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112 Terms
What are the three reasons cell division is important?
Reproduction; growth and development; tissue renewal and repair.
How does cell division enable reproduction?
In unicellular organisms, division of one cell reproduces the entire organism.
How does cell division enable growth and development?
It allows a multicellular organism to develop from one fertilized egg into a complex organism.
How does cell division enable tissue renewal and repair?
It replaces cells that die from normal wear and tear or accidents, such as bone marrow cells producing new blood cells.
What is a genome?
A cell's total endowment of DNA and genetic information.
What is a chromosome?
A structure made of a very long DNA molecule and associated proteins that package and manage DNA.
What is chromatin?
The complex of DNA and proteins that builds chromosomes and varies in condensation during the cell cycle.
What is a somatic cell?
A body cell in a multicellular organism, excluding reproductive cells.
What is a gamete?
A reproductive cell, such as a sperm or egg, containing half as many chromosomes as a somatic cell.
What are sister chromatids?
Two identical, joined copies of a duplicated chromosome that contain identical DNA molecules.
What is a centromere?
A specialized chromosome region where sister chromatids are attached most closely, creating a narrow waist.
What is mitosis?
The division of the genetic material in the nucleus.
What is cytokinesis?
The division of the cytoplasm that produces two separate daughter cells.
What is the difference between mitosis and cytokinesis?
Mitosis divides the genetic material in the nucleus; cytokinesis divides the cytoplasm.
What are the four main phases of the cell cycle?
G1, S, G2, and M.
What is interphase, and approximately how much of the cell cycle does it occupy?
Interphase consists of G1, S, and G2; it occupies approximately 90% of the cell cycle.
What happens during G1 phase?
The cell grows by producing proteins and cytoplasmic organelles. G1 means first gap.
What happens during S phase?
Chromosomes are duplicated through DNA synthesis. S stands for synthesis.
What happens during G2 phase?
The cell grows further and completes preparations for cell division. G2 means second gap.
What happens during the M phase?
Mitosis (nuclear division) and cytokinesis (cytoplasmic division) occur.
What is G0 phase?
A nondividing state entered when cells do not receive a go-ahead signal at the G1 checkpoint or when specialized cells remain nondividing.
Which specialized cells can reside in G0?
Mature nerve cells and muscle cells.
What is a mitotic spindle?
An apparatus of microtubule fibers and associated proteins that controls chromosome movement during mitosis.
What structures are associated with the mitotic spindle?
Centrosomes, spindle microtubules, and asters.
What is the function of the mitotic spindle?
It manages and controls chromosome movement during mitosis.
What is an aster?
A radial array of short microtubules extending from each centrosome.
What is a kinetochore?
A protein structure assembled at specific chromosome DNA regions near each centromere where spindle microtubules attach.
Where does mitotic spindle assembly begin?
At the centrosome during prophase.
What happens to centrosomes as the mitotic spindle develops?
They move apart as spindle microtubules grow, reaching opposite poles by the end of prometaphase.
What is the metaphase plate?
An imaginary plane in the middle of the cell where duplicated chromosomes align.
How are sister chromatids attached to spindle microtubules during metaphase?
Their kinetochores attach to microtubules from opposite poles.
What holds sister chromatids together before anaphase?
Cohesin proteins.
What triggers the beginning of anaphase?
The enzyme separase cleaves the cohesin proteins holding sister chromatids together.
What happens to daughter chromosomes during anaphase?
They move toward opposite poles as kinetochore microtubules shorten.
How do kinetochore microtubules help move chromosomes?
Motor proteins move chromosomes along depolymerizing microtubules, and/or the microtubules reel chromosomes toward the poles.
What is the function of nonkinetochore microtubules during anaphase?
They push the poles apart, elongating the cell.
What is the M checkpoint checking?
Whether sister chromatids are firmly attached to opposite ends of the mitotic spindle before the cell proceeds.
What happens during prometaphase?
The nuclear envelope breaks down, allowing spindle microtubules to access the chromosomes and attach to their kinetochores.
What happens during metaphase?
Chromosomes align at the metaphase plate, centrosomes are at opposite poles, and the spindle attachment checkpoint is assessed.
What happens during anaphase?
Separase cleaves cohesins, sister chromatids separate into daughter chromosomes, and the cell elongates as the chromosome sets move apart.
What happens during telophase?
Two new nuclei form, chromosomes loosen into chromatin, and spindle microtubules disassemble.
What is the result of nuclear division in mitosis?
Two genetically identical nuclei.
What is a centrosome according to the class notes?
The notes describe a centrosome as containing two centrioles; after duplication, there are two pairs of centrioles in the cell.
What happens to chromatin during interphase?
It remains relatively loose and spread throughout the nucleus, rather than being tightly condensed into visible chromosomes.
What happens to DNA during the S phase of interphase?
The DNA is replicated, producing duplicated chromosomes with two sister chromatids each.
What happens to chromatin during prophase?
It condenses into distinct, tightly packed chromosomes, each consisting of two sister chromatids joined at the centromere.
What happens to the cytoskeleton during prophase according to the notes?
The cytoskeleton disassembles, allowing its components to be reused as the mitotic spindle forms.
What happens to microtubules during prophase?
Microtubules grow between the centrosomes, helping them move farther apart and forming the mitotic spindle.
What happens to the nuclear envelope during prometaphase?
It breaks down, allowing spindle microtubules to attach to kinetochores on the chromosomes.
Where are centrosomes and asters positioned during metaphase?
Centrosomes are at opposite poles; asters extend outward, with microtubules reaching toward the cell cortex.
What are cohesins?
Proteins that hold sister chromatids together until anaphase.
What is separase?
An enzyme that cleaves cohesin proteins, allowing sister chromatids to separate at anaphase.
