Cell Cycle, Mitosis and Meiosis Covered in these slides, in the Concepts & Connections book- Chapter 8 to page 143 In Raven and Johnson Book- Chapter 10 pages And in your packet on The Cell Cycle

 The cell cycle is an ordered sequence of events that extends –from the time a cell is first formed from a dividing parent cell –until its own division. The cell cycle multiplies cells © 2012 Pearson Education, Inc.

 During cytokinesis, the cytoplasm is divided into separate cells.  The process of cytokinesis differs in animal and plant cells. Cell division is a continuum of dynamic changes

Cytokinesis Cleavage furrow Contracting ring of microfilaments Daughter cells Cleavage furrow

 The cells within an organism’s body divide and develop at different rates.  Cell division is influenced externally by –the presence of essential nutrients, –growth factors, proteins that stimulate division, there are over 50 different growth factors which work for one or more cell type –density-dependent inhibition, in which crowded cells stop dividing, –anchorage dependence, the need for cells to be in contact with a solid surface to divide. Anchorage, cell density, and chemical growth factors affect cell division

 The cell cycle control system is a cycling set of molecules in the cell that –triggers and –coordinates key events in the cell cycle.  Checkpoints in the cell cycle can –stop an event or –signal an event to proceed. Growth factors signal the cell cycle control system

 There are three major checkpoints in the cell cycle. Growth factors signal the cell cycle control system G1- commitment to divide, growth factors present?, Size of cell ok?, G2- check for proper DNA replication M- all chromosomes attached to spindle fibers

Cell Cycle progresses by action of Cdks Cyclins proteins produced by the cell during cell division Cyclin-dependent kinases (Cdk) cyclin is required to activate these enzymes activates cell proteins by phosphorylating them (proteins needed for S phase) needed to go through G1 checkpoint MPF Maturation-promoting factor (mitosis promoting factor) aka Mitosis- promoting factor is a cyclin-Cdk complex phosphorylates proteins needed for mitosis needed to go through G2 checkpoint

Rate of Cell Division Differs from one cell type to the next –Examples: red bone marrow cells divide every 12 hours to replace RBCs that wear out Cells at tip of root divide about every 19 hours. Neurons (nerve cells) normally never divide again once brain is fully formed in utero Control of Division, lost = CANCER –Cancer is different depending on the tissue affected –Common theme is lack of control over cell division –Abnormal, uncontrolled cell division –Mutation in genes (including p53) that target and control abnormal cells. –Abnormal cells impede functioning of normal cells

p53 gene ( tumor suppressor gene) Key role in G1 checkpoint P53 protein monitors DNA Found absent or damaged in most cancer cells

Cancer is failure of cell cycle control Tumor suppressor genes- prevents the development of mutated cells, prevents cancer/tumors Oncogenes- cancer causing genes Proto-oncogenes- normal genes that become mutated

Meiosis Production/formation of __________ Basis of sexual reproduction Only germ cells undergo meiosis

Haploid gametes (n  23) Egg cell Sperm cell Fertilization n n Meiosis Ovary Testis Diploid zygote (2n  46) 2n2n Mitosis Key Haploid stage (n) Diploid stage (2n) Multicellular diploid adults (2n  46)

A pair of homologous chromosomes in a diploid parent cell A pair of duplicated homologous chromosomes Sister chromatids I NTERPHASE M EIOSIS I M EIOSIS II How meiosis halves chromosome number…

Centrosomes (with centriole pairs) Centrioles Sites of crossing over Spindle Tetrad Nuclear envelope Chromatin Sister chromatids Fragments of the nuclear envelope Centromere (with a kinetochore) Spindle microtubules attached to a kinetochore Metaphase plate Homologous chromosomes separate Sister chromatids remain attached Chromosomes duplicate Prophase I Metaphase I Anaphase I I NTERPHASE: M EIOSIS I : Homologous chromosomes separate

Prophase II Metaphase II Anaphase II M EIOSIS II : Sister chromatids separate Sister chromatids separate Haploid daughter cells forming Telophase II and Cytokinesis

Meiosis Leads to Genetic Diversity  Three ways genetic diversity is increased by meiosis: 1.2 parents contribute ½ of the genetic material to offspring 2.Crossing-over in Prophase I 3.Chromosome Alignment in Metaphase I  Meiosis produces cells that are NOT identical, unique gametes

Tetrad (pair of homologous chromosomes in synapsis) Breakage of homologous chromatids Joining of homologous chromatids Chiasma Separation of homologous chromosomes at anaphase I Separation of chromatids at anaphase II and completion of meiosis Parental type of chromosome Recombinant chromosome Parental type of chromosome Gametes of four genetic types C ce E C ce E ce C E Ce e C E c cE C E C e c E e c Crossing Over increases genetic diversity by producing “new” chromosomes.

Independent orientation at metaphase I Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring