Flashcards in Chapter 12 - The Cell Cycle Deck (39):
What is one characteristic that distinguishes living organisms from nonliving matter?
The ability of organisms to produce more of their own kind; a unique capacity to procreate
What is the continuity of life based upon?
Cell division; the reproduction of cells
In what type of organisms does the division of one cell reproduce the entire organism?
What do multicellular eukaryotes depend on cell devision for?
- Development from a fertilized egg
What is the cell cycle?
The life of a cell from the time it is first formed during division of a parent cell until its own division into two daughter cells;
Cell division is an integral part of the cell cycle. Passing identical genetic material to cellular offspring is a crucial function of cell division.
What does most cell division result in?
Genetically identical daughter cells; daughter cells with identical genetic information (DNA)
*Exception - meiosis - a special type of eukaryotic cell division that can produce sperm and eggs
What is a genome?
A cells endowment of DNA, its genetic information; all the DNA in a cell
- A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells)
What are chromosomes?
DNA molecules in a cell are packaged into structures called chromosomes;
*Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus
What is chromatin?
Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division
What are somatic cells?
Nonreproductive cells; each contain 46 chromosomes, made up of 2 sets of 23, one set inherited from each parent
What are gametes?
Reproductive cells; sperm and eggs - have half as many chromosomes as somatic cells;
i.e. human gametes have one set of 23 chromosomes
What happens in preparation for cell division?
DNA replicates and the chromosomes condense
What are sister chromatids?
Each duplicated chromosome has two sister chromatids (joined copies of the original chromosome), attached along their lengths by protein complexes called cohesins; this attachment is known as sister chromatid cohesion
What is the centromere?
Each sister chromatid has a centromere; the region of the chromosomal DNA where the chromatid is attached most closely to its sister chromatid; the "narrow waist" of the duplicated chromosome
During cell division, what happens to the two sister chromatids?
The two sister chromatids of each duplicated chromosome separate and move into two nuclei; once separate, the chromatids are called chromosomes
Eukaryotic cell division consists of what two phases? (i.e. mitotic phase)
Mitosis and cytokinesis
What is mitosis?
The division of the genetic material in the nucleus
What is cytokinesis?
The division of the cytoplasm and the organelles within the cytoplasm
How are gametes produces?
Gametes are produced by meiosis; meiosis yields nonidentical daughter cells with half as many chromosomes as the parent cell
What are the two phases of the cell cycle?
Mitotic (M) phase - mitosis and cytokinesis (the shortest part of the cell cycle)
Interphase - cell growth and copying of chromosomes in preparation of cell division (accounts for 90% of the cell cycle)
What are the 3 sub-phases of interphase?
G1 phase (first gap)
S phase (synthesis)
G2 phase (second gap)
*The cell grows through all 3 phases, but chromosomes are duplicated only during the S phase
What are the 5 stages of mitosis?
What happens during G2 of interphase?
- A nuclear envelope encloses the nucleus; the nucleus contains one or more nucleoli
- 2 centrosomes have formed by duplication of a single centrosome; centrosomes are regions in animals cells that organize the microtubules of the spindle; each centrosome contains two centrioles
What happens during prophase?
- The chromatin fibers become more tightly coiled, condensing into discrete chromosomes
- The nucleoli disappear
- Each duplicated chromosome appears as two identical sister chromatids joined at their centromeres and, in some species, all along their arms by cohesins
- The mitotic spindle begins to form. It is composed of the centrosomes and the microtubules that extend from them; the radial arrays of shorter microtubules that extend from the centrosomes are called asters
- The centrosomes move away from each other, propelled partly by the lengthening microtubules between them
What happens during prometaphase?
- The nuclear envelope fragments
- The microtubules extending from each centrosome can now invade the nuclear area
- The chromosomes have become even more condensed
- Each of the two chromatids of each chromosome now has a kinetochore, a specialized protein structure at the centromere
- Some of the microtubules attach to the kinetochores, becoming "kinetochore microtubules" which jerk the chromosomes back and forth
- Nonkinetochore microtubules interact with those from the oppose pole of the spindle
What happens during metaphase?
