The Cell Cycle Chapter 12

Mitosis  Cell division  Produce 2 daughter cells  Same genetic information

Mitosis  Asexual reproduction  Growth  Repair

Genome  Genetic information  Prokayotes  Nucleoid  Circular DNA  No nucleus

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

Eukaryotes  Somatic cells:  Body cells  46 chromosomes  Gametes:  Sex cells  Sperm & eggs  23 chromosomes

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

Fig µmChromosomes Chromosome duplication (including DNA synthesis) Chromo- some arm Centromere Sister chromatids DNA molecules Separation of sister chromatids Centromere Sister chromatids

Fig S (DNA synthesis) MITOTIC (M) PHASE Mitosis Cytokinesis G1G1 G2G2

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

Interphase  Growth phase of the cell  G1, S, G2

Interphase  Where most of cycle is spent  Rate of division depends on job of 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

Interphase  G1 or Gap 1 phase  Cell is doing its job  Preparing for the S phase.  Chromosomes are single  Can last weeks to years or happen very quickly

Interphase  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

Interphase

Mitosis  Nucleus & its contents divide  Distributed equally  Forming two daughter cells  Prophase, metaphase, anaphase and telophase

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

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

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 control system  Check points  Control point with stop & go signals  G1, G2 and M phases

Fig S G1G1 M checkpoint G2G2 M Control system G 1 checkpoint G 2 checkpoint

Cell cycle control system  Special proteins  Protein kinases & cyclins  Cdks – cycle dependent kinases  MPF-cyclin-Cdk complex  “M-phase promoting factor”  Regulate if cell stops or proceeds in the cycle

Fig b Cyclin is degraded Cdk MPF Cdk M S G1G1 G 2 checkpoint Degraded cyclin Cyclin (b) Molecular mechanisms that help regulate the cell cycle G2G2 Cyclin accumulation

Figure 12.16a M MMG1G1 G2G2 G2G2 G1G1 G1G1 SS MPF activity (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle Time Cyclin concentration

Cell cycle control system  Go-ahead signal at G1  Divides  No signal  G0 phase  Does not divide

Figure G 1 checkpoint G0G0 G1G1 Without go-ahead signal, cell enters G 0. (a) G 1 checkpoint G1G1 G1G1 G2G2 S M M checkpoint (b) M checkpoint Without full chromosome attachment, stop signal is received. Prometaphase Anaphase M G2G2 G1G1 M G2G2 G1G1 With go-ahead signal, cell continues cell cycle. G 2 checkpoint Metaphase With full chromosome attachment, go-ahead signal is received.

Cell cycle control system  Receives signals  The environment  Other cells  Growth factors  Density-dependent inhibition  Anchorage dependence

Tumor  Abnormal growth of cells  Malfunction in control system  Abnormal cells grow uncontrollably  Benign:  Non-cancerous growth

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

p53  Protein  Works at a checkpoint at G1  p53 determines if DNA is damaged  If so 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

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 HeLa cell line  Helped in biomedical research