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Metabolism > Carbohydrates III > Flashcards

Carbohydrates III Flashcards

1
Q

what are the electron donors and acceptors of the ETC

A 
NAD, 
NADP, 
FAD or FMN, 
Coenzyme Q (UQ or ubiquinone), 
cytochromes, 
iron sulfur
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2
Q

how many hydrogen atoms are removed by NAD-linked dehydrogenases

A

2;

One is added to NAD and the other is released in the medium

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3
Q

How many electrons can FAD or FMN accept

A

it can accept either 1 to form semiquinone or 2 to form FADH2

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4
Q

what kind of enzyme is Coenzyme Q

A

a fat soluble benzoquinone with a isoprenoid side chain

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5
Q

what are other names for Coenzyme Q

A

UQ or Ubiquinone

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6
Q

what does coenzyme Q do?

A 
freely diffuses in the
lipid bilayer of the inner
mitochondrial membrane;
can shuttle reducing
equivalents between
other less mobile
electron carriers
in the membrane
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7
Q

what does coenzyme Q accept

A

one electron to become
semiquinone radical (.QH)
or 2 electrons to become
ubiquinol (QH2)

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8
Q

what prosthetic group do cytochromes contain

A

contain an iron heme

prosthetic group

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9
Q

what are the classes of cytochromes

A

classes a, b, and c

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10
Q

where can yo find cytochromes a, b and c

A

a, b, some c are
integral proteins of
the inner mitochondrial
membrane

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11
Q

what is special about Cyt C

A

soluble;
associates with outer
surface of inner
membrane

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12
Q

what can cytochromes absorb

A

light in the visible range about 390-700

cyt c mostly @ 400: absorbs more when reduced

B @ about 510-520

A @ about 540 -550

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13
Q

what type of iron heme does cyt b have

A

iron protoporphyrin IX (2 ethenes)

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14
Q

what type of iron heme does Cyt C have

A

heme C (2 cys groups)

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15
Q

what type of iron heme does Cyt a have

A

Heme A (long hydrocarbon)

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16
Q

what atoms is iron complexed with

A

inorganic sulfur atoms, sulfur atom of cysteine residues in protein or both

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17
Q

what do Iron-Sulfur proteins participate in

A

Participate in one electron
transfers where one Fe atom of
the Fe-S cluster is oxidized or
reduced

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18
Q

what is the order or electron complexes in ETC

A

Complex I, II, III, IV, ATP synthase

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19
Q

what kind of enzymes are the enzymes of the ETC

A

series of sequentially acting electron
carriers, mostly integral proteins with
prosthetic groups capable of accepting or
donating one or two electrons

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20
Q

how are they studied

A

Membrane-embedded
supramolecular complexes
can be physically
separated

digitonin treatment leads to osmotic rupture and inner membrane fragments are solubilized with detergent followed by ion-exchange chromatography

rxns catylized by isolated fractions in vitro helped elucidate them

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21
Q

what do complex I and Complex II do?

A

Catalyze electron transfer
To ubiquinone from two
different electron
donors:

NADH (Complex I) or
Succinate (Complex II)

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22
Q

what does complex III do

A

Carries electrons from
reduced ubquinone to
cytochrome c

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23
Q

what does complex IV do

A

Completes sequence by
transferring electrons
from cytochrome c to O2

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24
Q

what is the name of complex I and what is its structure

A

NADH dehydrogenase complex

multisubunit; 42 polupeptides

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25
Q

what does complex I catalyze

A 
1) exergonic transfer of a
hydride ion from NADH to
FMN, from which 2 e- pass
through a series of Fe-S
centers to the Fe-S
protein N2 to ubiquinone
2) endergonic transfer of 4
protons from mitochondrial
matrix to intermembrane
space (e- transfer drives
expulsion from the matrix of
4 H+/e- pair
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26
Q

