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Functional Ageing > Oxidative Stress and Mitochondria > Flashcards

Oxidative Stress and Mitochondria Flashcards

1
Q

What are mitochondria the site of?

A

ATP synthesis

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2
Q

What are mitochondria?

A

essential double membrane-bound organelles inherited from the mother

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3
Q

What is the outer mitochondrial membrane permeable to?

A

small ions

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4
Q

What are cristae?

A

invaginations of the inner membrane that enclose the mitochondria matrix

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5
Q

What is in the mitochondrial matrix?

A

most of the enzymes for the TCA cycle, the β-oxidation of fatty acids, and for mitochondrial DNA synthesis

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6
Q

What is embedded in the mitochondrial inner membrane?

A

ATP synthase and the protein complexes of ETC

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7
Q

What do endothelial cells do?

A
  • form a single cell layer that lines all blood vessels
  • regulate exchanges between the bloodstream and the surrounding tissues
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8
Q

What do the 37 genes of the mitochondrial genome encode for?

A

13 proteins that form the oxphos complex

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9
Q

What are the 4 general steps of ATP synthesis?

A
  1. glycolysis
  2. pyruvate processing
  3. TCA cycle
  4. ETC and chemiosmosis
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10
Q

How many complexes are in the ETC?

A

4 (although 5 involved in oxphos)

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11
Q

What are the major sources of ROS in the ETC?

A

complexes I and III since they can split electrons

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12
Q

What is the dual role of complex II?

A

succinate dehydrogenase in the ETC and TCA cycle that converts the FADH into FADH2 and also succinate to fumarate

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13
Q

What do complexes I, III and IV do?

A

pump electrons from the matrix to the EMS

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14
Q

What is the membrane potential of mitochondria?

A

the protons across the inner membrane generated by proton pumps that with the proton gradient, forms the transmembrane potential of hydrogen ions which is harnessed to make ATP

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15
Q

What do uncoupling proteins do?

A

bypass the ATP synthase to produce heat instead found in brown adipose mitochondria

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16
Q

What is the smallest motor in the human body?

A

ATP synthase

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17
Q

What happens if too much calcium enters into the mitochondria?

A

the membrane could rupture which would release pro-apoptotic factors to induce apoptosis

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18
Q

What do mitochondria use calcium for?

A
  • to activate the enzymes of the TCA cycle (it is a required co-factor)
  • cytosolic buffer
  • mitochondrial motility
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19
Q

What does the mitochondrial calcium uniporter do?

A

mediate the electrophoretic Ca²⁺ uptake into the matrix and control aerobic metabolism and apoptosis

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20
Q

What are mitoplasts?

A

mitochondria devoid of outer membrane

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21
Q

When is calcium uptake defective?

A

in aged mitochondria

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22
Q

What is biogenesis mediated by?

A

several TFs, especially PGC-1α

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23
Q

What is biogenesis?

A

the production of new mitochondrial material from pre-existing mitochondria

24
Q

What does a mutation in mtDNA lead to?

A

certain parts of the ETC not being produced

25
Q

How is damaged DNA removed?

A

mitophagy

26
Q

What is the lifecycle of mitochondria in normal cells?

A
  1. binding of transcriptional coactivators to TFs results in expression of nuclear genes encoding mitochondrial proteins and mRNAs
  2. mRNAs are exported from the nucleus and translated into proteins in the cytosol
  3. chaperones assist and direct proteins destined for mitochondria to the protein import machinery (PIM) for import into the organelle
  4. once inside, the proteins are directed to the appropriate mitochondrial compartment, and the organelle can expand to contain more ETC machinery
  5. Tfam binds mtDNA to regulate transcription and mtDNA replication
  6. 2 adjacent organelles can be tethered and fused together through the fusion proteins (Mfn1/2 and Opa1)
  7. healthy mitochondria consume oxygen and produce ATP in the ETC in accordance with the cellular demand
27
Q

What happens when a portion of the mitochondrial network becomes damaged?

A

fission proteins (Fis1, Mff, and Drp1) can be recruited to the dysfunctional site to cleave off the damaged portion

28
Q

How are dysfunctional mitochondria recognised?

A

through an increase in ROS emission and lower membrane potential

29
Q

What are the 4 steps of mitophagy?

A
  1. flaggeing for mitophagic degradation by ubiquitination of outer membrane proteins and binding of p62, LC3II, and NIX
  2. lipidated LC3II will initiate autophagosome formation to surround the organelle
  3. once fully encapsulated, the autophagosome is directed to the lysosome
  4. fusion of the autophagosome with the lysosome results in the degradation of the organelle by proteolytic enzymes to its basic constituents
30
Q

Why does mitophagy become defective with age?

