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Ch 12: The Cell Cycle

verview: Key Roles of Cellivision

ey concepts

12.1: most cell results in

enetically identical daughter

ell

istribution ofhromosomes eukaryotic

ell division

12.2: The mitotic phaseternates with interphase

n the cell

Ability of organism to make more of itself is difference of living and nonliving Continuity of life is based on reproduction of cells, or cell division Cell division is an integral part of cell cycle, the life of a cell from formation to its own divis C 12.1 most cell division (C) result in genetically identical daughter cells C 12.2 the mitotic phase alternates with interphase in the cell cycle C 12.3 the eukaryotic cell cycle is regulated by a molecular control system Unicellular organisms: division of one cell reproduces the entire organism Multicellular organism: division is important for

-Development from a fertilized cell-growth

-repair

Most C results in daughter cells with identically genetic info, DNA Exception is meiosis, a special type of that can produce sperm and egg cells All DNA is a cell constitutes the cells genome Genome consist of single DNA molecule (common in prokaryotic cells) or number of DNA

molecules (common in eukaryotic cells)

DNA molecules in a cell are packaged into chromosomes

Eukaryotic chromosomes can exist as- chromatin, an extended linear complex of DNA and protein transcription can occur

- chromosomes, condensed chromatin using histone proteins transcription cannot occur

Every eukaryotic species has a characteristic number of chromosomes in each cell nucleusSomatic cells (non-reproductive cells) have 2 sets of chromosomes (termed diploid)Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic ce

(termed haploid)

DNA replicates and the chromosomes condense when the cell ispreparing for cell division

Each duplicated chromosome has 2 sister chromatids (joined copies ofthe original chromosome) which separate during cell division

The centromere is the narrow waist of the duplicated chromosome, wherethe two chromatids are most closely attached once separate, thechromatids are called chromosomes

Eukaryotic cell division consists of- mitosis, the division of the genetic material in the nucleus

- cytokinesis, the division of the cytoplasm

Gametes are produced by a variation of cell division called meiosis thatyields non-identical daughter cells that have only one set ofchromosome, half as many as the parent cell

Sperm of father + egg of mother, make a single cell organism called aZygote which duplicates threw meiosis that later create a multicellular organism

1882, German anatomis Walther Flemming developed dyes to observe chromosomes duringmitosis and cytokinesis

Cell consists of- Interphase (Cell growth (Cw.) and copying of chromosomes in prep for C )- Mitotic (M) phase (mitosis and cytokinesis)

Interphase (~90% cell cycle) has sub-phases- G1phase (first gap)- S Phase (DNA synthesis)

- G2 phase (second gap)

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Mitotic spindle: A closer

ook

inary fission

volutions of Mitosis

12.3: the eukaryotic cellycle is regulated by a

molecular control system

vidence for cytoplasmicgnals

Mitosis is conventionally divided into five phases- prophase

- prometaphase- metaphase

- anaphase- telophase

Mitotic spindle is a structure of mictobules and associated proteins that controlchromosome movement during mitosis

In animal cells, but not plant cells, assembly of spindle mictobulues begins in thecentrsomsome, the microtubule organizing centerSpindle includes

- centrosome (replicates during interphase to 2 centromes, one in opposite ends of c

- spindle microtubules- aster (radial array of short microtubules) extends from each centrosome

During prometaphase, some spindle microtubules attach to kinetochores (proteincompleses associates with centromere) of chromosomes and move chromosome

At methaphase, chromosomes are all lined up at the metaphase plate, imaginary strucin between spindles 2 poles

In anaphase, sister chromatids separate and move along kienteochore microtubulestoward opposite ends of the cell

Microtubules shorten depolymerizing ate theirkinetochore ends (pacman mechanism)

Nonkinetochore microtubules from opposite polesoverlap and push against each other, elongating

cell

In telophase, genetically identical daughter nuclei form at opposite ends of the cellIn animal cells, cytokinesis occurs by cleavage, forming a cleavage furrowIn plant cells a cell plate forms during cytokenesisPlant cell mitotic division

- no centrosome- cell plate formation (part of current cell wall carried through vesicles to make newcell wall, also cytoplasm which cause plasmadesmata)

Prokaryotes (bacteria and archea) reproduce by a type of cell division called binaryfission

In binary fission, chromosome pelicates (beginning at the origin of replication), and ttwo daughter chromosomes actively move apart

Plasma membrane pinches inward, dividing cell into twoSince prokaryotes evolved first, mitosis probably evolved from binary fission

Certain protest exhibit types of cell division that seem intermediate between binaryfission and mitosis

Frequency of C varies with the type of cellDifferences result from regulation at the molecular levelCancer cell manage to escape the usual controls on the cell cycleCell cycle appear to be driven by specific chem. signals present in cytoplasmEvidence for hypotheses comes from experiment in which cultured mammalian cells

different phases of the cell cycle were fused to form a single cell with two nuclei

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ell cycle control system

ell cycle clock: cyclinisnd cyclin-dependent

inases

anchor

den.-dep.

cancer

oss of C controls in

ancer cells

ou should now be able to:

Sequential everts of the C are directed by a distinct cell cycle control system, which similar to a clock

C control system is regulated by both internal and external controlsClock has specific checkpoints where the C stops until a go-ahead signal is receivedFor many cells, G1 checkpoint seems to be the most important oneIf a cell receives a go-ahead signal at the G1 phase checkpoint, it will usually comple

the S, G2, and M phase and divide

If a cell doesnt receive the signal, it will exit the cycle and switch into a non-dividngphase, G0 phase

2 types of regulatory proteins are involved in the C control: cyclings and cyclin-dependent kinases (Cdks)

Cdks activity fluctuates during the C bcc its controlled by cyclins, so named bcc theconcentrations vary with the C

MPF (maturing-promoting factor) is a ci/clin-Cdk complex that triggers a cells passapast the G2 checkpoint into the M phase

An example of an internal signal is that kinetochores not attached to spindle microtusen a molecular signal that delays anaphase

Some external signal are groth factors, proteins releases by certain cells that stimulateother cells to divide

For Ex: platelet-derived growth factors (PDGF) stimulates the of human fibroblast in culture

Clear ex. of external signals- density-dependent inhibition, in which crowded cells stoMost animal cells also exhibit anchorage dependence, in which they must be attached

substratum in order to

Cancer cells exhibit neither density-dependence inhibition nor anchorage dependenceCancer cells do not respond normally to the bodys control mechanismsCancer cells may not need growth factors to grow and

-they may make their own growth factors

- they my convey a growth factors signal without the presence of growth factors- they may have an abnormal C control system

A normal cell converted to a cancerous cell by a process called transformationCancer cells form tumors, masses of abnormal cells within otherwise normal tissueIf abnormal cells remain at the original state, lump is called a begin tumorMalignant tumors invade surrounding tissues and can metastasize, exporting cancer c

to other body parts of the body, where they may from secondary tumors

1.Describe the structural organization of the prokaryotic genome and the eukaryotic

genome2.List the phases of the cell cycle; describe the sequence of events during each phase

3.List the phases of mitosis and describe the events characteristic of each phase4.Draw or describe the mitotic spindle, including centrosomes, kinetochore microtubul

nonkinetochore microtubules, and asters5.Compare cytokinesis in animals and plants

6.Describe the process of binary fission in bacteria and explain how eukaryotic mitosismay have evolved from binary fission

7.Explain how the abnormal cell division of cancerous cells escapes normal cell cyclecontrols

8. Distinguishable between benign, malignant, and metastatic tumors

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