How do chromosomes move toward opposite poles?
Kinetochore microtubules shorten, with motor proteins and microtubule dynamics helping move chromosomes toward the poles.
What happens to the cell during anaphase besides chromosome separation?
The cell elongates as the two chromosome sets move apart.
How do the two new nuclei form during telophase?
New nuclear envelopes form around each chromosome set.
What happens to chromosomes during telophase?
They decondense and return to a looser chromatin state.
How does cytokinesis occur in animal cells?
A contractile ring of actin microfilaments and myosin creates a cleavage furrow that pinches the cell in two.
What is a cleavage furrow?
An inward groove formed as an animal cell membrane pinches inward during cytokinesis.
What proteins form the contractile ring in animal-cell cytokinesis?
Actin microfilaments and myosin.
How does cytokinesis occur in plant cells?
Golgi-derived vesicles join in the middle of the cell to form a cell plate, which grows outward and fuses with the plasma membrane.
What is a cell plate?
A structure formed from coalescing vesicles that develops into the new separating wall between plant daughter cells.
Why do plant cells form a cell plate instead of a cleavage furrow?
The rigid plant cell wall prevents the cell from pinching inward like an animal cell.
What happens to the cell plate during plant-cell cytokinesis?
It grows outward until it fuses with the plasma membrane and deposits a new cell wall between daughter cells.
What is binary fission?
A process in which a prokaryotic cell grows and divides in half to produce two cells.
How does DNA replication occur during binary fission?
Replication begins at an origin of replication.
What happens to DNA origins during binary fission?
They move apart as the cell elongates.
How does a prokaryotic cell divide during binary fission?
The plasma membrane pinches inward while a new cell wall is deposited.
How might mitosis have evolved from binary fission?
Similarities between proteins involved in bacterial division and eukaryotic actin and tubulin suggest that mitosis evolved from simpler prokaryotic division.
What evidence suggests intermediate stages in the evolution of mitosis?
Some unicellular eukaryotes, such as dinoflagellates and diatoms, have intermediate forms of nuclear division in which the nuclear envelope remains intact.
How does cell division frequency differ among human cell types?
Skin cells divide frequently, liver cells divide when stimulated by injury repair, and mature nerve and muscle cells generally do not divide.
How do experiments with fused mammalian cells provide evidence for cytoplasmic control of the cell cycle?
Fusing cells in different phases showed that cytoplasmic molecules can cause a G1 nucleus to enter S phase or mitosis, demonstrating that cytoplasmic signals drive cell-cycle progression.
What happens when an S-phase cell is fused with a G1 cell?
The G1 nucleus immediately begins S phase.
What happens when an M-phase cell is fused with a G1 cell?
The G1 nucleus enters mitosis, showing chromatin condensation and spindle formation.
What are cell-cycle checkpoints?
Control points where internal stop and go-ahead signals ensure important processes are completed before the cell progresses.
Where are the main cell-cycle checkpoints?
G1, G2, and M phases.
What regulates the cell-cycle clock?
Regulatory proteins and protein complexes, including kinases and cyclins.
What are cyclins and kinases involved in?
Regulating progression through the cell cycle at the molecular level.
Why do cells need essential nutrients to progress through the cell cycle?
They require vital nutrients from their environment to continue dividing.
What are growth factors?
Proteins that bind to cell-surface receptors and trigger signaling pathways that can promote cell division.
What is PDGF?
Platelet-Derived Growth Factor, a growth factor that can stimulate signaling pathways allowing cells to pass the G1 checkpoint and divide.
How can PDGF promote cell division?
It binds to cell-surface receptors and activates signal transduction pathways that help cells pass the G1 checkpoint.
What is density-dependent inhibition?
The phenomenon in which crowded cells stop dividing because cell-to-cell protein contact sends growth-inhibiting signals.
What is anchorage dependence?
The requirement for animal cells to be physically attached to a substratum, such as a culture dish or extracellular matrix, in order to divide.
How do normal cells respond to cell-cycle regulatory signals?
They respond to internal and external regulatory signals and require appropriate growth factors.
How do normal cells respond to density-dependent inhibition and anchorage dependence?
They generally stop dividing when crowded and require attachment to a suitable surface.
How many times do normal cells typically divide in culture according to the notes?
Approximately 20–50 divisions.
What is apoptosis?
Programmed cell death.
How do normal cells respond to unrepairable DNA damage?
They can trigger apoptosis, preventing damaged cells from continuing to divide.
How do cancer cells respond to normal cell-cycle signals?
They ignore normal regulatory signals and divide excessively and uncontrollably.
Do cancer cells always require external growth factors to divide?
No. Cancer cells can grow without external growth factors.
How do cancer cells differ from normal cells in density-dependent inhibition?
Cancer cells often lack density-dependent inhibition and may continue dividing when crowded.
How do cancer cells differ from normal cells in anchorage dependence?
Cancer cells may lack anchorage dependence and divide without normal attachment requirements.
What does it mean that cancer cells are immortal in culture?
Under suitable conditions and with sufficient nutrients, they can divide indefinitely in culture.
How do cancer cells respond to apoptosis?
They can evade programmed cell death, allowing damaged cells to survive.
What chromosome abnormalities can occur in cancer cells?
Cancer cells often have abnormal chromosome numbers.
What is one dangerous ability of some cancer cells?
They can spread to other tissues.
What is a tumor?
An abnormal mass of cells produced by unchecked cell proliferation.
What do benign and malignant tumors have in common?
Both are abnormal masses of cells that multiply through unchecked cell proliferation.
What is a benign tumor?
A tumor that remains localized at its original site and generally does not invade other tissues.
Why do benign tumors usually remain localized?
Their cells lack the genetic and cellular changes needed to survive and spread elsewhere.