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Cytology > Lesson 4: The nucleus and the cell cycle > Flashcards

Lesson 4: The nucleus and the cell cycle Flashcards

1
Q

What is the nucleus’s primary function?

A

The nucleus contains genetic information encoded in DNA and directs protein synthesis via RNA.

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2
Q

Can the nucleus have different shapes?

A

Yes, its shape can vary and it is related to the cell shape (rounded, elliptical, fusiform, irregular (leukocytes, spermatozoa, plasma cells)).

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3
Q

What surrounds the nucleus?

A

A double-bilayer nuclear membrane containing nuclear pores.

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4
Q

What is the function of the nuclear pores?

A

They regulate the transport of molecules between the nucleus and cytoplasm.

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5
Q

What is the nuclear lamina’s role?

A

It provides shape, stability, and structural links between DNA and the nuclear envelope.

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6
Q

What are the two types of chromatin?

A

Heterochromatin (compact, inactive) and euchromatin (dispersed, active).

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7
Q

What is the function of the nucleolus?

A

Synthesizing ribosomal RNA (rRNA) and assembling ribosomes.

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8
Q

Is the nucleolus membrane-bound?

A

No, it is not enclosed by a membrane.

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9
Q

When does the nucleolus disappear?

A

During mitosis.

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10
Q

What determines the size of the nucleolus?

A

The functional status of the cell.

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11
Q

What are the phases of the cell cycle?

A

G1, S, G2 - interphase, M - mitotic phase, and sometimes G0 - quiescence.

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12
Q

What occurs during the G1 phase?

A

Cell growth, protein synthesis, and organelle doubling.

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13
Q

What happens during the S phase?

A

DNA duplication.

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14
Q

What is synthesized in the G2 phase?

A

Cytoplasmic components and mitotic spindle proteins.

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15
Q

What is the mitotic phase (M phase)?

A

The phase where mitosis and cytokinesis occur.

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16
Q

Name the four main steps of mitosis.

A

Prophase, Metaphase, Anaphase, and Telophase.

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17
Q

What happens in prophase?

A

Chromosomes condense, the spindle forms, and the nuclear envelope disintegrates.

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18
Q

What is the significance of metaphase?

A

Chromosomes align at the spindle’s equator, and spindle assembly is checked.

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19
Q

What defines anaphase?

A

Separation of sister chromatids as kinetochore microtubules shorten.

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20
Q

What follows telophase in mitosis?

A

Cytokinesis, the division of cytoplasm into two daughter cells.

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21
Q

During which phase are chromosomes most easily visualized?

A

Metaphase.

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22
Q

What is a karyotype?

A

A visual representation of the complete set of chromosomes in a cell.

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23
Q

What is the clinical relevance of cytogenetic testing?

A

It identifies chromosome abnormalities, aiding in the diagnosis of genetic disorders and cancers.

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24
Q

What is the Philadelphia chromosome?

A

A chromosomal translocation between chromosomes 9 and 22, associated with certain leukemias.

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25
Q

What are the three classifications of cells based on renewal capability?

A

Labile, stable, and static cells.

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26
Q

What defines labile cells?

A

Cells that continuously divide, such as epithelial cells.

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27
Q

What are stable cells?

A

Cells that do not continuously divide but can divide when needed, like liver cells

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28
Q

What are static cells?

A

Cells incapable of dividing, such as neurons and cardiac muscle cells.

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29
Q

What regulates cell differentiation?

A

Variations in gene expression.

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30
Q

What is apoptosis?

A

Programmed cell death mediated by an intracellular death program.

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31
Q

What triggers necrosis?

A

Unfavorable physical or chemical environments causing accidental cell death.

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32
Q

How does the cell membrane behave in apoptosis vs necrosis?

A

Apoptosis involves controlled fragmentation without inflammation; necrosis causes swelling and lysis with inflammation.

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33
Q

What organelle’s release is key in apoptosis?

