Chapter 12

Biology

Cell Division

Allows unicellular organisms to reproduce

Growth and Repair of multicellular organisms.

How Prokaryotic Cells Divide

Prokaryotic cells lack a nucleus and other membranous organelles.

Divide by Binary Fission

Chromosome Is Singular

Prokaryotic chromosome contains mostly DNA and some associated proteins

Asexual reproduction requires a single parent; offspring are genetically identical to parent.

Eukaryotic Chromosomes and the Cell Cycle

• Karyokinesis – nuclear division

• Cytokinesis – division of the cytoplasm

A. Chromosomes

• Histone proteins organize chromosomes.

• Each species has a characteristic number of chromosomes.

A. Chromosomes

• a. Diploid (2n) number includes two sets of chromosomes of each type.

• b. Haploid (n) number contains one of each kind of chromosome.

A. Chromosomes

• Sister chromatids are two parts of a chromosome

• Centromere---a region of constriction on a chromosome

Mitosis

• Centrosomes

– responsible for organizing the spindle.

– main microtubule organizing center of the cell

Mitosis

• The centrosome has divided before mitosis begins.

• Each centrosome contains a pair of barrel-shaped organelles called centrioles; plant cells lack centrioles.

Mitosis Diagram

B. How Animal Cells Divide

• 1. Mitosis:– Interphase

– Prophase

– Pro-metaphase

– Metaphase

– Anaphase

– Telophase.

Mitosis Movie

B. How Animal Cells Divide

Prophase

• a. Chromatin condenses and chromosomes become visible.

• b. Nucleolus disappears and the nuclear envelope fragments.

• c. Short microtubules radiate out from the pair of centrioles located in each centrosome; form starlike asters.

B. How Animal Cells Divide

Prometaphase

• a. attachment of chromosomes to the spindle and movement as they align at the metaphase plate (equator).

B. How Animal Cells Divide

Metaphase

• a. Chromosomes align at the metaphase plate.

B. How Animal Cells Divide

Anaphase

• a. Two sister chromatids of each duplicated chromosome separate at centromere.

• b. Daughter chromosomes, each with a centromere and single chromatid, move to opposite poles.

B. How Animal Cells Divide

Telophase

• a. Spindle disappears.

• b. Chromosomes decondense and return to chromatin; the nuclear envelope reforms and nucleoli reappear.

• c. Cytokinesis is nearly complete.

Cytokinesis in Animal Cells

• a. Cleavage furrow indents the plasma membrane between the two daughter nuclei at a midpoint; progressively divides cytoplasm during cell division.

Mitosis Video

C. How Plant Cells Divide

• 1. Plant meristematic tissue in tips of roots and shoots

• 2. Stages are same as in animal cells.

• 3. Plant cells - no centrioles, and asters do not form.

Cytokinesis in Plant Cells

• Golgi apparatus produces vesicles that move to the midpoint between the daughter cell nuclei

• Vesicles fuse, forming a cell plate

How the Cycle is Controlled

• 1. Some cells divide continuously

• 2. Other cells are arrested in at different stages

Mitosis Stages

How the Cycle is Controlled

• 4. Enzymes known as cyclin-dependent kinases (Cdks) regulate passage of cells through these checkpoints

How the Cycle is Controlled

• Oncogenes (cancer-causing genes) may code for cyclins that no longer function as they should.

Cancer Cells

Cancer Radiation

Cancer Histroy

Cancer Causes

Cancer

• Angiogenesis the formation of new blood vessels.

• Malignancy and Metastasis ability to move and movment of cancer cells to a new location.

Cancer Treatment

Cancer Genetics

The End.

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