The Cell Cycle
Telophase
phase of mitosis in which the distinct individual chromosomes begin to spread out into a tangle of chromatin
Anaphase
Sister chromatids separate and move toward opposite spindle poles by a combination of microtubule motor proteins and dynamic changes in the lengths of the microtubules as the spindle poles move farther apart.
Anaphase II
Sister chromatids separate into nonidentical haploid cells.
Terminally differentiated.
Some differentiated cells, such as those of the liver, renew cycling under certain conditions; others, including most muscle and nerve cells, are
Meiosis
Specialized process involving two unique and closely associated cell divisions that occurs only in the cells that will form sperm and egg cells.
Feature that characterize meiosis
The cells produced are haploid, having just one chromosome from each pair present in the body's somatic cells. The union of haploid eggs and sperm at fertilization forms a new diploid cell (the zygote) that can develop into a new individual.
Zygote
The cells produced are haploid, having just one chromosome from each pair present in the body's somatic cells. The union of haploid eggs and sperm at fertilization forms a new diploid cell known as the _________ that can develop into a new individual.
Prophase I
The chromosomes condense, and the nuclear envelope breaks down. crossing-over occurs.
G1 Phase
Usually the longest and most variable part of the cycle.
Haploid cells with new genetic combinations
What does meiosis produces?
Adds and replaces identical cells.
What does mitosis produces?
Step 3 in meiosis
When synapsis and crossing over are completed, the chromosomes become fully condensed and undergo metaphase, anaphase, and telophase as the cell divides. This first meiotic division separates the homologous chromosomes that paired during synapsis; each of the separated chromosomes still contains two chromatids held together at the centromere
Cyclins
With different _______ present during different cell cycle phases, each activates one or more specific cyclin-dependent kinases (CDKs).
Bcl-2 proteins
____________ associated with the outer mitochondrial membrane compromise membrane integrity stopping normal activity and releasing cytochrome c into the cytoplasm where it activates proteolytic enzymes called caspases.
Mitosis
cell division in which the nucleus divides into nuclei containing the same number of chromosomes
Prophase
chromosomes condense and spindle fibers form and becomes visible
Crossovers
During synapsis, double-stranded breaks and repairs occur in the DNA, some of which result in reciprocal DNA exchanges called ___________ between the aligned homologous chromosomes. This produces new combinations of genes in the chromosomes so that few if any chromosomes in the germ cells are exactly the same as those in the mother and father.
Step 4 in meiosis
Each of the two new cells now divides again, much more rapidly and without an intervening S phase. In the second meiotic division the chromatids separate to opposite poles as individual chromosomes. In each new cell a nuclear envelope forms around this new haploid set of chromosomes.
Synapsis
Early in the process the homologous chromosomes of each pair (one from the mother, one from the father) come together in an activity termed
Feature that characterize meiosis
Early in the process the homologous chromosomes of each pair (one from the mother, one from the father) come together in an activity termed synapsis.
Fragmentation of DNA.
Endonucleases are activated which cleave DNA between nucleosomes into small fragments. (The new ends produced in the fragmented DNA allow apoptotic cells to be stained histochemically using an appropriate enzyme that adds labeled nucleotides at these sites.)
Checkpoints
Entry or progression through other phases of the cycle is also monitored at other specific __________, where certain conditions must be met before the cell continues cycling.
Additional defects and the cellular changes
Failure to detect unregulated cell cycling can lead to _____________ and ____________ found in the various types of cancer.
Stem Cells and Tissue Renewal
Found in specific locations or niches where the microenvironment helps maintain their uniquely undifferentiated properties; they are often rare and inconspicuous by routine histologic methods.
Mitosis and periods termed G1, S, G2
Four distinct phases: of cell cycle includes:
Mitogen
Growth factors. Extracellular environment where protein signals from to activate cycling in postmitotic G0 cells.
Anaphase I
Homologous chromosomes are pulled to opposite ends of the cell. (Note that chromatids do not separate - each duplicated chromosome still has two chromatids.)
Apoptosis
If the problem encountered at any checkpoint cannot be corrected fairly quickly while cycling is halted, proteins encoded by tumor suppressor genes are activated and that cell's activity is redirected toward cell suicide or ____________.
replicated its DNA
In meiosis, a cell approaching the first meiotic division has just completed a typical S phase and ____________; each chromosome contains the two identical DNA molecules called sister chromatids.