what does NADH + H+ transfer its e- to

A

FMN to make FMNH2

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27
Q

FMNH2 transfer its e- to

A

Fe3+S to form Fe2+- S

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28
Q

Fe2+- S transfer its e- to

A

CoQ to form CoQH2

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29
Q

what are the proton pumps in ETC driven by

A

energy of electron transfer

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30
Q

what is the name of complex II

A

succinate dehydrogenase complex

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31
Q

what is the structure of complex II

A

contains 5 prosthetic groups and 4 protein subunits

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32
Q

what do subunits A and B contain

A

3 2Fe-2S centers

a bound FAD

a succinate binding site

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33
Q

what does complex II catalyze

A 
Catalyzes transfer of
e- from succinate to
FAD, through the 3
Fe-S centers to
ubiquinone
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34
Q

what does succinate transfer its e- to?

what does it become?

A

FAD to form FADH2

succinate becomes fumarate

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35
Q

FADH2 transfer its e- to

A

Fe3+ to form Fe2+S

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36
Q

Fe2+S transfer its e- to

A

CoQ to formCoQH2

37
Q

what enzyme also contributes electrons to the ETC

A

glycerol 3 phosphate dehydrogenase (has FAD cofactor)

38
Q

what are other enzymes pass electrons to mitochondrial dehydrogenases

A

acyl-CoA dehydrogenase and G-3-P dehydrogenase

Pass electrons into
electron transport
chain via ubiquinone,
but not through
Complex II
39
Q

when does acyl-CoA dehydrogenase contribute to ETC

A

-during β-oxidation of fatty acyl CoA

40
Q

What is Glycerol-3-P dehydrogenase, what does it do and when does it contribute to ETC

A

-a flavoprotein
- oxidizes Glycerol-3-P
- channels e- into chain by reducing ubiquinone
-shuttles reducing equiv from cytosolic NADH to
mitochondrial matrix

***glycerol or clyceraldehyde? look up

41
Q

what is the name of complex III

A

Cytochrome bc1 complex

42
Q

what is the structure of complex III

A

homodimer (each with 11 subunits)

43
Q

what makes up the core of complex III

A

Core:
cytochrome b (w/ 2 hemes,
R Fe-S protein w/ 2Fe-S)
& Cytochrome c1 (w/ heme)

44
Q

what does cyt C1 of complex III interact with

A

Cytochrome c1 interacts
with cytochrome c (not
part of complex) in
intermembrane space

45
Q

what does complex III do to Ubiquinone

A

oxidizes QH2 to Q;
reduces 2 molecules of
cytochrome c

46
Q

what does complex III couple

A 
Couples the transfer of
electrons from QH2
to cytochrome c with
transport of protons from
the matrix to the
intermembrane space
47
Q

what is the net equation of complex III

A

QH2 + 2 Cyt c1 (oxidized) + 2Hn+ –> Q + 2 cyt c1 (reduced) + 4Hp+

48
Q

what is the name of complex IV

A

cytochrome oxidase

49
Q

what does complex IV do

A 
-carries
electrons from
cytochrome c
to O2,
reducing it to
H20
50
Q

what is the structure of complex IV

A

large enzyme (core with 3 subunits) of inner mitochondrial membrane

51
Q

describe the path of e- in complex IV

A

path of electrons: 2 molecules of reduced cytochrome c donate an eto
binuclear center CuA; e- pass through heme a to Fe-Cu center
(heme a3, CuB); O2 binds a3 and is reduced to 2 molecules of H20;
uses 4 protons from matrix; 4 more protons pumped from matrix

52
Q

summarize the flow of e- and protons through 4 complexes of respiratory chain

A

1) Electrons reach Q through complexes I and II
2) QH2 serves as a mobile carrier of electrons and protons; passes
e- to Complex III, which passes them to mobile cytochrome c
3) Complex IV then transfers e- from reduced cytochrome c to O2
4) Electron flow is accompanied by proton flow from matrix to the
intermembrane space; proton gradient conserves energy of e- tranfer

53
Q

How is the concentration gradient of protons transformed into ATP?

