Mitosis and Cell Division Bio 11 September 5, 2008

Microfilaments differ from microtubules in that microfilaments A) are larger than microtubules. B) are found only in plants whereas microtubules are found in plants and animal cells. C) are mainly composed of actin whereas microtubules are composed of tubulin. D) help to anchor organelles, whereas microtubules primarily function to help cells change shape and move. E) form the inner core of cilia and flagella whereas microtubules regulate metabolism

Cell size is determined by physical principles Size limit of cells determined by surface area/volume ratio Large living things are made of multiple cells Living things divide cells in order to grow

Living things are extremely complex Cellular machinery is sophisticated and required for life Blueprints for all cellular machinery are contained in genes Genes are inherited from parents Humans have ~30,000 genes

All cells require a copy of the genome Genome- all the DNA of the cell DNA is similar in all cells Gene- 1 DNA Molecule (+ proteins the genetic information to produce a single product (protein) DNA replication copies all cellular DNA

Prokaryotic genomes consist of a single circular chromsome Chromosome- a single molecule of DNA

Prokaryotic cells reproduce by binary fission 1.DNA is copied 2.Copies migrate to opposite ends of cell 3.Cell membrane/cell wall pinches off to form two cells 4.Each daughter cell has exactly the same DNA as the parent cell

Eukaryotic cells have multiple linear chromosomes Eukaryotic chromosome = DNA + extra proteins inside nucleus Chromosomal proteins assist in DNA compaction Each chromosome contains different genes Chromosomes not always condensed and visible like this Chromatin – uncondensed chromosomal DNA In multicelluar organisms, DNA is identical in all cells (Excl. Gametes)

Diploid eukaryotes have chromsomes in pairs Karyotype- organized and numbered by size Humans: 2 x 23 homologous pairs of chromosomes = 46 total chromosomes Each contains ~1000 genes 1 or 2 strands per chromosome

Chromosome structure Decondensed chromosome- chromatin After copying, chromosome consists of two sister chromatids, joined at the centromere Kinetochore – proteins found on surface of centromere

Chromosomes look different at different stages of a cell’s life cycle Chromatin- uncoiled chromosome Not visible at this stage- being used for protein synth. Before cell division, strands of DNA are copied

Each chromosome must be copied before cells can divide Called “chromosome” at all stages Sister chromatids contain identical DNA

Mitosis vs. Meiosis Mitosis – asexual cellular reproduction (somatic cells) –Allows multicellular organisms to grow –Daughter cells are identical to parent cell Meiosis – cell division for formation of gametes (eggs and sperm) –Allows sexual reproduction to generate species diversity –Daughter cells have half the genetic information as parent cell

The Cell Cycle G1 – “Growth 1” or “Gap 1” – cell growth S phase – DNA synthesis G2 – interval of rest before cell division M – mitosis Cytokinesis – splitting of cell contents G O – A state of non- division

3. CELL CYCLE~24 hours total 1. Interphase - between cell div. G1 phase - cell growth, ~12 hrs S phase - synthesize DNA, ~6 hrs G2 phase - prep. mitosis, ~6 hrs 2. mitosis - ~half-hour Prophase, Metaphase, Anaphase, Telophase 3. Cytokinesis - ~minutes

LE 8-5 I NTERPHASE G1G1 G2G2 S (DNA synthesis) Cytokinesis Mitosis M ITOTIC PHASE (M)

Mitosis The sorting and separation of chromosomes in nucleus somatic eukaryotic cells during cell division Forms 2 identical daughter cells (1/2 size) For growth/replacement/healing Associated with cancer In humans: ~25 million/sec. Divided into phases

Phases of Mitosis Prophase* Metaphase Anaphase Telophase * Campbell text adds “prometaphase” Interphase – time in between mitotic phases –Normal cell functions (G1+S+G2) Cytokinesis- divides cytosol/organelles (creates daughter cells)

