CELL CYCLE & DIVISION Chapter 10

Cell Cycle Series of 4 ordered steps that result in duplication (copy) of the cell. When is it done? grow, repair, & reproduce!

Cell Cycle

46 Chromosomes Need a new cell Repair 46 Chromosomes Grow 23 Does this look right? What do you need to do? 92 Chromosomes S Phase 46 M Phase

Phases of Cell Cycle G 1, S, & G 2 are known as Interphase –Individual chromosomes are not visible Mitosis: process of sorting & distributing chromosomes –Individual chromosomes are visible visible with a light microscope

G 0 (Gap or Growth Zero)G 0 – Special stage within G 1 – For non-dividing cells or cells that have no reason to divide & make more of themselves

Special Parts of Cell Cycle Restriction or Checkpoints – Point of no return!Restriction or Checkpoints

What happens if something is wrong in cell cycle? Cells contain proteins that detect mistakes & damages. When a mistake or damage is detected  cell cycle stops until repairs can be made! Cell-cycle arrest If a cell can not be repaired, it will be destroyed!

WHY IS IT IMPORTANT TO DO CELL CYCLE CORRECTLY? Cells can not divide or leave a stage of cell cycle until they are ready & need to do so.  size & # of chromosomes could be affected!  Won’t have the complete or correct set of instructions!  The new cells will not function correctly!  New cells could be made when they are not needed or wanted!

When regulator proteins are inactivated, cells can grow improperly & out of control Uncontrolled cell growth & reproduction = Cancer Cancer

Cancer Progression There are many different forms of cancer, affecting different cell types and working in different ways. All start out with mutations in specific genes called “oncogenes”. The normal, unmutated versions of the oncogenes provide the control mechanisms for the cell. The mutations are caused by radiation, certain chemicals (carcinogens), and various random events during DNA replication. Once a single cell starts growing uncontrollably, it forms a tumor, a small mass of cells. No further progress can occur unless the cancerous mass gets its own blood supply. “Angiogenesis” is the process of developing a system of small arteries and veins to supply the tumor. Most tumors don’t reach this stage. A tumor with a blood supply will grow into a large mass. Eventually some of the cancer cells will break loose and move through the blood supply to other parts of the body, where they start to multiply. This process is called metastasis. It occurs because the tumor cells lose the proteins on their surface that hold them to other cells.

Cancer Treatment Two basic treatments: surgery to remove the tumor, and radiation or chemicals to kill actively dividing cells. It is hard to remove all the tumor cells. Tumors often lack sharp boundaries for easy removal, and metastatic tumors can be very small and anywhere in the body. Radiation and chemotherapy are aimed at killing actively dividing cells, but killing all dividing cells is lethal: you must make new blood cells, skin cells, etc. So treatment must be carefully balanced to avoid killing the patient. Chemotherapy also has the problem of natural selection within the tumor. If any of the tumor cells are resistant to the chemical, they will survive and multiply. The cancer seems to have disappeared, but it comes back a few years later in a form that is resistant to chemotherapy. Using multiple drugs can decrease the risk of relapse: it’s hard for a cell to develop resistance to several drugs at the same time.

Cell Cycle

Chromosome Dense rod-shaped structures made of DNA & proteins. Proteins  Histones

Stuff you need to know! ChromosomeChromosome: –in all living cells –consists of a single molecule of DNA –Dyed – specific banding pattern –carries genes –Humans have 46 in the form of 23 pairs! Sister ChromatidsSister Chromatids –2 connected copies of each chromosome CentromereCentromere –center proteins that hold sister chromatids together

Types of Chromosomes Autosomes –Pairs 1 to 22 Sex Chromosomes –Pair 23 –Determine the sex of an organism –X or Y (in humans)

The two copies of each autosome = homologous chromosomes –same size & shape –Same banding pattern –Carry genes for the same trait

Picture of an individuals chromosomes Used to –Test for sex of a baby –examine & test for genetic disorders

Mitosis Four distinct steps! Prophase Metaphase Anaphase Telophase

Prophase Nucleus membrane breaks down Chromosomes condense & become visible Centrioles move to opposite sides of cell Spindle Fibers begin to formSpindle Fibers

Metaphase Chromosomes line up in the middle of the cell  metaphase plate

Anaphase Spindle fibers contract & pull sister chromatids to opposite poles Sister chromotids separate –Now considered a single chromosome.

Telophase Chromosomes expand & begin to disappear. Nuclear envelop reforms for each new cell. –Produces 2 new nuclei Cytoplasm divides cells into two! Cytokinesis Cytokinesis –Called CytokinesisCytokinesis

Summary