Cell Cycle and Cell Division Chapter 5 Belk and Borden Biology: Science for Life

Cell Division - the process a cell undergoes in order to make copies of itself. Why do cells divide?

What is Cancer? “mitosis gone mad” - a disease that begins when a single cell escapes from the regulation of its own division Tumor Benign vs Malignant

The Cell Cycle -all the events that occur when a cell divides -time required can vary from minutes to days, depending on the cell –Salmonella = 29 min –Red B. C. = 120 days

DNA & Chromosomes DNA as chromatin strands and chromosomes Sister Chromatids Centromere Why do chromosomes form?

Interphase (G1, S, G2) (about 90% of the cell cycle time) Cell grows during all 3 subphases by making proteins and organelles G 1 = first growth phase

Interphase (G1, S, G2) (about 90% of the cell cycle time) S phase = DNA is copied (synthesis) so each daughter cell has a complete set of chromosomes at the end of the cell cycle

Interphase (G1, S, G2) (about 90% of the cell cycle time) G 2 phase = second growth phase All through interphase, the cell is fulfilling its function At maximum volume to surface ratio, cell either remains in interphase or enters mitosis

Mitosis: Prophase Chromatin condenses into chromosomes Each duplicated chromosome appears as 2 identical sister chromatids Mitotic spindle begins to form in cytoplasm

Mitosis: Prometaphase Nuclear membrane disintegrates Spindle fibers interact with chromosomes The “dance of the chromosomes” begins

Mitosis: Metaphase Chromosomes are aligned at middle of cell Identical chromatids of each chromosome are attached to spindle fibers radiating from opposite poles of the cell

Mitosis: Anaphase Paired centromeres of each chromosome separate, freeing sister chromatids from eachother Each chromatid now a chromosome Sister chromatids are pulled to opposite poles of the cell

Mitosis: Telophase 2 new nuclei form at two poles of the cell where chromosomes have gathered Chromosomes uncoil and revert to chromatin form Mitosis (division of one nucleus into two identical nuclei) is complete

Cytokinesis

Allium root tip (onion) a mitosis classic!

Classify Cells relative to Cell Cycle Phase link link

Control of the Cell Cycle Cells require nutrients and growth factors to divide (example PDGF & fibroblasts) Density dependent inhibition also regulates cell division Adhesion of cells is also involved. Cells normally stop dividing if they lose their anchorage. The role of regulatory proteins at the G 1 “restriction point” is also critical.

Control of the Cell Cycle Regulatory proteins pace and control cell cycle events at “checkpoints” G 1 checkpoint—monitors nutritional status, growth factors, & cell density; “restriction point” G 2 checkpoint—monitors DNA replication and cell size Metaphase checkpoint—monitors chromosome attachment to spindle fibers

Mutations Changes (errors) in the genes that code for cell cycle regulatory proteins and tumor suppressor proteins are involved in cancer Proto-oncogenes code for growth factors Mutated proto-oncogenes (oncogenes) can overstimulate cell division and override the G 1 checkpoint Mutated tumor supressor genes fail to produce the proteins that prevent tumors

Healthful Decisions to reduce Cancer Risk Avoid carcinogenic addictions! Eat whole foods (fresh fruit and grains) Exercise regularly to boost immune system Don’t drink alcohol in excess Don’t get sunburned Undergo regular screening and self- examination