Chpt. 12 ~ The Cell Cycle  Cell division results in genetically identical daughter cells.  The mitotic phase alternates with interphase in the cell cycle.  The cell cycle is regulated by a molecular control system.

Key Roles of Cell Division  When a unicellular organism divides and forms duplicate offspring, the division of one cell reproduces an entire organism  Cell division on a larger scale can produce progeny from some multicellular organisms such as plants that grow from cuttings  Cell division also enables sexually reproducing organisms to develop from a single cell~ the fertilized egg or zygote  Cell division continues after an organism is fully grown to repair and replace cells that die from normal wear and tear or accidents

Cellular Organization of Genetic Material  Genome: cell’s genetic information Prokaryotic single circular or elongated DNAProkaryotic single circular or elongated DNA Eukaryotic genomes made of DNA moleculesEukaryotic genomes made of DNA molecules  DNA molecules are packaged into chromosomes making the replication and distribution more manageable Eukaryotic species chromosome # unique by speciesEukaryotic species chromosome # unique by species Somatic cells - body cellsSomatic cells - body cells Gametes – sperm & egg cellsGametes – sperm & egg cells  Eukaryotic chromosomes are made of chromatin a DNA-protein complex

Chromosome duplication & distribution during cell division  When a cell is not dividing each chromosome is in the form of a long, thin chromatin fiber  After DNA duplication the chromosomes condense  Each duplicated chromosome has: Two sister chromatidsTwo sister chromatids –Each contain identical DNA –Attached at centromere a narrowing “waist” of sister chromatids –Each sister chromatids have a kinetochore, a structure of proteins associated with specific sections of chromosomal DNA at the centromere –Later in cell division the sister chromatids separate and move into two new nuclei –Once sister chromatids separate they are called chromosomes

Cell Division  Mitosis Division of the nucleusDivision of the nucleus Each new nucleus receives a group of chromosomes identical to the original groupEach new nucleus receives a group of chromosomes identical to the original group  Meiosis Division of gametes (egg & sperm cells)Division of gametes (egg & sperm cells) Yields non-identical daughter cells that have only one set of chromosomesYields non-identical daughter cells that have only one set of chromosomes Daughter cells have half as many chromosomes as the parent cellDaughter cells have half as many chromosomes as the parent cell

The Cell Cycle  Interphase (90% of cycle) G 1 phase - growthG 1 phase - growth S phase - synthesis of DNAS phase - synthesis of DNA G 2 phase - grows and prepares for cell divisionG 2 phase - grows and prepares for cell division  Mitotic phase Mitosis - nuclear division Cytokinesis - cytoplasm division A typical human cell might undergo one division in 24 hours! Cells Alive Animation!

Mitosis  Prophase  Prometaphase  Metaphase  Anaphase  Telophase Interactive timedia/mitosis/ timedia/mitosis/

Mitotic Spindle  Constructed of fibers made of microtubules and associated proteins  Kinetichore - chromosome attached  Nonkinetichore or Polar – no chromosome attached  Begins to form in the cytoplasm during prophase at the centrosome  The spindle includes the centrosomes, the spindle microtubules, and the asters.

Centrosome  In animal cells, a pair of centrioles is located at the center of the centrosome but are not essential for cell division  Most plant cells centrosomes lack centrioles  Centrosome replicates during interphase and remain together near the nucleus  The two centrosomes move apart from each other during prophase and prometaphase of mitosis as spindle microtubules grow out from them   By the end of prometaphase, the two centrosomes, at are opposite poles of the cell with an aster radiating from each centrosome F113/SA jpg people's%20pages/lab%20website/RusanColor2s mall.jpg

Prophase  Chromatin fibers condense into visible Chromosomes  Nucleoli disappear  Each duplicated chromosome appears as two identical Sister chromatids joined together  Mitotic spindle begins to form  Centrosomes move away from each other

Prometaphase  Nuclear membrane fragments  Spindle interaction with chromosomes  Kinetochore develops at centromere of each chromatid  Microtubules making up spindle  Kinetochore microtubule  connect to kinetochore  Nonkinetochore microtubules  communicate only with poles

Metaphase  Centrosomes at opposite poles  Centromeres are aligned  Kinetochores of sister chromatids attached to microtubules (spindle)

Anaphase  Paired centromeres separate; sister chromatids liberated  Chromosomes move to opposite poles  Each pole now has a complete set of chromosomes

Telophase  Daughter nuclei form  Nuclear envelopes arise  Chromatin becomes less coiled  Two new nuclei complete mitosis

Cytokinesis  Cytoplasmic division  Animals: cleavage furrow  Plants: cell plate Mitosis animation om/mitosis.html om/mitosis.html om/mitosis.html

Binary Fission  Cell division of prokaryotes  DNA replication begins at a specific sites on chromosome called origin of replication  As DNA replicates one origin moves rapidly toward the opposite end of the cell while the cell elongates  When replication is complete its plasma membrane grows inward producing two daugther cells

Cell Cycle Control System  Molecules present in the cytoplasm regulate progress through the cell cycle  Cyclic changes in regulatory proteins works as a cell cycle clock through signal transduction pathways Cyclin-Dependent Kinases, CdksCyclin-Dependent Kinases, Cdks CyclinsCyclins  External factors Density-dependent inhibition of cell divisionDensity-dependent inhibition of cell division Crowded cells stop dividingCrowded cells stop dividing Anchorage DependenceAnchorage Dependence Cell must be attached to a substrate in order to divideCell must be attached to a substrate in order to divide

Checkpoints  G 1 Most important restriction pointMost important restriction point If cell does not receive a go-ahead signal at this checkpoint, the cell exits the cell cycle and goes into G 0If cell does not receive a go-ahead signal at this checkpoint, the cell exits the cell cycle and goes into G 0  G 2  M  G 0 Non-dividing stateNon-dividing state

Cancer ~ Loss of Cell Cycle Controls  Transformation Process that converts a normal cell into a cancer cellProcess that converts a normal cell into a cancer cell If left unchecked by the immune system a tumor may developIf left unchecked by the immune system a tumor may develop BenignBenign MalignantMalignant  Metastasis Spread of cancer cells to new locationsSpread of cancer cells to new locations