Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Cell Cycle
Document related concepts
Transcript
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 DNA • Eukaryotic genomes made of DNA molecules DNA molecules are packaged into chromosomes making the replication and distribution more manageable • Eukaryotic species chromosome # unique by species • Somatic cells - body cells • Gametes – 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 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 nucleus • Each new nucleus receives a group of chromosomes identical to the original group Meiosis • Division of gametes (egg & sperm cells) • Yields non-identical daughter cells that have only one set of chromosomes • Daughter cells have half as many chromosomes as the parent cell The Cell Cycle Interphase (90% of cycle) • G1 phase - growth • S phase - synthesis of DNA • G2 phase - grows and prepares for cell division Mitotic phase • Mitosis - nuclear division • Cytokinesis - cytoplasm division Cells Alive Animation! http://www.cellsalive.com/cell_cycle.htm A typical human cell might undergo one division in 24 hours! Mitosis Prophase Prometaphase Metaphase Anaphase Telophase Interactive http://www.sci.sdsu.edu/mul 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. http://www.meta-library.net/media/mito2-sm.jpg Centrosome http://www.biology.ucsc.edu/mcd/images/centrosome.jpg 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 http://www.fotosearch.com/comp/LIF/LI F113/SA202005.jpg http://www.bio.unc.edu/faculty/peifer/documents/ 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 http://www.johnkyrk.c 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, Cdks • Cyclins External factors • Density-dependent inhibition of cell division • Crowded cells stop dividing • Anchorage Dependence • Cell must be attached to a substrate in order to divide Checkpoints G1 •Most important restriction point •If cell does not receive a go-ahead signal at this checkpoint, the cell exits the cell cycle and goes into G0 G2 M G0 •Non-dividing state Cancer ~ Loss of Cell Cycle Controls Transformation • Process that converts a normal cell into a cancer cell • If left unchecked by the immune system a tumor may develop • Benign • Malignant Metastasis • Spread of cancer cells to new locations