Sister chromatids
In meiosis, a cell approaching the first meiotic division has just completed a typical S phase and replicated its DNA; each chromosome contains the two identical DNA molecules called
S phase
In meiosis, a cell approaching the first meiotic division has just completed a typical ________ and replicated its DNA; each chromosome contains the two identical DNA molecules called sister chromatids.
Synapsis
In meiosis, during a greatly elongated prophase of the first meiotic division (prophase I), the partially condensed chromatin of homologous chromosomes begins to come together and physically associate along their lengths during ________. Because each of the paired chromosomes has two chromatids, geneticists refer to synaptic chromosomes as tetrads to emphasize that four copies of each genetic sequence are present. During synapsis recombination or crossing over occurs among the four chromatids, which mixes up the genes inherited from each parent and yields a new and different set of genes to be passed on to the next generation.
Tetrads
In meiosis, during a greatly elongated prophase of the first meiotic division (prophase I), the partially condensed chromatin of homologous chromosomes begins to come together and physically associate along their lengths during synapsis. Because each of the paired chromosomes has two chromatids, geneticists refer to synaptic chromosomes as ____________ to emphasize that four copies of each genetic sequence are present. During synapsis recombination or crossing over occurs among the four chromatids, which mixes up the genes inherited from each parent and yields a new and different set of genes to be passed on to the next generation.
Four copies
In meiosis, during a greatly elongated prophase of the first meiotic division (prophase I), the partially condensed chromatin of homologous chromosomes begins to come together and physically associate along their lengths during synapsis. Because each of the paired chromosomes has two chromatids, geneticists refer to synaptic chromosomes as tetrads to emphasize that ___________ copies of each genetic sequence are present. During synapsis recombination or crossing over occurs among the four chromatids, which mixes up the genes inherited from each parent and yields a new and different set of genes to be passed on to the next generation.
Mixes up
In meiosis, during a greatly elongated prophase of the first meiotic division (prophase I), the partially condensed chromatin of homologous chromosomes begins to come together and physically associate along their lengths during synapsis. Because each of the paired chromosomes has two chromatids, geneticists refer to synaptic chromosomes as tetrads to emphasize that four copies of each genetic sequence are present. During synapsis recombination or crossing over occurs among the four chromatids, which ________ the genes inherited from each parent and yields a new and different set of genes to be passed on to the next generation.
Intervening S phase
In meiosis, each of the two new cells now divides again, much more rapidly and without an __________________. In the second meiotic division the chromatids separate to opposite poles as individual chromosomes. In each new cell a nuclear envelope forms around this new haploid set of chromosomes.
Chromatids
In meiosis, each of the two new cells now divides again, much more rapidly and without an intervening S phase. In the second meiotic division the ___________ separate to opposite poles as individual chromosomes. In each new cell a nuclear envelope forms around this new haploid set of chromosomes
Individual chromosomes
In meiosis, each of the two new cells now divides again, much more rapidly and without an intervening S phase. In the second meiotic division the chromatids separate to opposite poles as __________________. In each new cell a nuclear envelope forms around this new haploid set of chromosomes.
Nuclear envelope
In meiosis, each of the two new cells now divides again, much more rapidly and without an intervening S phase. In the second meiotic division the chromatids separate to opposite poles as individual chromosomes. In each new cell a ______________ forms around this new haploid set of chromosomes.
Fully condensed
In meiosis, when synapsis and crossing over are completed, the chromosomes become ____________ and undergo metaphase, anaphase, and telophase as the cell divides. This first meiotic division separates the homologous chromosomes that paired during synapsis; each of the separated chromosomes still contains two chromatids held together at the centromere
Metaphase, anaphase, telophase
In meiosis, when synapsis and crossing over are completed, the chromosomes become fully condensed and undergo ___________, __________, and _____________ as the cell divides. This first meiotic division separates the homologous chromosomes that paired during synapsis; each of the separated chromosomes still contains two chromatids held together at the centromere
Homologous chromosomes
In meiosis, when synapsis and crossing over are completed, the chromosomes become fully condensed and undergo metaphase, anaphase, and telophase as the cell divides. This first meiotic division separates the ________________ that paired during synapsis; each of the separated chromosomes still contains two chromatids held together at the centromere
Apoptosis
In the ovary, ___________ is the mechanism for both the monthly loss of luteal cells and the removal of excess oocytes and their follicles
Stem Cells and Tissue Renewal
In tissues with stable cell populations, such as most connective tissues, smooth muscle, and the cells lining blood vessels, stem cells are not readily apparent and differentiated cells appear to undergo slow and episodic division to maintain tissue integrity.
Meiosis
It involves two cell divisions and produces four haploid cells.
