Cell Cycle and Mitosis Watch how the cells

Cell Cycle and Mitosis

Watch how the cells divide in the following video 4. 3. For To 2. keep the reproduction cell sizes small of unicellular for increased organisms efficiency (like To heal/repair tissue For 1. multicellular organisms to grow in size Why do cells divide? clip. What do you notice happening? bacteria)

How many stages of cell division do you see in this image?

Cell Cycle The cell cycle is the life cycle of a cell First, we will look at Interphase… )

Interphase • • • Longest stage of cell division (90% of cell cycle) Nucleus is visible 3 sub-phases: G 1: Cell growth S: DNA is copied (DNA Replication) G 2: Organelles copied/duplicated to prepare for division. )

How do you know these cells are in Most of interphase? these cells are in Interphase Intact Nucleus

How is DNA packaged into chromosomes? DNA coils around set of 4 histone proteins, creating a “bead on a string” called a nucleosome The nucleosome coils into structures called chromatin Chromatin supercoils = chromosome!

Key Vocabulary • DNA molecules are packaged into chromosomes. – Human somatic cells (body cells) have 46 chromosomes. – Human gametes (sperm or eggs) have 23 chromosomes. • Chromosomes are made of a material called chromatin.

Key Vocabulary DNA • Chromatin is composed of proteins and _____ • It is supercoiled around proteins, called histones. • Together the DNA and histone molecules form bead-like structures called nucleosome

Key Vocabulary • The chromosome is duplicated (during S) • Each duplicated chromosome consists of two sister chromatids. • These are connected by a centromere.

Preparing for Division (G 2 of interphase) Late Interphase: G 2 Centrosomes (with centriole pairs) Nuclear membrane still visible Nucleolus Chromatin has been replicated

Mitosis (M Phase) The M Phase consists of: • Mitosis and Cytokinesis Mitosis: the division of the nucleus Cytokinesis: the division of the cytoplasm Four Stages of Mitosis: • Prophase • Metaphase • Anaphase • Telophase

Preparing for Division Late Interphase: G 2 Early Spindle Apparatus Prophase Centromere Nuclear membrane disappears Chromosome consisting of two sister chromatids becomes visible

Metaphase Chromosomes line up at an imaginary line between the centrosomes at opposite ends of the cell. The spindle attaches to the centromeres.

Anaphase Spindles pull the “daughter” chromosomes appart

Telophase Two nuclei become visible In animal cells, a Cleavage Furrow is visible In plant cells, a cell plate is now visible Cytokinesis The cytoplasm and organelles divide. Telophase & Cytokinesis

What’s the end product? • Two identical daughter cells ready to start the cycle again… or not. • Some cells (like your nerve and muscle cells) do not undergo division. • For those that do (your skin and the lining of your intestinal tract) how would you know how quickly division takes place? http: //www. biology. arizona. edu/cell_bio/activities/cell _cycle/01. html