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06May25 > mitochondria > Flashcards

mitochondria Flashcards

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1
Q

What is a mitochondrion?

A

An organelle found in the cells of most eukaryotes, involved in aerobic respiration and ATP generation

Mitochondria are often referred to as the ‘powerhouse of the cell’.

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2
Q

Who discovered mitochondria and when?

A

Albert von Kölliker in 1857

He discovered them in the voluntary muscles of insects.

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3
Q

What is the term ‘mitochondrion’ derived from?

A

A thread-like granule

The term was coined by Carl Benda in 1898.

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4
Q

What is the main function of mitochondria?

A

To generate ATP through aerobic respiration

They also play roles in signaling, cellular differentiation, and cell death.

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5
Q

What is the typical size range of mitochondria?

A

0.75 to 3 μm² in cross section

Their size can vary considerably.

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6
Q

What are the compartments of a mitochondrion?

A
  • Outer membrane
  • Intermembrane space
  • Inner membrane
  • Cristae
  • Matrix
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7
Q

What is the outer mitochondrial membrane composed of?

A

Phospholipid bilayers and proteins

It has a protein-to-phospholipid ratio similar to that of the cell membrane.

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8
Q

What is the role of porins in the outer mitochondrial membrane?

A

They form channels that allow the passage of small molecules

The voltage-dependent anion channel (VDAC) is a major trafficking protein.

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9
Q

What is the purpose of the intermembrane space in mitochondria?

A

It serves as a compartment for certain proteins and ions

Its protein composition differs from that of the cytosol.

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10
Q

What type of proteins are found in the inner mitochondrial membrane?

A
  • Proteins for electron transport chain reactions
  • ATP synthase
  • Specific transport proteins
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11
Q

What is cardiolipin and where is it found?

A

A phospholipid characteristic of mitochondrial and bacterial membranes

It contains four fatty acids and contributes to membrane impermeability.

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12
Q

What are cristae in mitochondria?

A

Folds of the inner membrane that increase surface area for ATP production

They are more abundant in cells with higher ATP demands.

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13
Q

What is contained within the mitochondrial matrix?

A
  • Enzymes
  • Mitochondrial ribosomes
  • tRNA
  • Mitochondrial DNA
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14
Q

What is the primary function of the citric acid cycle?

A

To oxidize acetyl-CoA and produce ATP and reduced cofactors

It is also known as the Krebs cycle.

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15
Q

What are the main energy-releasing reactions in mitochondria?

A
  • Reactions at protein complexes I, III, and IV in the inner mitochondrial membrane
  • Reactions involving NADH and FADH2
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16
Q

True or False: Mitochondria have their own genome.

A

True

The mitochondrial genome is similar to bacterial genomes.

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17
Q

Fill in the blank: Mitochondrial biogenesis is temporally coordinated with _______.

A

cellular processes

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18
Q

What is the role of the ATP synthase in mitochondria?

A

To generate ATP from ADP and inorganic phosphate in the matrix

It utilizes the proton gradient established by the electron transport chain.

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19
Q

What are the protein complexes where energy-releasing reactions occur in mitochondria?

A

Protein complexes I, III, and IV

These include NADH dehydrogenase (ubiquinone), cytochrome c reductase, and cytochrome c oxidase.

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20
Q

What is the reaction that occurs at complex IV of the electron transport chain?

A

O2 + 4H+ (aq) + 4Fe2+ (cyt c) ⟶ 2H2O + 4Fe3+ (cyt c)

ΔrGo′ = -218 kJ/mol, releasing a lot of free energy.

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21
Q

What is the reaction that occurs at complex III involving cytochrome c?

A

2Fe3+ (cyt c) + QH2 ⟶ 2Fe2+ (cyt c) + Q + 2H+ (aq)

ΔrGo′ = -30 kJ/mol.

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22
Q

What is the reaction at complex I involving NADH?

A

Q + H+ (aq) + NADH ⟶ QH2 + NAD+

ΔrGo′ = -81 kJ/mol.

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23
Q

What mechanism allows protons to return to the mitochondrial matrix and synthesize ATP?

A

Chemiosmosis

This process was first described by Peter Mitchell.

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24
Q

What is mitochondrial uncoupling or proton leak?

A

Protons re-enter the mitochondrial matrix without contributing to ATP synthesis

Mediated by the proton channel thermogenin (UCP1).