- The centrosomes are now at opposite poles of the cell
- The chromosomes have all arrived at the metaphase plate, a plane that is equidistant between the spindle's two poles. The chromosomes' centromeres lie at the metaphase plate
- For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles
What happens during anaphase?
- The shortest stage of mitosis, often lasting only a few minutes
- Begin when the cohesin proteins are cleaved; this allows the two sister chromatids of each pair to part suddenly; each chromatid thus becomes a full fledged chromosome
- The two liberated daughter chromosomes begin moving toward the opposite ends of the cell as their kinetochore microtubules shorten; because these microtubules are attached at the centromere region, the chromosomes move centromeres first
- The cell elongates as the nonkinetochore microtubules lengthen
- By the end of anaphase, the two ends of the cell have equivalent - and complete - collections of chromosomes
What happens during telophase?
- 2 daughter nuclei form in the cell; nuclear envelopes arise from the fragments of the parent cell's nuclear envelope and other portions of the endomembrane system
- Nucleoli reappear
- The chromosomes become less condensed
- Any remaining spindle microtubules are depolymerized
- Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete
What happens during cytokinesis?
- The division of the cytoplasm is usually under way by late telophase, so the two daughter cells appear shortly after the end of mitosis
- In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two
What is the mitotic spindle?
Begins to form in the cytoplasm during prophase; this structure consists of fibers made of microtubules and associated proteins, which control chromosome movement during mitosis.
What is the centrosome?
In animal cells, assembly of spindle microtubules begins in the centrosome, the microtubule organizing center;
The centrosome replicates during interphase, forming two centrosomes that migrate to opposite ends of the cell during prophase and prometaphase.
*An aster (a radical array of short microtubules) extends from each centrosome
What does the spindle include?
The centrosomes, the spindle microtubules, and the asters
*During prometaphase, some spindle microtubules attach tothe kinetochores of chromosomes and begin to move the chromosomes
What are kinetochores?
A structure made up of proteins that have assembled on specific sections of DNA at each centromere; the chromosome's two kinetochores face in opposite directions
What is the metaphase plate?
At metaphase, the centromeres of all the duplicated chromosomes are on a plane midway between the spindle's two poles; this plane is called the metaphase plate, which is an imaginary plate rather than an actual cellular structure
Anaphase begins suddenly when...?
Anaphase begins suddenly when the cohesins holding together the sister chromatids of each chromosome are cleaved by an enzyme called separase; once separated, the chromatids become full fledge chromosomes that move along kinetochore microtubules toward opposite ends of the cell.
*The microtubules shorten by depolymerizing at their kinetochore ends
In animal cells, what is responsible for elongating the whole cell during anaphase?
The nonkinetochore microtubules; these overlap and push against each other, elongating the cell.
*At the end of anaphase, duplicate groups of chromosomes have arrived at opposite ends of the elongated parent cell
*In telophase, genetically identical daughter nuclei form at opposite ends of the cell
*Cytokinesis begins during anaphase or telophase and the spindle eventually disassembles
What is cleavage?
In animal cells, cytokinesis occurs by a process known as cleavage forming a cleavage furrow;
Characterized by the pinching of the plasma membrane
What is the cleavage furrow?
A shallow groove in the cell surface near the old metaphase plate; on the cytoplasmic side of the furrow is a contractile ring of actin microfilaments associated with molecules of the protein myosis; the actin microfilaments interact with the myosin molecules, causing the ring to contract; the contraction of the dividing cell's ring of microfilaments is like the pulling of a drawstring; the cleavage furrow deepens until the parent cell is pinched in two, producing two completely separated cells, each with its own nucleus and its own share of cytosol, organelles, and other subcellular structures