogen in oxidized state
anabolic redox reactions use
NADP+/NADPH
Acetate
covalently attached to CoA through activated thiosester bond
requires high deltaG^0’ values
