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BIOS4007 - Bioenergetics and Primary Metabolism > Oxidative Phosphorylation > Flashcards

Oxidative Phosphorylation Flashcards

1
Q

What 2 processes are involved in oxidative phosphorylation?

A
  • electron transport chain
  • chemiosmosis
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2
Q

Is mitochondria double-membraned?

A

yes - has inner & outer membrane

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3
Q

What is the structure of the inner membrane of mitochondria?

A

many fold called cristae
- cristae increases surface area

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4
Q

Why is it important for mitochondria to have a double layered membrane?

A

enables the maintenance of a proton gradient over the inner membrane

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5
Q

What is the region between the 2 mitochondrial membranes called?

A

intermembrane space

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6
Q

How does the intermembrane space differ from the matrix of the mitochondria?

A

intermembrane:
- low pH
- high H+ conc

matrix:
- high pH
- low H+ con

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7
Q

What is chemiosmosis?

A

describes the movement of ions across a membrane following their electrochemical gradient (to generate an AP)

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8
Q

Where is the ATP synthase located?

A

inner membrane of mitochondria

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9
Q

What does the ATP synthase do?

A

transport H+ (protons) from intermembrane space back to matrix

ADP + Pi → ATP

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10
Q

What does the electron transport chain maintain?

A

maintains H+ gradient

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11
Q

What happens in complex I of the electron transport chain?

A

(slide 9)
NADH → NAD+ + 2e-
- NADH converts to NAD+ and donates an e- (supercharge) to coenzyme Q / ubiquinone
- movement of e- drives H+ into intermembrane space

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12
Q

What happens in complex II of the electron transport chain?

A

(slide 10)
FADH2 → FAD+ + 2e-
- FADH2 converts to FAD+ and donates 2e- (supercharge) to coenzyme Q / ubiquinone

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13
Q

What happens in complex III of the electron transport chain?

A

(slide 11)
- Q donates all e- to complex III (now supercharged)
- all e- move out of III to cytochrome C
- movement of e- drives H+ to intermembrane region

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14
Q

What happens in complex IV of the electron transport chain?

A

(slide 12)
- e- moves from cytochrome C through IV
- movement of e- causes another H+ to move to intermembrane
- e- donated from O2 to form H2O

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15
Q

How many electrons are donated from all complexes in the electron transport chain?

A

6

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16
Q

How many H+ (protons) move to the intermembrane space in the electron transport chain?

A

10 for 2e-

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17
Q

What type of group do electrons flow as through complexes?

A

via groups of increasing e- affinity

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18
Q

What is Redox Potential?

A

the measure of the ease with which a molecule accepts e-
- more +ve the redox, the more readily e- is accepted

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19
Q

How does redox potential and free energy of an electron change as electrons move along the electron transport chain complexes?

A
  • redox potential: increases
  • free energy: decreases
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20
Q

What is Ubiquinone?

A

electron carriers (aka Coenzyme Q)

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21
Q

What is Ubiquinone?

A

electron carriers (aka Coenzyme Q)

22
Q

What are cytochromes?

A

A protein shell that surrounds a haem group (containing Fe) in the centre
- Fe is the electron carrier

23
Q

How is electron flow through complexes achieved?

A

via Fe-S / Haem groups

24
Q

How does Fe-S move electrons through complex I?

A
  • NADH donates e- to flavin mononucleotide (FMN)
  • Electrons transferred through 7 Fe-S clusters
  • Final Fe-S donates to ubiquinone
  • Negative charge on ubiquinone drives conformational changes in the E-channel
  • Moves through ‘Open’ and ‘Closed’ states driving proton transport through the membrane region
25
Q

How does Fe-S move electrons through complex II?

A
  • Complex 2 is a four-subunit protein complex
  • Succinate to Fumarate conversion transfers electrons to FAD to generate FADH2
  • Electrons are then passed through 3 Fe-S groups to ubiquinone
  • (FADH2 → FAD again as it transfers e- gained from FAD)
26
Q

How does Fe-S move electrons through complex III?

A
  • 11 subunits: 3 respiratory subunits, 2 core proteins and 6 low-molecular weight proteins
  • Initiates proton flow via the Q cycle
27
Q

How does Fe-S move electrons through complex IV?

A
  • enzyme: cytochrome c oxidase
  • 14 subunits
  • 2 haem groups, (a3 & a) and 2 copper centres
28
Q

What is complex V?

A

A large multi-subunit protein complex that has 2 domains:
- FO
- F1

29
Q

What is FO?

A
  • Membrane bound
  • Ring of c subunits, freely able to rotate
  • a subunit bound to c ring
  • b subunit bound to a subunit, links to α/β dimer ring of F1
30
Q

What is F1?

A
  • Protrudes into matrix
  • Central γ subunit stalk, rotates with the c ring
  • Ring of α/β dimers, held static by the b subunit
31
Q

How do protons move through the FO subunit in Complex V?

A

Proton movement through FO drives rotation of the γ subunit which drives ATP formation in F1:

  • Protons enter the a subunit, then to the c subunit, driving rotation of the c ring
  • Following a complete rotation protons are released on the matrix side through the a subunit
  • Rotation of the c ring drives rotation of the γ subunit connecting to the F1
32
Q

What are the 3 sites of γ rotation?