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25
What is the primary end product of mitochondrial fatty acid synthesis (mtFASII)?
Octanoyl-ACP (C8) ## Footnote It is also involved in lipoic acid biosynthesis.
26
What is the role of mitochondria in calcium ion regulation?
Mitochondria can transiently store calcium and regulate cellular calcium homeostasis ## Footnote They act as cytosolic buffers for calcium.
27
How do mitochondria influence cellular proliferation?
Mitochondria generate ATP via oxidative phosphorylation, which is vital for cell division and differentiation ## Footnote Interference with OxPhos can cause cell cycle arrest.
28
What is programmed cell death (PCD) and its role?
PCD is crucial for organ development and cellular homeostasis ## Footnote It prevents malignant transformation and aids in immunity.
29
What role do mitochondria play in apoptosis?
Mitochondria release cytochrome c, which induces the formation of apoptosomes ## Footnote They also release damage-associated molecular patterns (DAMPs).
30
What are some additional functions of mitochondria?
* Signaling through mitochondrial reactive oxygen species * Regulation of the membrane potential * Calcium signaling * Regulation of cellular metabolism ## Footnote Mitochondria are involved in heme and steroid synthesis, hormonal signaling, and immune cell development.
31
What is the chondriome?
The population of all mitochondria in a given cell ## Footnote Mitochondria vary in number and location according to cell type.
32
What is the mitochondria-associated ER membrane (MAM)?
A structural element that plays a critical role in cellular physiology and homeostasis ## Footnote It is the interface between mitochondria and the ER.
33
What is the significance of the physical coupling between mitochondria and the ER?
It regulates cellular lipid stores and signal transduction ## Footnote MAM may comprise up to 20% of the mitochondrial outer membrane.
34
What is the role of the MAM in cellular physiology?
The MAM integrates mitochondria and endomembrane systems, influencing processes such as intrinsic apoptosis and calcium signaling ## Footnote MAM stands for Mitochondria-Associated Membranes
35
What enzymes are enriched in the MAM?
Phosphatidylserine synthase and phosphatidylserine decarboxylase ## Footnote These enzymes are involved in lipid biosynthesis
36
What is the significance of lipid transfer at the MAM?
It facilitates the transfer of lipid intermediates between organelles without requiring ATP ## Footnote This process occurs through lipid flipping between opposed bilayers
37
What is the ER-mitochondria encounter structure (ERMES)?
A multiprotein tethering structure that may facilitate lipid transfer and maintain close proximity between ER and mitochondrial membranes ## Footnote ERMES is crucial for lipid transfer at the MAM
38
How does the MAM function in calcium signaling?
It creates Ca2+ microdomains that facilitate efficient Ca2+ transmission from the ER to mitochondria ## Footnote This occurs during cellular events called 'Ca2+ puffs'
39
What role does VDAC1 play at the MAM?
VDAC1 serves as a low-affinity Ca2+ receptor that aids in Ca2+ tunneling from the cytosol to mitochondria ## Footnote VDAC1 is physically tethered to IP3R clusters on the ER membrane
40
True or False: Calcium signaling is unidirectional at the MAM.
False ## Footnote Calcium signaling at the MAM is bidirectional, involving feedback regulation
41
What happens when Ca2+ signaling in mitochondria exceeds a certain threshold?
It stimulates the intrinsic pathway of apoptosis by collapsing the mitochondrial membrane potential ## Footnote This process is influenced by pro- and anti-apoptotic factors such as Bcl-2
42
What are the two hypotheses regarding the origin of mitochondria?
* Endosymbiotic hypothesis * Autogenous hypothesis ## Footnote The endosymbiotic hypothesis is more widely accepted due to the similarities between mitochondria and prokaryotes
43
How is mitochondrial DNA structured?
It is a circular double-stranded DNA molecule containing 37 genes ## Footnote The genes include those for respiratory complexes, tRNA, and rRNA
44
What is the significance of the heavy and light strands in mitochondrial DNA?
The heavy strand has a higher ratio of adenine and guanine, allowing separation by centrifugation ## Footnote This difference helps in the identification of mitochondrial DNA strands
45
What are MROs and which organelles are classified as such?
* Hydrogenosomes * Mitosomes * Other related organelles ## Footnote MROs are mitochondrion-related organelles found in some unicellular eukaryotes
46
What is the circular human mitochondrial genome's approximate length?
About 16 kilobases ## Footnote This genome encodes essential genes for mitochondrial function
47
What is the role of mitochondrial tRNA compared to nuclear tRNA?
Mitochondrial tRNA has different sequences but resembles bacterial tRNA ## Footnote This difference is crucial for mitochondrial protein synthesis
48
What is a unique feature of mitochondrial genomes in animals?
Typically a single circular chromosome approximately 16 kb long ## Footnote This pattern differs in some species, such as the human body louse