Peripheral elements of Mitosis Centrosomes (2) – anchors the spindle fibers, and consist (in animal cells) of 2 centrioles each Spindle fibers – made of microtubules, they pull apart sister chromatids of chromosomes

LE 8-6a I NTERPHASE P ROPHASE P ROMETAPHASE Kinetochore Fragments of nuclear envelope Centrosome Early mitotic spindle Chromatin Centrosomes (with centriole pairs) LM 250  Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Centromere Spindle microtubules

LE 8-6b M ETAPHASE A NAPHASETELOPHASE AND C YTOKINESIS Metaphase plate Spindle Daughter chromosomes Nuclear envelope forming Cleavage furrow Nucleolus forming

Prophase mitosis - in most cells (exc. gonads) - produces 2 daughter cells identical to original but half size - for growth + replace., also cancer - humans ~25 million/sec. Prophase - begins mitosis - 2-stranded chromosomes visible - nuclear envelope breaks up

M etaphase - single chromosomes line up at equator - carried by spindle (microtubules) - centrosome (pairs of centrioles) in animals, anchors the spindle A naphase - chromosomes divide between strands - 1-stranded chromosomes move to opposite poles of cell

Anaphase - chromosomes divide between strands - 1-stranded chromosomes move to opposite poles of cell Telophase - 2 nuclei form around separate sets of chromosomes

( Cytokinesis - finishes mitosis ) - divides cytosol + other organelles - results in 2 daughter cells ( Interphase - prep. next mitosis ) - cells return to normal cell activity - chromosomes spread as chromatin - each 1-stranded chromosome duplicates 2nd strand

Cytokinesis in animal cells is different from plant cells Actin and myosin filaments work to contract cell in center Cell furrow is formed

Plant cell walls aren’t flexible Vesicles containing cellulose form in center of cell Fusion of vesicles forms cell plate Cell plate forms cell wall of new cells

Control of the mitotic cycle is critical G 1 checkpoint G0G0 G1G1 G2G2 G 2 checkpoint M checkpoint M S Control system

External signals can activate or deactivate the cell cycle Signals include hormones, growth factors Contact inhibition, density inhibition, anchorage dependence are important signals

LE 8-8a Cells anchor to dish surface and divide. When cells have formed a complete single layer, they stop dividing (density-dependent Inhibition). If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition).

LE 8-8aa Cells anchor to dish surface and divide. When cells have formed a complete single layer, they stop dividing (density-dependent inhibition).

LE 8-8ab If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition).

LE 8-8b After forming a single layer, cells have stopped dividing. Providing an additional supply of growth factors stimulates further cell division.

LE 8-10 Tumor Glandular tissue Lymph vessels Blood vessel A tumor grows from a single cancer cell. Cancer cells invade Neighboring tissue. Cancer cells spread through lymph and blood vessels to other parts of the body.

LE 8-10a Tumor Glandular tissue A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue.

LE 8-10b Cancer cells invade neighboring tissue. Cancer cells spread through lymph and blood vessels to other parts of the body. Lymph vessels Blood vessel

Figure 8.11A

Figure 8.11B

Figure 8.11C

LE 8-12 Chromosomes Centromere Sister chromatids

LE 8-13 Haploid gametes (n  23) Egg cell Sperm cell FertilizationMeiosis Diploid zygote (2n  46) n Multicellular diploid adults (2n  46) Mitosis and development 2n n

LE 8-14a I NTERPHASE P ROPHASE  M ETAPHASE  A NAPHASE  M EIOSIS  Centrosomes (with centriole pairs) Sites of crossing over Spindle Microtubules attached to kinetochore Metaphase plate Sister chromatids remain attached Homologous chromosomes separate Centromere (with kinetochore) Tetrad Sister chromatids Chromatin Nuclear envelope : Homologous chromosome separate

LE 8-14b Cleavage furrow T ELOPHASE  P ROPHASE  M ETAPHASE  A NAPHASE  T ELOPHASE  Sister chromatids separate Haploid daughter cells forming M EIOSIS  : Sister chromatids separate  AND C YTOKINESIS