Chapter Twelve: the cell cycle

Q1: how important is reproduction?
A1: the ability of organisms to reproduce their own kind is the one characteristic that best distinguishes living things from nonliving matter. living things reproduce to pass their gene to their offsprings so that they won't be extinct.
Q2: what is the difference between cell cycle and cell division?
A2: cell division is an integral part of cell cycle. cell division is the cell reproduction. cell cycle is the life of a cell from the time it is first formed from a dividing parent cell until its own division into two cells.
Q3: what is the difference between unicellular and multicellular organism reproduction?
A3: a unicellular organism reproduces the entire organism; in multicelllar organimsm, by producing eggs and sperms.

Five Facts:
1. the continuity of life is based on the reproduction of cells, or cell division
2. the cell division process is an integral part of the cell cycle, the life of a cell from the time is first formed from a dividing parent cell until its own division into two cells.
3. cell division results in gentically identical daghter cells
4. the mitotic ohase alternates with interphase in the cell cycle
5. the eukaryotic cell cycle is regulated by a molecular control system.

Figure:







DNA and histone proteins are packaged into structures called chromosomes. each chromosome has two sister chromatids. centromere between two sister chromatids connects them.

Summary:
Most cell division involves the distribution of identical genetic material-DNA-to two daughter cells. a cell's endowment of DNA, its genetic information, is called its genome. the replication and distribution of so much DNA is manageable because the DNA molecules are packaged into chromosomes. reproductive cells, or gametes-sperm and eggs-have one set of 23 chromosome in humans. eukaryotic chromosomes are made of chromatin, a complex of DNA and associated protein molecules. each duplicated chromosome has two sister chromatids. the two chromatids, each containning an identical DNA molecule, are initially attached all along their lengths by adhesive protein complexes called cohesins. Mitosis is the division of the nucleus is usually followed immediately by cytokinesis, the division of the sytoplasm. producing gametes-eggs or sper- by a variation of cell division called meiosis, which yields nonidentical daughter cells that have only one set of cell.
in one cell cycle, interphase has 90%, which includes G1 phase, S phase, and G2 phase. chromosomes are suplicated only during the S phase. the mitotic(M) phase, which includes both mitosis and cytokinesis, is usually the shortest part of the cell cycle about 10%. Mitosis has five stages: prophase, prometaphase, metaphase, anaphase, and telophase. Many of events of mitosis deoent on the mitotic spindle, which begins form in the cytoplasm during prophase. it consisits of fibers made of microtubules and associated proteins. centrosome is a subcellular region containing material that functions throughout the cell cycle to orgaize the cell's microtubules. A pair pf centrioles is located at the center of the centrosome. In animal cells, cytokinesis occurs by a process know as cleavage. Cell cycle control system is a cyclically operating of molecules in the cell that both triggers and coordiantes key events in the cell cycle. a checkpoint is a control point were stop and go-ahead signals can regulate the cycle: G1, G2, and M phrase. the G1 point is the restriction pont will switch to a nondiving state called Go phase. the regulartory molecules are mainly proteins of teo types: protein kinases and cyclins.

Key Terms:

1. anchorage dependence-The requirement that a cell must be attached to a substratum in order to divide.
2. aster-A radial array of short microtubules that extends from each centrosome toward the plasma membrane in an animal cell undergoing mitosis
3. benign tumor-A mass of abnormal cells that remains at the site of its origin.
4. binary fission-A method of asexual reproduction by “division in half.” In prokaryotes, binary fission does not involve mitosis; but in single-celled eukaryotes that undergo binary fission, mitosis is part of the process.
5. cell plate-A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis.
6. cleavage-(1) The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. (2) The succession of rapid cell divisions without significant growth during early embryonic development that converts the zygote to a ball of cells.
7. cleavage furrow-The first sign of cleavage in an animal cell; a shallow groove in the cell surface near the old metaphase plate.
8. cyclin-dependent kinase (Cdk)-A protein kinase that is active only when attached to a particular cyclin.
9. density-dependent inhibition-The phenomenon observed in normal animal cells that causes them to stop dividing when they come into contact with one another
10. somatic cell-Any cell in a multicellular organism except a sperm or egg.

Video:

http://www.youtube.com/watch?v=VlN7K1-9QB0