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Cytology > Lesson 3: The mitochondria and the cellular cytoskeleton > Flashcards

Lesson 3: The mitochondria and the cellular cytoskeleton Flashcards

1
Q

Why are mitochondria referred to as the “powerhouse” of the cell?

A

They produce ATP, the primary energy currency for cellular activities.

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2
Q

Name the key structural components of mitochondria.

A

Outer membrane, inner membrane with cristae, intermembrane space, and matrix.

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3
Q

What is the function of mitochondrial cristae?

A

They increase the surface area for oxidative phosphorylation.

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4
Q

Describe the composition of the outer mitochondrial membrane.

A

Rich in lipids (50%), contains enzymes for lipid synthesis, and has VDAC porin channels for molecules <5 kDa.

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5
Q

What unique lipid is found in the inner mitochondrial membrane?

A

Cardiolipin, which renders the membrane impermeable to ions.

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6
Q

Where is mitochondrial DNA located, and what are its key features?

A

In the matrix; it is circular, unbound to proteins, and encodes some mitochondrial proteins.

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7
Q

What is the endosymbiotic hypothesis regarding mitochondria?

A

Mitochondria evolved from aerobic bacteria engulfed by ancestral eukaryotic cells.

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8
Q

How are mitochondria inherited in humans?

A

Through maternal inheritance.

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9
Q

What processes are mitochondria involved in besides energy production?

A

Lipid metabolism, steroid hormone synthesis, accumulation of cations, heat production, and apoptosis.

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10
Q

What is the role of cytochrome c in apoptosis?

A

It triggers caspase activation, initiating programmed cell death.

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11
Q

How do mitochondria replicate?

A

Through segmentation and division, similar to bacterial fission.

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12
Q

Where are mitochondria typically located within a cell?

A

Near regions of high energy demand, such as muscle fibers and sperm tails.

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13
Q

What is the average lifespan of mitochondria in rat hepatocytes?

A

9–10 days.

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14
Q

How are aged mitochondria degraded?

A

By autophagy through lysosomal enzymes.

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15
Q

What role do mitochondria play in steroid hormone synthesis?

A

They produce precursors for steroid hormone synthesis.

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16
Q

How does the mitochondrial matrix differ from the cytoplasm?

A

It contains unique enzymes, mtDNA, ribosomes, and is specialized for fatty acid oxidation and the Krebs cycle.

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17
Q

What is the significance of cardiolipin in the inner mitochondrial membrane?

A

It maintains membrane integrity and supports oxidative phosphorylation.

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18
Q

What is the role of mitochondrial ribosomes?

A

They synthesize some of the proteins required for mitochondrial function.

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19
Q

Why are mitochondria considered semi-autonomous?

A

They have their own DNA and machinery for protein synthesis but depend on nuclear DNA for most proteins.

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20
Q

How does mitochondrial DNA differ from nuclear DNA?

A

It is circular, maternally inherited, and lacks protective histones.

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21
Q

What is oxidative phosphorylation?

A

A process in the inner membrane that generates ATP using the electron transport chain and ATP synthase.

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22
Q

How do mitochondria contribute to thermogenesis?

A

By producing heat through uncoupling proteins in brown adipose tissue.

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23
Q

What are the two main types of cristae in mitochondria?

A

Lamellar cristae and tubular cristae.

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24
Q

How are lamellar cristae arranged in mitochondria?

A

They are arranged perpendicular to the longitudinal axis of the mitochondrion.