A 
Proton-motive force
conserves more than
enough free energy
(~200 kJ) per “mole”
of e- pairs to drive
the formation of a
mole of ATP (which
requires 50 kJ)
54
Q

what drives ATP synthesis

A

Electrochemical energy
in proton gradient ATP synthesis

  • due to difference in [ ] of chemical species in 2 regions separated by membrane

-results from separation of charge
when proton moves across the
membrane w/o a counterion

55
Q

chemiosmotic model

A

Electrochemical gradient inherent in the differences in proton
concentration and separation of charge across the inner
mitochondrial membrane - the proton-motive force - drives the
synthesis of ATP as protons flow passively back into the matrix
through a proton pore associated with ATP synthase

56
Q

what is the name of complex V

A

ATP synthase complex

57
Q

what are complex V’s subunits (F0F1 ATPase)

A

F1

F naught

58
Q

what does F naught F1 ATPase do and what is its structure

A

-FoF1 ATPase - ATP synthesizing component on inner mitochondrial
membrane; multisubunit of F1 and Fo >12 polypeptides

59
Q

what is the structure of F1 and what is it attached to

A

-F1 contains 9 subunits (α3β3γδε), with binding sites for ATP and ADP,
and catalytic site of ATP synthesis; bound to mitochondrial
membrane through its interaction with Fo

60
Q

what is the structure of F naught and what is it attached to

A

is an integral membrane complex that forms the transmembrane

channel for the transport of protons (proton pore)

61
Q

what does flow of proteon through F0 cause

A

-Flow of protons through Fo of ATP synthase causes each of the
three nucleotide-binding sites in F1 to cycle from (ADP + Pi)
-bound to ATP-bound to empty conformation

62
Q

what is the Key to Binding •C R

Change Mechanism for ATP Synthesis

A

Rotational Catalysis

63
Q

how many nucleotide binding sites for ATP synthase have

A

-3 nucleotide binding sites, one for each pair of α and β subunits;
At any moment, one of sites is in β-ATP form (binds ATP tightly),
a 2nd is in the β-ADP form (loose-binding), and a 3rd in β-empty
(very loose binding) form.

64
Q

summarize rotational catalysis

A

1) Proton-motive force cause rotation of the central shaft
2) This produces a change where β-ATP site is converted to
β-empty form, and ATP dissociates;
3) β-ADP site is converted to a β-ATP site; promotes ATP formation
4) β-empty site becomes β-ADP site (loosely binds ADP + Pi)

65
Q

what is another thing that proton motor force also drive

A

Proton Motive Force also drives transport processes

essential to oxidative phosphorylation

66
Q

(in inner mitochondrial membrane) carry ADP and Pi into the matrix and newly synthesized ATP into the cytosol

A

-Adenine nucleotide and phosphate translocases

67
Q

what does phosphate translocase do

A

promotes symport of H2PO4- and 1 H+ into

the matrix; at pH 7, Pi is present as both HPO42- and H2PO4-

68
Q

what do you can ATP synthase + both tranlocases

A

ATP synthasome

69
Q

how is cytosolic NADH transported into mitochondria for oxidation

A

via the malate aspartate shuttle

70
Q

what organs is the malate asparte shuttle used in

A

liver, kidney, heart

-where rapid regeneration of NAD+ is not necessary

71
Q

In malate asparte shuttle: reducing equivalents are reacted with OAA to form what? what is the enzyme? what happens to it?

A

malate (via malate dehydrogenase) which is transported to matrix from intermembrane space (cytosol?) through MAlate - alpha ketogluterate transporter

72
Q

what happens to malate once transported into matrix? what happens to the NADH?