Mitosis
It is a cell division that produces two diploid cells
disassemble and disperse
Late in prophase, lamins and inner nuclear membrane are phosphorylated, causing the nuclear lamina and nuclear pore complexes to ________________ in cytoplasmic membrane vesicles.
Formation and phagocytic removal.
Membrane-bound remnants of cytoplasm and nucleus separate as very small apoptotic bodies. Newly exposed phospholipids on these bodies induce their phagocytosis by neighboring cells or white blood cells.
G2 Phase
Proteins required for mitosis accumulate
Apoptosis
Rapid, highly regulated cellular activity that shrinks and eliminates defective and unneeded cells.
Progenitor Cells
Rapidly dividing progeny of the cells committed to differentiation.
Cell Cycle
Regular sequence of events that produce new cells.
Apoptosis
Results in small membrane-enclosed apoptotic bodies, which quickly undergo phagocytosis by neighboring cells or cells specialized for debris removal.
Important events of meiosis unfold as follows
1. A cell approaching the first meiotic division has just completed a typical S phase and replicated its DNA; each chromosome contains the two identical DNA molecules called sister chromatids. 2. During a greatly elongated prophase of the first meiotic division (prophase I), the partially condensed chromatin of homologous chromosomes begins to come together and physically associate along their lengths during synapsis. Because each of the paired chromosomes has two chromatids, geneticists refer to synaptic chromosomes as tetrads to emphasize that four copies of each genetic sequence are present. During synapsis recombination or crossing over occurs among the four chromatids, which mixes up the genes inherited from each parent and yields a new and different set of genes to be passed on to the next generation. 3. When synapsis and crossing over are completed, the chromosomes become fully condensed and undergo metaphase, anaphase, and telophase as the cell divides. This first meiotic division separates the homologous chromosomes that paired during synapsis; each of the separated chromosomes still contains two chromatids held together at the centromere. 4. Each of the two new cells now divides again, much more rapidly and without an intervening S phase. In the second meiotic division the chromatids separate to opposite poles as individual chromosomes. In each new cell a nuclear envelope forms around this new haploid set of chromosomes.
G1/S "boundary"
Cells are then maintained at the restriction point at the _____________ until sufficient nutrients and enzymes required for DNA synthesis have accumulated, and when all is ready DNA replication (S phase) begins.
Telophase
A belt-like contractile ring of actin filaments associated with myosins develops in the cortical cytoplasm at the cell's equator.
Step 1 in meiosis
A cell approaching the first meiotic division has just completed a typical S phase and replicated its DNA; each chromosome contains the two identical DNA molecules called sister chromatids.
1. Loss of mitochondrial function and caspase activation. 2. Fragmentation of DNA. 3. Shrinkage of nuclear and cell volumes. 4. Cell membrane changes. 5. Formation and phagocytic removal.
Apoptosis can be activated by either external signals or irreversible internal damage, specific Bcl-2 proteins induce a process with the following features:
p53
Apoptosis is triggered by ________ and other tumor suppressor proteins, apoptosis is the method for eliminating cells whose survival is blocked by lack of nutrients or by damage caused by free radicals or radiation.
G0 phase
As new postmitotic cells specialize and differentiate, cell cycle activities may be temporarily or permanently suspended, with the cells sometimes referred to as being in the _________.
Caspases
Bcl-2 proteins associated with the outer mitochondrial membrane compromise membrane integrity stopping normal activity and releasing cytochrome c into the cytoplasm where it activates proteolytic enzymes called
Loss of mitochondrial function and caspase activation.
Bcl-2 proteins associated with the outer mitochondrial membrane compromise membrane integrity stopping normal activity and releasing cytochrome c into the cytoplasm where it activates proteolytic enzymes called caspases.
Stem Cells and Tissue Renewal
Best studied in tissues with rapidly renewing cell populations, including blood cells, skin cells, and cells lining the digestive tract.
Mitogen
Bind to cell surface receptors and trigger a cascade of kinase signaling in the cells.
Meiosis
Cell division that produces reproductive cells in sexually reproducing organisms
Interphase
Cell grows, performs its normal functions, and prepares for division; consists of G1, S, and G2 phases
Metaphase
Cell is now more spherical and the chromosomes are moved into alignment at the equatorial plate.
Mitosis
Cell turnover rate is rapid in the epithelium lining the digestive tract and uterus or covering the skin.
G1 Phase
Cell volume, reduced by half during mitosis, returns to its previous size.