A

The γ rotation drives conformational changes at the three active sites in a cycle of:
- Binding of ADP & Pi (loose state)
- Confirmation change brings ADP & Pi together to form ATP (tight state)
- Release of ATP (open state)

33
Q

How is ATP released from the mitochondria?

A

ATP is released from the mitochondria by the ATP/ADP translocase

  • a protein located in the inner mitochondrial membrane that acts as an antiporter, exchanging ATP for ADP
  • transport follows concentration gradient
34
Q

What is the role of the ATP/ADP translocase in ATP transport?

A

responsible for transporting ATP out of the mitochondrial matrix and into the cytoplasm
- translocase acts as an antiporter, exchanging ATP for ADP and following concentration gradients to drive the transport process

35
Q

What are uncouplers?

A

Uncouplers are chemicals or proteins that disrupt the coupling of electron transport and ATP synthesis in mitochondria by removing the proton gradient that drives ATP synthesis.

36
Q

What is the effect of uncouplers on mitochondrial function?

A

Inhibit ATP synthesis without affecting the respiratory chain and ATP synthase (H(+)-ATPase)

37
Q

What are some examples of uncoupling chemicals?

A
  • 2,4-dinitrophenol (DNP)
  • carbonyl cyanide m-chlorophenyl hydrazone (CCCP)
  • desaspidin
  • pentachlorophenol
  • triclosan
38
Q

What are the uncoupling proteins?

A
  • UCP1 (thermogenin)
  • UCP2
  • UCP3
  • UCP4
  • UCP5
39
Q

What does 2,4-dinitrophenol (DNP) function as?

A

Functions as a protonophore
- Hydrophobic, diffuses across membrane
- Carries protons
- Removes the proton gradient

40
Q

What inhibitors (drugs/toxins) disrupt complexes of the ECT?

A
  • complex I: rotenone
  • complex II: ——-
  • complex III: antimycin A
  • complex IV: cyanide
  • complex V: oligomycin
41
Q

How can mitochondrial function be measured?

A

via oxygen consumption

42
Q

How can inhibitors be used to measure mitochondrial function?

A

The addition of different inhibitors can characterise different facets of mitochondrial function:

No treatment – basal rate of respiration

Oligomycin – respiration coupled to ATP production

Uncoupler – maximum respiration capacity

Rotenone/Antimycin A – Non-mitochondrial oxygen consumption

43
Q

What are some examples of mitochondrial disorders that affect OxPhos?

A
  • Diabetes mellitus & deafness (DAD)
  • Leber’s hereditary optic neuropathy (LHON)
  • Leigh syndrome
  • Neuropathy, ataxia, retinitis pigmentosa (NARP)
  • Myoneurogenic gastrointestinal encephalopathy (MNGIE)
  • MERRF syndrome
  • MELAS syndrome
  • Kearns–Sayre syndrome (KSS)
  • Mitochondrial DNA depletion syndrome
44
Q

What is Leber hereditary optic neuropathy (LHON)?

A

Non-Mendilian, maternal inheritance
- painless, progressive loss of vision

  • Usually begins between 25 to 35 years old, but can occur at any age
  • Prevalence of 1 in 30,000 to 1 in 50,000
  • More common in males than in females
  • Characterised by degeneration of retinal ganglion cells and optic nerve
45
Q

What are treatments and preventatives for LHON?

A
  • Idebenone (Raxone, Sovrima) is protective against vision loss in LHON
  • Idebenone is a strong antioxidant
  • Also allows the ECT to bypass complex I, carrying electrons directly to complex III
46
Q

What is Neuropathy, ataxia, retinitis pigmentosa (NARP) ?

A

Rare disease, symptoms commonly begin in childhood
- Muscle weakness, sensory neuropathy, vison loss
- Developmental delay, seizures and hearing loss sometimes observed

Maternal (mitochondrial inheritance)
- Identified mutations in the MT-ATP6 gene
- Mutation found in 70-90% of mitochondria
- More than 90%, Leigh syndrome presents

MT-ATP6 encodes part of the proton channel in the FO portion of complex V

47
Q

How are Reactive Oxygen Species involved in the ETC?

A

reduce O2 to water in final step of ETC

48
Q

Why is the reduction of O2 during the ETC potentially dangerous?

A

The reduction of O2 can generate partially reduced reactive oxygen species (ROS), which are highly reactive and can cause oxidative damage to cells

49
Q

What can lead to the accumulation of ROS in cells?

A

Failures in the ETC complexes can lead to the accumulation of electrons or protons, increasing the levels of ROS produced

50
Q

What is Leigh Syndrome?

A

Variable symptoms, but commonly developmental delay, muscle weakness and seizures

Loss of muscle control often occurs with progression

Most commonly seen in infants following a period of infection or illness

Thus far over 75 genes have been associated with the condition
Both nuclear and mitochondrial

All link to OxPhos

51
Q

Leigh syndrome mutations

A

Unlike LHON, Leigh syndrome mutations reduce ATP production

Notable the onset of symptoms coincides with developmental periods requiring increased metabolic loads

Suggested that lack of energy at these critical times causes the disease symptoms

BIOS4007 - Bioenergetics and Primary Metabolism (6 decks)

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