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