Cellular Reproduction Chapter 2: pp Chapter 3: pp Fat Cells

Chromosomes- DNA tightly coiled around proteins Humans have 46

The Cell Cycle (figs & 2.17) Interphase: 90% of time 1.First Growth (G 1 ) 2.Synthesis Phase (S) 3.Second Growth (G 2 )  Prepare for Mitosis

G1G1  Cell Grows Rapidly  Length varies greatly depending on cell type Liver cells enter G 0 and may be there for yrs. Bone marrow only in G 1 for hrs. Early cells in embryo skip this phase all together

S  Cell’s DNA copied  Each chromosome consists of 2 copies (2 chromatids) joined together by a centromere  ~ 8-10 hrs.

 More protein synthesis  Membranes formed and stored in vesicles near cell membrane to be used for daughter cells G2G2

Cell Division  Surface area to volume ratios Surface area ÷ Volume =  Cells must divide because Volume of cell becomes greater than the Surface Area or the ratio is too low.  Big cells are inefficient

Skin Cells Mitosis –(Fig 2.16)  Occurs in Somatic Cells- all cells but sperm & egg cells.  Nucleus of cell divides Nuclear Division In your book

Cellular Reproduction Link!Mitosis animation Cellular Reproduction Begins with division of nucleus

Prophase  DNA coils up and thickens and tightens the chromosomes. Enables them to separate easier  Microtubules assemble to form spindle fibers  The nuclear envelope begins to break down  Nucleolus no longer visible Aster- fasten centrioles to cell membrane

Metaphase  Chromosomes move to the middle of the cell and line up along the equator.  Spindle fibers link the chromatids of each chromosome to opposite poles.  Centrioles (Centrosome)

Anaphase Centromeres divide Chromatids (now called chromosomes) move toward opposite poles Very brief phase

Telophase  A nuclear envelope forms around the chromosomes at each pole  Chromosomes uncoil  LAST step in mitosis

Cytokinesis Cytoplasm is divided in ½ Organelles distributed to 2 daughter cells Microfilament contracts like a drawstring Cell membrane encloses each cell

Control of the Cell Cycle  Groups of interacting proteins function at times called checkpoints- ensure correct replication of chromosomes 1. DNA damage -repair DNA 2. Apoptosis -keep cell alive (survivins) 3. Spindle Assembly - oversees spindle construction

When do divisions stop?  Telomeres- act as fuses 100s-1000s of nucleotides used during mitosis Mitosis stops Cell may die or live long

Apoptosis  Cell Death  Rapidly dismantles cell into membrane bound pieces that other cells (phagocytes) can pick up  Death receptor  Mitosis and Apoptosis are synchronized Except in Cancer ?’s 1-14

Production of sex cells 1/2 the number of Chromosomes Gametes-reproductive cells Meiosis: (Fig. 3.3) Link!-video In your book

Definitions for Meiosis  Occurs in germ cells- inherited sex cells (gametes)  Homologous Chromosomes- Chromosomes that are similar in size, shape and content  Crossing Over- Portions of one chromatid are shared with a chromatid on another (Homologous Chromosome) Tetrad

Definitions for Meiosis  Haploid- containing one set of chromosomes 23 for humans (sex cells)  Diploid- containing two sets of chromosomes  Zygote- fertilized egg 46 chromosomes in humans 78 chromosomes in dogs Some plants have thousands

Definitions for Meiosis  Asexual Reproduction-a single parent passes copies of all of its genes to each of its offspring. (Clones)  Sexual Reproduction-two parents, each donating a haploid reproductive cell

Meiosis  Two divisions Reduction division (Meiosis 1) Reduces chromosomes from Separates Homologous Chromosomes Equational division (Meiosis 2) 2 cells become 4 cells Separates sister chromatids

Prophase 1  90% of meiosis  The chromosomes. become visible  Nuclear envelope breaks down  Homologs line up-Synapsis  Crossing over- Homologous chromosomes (homologs) exchange parts

Metaphase 1:  Pairs of homologous chromosomes move to the equator of the cell  Independent Assortment- Random arrangement of the members of homolog pairs in metaphase

Anaphase 1:  Homologous chromosomes move to opposite poles of cell

Telophase 1:  Chromosomes gather at the poles of the cell  Cytoplasm divides  Short Interphase after Telophase 1  NO REPLICATION!

Prophase 2:  A new spindle forms around the chromosomes

Metaphase 2:  Chromosomes line up at the equator

Anaphase 2  Centromeres divide.  Chromatids are now called chromosomes  Chromosomes move to opposite poles of the cell.

Telophase 2:  Cells begin split  Cell membrane between cells  Four gametes are formed  4 HAPLOID gametes  All cells different

Comparison of Mitosis and Meiosis Table 3.1!!

46 Chromosomes (Diploid)-23 pairs

Trisomy 21 or Downs Syndrome Extra Chromosome ?’s 14-20

Compare Mitosis and Meiosis 1.What kind of cells? 2.# of nuclear divisions 3.Compare daughter cells and parent cells 4.Chromosome # after division 5.Do homologous chromosomes pair? 6.Does Crossing over occur 7.When do the centromeres divide? 8.When is each type of cell division used? Answer these on a clean sheet of paper

Comparison of Mitosis and Meiosis Mitosis 1.Somatic Cells 2.1 nuclear division 3.Daughter cells identical to parent cells 4.Diploid (remain constant) 5.No pairing of homologous Chromosomes 6.Crossing over rare 7.Centromeres divide at Anaphase 8.Growth, repair, asexual repro Meiosis 1.Germ Cells 2.2 nuclear divisions 3.Daughter cells differ from parent cells 4.Haploid (Halved) 5.Pairing of homologous Chromosomes 6.Crossing over 7.Centromeres Divide at Anaphase 2 8.Sexual repro., new gene combinations arise KEY