The Cell Cycle Mitosis …

THINK: Of how many cells are you composed? When an organism grows bigger do you get more cells or just bigger cells or both? When do your cells divide the fastest? Slowest? Do cells ever stop dividing? Are all cells capable of division and replacement?

Why does a cell divide? As a cell absorbs nutrients and gets larger, the volume of the cell increases faster than the surface area. -Therefore, the demands of the cell (the volume) exceed the ability of the cell to bring in nutrients and export wastes. Solution? Divide into two smaller cells

When is cell division occurring? GROWTH -increase number of cells REPAIR -replace lost cells due to injury, disease CANCER – Abnormally high rates of cell division due to mutation Different kinds of cells divide at different rates: E. coli – 20 minutes Yeast cell – 2 hours Amoeba – a few days Human embryo cell – 15-20 minutes Human adult cell – 8 hours to 100 days

How long is one cell cycle. Depends on the type of cell. Ex How long is one cell cycle? Depends on the type of cell. Ex. Skin cells every 24 hours. Some bacteria every 2 hours. Some cells every 3 months. Nerve cells, never. Cancer cells very short. Programmed cell death: Each cell type will only do so many cell cycles then die. (Apoptosis)

Aging All cells die after a certain number of divisions (programmed cell death-”apoptosis”). At any given time some cells are dividing and some cells are dying. Childhood Cell division > cell death Adulthood Cell division = cell death Aging Cell division < cell death

Control of the Cell Cycle Cell proliferation

Interphase ~ 90% of the time. Ø   G1: Little new cell absorbs nutrients and grows larger. Does protein synthesis, its job. Ø   S phase: Synthesis of new DNA (DNA replication) for daughter cells in preparation for mitosis. Ø   G2: Cell continues to grow, do protein synthesis, do its job. Gets too large, needs to divide.

What do chromosomes look like? Chromosomes exist in 2 different states, before and after they replicate their DNA. Before replication, chromosomes have one chromatid. After replication, chromosomes have 2 sister chromatids, held together at the centromere. Each chromatid is one piece of DNA with its supporting proteins.

Remember that diploid cells have two copies of each chromosome, one from each parent. These pairs of chromosomes are NOT attached together.

Structure of a eukaryotic chromosome unreplicated chromosome arm centromere

Prior to cell division: chromosomes (DNA) are replicated (duplicated) duplicated chromosome – attached at their centromeres – while attached, known as sister chromatids duplicated chromosome

daughter chromosomes sister chromatids

MITOSIS Equal division of the 2 sets of DNA amongst the 2 daughter cells. 4 Stages: “PMAT” 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase How the Cell Cycle Works Mitosis Animation Cell Cycle

What is Mitotic Cell Division? Division of somatic cells (body cells) (non reproductive cells) in eukaryotic organisms A single cell divides into two identical daughter cells (cellular reproduction) => Maintains chromosome ploidy of cell

Ploidy – refers to the number of pairs of chromosomes in cells haploid – one copy of each chromosome – designated as “n” diploid – two copies (= pair) of each chromosome – designated as “2n”

As a cell enters mitosis from interphase it has 2 complete sets of chromosomes because of replication in the S phase. Each set must be re-arranged and distributed into the 2 new daughter nuclei. This is mitosis.

Prophase…   -Chromatin condenses (coils) into chromosomes. Sister chromatids joined by centromere. -Nuclear membrane dissolves. -Centrioles divide and move to opposite poles forming spindle between them.

chromatin nucleolus nucleus centrioles condensing chromosomes

Metaphase -Centromeres lock on to spindle fiber -Sister chromatids line up on metaphase plate. -Centromeres lock on to spindle fiber

Anaphase -Centromeres divide. -Spindle fibere contract pulling sister chromatids apart to poles.

Telophase: -New nuclear membranes form around new nuclei Mitosis Movie

CYTO KINESIS – cytoplasm divides Cytoplasm splits into 2 cells. -Animal cells: Cleavage furrow forms from outside in. - Plant cells: Division/cell plate forms from inside out.  

Cell now returns to interphase Cell now returns to interphase . The chromosomes uncoil back into chromatin. The whole cell cycle starts over again….. Control of the Cell Cycle

At any point in time the cells in a tissue will be at different stages in the cell cycle.

Mitosis Stages Put these in the correct order..

The Guarantee of Mitosis… The 2 daughter cells formed are identical to each other and identical to the mother cell. Why is this so important? Mitosis The Movie

Mitosis is asexual In Mitosis, each daughter cell is exactly the same as the original mother cell. Cell Differentiation

Propogation of plants by cuttings Budding of Yeast These are other examples of the uses of mitosis to create new organisms asexually: Propogation of plants by cuttings Runners from plants like strawberries

Resources Mitosis Dance Mitosis  CANCER http://www.biology.iupui.edu/biocourses/N100H/ch8mitosis.html http://www.schoolscience.co.uk/content/4/biology/abpi/cancer/cancer3.html http://genetics.gsk.com/chromosomes.htm http://www.horton.ednet.ns.ca/staff/selig/handouts/bio12/cellrepro/cancermitosis.pdf#search=%22%22cancer%20animation%22%20mitosis%22 How Cancer grows http://www.pbs.org/wgbh/nova/cancer/grow_flash.html Mitosis: http://pages.csam.montclair.edu/~smalley/mitosis.mov http://faculty.pingry.org/thata/pingry_upload/movies/cellular_reproduction/plantcell_lily_mitosis.mov http://www.zo.utexas.edu/faculty/delozanne/celldivision/Mitosis%20Video.mov Cell Cycle & Cancer Animations: http://science.education.nih.gov/supplements/nih1/cancer/activities/activity2_animations.htm Cell Biology & Cancer Animations: http://www.learner.org/channel/courses/biology/units/cancer/images.html Mitosis & Meiosis Interactive Exercise: http://biologyinmotion.com/cell_division/ Mitosis Animations: http://www.sci.sdsu.edu/multimedia/mitosis/navigator.html Plant Cell Mitosis: http://www.teachersdomain.org/resource/tdc02.sci.life.stru.dnadivide/ Mitosis Dance Meiosis Square Dance