Chapter 12 b The Cell Cycle

The Cell Cycle b The cell cycle is the life of the cell from being formed to it’s devision into two cells b The entire DNA library for a cell is called the genome b Before any division occurs, the genome must first be copied

b All eukaryotic cells have a characteristic number of chromosomes b Human somatic cells have 46 chromosomes (which is the diploid number) (2n) b mitosis – the process where somatic cells divide, forming cells with the same chromosome as the original b Meiosis – deals with gametes (sperm, egg) which are haploid (n), having half the number of chromosomes as a somatic cell

Cell Division: Key Roles b In replication, each chromosome is made of 2 sister chromatids attached by a centromere b Sister chromatids have identical DNA b Sister chromatids separate during cell division

Cell Division: Key Roles b A cell’s life is spend mostly (90%) in interphase whihch can be divided into 3 stages G1 Phase – cell grows and carries out it’s functionsG1 Phase – cell grows and carries out it’s functions S Phase – continue to carry out life functions, but also duplicates it’s chromosomes (copying DNA)S Phase – continue to carry out life functions, but also duplicates it’s chromosomes (copying DNA) G2 Phase – gap after all copying is done and ready for mitosisG2 Phase – gap after all copying is done and ready for mitosis

Mitosis b Prophase b Prometaphase b Metaphase b Anaphase b Telophase

Mitosis Animation

Prophase b Chromosomes visible b Nucleoli (nucleus) disappear b Sister chromatids b Mitotic spindle forms b Centrosomes move

Prometaphase b Nuclear membrane fragments b Spindle interaction with chromosomes b Kinetochore develops

Metaphase b Centrosomes at opposite poles b Centromeres are aligned b Kinetochores of sister chromatids attached to microtubules (spindle)

Anaphase b Paired centromeres separate; sister chromatids liberated b Chromosomes move to opposite poles b Each pole now has a complete set of chromosomes

Telophase b Daughter nuclei form b Nuclear envelopes arise b Chromatin becomes less coiled b Two new nuclei complete mitosis

Cytokinesis b Cytoplasmic division b Animals~ cleavage furrow b Plants~ cell plate

Cell Cycle Regulation b Steps of the cycle are controlled by cell cycle control system with “checkpoints”along the way b Checkpoints include: G1 phase checkpointG1 phase checkpoint G2 phase checkpointG2 phase checkpoint M phase checkpointM phase checkpoint ***G1 phase checkpoint is the most important. This signal gives the go-ahead for cells to divide. (if not, it goes into G 0 phase

Normal cell division regulation b Density-dependant inhibition – process where crowded cells stop dividing b Anchorage dependency - normal cells must be attached to a substratum, like extracellular matrix, to divide

Cancer b Transformation – process where normal cell becomes a cancer cell b Tumor – mass of abnormal cells within normal cells b benign – non-invasive tumor b malignant – invasive tumor b Metastasis – spread of cancer cells that enter into blood or lymph vessels