Cell Cycle and Mitosis

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

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.

Most of these cells are in Interphase How do you know 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. –Human (body cells) have 46 –Human (sperm or eggs) have 23 Chromosomes are made of a material called. chromosomes somatic cells gametes chromosomes. chromatin

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

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

Late Interphase: G 2 Centrosomes (with centriole pairs) Preparing for Division (G 2 of interphase) 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: P rophase M etaphase A naphase T elophase

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

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 & Cytokinesis 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.

What’s the end product? Two identical daughter cells ready to start the cycle again… or not. _cycle/01.html 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?