A

it is oxidized back to OAA (via malate dehydrogenase) and regenerates NADH

NADH can be taken to complex I and yield 2.5 ATP via ETC

73
Q

OAA in the matrix is reacted with what to make what? what enzyme is used? what happens after that

A

OAA reacted with glutamate to form aspartate and alpha ketogluterate via aspartate aminotransferase.

aspartate is shuttled out of matrix through Glutamate-aspartate transporter

alpha ketogluterate is transported to cytosol/intermembrane space through mallate -alpha ketogluterate transporter

74
Q

what does aspartate react with in the cytosol/intermembrane space? what does it form? what enzyme is used?

A

aspartate reacts with alpha-ketogluterate to make glutamate and OAA via aspartate aminotransferase

OAA reused again to start new transport of NADH

glutamate is transported to matric via Glutamate-aspartate transporter

75
Q

name another NADH shuttle

A

glycerol 3 phoshate shuttle

76
Q

what tissues use glycerol 3 phoshate shuttle? why?

A

operates in the skeletal muscle and the

brain where rapid and efficient regeneration of NAD+ can be critical.

77
Q

what does glycerol 3 phoshate shuttle do

A

NAD+ from glycolysis is regenerated by reducing dihydroxyacetone phosphate to glycerol 3-phosphate. Glycerol 3-phosphate is reoxidized to
dihydroxyacetone phosphate by mitochondrial glycerol 3-phosphate dehydrogenase, which is bound to the inner membrane.

78
Q

what does glycerol 3 phosphate dehydrogenase do with e- it recieves

A

delivers electrons to ubiquinone rather than Complex III, thus yielding
only 1.5 ATP per pair of electrons.

79
Q

ATP Yield from Complete Oxidation of Glucose

A

Stoichiometry: Consensus Values
• Number of protons pumped out per pair of electrons: 10
from NADH and 6 from succinate
• Number of protons required to make to make ATP: 4
• Net yield: 2.5 ATP per NADH oxidized:
1.5 ATP per succinate oxidized

80
Q

there is interlocking regulation of backbone by what molecules?

what 3 changes in these lead cause what regulatory response?

A

ATP, ADP, AMP and NADH

  1. high ATP or low ADP and AMP causes low rates
  2. pathways accelerated when ATP consumption goes up and when formation of ADP, AMP and Pi increases
  3. increased levels of NADH and
    acetyl-CoA inhibits pyruvate
    oxidation to Acetyl-CoA and
    dehydrogenase reactions of TCA
81
Q

what activate oxidative phosphorylation

A

ADP and Pi

82
Q

what effect does brown fat have on ETC?

what molecule in brown fat is important for this and what does it cause?

A 
Brown fat: adipose tissue
in which fuel oxidation
serves not to produce ATP
but to generate heat to
keep newborns warm;
-Thermogenin= “uncoupling
protein” in mitochondria
provides path for protons to
return to matrix w/o passing
ATP synthase- no ATP prod
83
Q

what happens in ETC of ischemic cells?

what mechanism leads to this effect?

A

electron transfer ceases, and
proton-motive force collapses-ATP drop

-a small dimeric inhibitory protein IF1
binds to ATP synthase, inhibits their
ATPase activity; favored at low pH,
when O2-starved cells mostly undergo
glycolysis and produce pyruvate,lactate
84
Q

what inhibits the tranport of e- to Q

A

rotenone and Amytal

85
Q

what blocks the electron transfer from cyt b to c

A

antimycin A

86
Q

what inhibits cytochrome oxidase

A

cyanide, azide, carbon monoxide

87
Q

what inhibits ATPase F1

A

Oligomycin

88
Q

By what mechanism does cyanide work?

what is the treatment?

A 
-Cyanide inhibits the cytochrome
oxidase step
-it binds Fe3+ in the heme of
cytochrome a, a3 component
(tissue asphyxia)
-treatment: inhalation of amyl
nitrite or intravenous
NaNo2, which converts
oxyhemoglobin to
methemoglobin

Metabolism (8 decks)

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