Lesson 4: The nucleus and the cell cycle Flashcards
What is the nucleus’s primary function?
The nucleus contains genetic information encoded in DNA and directs protein synthesis via RNA.
Can the nucleus have different shapes?
Yes, its shape can vary and it is related to the cell shape (rounded, elliptical, fusiform, irregular (leukocytes, spermatozoa, plasma cells)).
What surrounds the nucleus?
A double-bilayer nuclear membrane containing nuclear pores.
What is the function of the nuclear pores?
They regulate the transport of molecules between the nucleus and cytoplasm.
What is the nuclear lamina’s role?
It provides shape, stability, and structural links between DNA and the nuclear envelope.
What are the two types of chromatin?
Heterochromatin (compact, inactive) and euchromatin (dispersed, active).
What is the function of the nucleolus?
Synthesizing ribosomal RNA (rRNA) and assembling ribosomes.
Is the nucleolus membrane-bound?
No, it is not enclosed by a membrane.
When does the nucleolus disappear?
During mitosis.
What determines the size of the nucleolus?
The functional status of the cell.
What are the phases of the cell cycle?
G1, S, G2 - interphase, M - mitotic phase, and sometimes G0 - quiescence.
What occurs during the G1 phase?
Cell growth, protein synthesis, and organelle doubling.
What happens during the S phase?
DNA duplication.
What is synthesized in the G2 phase?
Cytoplasmic components and mitotic spindle proteins.
What is the mitotic phase (M phase)?
The phase where mitosis and cytokinesis occur.
Name the four main steps of mitosis.
Prophase, Metaphase, Anaphase, and Telophase.
What happens in prophase?
Chromosomes condense, the spindle forms, and the nuclear envelope disintegrates.
What is the significance of metaphase?
Chromosomes align at the spindle’s equator, and spindle assembly is checked.
What defines anaphase?
Separation of sister chromatids as kinetochore microtubules shorten.
What follows telophase in mitosis?
Cytokinesis, the division of cytoplasm into two daughter cells.
During which phase are chromosomes most easily visualized?
Metaphase.
What is a karyotype?
A visual representation of the complete set of chromosomes in a cell.
What is the clinical relevance of cytogenetic testing?
It identifies chromosome abnormalities, aiding in the diagnosis of genetic disorders and cancers.
What is the Philadelphia chromosome?
A chromosomal translocation between chromosomes 9 and 22, associated with certain leukemias.
What are the three classifications of cells based on renewal capability?
Labile, stable, and static cells.
What defines labile cells?
Cells that continuously divide, such as epithelial cells.
What are stable cells?
Cells that do not continuously divide but can divide when needed, like liver cells
What are static cells?
Cells incapable of dividing, such as neurons and cardiac muscle cells.
What regulates cell differentiation?
Variations in gene expression.
What is apoptosis?
Programmed cell death mediated by an intracellular death program.
What triggers necrosis?
Unfavorable physical or chemical environments causing accidental cell death.
How does the cell membrane behave in apoptosis vs necrosis?
Apoptosis involves controlled fragmentation without inflammation; necrosis causes swelling and lysis with inflammation.
What organelle’s release is key in apoptosis?
Mitochondria, releasing cytochrome c.
What are apoptotic bodies?
Cell fragments that are phagocytosed without triggering inflammation.
How does meiosis differ from mitosis in the number of divisions?
Meiosis involves one DNA replication and two cell divisions.
What is the result of meiosis?
Four haploid daughter cells, each genetically unique.
What restores the diploid genetic content in humans?
Fertilization of an egg by a sperm.
How does meiosis contribute to genetic diversity?
Through genetic recombination and independent assortment of chromosomes.
What cells undergo meiosis?
Gametes (egg and sperm cells).
What is the primary function of nuclear pores?
Facilitating selective transport of molecules between the nucleus and cytoplasm.
What is an NLS?
Nuclear Localization Signal, a sequence tagging proteins for nuclear import.
What allows RNA to exit the nucleus?
Nuclear export sequences.
How does the number of nuclear pores differ among cell types?
Active cells like oocytes have more pores (40-50/µm²) compared to somatic cells (10-20/µm²).
What happens to the nuclear envelope during prophase?
Lamins are phosphorylated, causing the nuclear envelope to disassemble.
What is autophagy’s primary role?
Eliminating aged and damaged organelles and molecules.
What is a phagophore?
A vesicle that forms during the initial phases of autophagy.
What is an autophagosome?
A vesicle that engulfs cytoplasmic components and fuses with lysosomes for degradation.
How does autophagy prevent DNA damage?
By eliminating damaged mitochondria, reducing reactive oxygen species (ROS).
