Transcript Slide 1
DNA and Cell Division Mitosis in Animals Background Information Once an egg becomes fertilized, cellular divisions begins, eventually producing a whole organism All cells derived from the zygote contain the same genetic material An Integrated Organism Organization of DNA • All cells have DNA (chromosomes). • Almost all cells divide for reproduction, growth or repair. • Each new cell needs the exact same DNA as the original cell. • The original cell is called the mother cell and the two new cells are called daughter cells. • The DNA in the nucleus must replicate before the cell divides. Chromosome Number in Different Species Diploid Chromosome Number Common Name Genus and Species Buffalo Bison bison 60 Cat Felis catus 38 Cattle Bos taurus, B. indicus 60 Dog Canis familiaris 78 Donkey E. asinus 62 Goat Capra hircus 60 Horse Equus caballus 64 Human Homo sapiens 46 Pig Sus scrofa 38 Sheep Ovis aries 54 Number of genes in sequenced genomes • • • • • • • E. coli Yeast Roundworm Fruit fly Mosquito Mouse Human 4300 6000 18,600 13-14,000 13-14,000 30-35,000 30-35,000 A non-dividing cell: • 90% of a cell’s life is spent growing, not dividing • This phase is called interphase • The DNA in this phase is not condensed; thus is chromatin • At some point during this phase the DNA is doubled or replicated • Two copies are made, one for each of the new cells • Once replication occurs, the chromatin folds up to form chromosomes • This only occurs when the cell is about to divide • The duplicated chromosomes attach to each other at the centromere • Each individual copy of one chromosome is known as a chromatid • When chromatids are joined at the centromere, they are known as a single chromosome. sister chromatids centromere A piece of DNA or chromosome in an undividing cell Same piece now has replicated and super coiled ready for cell division. Also during interphase… • Additional organelles are produced • Cell membrane enlarged to allow cell growth • When the cell becomes too big to function it must divide – What would the SA/V ratio of this cell be…large or small? Interphase • • • • The cell grows New organelles are formed Duplicate chromosomes are produced The chromosomes are uncoiled and invisible • This uncoiled chromosomes are known as a chromatin Cell division/reproduction • Interphase is not considered to be part of cell reproduction. • It is simply the growth of the cell and the duplication of the chromosomes. • Cell reproduction consists of two separate stages known as mitosis and cytokinesis. • Cell division = mitosis + cytokinesis • A parent cell will produce 2 daughter cells. In cell division each chromosome is replicated and then the cell (and nucleus) divides Cell Reproduction • Original cell divides into two genetically identical daughter cells • Complete set of genetic information passed onto each daughter cell – DNA must be accurately duplicated before cell division • Mitosis: paired chromatids separate and move to opposite ends of the cell • Cytokinesis: cytoplasm + organelles divide into roughly equal halves http://www.stolaf.edu/people/gia nnini/flashanimat/celldivision/cro me3.swf Mitosis Animation MITOSIS/ CELL DIVISION • Stages include: • Prophase • Metaphase • Anaphase • Telophase Mitosis Duplicated chromosomes remain elongated Chromosomes condense and shorten Late Interphase Early Prophase Centrioles have also been duplicated Centrioles begin to move apart; Spindle forms Nucleolus disappears; Nuclear envelope breaks down Late Prophase Microtubules attach to Centromeres Metaphase Centromeres align at cell’s equator Mitosis: Spindle fibers pull chromatids to opposite poles Anaphase Chromatids become independent chromosomes Chromosomes begin unwinding Telophase Nuclear envelope reforms, spindle fibres disappear Cytoplasm divided along equator Cytokinesis Each daughter gets 1 nucleus & half of cytoplasm Next Interphase • Chromatin condenses (into chromosomes) • Chromosomes appear as “X”s. • Nuclear envelope dissolves (DNA free in cell) • Animals cells only: Centrioles move to opposite ends of cell + form spindle fibers • Centromere attaches to spindle fibre Prophase Metaphase • Each chromosome lines up in the middle of the cell. • Highly organized so that both cells get exactly the same DNA. • Spindle fibers attached to centromeres of chromosomes Anaphase • Each pair of chromatids splits at the centromere • Each chromatid is now an individual chromosome • Paired chromosomes are pulled to opposite ends by spindle fibres Telophase • Chromosomes end up at separate poles, spindle fibers begin to dissolve. • New nuclear envelope begins to form around chromosomes • chromosomes begin to uncoil • Cell starts to pinch off through cytokinesis Cytokinesis • Division of all the rest of cell parts but not equally (organelles) • Animals: cell membrane pinches to form two cells • Plants: new cell plate created between the two cells (becomes cell wall) The Cell Cycle: An Overview 1)Interphase 2)Mitosis a) Prophase b) Metaphase c) Anaphase d) Telophase 3)Cytokinesis Cell Division (Cell Reproduction) = mitosis + cytokinesis Use an Acronym For Mitosis: • • • • Prophase = P Metaphase = M Anaphase = A Telophase = T Make a sentence: • Please Meet At Ten • Phil, Mary, And Tom Figure 112 Links • http://en.wikipedia.org/wiki/Trisomy#Triso my • http://www.medgen.ubc.ca/wrobinson/mos aic/mos_how.htm Mitosis Drawing • Fold a large sheet of paper in 3 – You should have 3 columns on the front and 3 on the back • • • You will draw a cell in each stage of mitosis and include a written description of what is occurring at each stage Stages: Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis Notice that there are 6 stages and 6 coulmns on your sheet...1 stage per column! Some facts • 500,000 deaths per year (more males) • Older age group stricken more often • More than 100 types of cancer, many due to mutations triggered by environmental factors • Highest cancer incidence: male prostate female - breast • Highest cancer deaths: lung Normal cells in culture • Organized structure • Limited cell growth • No overlapping Cancer cells in culture • Disorganized • Overlapping structure • Uncontrolled cell growth Some images to make this real: look first at normal skin Cancerous Skin What causes a normal cell to become a cancer cell?