A

Mitochondria, releasing cytochrome c.

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34
Q

What are apoptotic bodies?

A

Cell fragments that are phagocytosed without triggering inflammation.

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35
Q

How does meiosis differ from mitosis in the number of divisions?

A

Meiosis involves one DNA replication and two cell divisions.

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36
Q

What is the result of meiosis?

A

Four haploid daughter cells, each genetically unique.

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37
Q

What restores the diploid genetic content in humans?

A

Fertilization of an egg by a sperm.

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38
Q

How does meiosis contribute to genetic diversity?

A

Through genetic recombination and independent assortment of chromosomes.

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39
Q

What cells undergo meiosis?

A

Gametes (egg and sperm cells).

40
Q

What is the primary function of nuclear pores?

A

Facilitating selective transport of molecules between the nucleus and cytoplasm.

41
Q

What is an NLS?

A

Nuclear Localization Signal, a sequence tagging proteins for nuclear import.

42
Q

What allows RNA to exit the nucleus?

A

Nuclear export sequences.

43
Q

How does the number of nuclear pores differ among cell types?

A

Active cells like oocytes have more pores (40-50/µm²) compared to somatic cells (10-20/µm²).

44
Q

What happens to the nuclear envelope during prophase?

A

Lamins are phosphorylated, causing the nuclear envelope to disassemble.

45
Q

What is autophagy’s primary role?

A

Eliminating aged and damaged organelles and molecules.

46
Q

What is a phagophore?

A

A vesicle that forms during the initial phases of autophagy.

47
Q

What is an autophagosome?

A

A vesicle that engulfs cytoplasmic components and fuses with lysosomes for degradation.

48
Q

How does autophagy prevent DNA damage?

A

By eliminating damaged mitochondria, reducing reactive oxygen species (ROS).

49
Q

What structural component supports the nuclear envelope?

A

The nuclear lamina, made of intermediate filaments.

50
Q

How does the nuclear pore complex function?

A

It selectively transports molecules via active and passive mechanisms.

51
Q

What regulates transport through nuclear pores?

A

Signals like Nuclear Localization Signals (NLS) for import and Nuclear Export Sequences for export.

52
Q

What is the composition of the nucleoplasm?

A

85% proteins, 15% nucleic acids, and 1% lipids.

53
Q

What is the role of intranucleolar chromatin?

A

It assists in ribosomal RNA (rRNA) synthesis within the nucleolus.

54
Q

What determines the timing of the cell cycle?

A

Factors like cell type and functional requirements (e.g., neurons remain in G0 permanently).

55
Q

How long does the cell cycle last in human intestinal epithelial cells?

A

Approximately 12-24 hours.

56
Q

What is the G0 phase?

A

A quiescent phase where cells exit the cycle but may re-enter if needed.

57
Q

What clinical marker indicates cell proliferation?

A

Ki67, a nuclear protein present in all active phases of the cell cycle but absent in G0.

58
Q

How is the Ki67 index used clinically?

A

To assess cancer proliferation rates for diagnosis and prognosis.

59
Q

What plasma membrane modification occurs during apoptosis?

A

Phosphatidylserine flips to the extracellular side.

60
Q

What happens to mitochondrial physiology in apoptosis?

A

Mitochondrial membrane potential depolarizes, releasing cytochrome c.

61
Q

How are apoptotic bodies cleared?

A

By macrophages through phagocytosis without inflammation.

62
Q

What causes cell swelling in necrosis?

A

Damage to the cell membrane leading to water and ion influx.

63
Q

What key difference distinguishes necrosis from apoptosis?

A

Necrosis triggers inflammation, while apoptosis does not.

64
Q

What are the two stages of meiotic division?

A

Meiosis I (reductional division) and Meiosis II (equational division).

65
Q

How does crossing over contribute to genetic diversity?

A

By exchanging genetic material between homologous chromosomes during Meiosis I.

66
Q

What is the ploidy level of cells after Meiosis I?