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25
In which type of cells are mitochondria with tubular cristae typically found?
Steroid-secreting cells, such as those in the adrenal cortex.
26
What distinguishes mitochondria with lamellar cristae from those with tubular cristae?
Lamellar cristae are flat and shelf-like, while tubular cristae are circular or tubular.
27
What is the arrangement of cristae in active mitochondria?
Tightly packed shelf cristae cross the organelle to increase the surface area for ATP production.
28
What does the presence of tubular cristae in mitochondria indicate about the cell's function?
It suggests the cell is involved in steroid secretion.
29
How do mitochondrial cristae adapt to the functional needs of a cell?
Their arrangement and density change depending on the cell's energy requirements or specialized functions.
30
What is the number of mitochondria in cells?
 The number of mitochondria in different cells is very variable, usually they are 1.000-2.000/cell  Oocytes of some animals contains 30.000/cell  Cells with low metabolism contain only few tens of mitochondria
31
What is the roll of mitochondria in ciliated cells?
ATP is needed to move the microtubules in the cilia
32
How is energy produced in mitochondria?
oxidizing the major product of glucose: pyruvate. This type of cellular respiration, known as aerobic respiration, is dependent on the presence of oxygen Glycolysis -> Pyruvate (in the presence of oxygen) -> aerobic respiration
33
What is the cytoskeleton?
A dynamic network of protein filaments that provide structural support, shape, and intracellular transport
34
Name the three types of cytoskeletal filaments.
Microfilaments (actin filaments), intermediate filaments, and microtubules.
35
List the main functions of the cytoskeleton.
Maintaining cell shape, organelle positioning, vesicle trafficking, and enabling cell motility and division, Supports the plasma membrane and provides the mechanical links allowing the cell to bear stress and tension.
36
What is the primary protein in microfilaments?
Actin.
37
What is the difference between G-actin and F-actin?
G-actin is the globular monomer, while F-actin is the filamentous polymer.
38
How are actin filaments organized in epithelial cells?
They form the structural core of microvilli.
39
What structures are formed by actin filaments in motile cells?
Lamellipodia and filopodia.
40
What role do actin filaments play in dividing cells?
They form the contractile ring during cytokinesis.
41
What is the function of invadopodia in cancer cells?
They degrade the extracellular matrix, facilitating metastasis.
42
Describe actin-mediated motility in leukocytes.
Actin filaments extend lamellipodia and adhesion plaques for cell migration.
43
What are the two primary functions of lamellipodia?
Facilitating cell migration and adhesion to substrates.
44
What is the structural arrangement of actin filaments in filopodia?
Parallel bundles that extend membrane protrusions.
45
How do actin filaments aid in intracellular transport?
By providing tracks for motor proteins like myosin.
46
What happens to actin structures during cell division?
Actin forms the contractile ring that helps separate daughter cells during cytokinesis.
47
What cellular processes does actin participate in?
Anchorage and movement of membrane proteins Formation of the structural core of microvilli Locomotion of cells (lamellipodia) Extension of cell protrusion (filopodia)
48
What are adhesion plaques, and how do they relate to actin filaments?
Adhesion plaques anchor actin filaments to the extracellular matrix, aiding in cell stability and movement.
49
What proteins regulate the assembly and disassembly of actin filaments?
Actin-binding proteins like profilin and cofilin.
50
How do the diameters of the cytoskeleton components compare?
Microfilaments: Smallest diameter -7 nm Intermediate filaments: Intermediate diameter - 10 nm Microtubules: Largest diameter -25 nm
51
Which cytoskeletal components are considered dynamic?
Microfilaments and microtubules.
52
Which cytoskeletal component is more stationary?
Intermediate filaments.
53
Why are microfilaments and microtubules considered dynamic?
They undergo rapid polymerization and depolymerization, allowing quick structural changes.
54
How does the stability of intermediate filaments contribute to their function?
Their stability provides consistent mechanical support and maintains cell shape under stress.
55
What structures are supported by cytoskeletal components like cilia, flagella, and sarcomeres?
Cilia and flagella: Supported by microtubules. Sarcomeres: Supported by actin filaments (microfilaments).
56
Actin is ...
