Cell Cycle Mitosis and Meiosis Covered in these

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 192 -204 And in your packet on The Cell Cycle

The cell cycle multiplies cells § 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. © 2012 Pearson Education, Inc.

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

Cytokinesis Cleavage furrow Contracting ring of microfilaments Daughter cells Cleavage furrow

Anchorage, cell density, and chemical growth factors affect cell division § 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.

Growth factors signal the cell cycle control system § 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. G 1 - commitment to divide, growth factors present? , Size of cell ok? , G 2 - 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 G 1 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 G 2 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 p 53) that target and control abnormal cells. – Abnormal cells impede functioning of normal cells

p 53 gene ( tumor suppressor gene) • Key role in G 1 checkpoint • P 53 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) n Egg cell n Sperm cell Meiosis Ovary Fertilization Testis Diploid zygote (2 n 46) 2 n Key Multicellular diploid adults (2 n 46) Mitosis Haploid stage (n) Diploid stage (2 n)

How meiosis halves chromosome number… MEIOSIS I INTERPHASE MEIOSIS II Sister chromatids 2 1 A pair of homologous chromosomes in a diploid parent cell A pair of duplicated homologous chromosomes 3

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

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

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

Crossing Over increases genetic diversity by producing “new” chromosomes. C E c e 1 Breakage of homologous chromatids C E c e 2 Tetrad (pair of homologous chromosomes in synapsis) Joining of homologous chromatids E C Chiasma c e 3 Separation of homologous chromosomes at anaphase I C E C c e E c e 4 Separation of chromatids at anaphase II and completion of meiosis C E C e c E c e Parental type of chromosome Recombinant chromosome Parental type of chromosome Gametes of four genetic types

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