A

Haploid, with each cell containing one set of chromosomes.

67
Q

What happens if meiosis fails to segregate chromosomes properly?

A

It can result in aneuploidy, leading to disorders like Down syndrome.

68
Q

What three processes maintain tissue homeostasis?

A

Proliferation, differentiation, and cell death.

69
Q

How is differentiation regulated?

A

By selective gene expression in response to signals.

70
Q

What are housekeeping genes?

A

Genes that are constitutively expressed for basic cellular functions.

71
Q

What determines a cell’s specialization?

A

The specific set of genes expressed at a given time.

72
Q

What is the role of differentiation in intestinal crypts?

A

To renew the epithelial lining by producing specialized cell types.

73
Q

What are the stages of autophagy?

A

Phagophore formation, autophagosome formation, and lysosomal fusion.

74
Q

How does autophagy aid during calorie restriction?

A

It recycles cellular components to generate fuel and repair cells.

75
Q

What is mitophagy?

A

The selective degradation of damaged mitochondria via autophagy.

76
Q

How does autophagy prevent cancer?

A

By eliminating damaged organelles, reducing the risk of ROS-induced DNA damage.

77
Q

What is the hallmark of cancer in terms of cell proliferation?

A

Uncontrolled proliferation due to mutations.

78
Q

Why is metaphase crucial in cytogenetics?

A

Chromosomes are most condensed and easily visualized.

79
Q

What is colchicine used for in cytogenetic testing?

A

To arrest cells in metaphase by inhibiting spindle formation.

80
Q

What does a high Ki67 index indicate in cancer?

A

A higher proliferation rate, often associated with aggressive tumors.

81
Q

How do banding techniques help in cytogenetics?

A

By identifying specific chromosomal abnormalities.

82
Q

Why are neurons considered static cells?

A

They are permanently in G0 and do not divide after maturation.

83
Q

What role do differentiation and apoptosis play in stem cell niches?

A

Balancing renewal and removal of excess or damaged cells.

84
Q

How does tissue renewal vary across organs?

A

Based on cell turnover rates, e.g., epithelial cells vs. liver cells.

85
Q

What triggers the phosphorylation of nuclear lamins during mitosis?

A

Cyclin-dependent kinase activity.

86
Q

Why are ribosomes assembled in the nucleolus?

A

It provides a concentrated environment of rRNA and proteins.

87
Q

What is the importance of selective transport in nuclear pores?

A

It ensures only necessary molecules enter or exit the nucleus.

88
Q

How does autophagy contribute to immunity?

A

By degrading intracellular pathogens

89
Q

How do reactive oxygen species (ROS) affect cells?

A

They cause DNA damage and promote mutations.

90
Q

How does cytokinesis differ in animal and plant cells?

A

Animal cells use a cleavage furrow, while plant cells form a cell plate.

91
Q

What is the final outcome of cell division in mitosis?

A

Two genetically identical daughter cells.

92
Q

What is chromatin, and what is it composed of?

A

Chromatin is a complex network of macromolecules within the nucleus, consisting of DNA, RNA, and proteins (primarily histones).
It serves as the structural framework for organizing and regulating the genome.

93
Q

How is chromatin dynamically regulated during the cell cycle?

A

During interphase, chromatin exists in a decondensed state (euchromatin) for transcription and DNA replication.
During mitosis, chromatin condenses into visible chromosomes to ensure accurate segregation to daughter cells.

94
Q

What role do histone proteins play in chromatin structure?

A

Histone proteins form octameric complexes around which DNA is wrapped, creating nucleosomes, the fundamental unit of chromatin. Post-translational modifications of histones, like methylation and acetylation, regulate chromatin compaction and gene accessibility.

95
Q

What is the timeline of the cell cycle?

A

G1 - 9-12 hours
S - 7.5-10 hours
G2 - 3.5-4.5 hours
M - 1 hour

Cytology (5 decks)

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