Mitosis Chapter 12

Mitosis Cell division Produce 2 daughter cells Same genetic information Genome

Mitosis Asexual reproduction Growth Repair

Prokaryotes Nucleoid Circular DNA No nucleus

Eukaryotes Chromosomes: DNA Chromatin: Complex of DNA & proteins Makes up chromosomes Humans 46 chromosomes Dogs 78 chromosomes

Karyotype Display of the chromosomes

Karyotype

Turners syndrome

Eukaryotes Haploid(n): Single set of chromosomes (23 in humans) Diploid(2n): Twice the haploid number or two sets (46) Homologous chromosomes: 2 chromosomes that match up One from the mother one from the father Homologs: One of the pair of chromosomes

Eukaryotes Chromatid: Duplicated chromosome Centromere:                                                       Chromatid: Duplicated chromosome Centromere: Attachment to another chromatid Prior to cell division each chromosome replicates

S (DNA synthesis) G1 Cytokinesis G2 Mitosis Fig. 12-5 INTERPHASE S (DNA synthesis) G1 Cytokinesis G2 Mitosis Figure 12.5 The cell cycle MITOTIC (M) PHASE

Cell cycle Cell cycle: Events that occur to produce two cells 1. Interphase (G1, S, G2) 2. Mitosis 3. Cytokinesis

Cell cycle Most of cycle is spent in interphase Rate of division depends on job of the cell. Liver cells may divide rapidly Mature muscle cells do not divide at all Few cells will be in mitosis at a time Most are in interphase

Cell cycle G1 or Gap 1 phase the cell is preparing for the S phase. Chromosomes are single Can last weeks to years or happen very quickly

Cell cycle S phase DNA replication happens 2 sister chromatids G2 or Gap 2 phase cell prepares for division Mitochondria & other organelles replicate Microtubules begin to form Chromosomes condense

Cell cycle Mitosis: Nucleus & its contents divide Distributed equally Forming two daughter cells Cytokinesis: Cytoplasm divides in two.

Interphase Growth phase of the cell G1, S, G2

Interphase

Prophase Beginning of mitosis Chromosomes continues to condense Mitotic spindle forms Begins to move chromosomes to center Nuclear membrane disintegrates Nucleolus disappears

Prophase

Metaphase Chromosomes line up in center of cell Centromeres become aligned along the cells center

Metaphase

Anaphase Microtubules shorten Separates the sister chromatids Chromosomes move towards the poles

Anaphase

Telophase Chromosomes are at the poles Nuclear envelope reforms Nucleolus reappears Chromosomes uncoil or de-condense

Telophase

Cytokinesis Cytoplasm separates Animal cells: cleavage furrow pinches the cells in two Plant cells: cell plate is formed between the cells Grows until a new cell wall is formed

Cytokinesis

Figure 12.9 Cytokinesis in animal and plant cells Vesicles forming cell plate Wall of parent cell 1 µm 100 µm Cleavage furrow Cell plate New cell wall Figure 12.9 Cytokinesis in animal and plant cells Contractile ring of microfilaments Daughter cells Daughter cells (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)

Binary fission Prokaryotes produce 2 daughter cells by binary fission

Binary fission 1. Replication of the DNA Origin of replication: Specific location on the DNA 2. Two DNA molecules move to the ends of the cell 3. Septation Formation of a new cell membrane & a septum.

Binary fission 4. Septum begins to grow inward 5. Cell pinches into two cells.

Cell cycle

Cell cycle control system Consists of special proteins Protein kinases & cyclins Regulate if cell stops or proceeds in the cycle Receives information from the environment Other cells determine if the cell should divide or not

Cell cycle control system Check points G1, G2 and M Signals Growth factors Density-dependent inhibition Anchorage dependence

G1 checkpoint Control system S G1 G2 M M checkpoint G2 checkpoint Fig. 12-14 G1 checkpoint Control system S G1 G2 M Figure 12.14 Mechanical analogy for the cell cycle control system M checkpoint G2 checkpoint

p53 Protein that works at a checkpoint at G1 in the cell cycle p53 determines if the DNA is damaged If so it stimulates enzymes to fix it Cell division continues Unable to repair damage Cell suicide occurs

p53 Helps keep damaged cells from dividing Cancer cells p53 is absent or damaged p53 protein is found on the p53 gene Considered a tumor-suppressor gene Cigarette smoking causes mutations in this gene

Tumor Abnormal growth of cells Due to a malfunction in the control system Abnormal cells grow uncontrollably Benign: Non-cancerous growth

Tumor Malignant: Cancerous growth Metastasis: Spread of cancer to distant locations

Henrietta Lacks 1951 developed cervical cancer Before cancer treatment Cells were removed First cells to grow in vitro Outside of the body Cell line is now known as the HeLa cell line Helped in biomedical research