S Phase
Characterized by DNA replication, histone synthesis, and the beginning of centrosome duplication.
Metaphase
Chromosomes condense further and protein complexes called kinetochores at each centromere attach to the mitotic spindle.
Metaphase II
Chromosomes line up single file in haploid cells.
Mitosis
Chromosomes replicated during the preceding S phase are distributed to the daughter cells.
Apoptosis
Controlled by cytoplasmic proteins in the Bcl-2 family which regulate the release of death-promoting factors from mitochondria.
Stem Cells and Tissue Renewal
Cycling serves to renew the differentiated cells of tissues as needed.
Shrinkage of nuclear and cell volumes
Destruction of the cytoskeleton and chromatin causes the cell to shrink quickly, producing small structures with dense, darkly stained pyknotic nuclei that may be identifiable with the light microscope.
Stem Cells and Tissue Renewal
Divide infrequently and the divisions are asymmetric.
Cytokinesis
Division of the cytoplasm during cell division
Apoptosis
Do not rupture and release none of their contents, unlike cells that die as a result of injury and undergo necrosis.
Meiotic crossing over
During ________________________, new combinations of genes are produced and every haploid cell is genetically unique. Lacking synapsis and the opportunity for DNA recombination, mitosis yields two cells that are the same genetically.
Step 2 in meiosis
During a greatly elongated prophase of the first meiotic division (prophase I), the partially condensed chromatin of homologous chromosomes begins to come together and physically associate along their lengths during synapsis. Because each of the paired chromosomes has two chromatids, geneticists refer to synaptic chromosomes as tetrads to emphasize that four copies of each genetic sequence are present. During synapsis recombination or crossing over occurs among the four chromatids, which mixes up the genes inherited from each parent and yields a new and different set of genes to be passed on to the next generation.
Telophase
During cytokinesis at the end of _________, constriction of this ring produces a cleavage furrow and progresses until the cytoplasm and its organelles are divided into two daughter cells, each with one nucleus.
Mitosis
Most tissues undergo cell turnover with slow cell division and cell death. Nerve tissue and cardiac muscle are exceptions because their differentiated cells cannot undergo mitosis.
Mitosis
Only cell cycle phase that can be routinely distinguished with the light microscope.
Cyclins
Overall cycling is regulated by a family of cytoplasmic proteins.
Metaphase I
Pairs of homologous chromosomes move to the equator of the cell.
Mitosis
Parent cell divides and each of the two daughter cells receives a chromosomal set identical to that of the parent cell.
G1 Phase
Period of active RNA and protein synthesis, including proteins controlling progress through the cell cycle.
Anaphase
Phase of mitosis in which the chromosomes separate and move to opposite ends of the cell
metaphase plate
Plane midway between the two poles of the cell where chromosomes line up during metaphase.
they are in transit along the path from the stem cell niche to a differentiated state, while still amplifying by mitosis the number of new cells available for the differentiated tissue.
Progenitor Cells transit amplifying cells because
1. Inadequate nutrition (nutrient stress) 2. Inappropriate cellular microenvironments 3. DNA damage.
Progression through the cell cycle is halted by adverse conditions such as
Meiosis I
The first division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the number of chromosome sets as the original cell.
Interphase
The long period between mitoses (the G1, S, and G2 phases).
Prophase
The nucleolus disappears and the replicated chromatin condenses into discrete threadlike chromosomes, each consisting of duplicate sister chromatids joined at the centromere.
Cell membrane changes.
The plasma membrane of the shrinking cell undergoes dramatic shape changes such as "blebbing" as membrane proteins are degraded and lipid mobility increases
Cell Cycle
The regular sequence of growth and division that cells undergo.
Meiosis II
The second phase of meiosis consisting of chromatids separating, along with the two diploid cells splitting in two
Telophase
The spindle depolymerizes and the nuclear envelope begins to reassemble around each set of daughter chromosomes.
Telophase II
The spindle fibres disappear, and a nuclear membrane forms around each set of chromosomes.
Prophase
The two centrosomes with their now-duplicated centrioles separate and migrate to opposite poles of the cell and organize the microtubules of the mitotic spindle.
Telophase
The two sets of chromosomes are at the spindle poles and begin reverting to their decondensed state.
Progenitor Cells
Transit amplifying cells.
Metaphase
second phase of mitosis, during which the chromosomes line up across the center of the cell
Interphase
the resting phase between successive mitotic divisions of a cell, or between the first and second divisions of meiosis.
Meiosis II
the second phase of meiosis consisting of chromatids separating, along with the two diploid cells splitting in two