ubiquitous (found everywhere) - 2-15% of cell proteins
57
How are actin filaments (F-actin) formed?
by polimerization of globular actin arranged in a double helix structure
58
What happens to microfilaments in dividing cells?
Actin-based motile structures are disassembled before cell division, which causes the cell to stop moving and become more rounded. More stable actin bundles remain polarized and contribute to the orientation of the microtubule network that serves as the mitotic spindle.
59
What is the primary role of intermediate filaments?
Providing mechanical strength to cells and tissues.
60
Name five tissue-specific intermediate filament proteins.
Keratin (epithelial), vimentin (connective), desmin (muscle), Glial Fibrillar protein - GFAP (neural), lamins (nucleus).
61
How are intermediate filaments useful in cancer diagnosis?
Tumor origin can be identified based on the type of intermediate filaments present.
62
What is the nuclear lamina?
A network of intermediate filaments beneath the nuclear envelope.
63
What happens to cell-cell junctions without intermediate filaments?
They are weakened, compromising tissue integrity.
64
How are intermediate filaments linked to cell junctions?
They anchor desmosomes (cell-cell junctions) and hemidesmosomes (cell-matrix junctions).
65
Why are intermediate filaments crucial in neurons?
They maintain axonal integrity and support long-distance transport.
66
What happens when nuclear lamins are defective?
Intermediate filaments localized beneath the nuclear envelope form the nuclear lamina * Provide a link for chromatin * Have a role in mitosis It can lead to diseases like progeria, which causes premature aging.
67
What is the difference between vimentin and desmin?
Vimentin is found in connective tissue, while desmin is specific to muscle cells.
68
What mechanical property do intermediate filaments provide to tissues?
Resistance to shear and tensile forces.
69
What is the structural organization of intermediate filaments?
Intermediate filament proteins are rope-shaped Monomers form dimeric coiled-coil structures (spiral). Dimers are arranged head-to-tail to form tetramers. Tetramers assemble laterally to form filament structures.
70
What are sarcomas?
connective tissue tumors characterized by the presence of vimentin
71
What are carcinomas?
epithelial tumors characterized by the presence of keratins
72
What are the building blocks of microtubules?
Alpha- and beta-tubulin dimers.
73
What is the structure of a microtubule?
Hollow tubes made of 13 protofilaments arranged in a circular pattern.
74
Where do microtubules originate?
At the microtubule-organizing center (MTOC), also called the centrosome (composed of two orthogonally arranged centrioles).
75
What are the two ends of a microtubule, and how do they differ?
The plus end grows rapidly, while the minus end is slower and anchored at the MTOC.
76
How do dynein and kinesin function on microtubules?
Dynein moves cargo toward the minus end, and kinesin moves cargo toward the plus end.
77
What is the role of microtubules during mitosis?
They form the mitotic spindle to segregate chromosomes.
78
What are cilia and flagella composed of?
Microtubules arranged in a "9+2" structure.
79
How do microtubules contribute to neuronal function?
They mediate axonal transport of organelles and vesicles.
80
What are the main roles of the microtubule-organizing center (MTOC)?
Controlling microtubule number, position, and orientation.
81
What is the structure of centrioles?
Nine sets of triplet microtubules arranged in a cylindrical shape.
82
How do microtubules contribute to intracellular trafficking?
By serving as tracks for motor proteins like kinesin and dynein.
83
How do cilia and flagella differ in function?
Cilia move substances across cell surfaces, while flagella enable cell locomotion.
84
What is the "9+2" arrangement in cilia?
Nine doublets of microtubules surrounding two central microtubules.
85
How does Taxol affect microtubule dynamics?
It stabilizes microtubules, preventing their depolymerization and halting cell division.
86
Why are microtubules essential for axonal transport?
They facilitate long-distance transport of materials in neurons.
87
How do basal bodies contribute to cilia formation?
They act as anchors for cilia and organize their microtubule structure.
88
What are the effects of microtubule inhibitors on cancer cells?
They prevent mitotic spindle formation, blocking cell division.
89
What are the functions of microtubules?
Scaffold for cell organelles Maintenance of cell shape Micro-transport and vesicle trafficking Axonic transport in neurons Cell division (mitotic spindle)

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