What structural component supports the nuclear envelope?
The nuclear lamina, made of intermediate filaments.
How does the nuclear pore complex function?
It selectively transports molecules via active and passive mechanisms.
What regulates transport through nuclear pores?
Signals like Nuclear Localization Signals (NLS) for import and Nuclear Export Sequences for export.
What is the composition of the nucleoplasm?
85% proteins, 15% nucleic acids, and 1% lipids.
What is the role of intranucleolar chromatin?
It assists in ribosomal RNA (rRNA) synthesis within the nucleolus.
What determines the timing of the cell cycle?
Factors like cell type and functional requirements (e.g., neurons remain in G0 permanently).
How long does the cell cycle last in human intestinal epithelial cells?
Approximately 12-24 hours.
What is the G0 phase?
A quiescent phase where cells exit the cycle but may re-enter if needed.
What clinical marker indicates cell proliferation?
Ki67, a nuclear protein present in all active phases of the cell cycle but absent in G0.
How is the Ki67 index used clinically?
To assess cancer proliferation rates for diagnosis and prognosis.
What plasma membrane modification occurs during apoptosis?
Phosphatidylserine flips to the extracellular side.
What happens to mitochondrial physiology in apoptosis?
Mitochondrial membrane potential depolarizes, releasing cytochrome c.
How are apoptotic bodies cleared?
By macrophages through phagocytosis without inflammation.
What causes cell swelling in necrosis?
Damage to the cell membrane leading to water and ion influx.
What key difference distinguishes necrosis from apoptosis?
Necrosis triggers inflammation, while apoptosis does not.
What are the two stages of meiotic division?
Meiosis I (reductional division) and Meiosis II (equational division).
How does crossing over contribute to genetic diversity?
By exchanging genetic material between homologous chromosomes during Meiosis I.
What is the ploidy level of cells after Meiosis I?
Haploid, with each cell containing one set of chromosomes.
What happens if meiosis fails to segregate chromosomes properly?
It can result in aneuploidy, leading to disorders like Down syndrome.
What three processes maintain tissue homeostasis?
Proliferation, differentiation, and cell death.
How is differentiation regulated?
By selective gene expression in response to signals.
What are housekeeping genes?
Genes that are constitutively expressed for basic cellular functions.
What determines a cell’s specialization?
The specific set of genes expressed at a given time.
What is the role of differentiation in intestinal crypts?
To renew the epithelial lining by producing specialized cell types.
What are the stages of autophagy?
Phagophore formation, autophagosome formation, and lysosomal fusion.
How does autophagy aid during calorie restriction?
It recycles cellular components to generate fuel and repair cells.
What is mitophagy?
The selective degradation of damaged mitochondria via autophagy.
How does autophagy prevent cancer?
By eliminating damaged organelles, reducing the risk of ROS-induced DNA damage.
What is the hallmark of cancer in terms of cell proliferation?
Uncontrolled proliferation due to mutations.
Why is metaphase crucial in cytogenetics?
Chromosomes are most condensed and easily visualized.
What is colchicine used for in cytogenetic testing?
To arrest cells in metaphase by inhibiting spindle formation.
What does a high Ki67 index indicate in cancer?
A higher proliferation rate, often associated with aggressive tumors.
How do banding techniques help in cytogenetics?
By identifying specific chromosomal abnormalities.
Why are neurons considered static cells?
They are permanently in G0 and do not divide after maturation.
What role do differentiation and apoptosis play in stem cell niches?
Balancing renewal and removal of excess or damaged cells.
How does tissue renewal vary across organs?
Based on cell turnover rates, e.g., epithelial cells vs. liver cells.
What triggers the phosphorylation of nuclear lamins during mitosis?
Cyclin-dependent kinase activity.
Why are ribosomes assembled in the nucleolus?
It provides a concentrated environment of rRNA and proteins.
What is the importance of selective transport in nuclear pores?
It ensures only necessary molecules enter or exit the nucleus.
How does autophagy contribute to immunity?
By degrading intracellular pathogens
How do reactive oxygen species (ROS) affect cells?
They cause DNA damage and promote mutations.
How does cytokinesis differ in animal and plant cells?
Animal cells use a cleavage furrow, while plant cells form a cell plate.
What is the final outcome of cell division in mitosis?
Two genetically identical daughter cells.
What is chromatin, and what is it composed of?
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.
How is chromatin dynamically regulated during the cell cycle?
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.
What role do histone proteins play in chromatin structure?
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.
What is the timeline of the cell cycle?
G1 - 9-12 hours
S - 7.5-10 hours
G2 - 3.5-4.5 hours
M - 1 hour