A
  • increased production in ROS
  • decreased mtDNA replication
  • increased fission
31
Q

What are the results of fusion?

A
  • increase in oxidative capacity
  • repair of reversibly damaged mitochondria
  • limitation of mtDNA mutations during ageing
32
Q

What are the results of fission?

A
  • increase in resistance to oxidative stress
  • segregation of damaged mitochondria
  • mitophagy
33
Q

What are the 7 points of the mitochondrial theory of ageing?

A
  1. free radicals play a major role in ageing, and most are of mitochondrial origin
  2. mitochondrial DNA damage
  3. mutation of the mitochondrial DNA polymerase-gamma
  4. impaired energy production
  5. reduced expression of mitochondrial genes
  6. reduced antioxidant expression
  7. mitochondrial unfolded protein response
34
Q

What is a free radical?

A

any atom or molecular fragment with an unpaired electron

35
Q

Give examples of free radicals

A

superoxide, hydroxyl radicals, nitric oxide, nitrogen dioxide and hydrogen peroxide

36
Q

Where are free radicals produced?

A
  • internally (mitochondria, macrophages, ER, brain tissue)
  • externally (UV, smoking, radiation)
37
Q

What are the sources of ROS in macrophages?

A

NADPH oxidases (NOX2)

38
Q

What is ROS essential for?

A

the activation of uncoupling protein 1

39
Q

Give examples of irreversible damage induced by ROS

A
  • lipid peroxidation of membranes of cells, organelles
  • abnormal post-synthetic modifications of proteins
  • DNA mutations/damage
  • Inefficient mitochondria
40
Q

What are antioxidants?

A

substances that prevent the harmful effects of oxidation e.g. vitamin C, vitamin E and β-carotene

41
Q

What do free radical scavengers do?

A

seek out free radicals and harmlessly bind them before they initiate damage

42
Q

What are lipofuscins?

A

“wear-and-tear” pigments that collect in the more permanent cells (heart, liver, and neurons) of older people

43
Q

What is lipofuscin?

A

the accumulation of lysosomes, which have absorbed the worn-out, undigestible parts of the cell

44
Q

What can oxidant production greater than antioxidant defences lead to?

A

DNA, lipid and protein damage

45
Q

What does oxidative metabolism produce?

A

highly reactive free radicals that subsequently damage protein and DNA

46
Q

What is the evidence from model organisms that support the free radical theory?

A
  • superoxide dismutase (SOD) transgenes can extend the life span of Drosophila
  • chemicals that mimic catalase (peroxidase) activity can extend C. elegans life span
  • long lived mutants are typically stress resistant, including resistant to drugs (i.e. paraquat stress, which induces increased production of free radicals)
47
Q

What is the relationship between superoxide production and longevity in both mammals and insects?

A

inverse relationship i.e. animals that produce more ROS have a shorter lifespan

48
Q

Give examples of signalling pathways activated by oxidative stress

A
  • p53
  • HSF1
  • ERK
  • p38
  • JAK/STAT
49
Q

What do mitochondrial ROS do?

A
  • attack the redox sensitive ETC components to reduce their function
  • oxidise mitochondrial proteins and lipids
  • damage the mtDNA
  • reduce the antioxidant defence
50
Q

What is mtDNA?

A

a double stranded, closed and circular DNA ~16,569 bp that encodes for 37 genes

51
Q

What percentage of genetic material in animal cells is mtDNA?

A

1-3%

52
Q

Why does mtDNA experience a higher rate of mutations than nuclear DNA?

A

due to its close proximity to the ETC (i.e. exposed to high concentrations of free radicals) and also it lacks protective histones

53
Q

Why is longevity more strongly associated with the age of maternal death than paternal death?

A

mtDNA inheritance

54
Q

How much faster does mtDAN acquire mutations than nDNA?

A

6-7x

55
Q

What are the consequences of mitochondrial dysfunction?

A
  • ↑ oxidative stress
  • ↑ mtDNA damage
  • ↑ mtDNA deletions
  • ↑ oxidised proteins
  • ↑ lipid peroxidation
  • ↑ lipid adduct formation
  • ↓ repair mechanisms
56
Q

What happens when FeS complexes can’t enter into the organelle?

A

reused ox-phos complexes produce ROS which damages the complexes further

Functional Ageing (4 decks)

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