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 number does not correlate to complexity Oriental Small-clawed Otter 38Oriental Small-clawed Otter Pea 14Pea Pig 38Pig Pigeon 80Pigeon Pine Marten 38Pine Marten Potato 48Potato Rabbit 44Rabbit Raccoon 38Raccoon Radish 18Radish Rat 42Rat Red Deer (Elk/Wapiti) 68Red Deer Red Fox 38Red Fox Red Panda 36Red Panda Rice 24Rice Dog 78Dog Wolf 78Wolf Pigeon 80Pigeon Turkey 82Turkey Hedgehog Genus Erinaceus (Woodland hedgehogs) 88HedgehogErinaceus Hedgehog Genus Atelerix (African hedgehogs) 90HedgehogAtelerix Ichthyomys pittieri (semiaquatic rodent) 94 [highest for a mammmal] Carp 104Carp Algae 148Algae

Figure 8.3

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

Figure 8.5

Chromosome structure Loci (sing: Locus)

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

Which one of the following is false? A) Prokaryotic chromosomes are more complex than those of eukaryotes. B) Most prokaryotes reproduce by binary fission. C) Prokaryotic cells are generally smaller and simpler than eukaryotic cells. D) In prokaryotes, most genes are carried on a circular DNA molecule. E) Daughter prokaryotic chromosomes are separated by some sort of active movement away from each other and the growth of new plasma membrane between them

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

Cancer, Meiosis, and Mendelian genetics

Mybiology.com Chapter 8 Key Concepts quiz- 10 lecture points Complete by Tues, 10/14 >70% correct  full credit 40-69% correct  half credit

Sister chromatids are A) found right after a cell divides. B) tightly linked together at a centromere. C) formed when chromatids separate during cell division. D) made only of DNA. E) unique to prokaryotes

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

If the S phase was eliminated from the cell cycle, the daughter cells would A) have half the genetic material found in the parental cell. B) be genetically identical. C) be genetically identical to the parental cell. D) synthesize the missing genetic material on their own. E) None of the choices are correct.

What happens when the system of checkpoints goes awry?

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). Mitosis facilitates growth and repair Contact- and density- dependent signals tell a cell when to start and stop dividing

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. Cancer is unrestricted mitotic cell growth

Metastatic cancer is caused by an accumulation of many errors Density-dependent inhibition Apoptosis Cell growth Nutrient supply (angiogenesis) Immune system evasion

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

DNA damage causes mutations that lead to cancer Chromosomes can be repaired, or misrepaired, in a living cell Damage to whole chromosomes causes harmful mutations

LE 8-23a Deletion Duplication Inversion Homologous chromosomes

LE 8-23b Reciprocal translocation Nonhomologous chromosomes

LE 8-23c Reciprocal translocation “Philadelphia chromosome” Activated cancer-causing gene Chromosome 22 Chromosome 9

Which one of the following does not occur during mitotic anaphase? A) The centromeres of each chromosome divide. B) Sister chromatids separate. C) The chromatid DNA replicates. D) Daughter chromosomes begin to move toward opposite poles of the cell. E) All of the choices occur during mitotic anaphase.

Figure 8.11A

Figure 8.11B

Meiosis

Asexual Reproduction is a primary means of propagation for many species

Sexual reproduction generates diversity Variety in offspring improves chances of adaptation to changing environments

The offspring of sexual reproduction inherit parental traits Offspring inherit DNA from each parent Offspring are not the same DNA is from the same source

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 Meiosis is the process of cell division that allows gamete formation Gametes are haploid (n), somatic cells are diploid (2n)

Chromosomes come in pairs For diploid organims (2n) One chromosome in a paired set comes from each parent #’s 1-22 are autosomes X and Y are sex chromosomes

LE 8-12 Homologous Chromosomes Centromere Sister chromatids

Homologous chromosomes Pairs of chromosomes are homologous The site for particular genes are called loci (singular: locus) Identical strands of the same chromosome are sister chromatids Loci 

LE 13-6 Key Haploid Diploid Gametes n Diploid multicellular organism (sporophyte) Mitosis Diploid multicellular organism FERTILIZATION MEIOSIS Zygote n n 2n2n 2n2n Animals Plants and some algae Most fungi and some protists n n n n n n n n n n FERTILIZATION MEIOSIS Gametes Zygote Mitosis 2n2n 2n2n 2n2n Spores Haploid multicellular organism (gametophyte) Haploid multicellular organism

Overview of Meiosis Meiosis consists of 2 major stages, Meiosis I and Meiosis II Cell copies DNA once, divides twice, creating 4 haploid cells In meiosis I, homologous pairs of chromosomes are grouped, recombined, and then segregated into two intermediate cells In meiosis II, those cells are divided

The Stages of Meiosis In (meiosis I), homologous chromosomes separate Meiosis I results in two haploid daughter cells with replicated chromosomes In the second cell division (meiosis II), sister chromatids separate Meiosis II results in four haploid daughter cells with unreplicated chromosomes

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 13-8aa Centrosomes (with centriole pairs) Nuclear envelope Chromatin Chromosomes duplicate INTERPHASE MEIOSIS I: Separates homologous chromosomes METAPHASE I ANAPHASE I (Interphase precedes meiosis, of course)

Division in meiosis I occurs in four phases: Prophase I Metaphase I Anaphase I Telophase I

Prophase I >90% of the time required for meiosis Chromosomes condense Synapsis: homologous chromosomes pair up Crossing over: nonsister chromatids exchange DNA segments Tetrad: four chromatids Chiasmata: X-shaped regions where crossing over occurred

Crossing-Over in Prophase I

Crossing-over in Prophase I

LE 13-8ab Sister chromatids Chiasmata Spindle Centromere (with kinetochore) Metaphase plate Homologous chromosomes separate Sister chromatids remain attached Microtubule attached to kinetochore Tetrad MEIOSIS I: Separates homologous chromosomes PROPHASE I METAPHASE I ANAPHASE I Homologous chromosomes (red and blue) pair and exchange segments; 2n = 6 in this example Pairs of homologous chromosomes split up Tetrads line up

Metaphase I Tetrads line up at the metaphase plate Microtubules from one pole are attached Microtubules from the other pole are attached to the kinetochore of the other chromosome Animation: Metaphase I Animation: Metaphase I

Independent Assortment in Metaphase I Random alignment of maternal/paternal chromosomes at the metaphase plate Produces genetic variability within populations

Independent Assortment in Metaphase I

Independent Assortment of Chromosomes Homologous pairs of chromosomes orient randomly at metaphase I of meiosis Each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs The number of combinations possible when chromosomes assort independently into gametes is 2 n-1, where n is the haploid number For humans (n = 23), there are more than 8 million (2 22 ) possible combinations of chromosomes

LE 13-8ab Sister chromatids Chiasmata Spindle Centromere (with kinetochore) Metaphase plate Homologous chromosomes separate Sister chromatids remain attached Microtubule attached to kinetochore Tetrad MEIOSIS I: Separates homologous chromosomes PROPHASE I METAPHASE I ANAPHASE I Homologous chromosomes (red and blue) pair and exchange segments; 2n = 6 in this example Pairs of homologous chromosomes split up Tetrads line up

Anaphase I homologous chromosomes separate One chromosome moves toward each pole Sister chromatids remain attached at the centromere

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