49
What is the main function of the MAM in relation to VLDL?
It serves as an intermediate destination between the rough ER and Golgi for VLDL assembly and secretion ## Footnote VLDL stands for very-low-density lipoprotein
50
What is the typical structure of the mitochondrial genome in animals?
A single circular chromosome that is approximately 16 kb long and has 37 genes.
51
How does the mitochondrial genome of the human body louse differ from typical animal mitochondrial genomes?
It is arranged in 18 minicircular chromosomes, each 3–4 kb long with one to three genes.
52
What is the significance of mitochondrial DNA in population genetics?
It is a useful source for studying population genetics due to its near-absence of genetic recombination.
53
What is a haplotype in the context of mitochondrial DNA?
A single unit of inherited mitochondrial DNA.
54
What does the molecular clock in mitochondrial genetics suggest about human evolution?
It supports a recent modern human expansion out of Africa.
55
What is a classic example of mitochondrial DNA studies related to human ancestry?
The sequencing of mitochondrial DNA from Neanderthal bones.
56
True or False: Mitochondrial DNA reflects both male and female ancestry.
False.
57
What is the mutation rate for mitochondrial DNA as reported in recent studies?
1 mutation every 7884 years.
58
What are some exceptions to the standard genetic code found in mitochondria?
In mammals: AGA, AGG are stop codons instead of arginine.
59
What process do mitochondria use to divide?
Mitochondrial fission.
60
How are mitochondria inherited in humans?
Mitochondrial genes are inherited only from the mother.
61
What is the mtDNA bottleneck?
A process that increases cell-to-cell variability in mutant load during development.
62
What is the primary DNA repair mechanism employed in mitochondria?
Base excision repair.
63
Which organisms have completely lost mitochondrial DNA?
Cryptosporidium.
64
What are some diseases associated with mitochondrial dysfunction?
Kearns–Sayre syndrome, MELAS syndrome, Leber's hereditary optic neuropathy.
65
What is mitochondrial replacement therapy (MRT)?
A form of in vitro fertilization that uses donor mitochondria.
66
What role do mitochondria play in aging?
They are involved in oxidative stress and high mutation rates of mitochondrial DNA.
67
Fill in the blank: Mitochondrial dysfunction has been linked to diseases such as _______.
Parkinson's disease.
68
What is the impact of mitochondrial dysfunction on cardiac health in type 2 diabetics?
It leads to reduced cardiac efficiency and contractile dysfunction.
69
What is the relationship between mitochondrial function and ovarian aging?
Decreased mitochondrial function can lead to inflammation and premature ovarian failure.
70
What genetic changes can occur in mitochondria during aging?
Decreased enzymatic activity and accumulation of mutated mtDNA.
71
True or False: Mitochondria can undergo recombination.
True.
72
What is the main function of the proteins involved in mtDNA repair?
They are encoded by nuclear genes and translocated to the mitochondria.
73
What is the primary role of mitochondria in ovarian function?
Providing ATP necessary for the development from germinal vesicle to mature oocyte
74
What can decreased mitochondrial function lead to in ovarian health?
Inflammation, resulting in premature ovarian failure and accelerated ovarian aging
75
What are the three types of dysfunction associated with decreased mitochondrial function?
* Quantitative dysfunction (mtDNA copy number and deletions) * Qualitative dysfunction (mutations and strand breaks) * Oxidative damage (dysfunctional mitochondria due to ROS)
76
How do mitochondrial dysfunctions affect oocyte-cumulus crosstalk?
They perturb oocyte-cumulus crosstalk in the ovary
77
What genetic disorder is linked to mitochondrial dysfunction?
Fragile X
78
Who published the first observations of intracellular structures that likely represented mitochondria?
Albert von Kolliker in 1857
79
What term did Carl Benda coin for mitochondria in 1898?
Mitochondria
80
What was the significance of Friedrich Meves' observation in 1904?
First recorded observation of mitochondria in plants
81
What did Benjamin F. Kingsbury relate to mitochondria in 1912?
Cell respiration
82
Who discovered cytochromes and when?
David Keilin in 1925
83
What did Eugene Kennedy and Albert Lehninger discover about mitochondria in 1948?
Mitochondria are the site of oxidative phosphorylation in eukaryotes
84
When were the first high-resolution electron micrographs of mitochondria produced?
1952
85
What popular term was coined by Philip Siekevitz in 1957?
Powerhouse of the cell
86
In what year was it discovered that mitochondria contain ribosomes?
1967
87
What was completed in 1976 regarding mitochondrial DNA?
The genetic and physical map of yeast mitochondrial DNA
88
What discovery did researchers make in November 2024 regarding mitochondria?
Mitochondria divide into two distinct forms when cells are starved

06May25 (3 decks)

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