Cell Growth and Reproduction Cell Size Mitosis Meiosis

Growth in Organisms For an organism to grow, its cells divide instead of getting larger.

Cell Size Limitations 1 Large cells would have to wait too long to diffuse nutrients in and waste out. Ex. a/c

Cell Size Limitations 2 One set of DNA can’t make enough proteins and enzymes fast enough for a large cell. Ex. Only one cook

Cell Size Limitations 3 Surface area-to-volume ratio: The volume (inside) of the cell increases a lot faster than the surface area (membrane). Ex. Solar panels 1mm 2mm 4mm Surface area =6mm2 Surface area= 24mm2 Surface area= 96mm2 Volume= 1mm3 Volume = 8mm3 Volume= 64mm3 12:2 ratio 6:2 ratio 3:2 ratio

Cell Cycle Cell cycle – stages of growth, preparation, and division (Interphase and Mitosis)

Interphase Interphase- period of normal growth and maintenance. (3 stages) G1=growth Synthesis=copy chromosomes G2= maintenance.

Prokaryotic Chromosome The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane copyright cmassengale

Eukaryotic Chromosomes All eukaryotic cells store genetic information in chromosomes Most eukaryotes have between 10 and 50 chromosomes in their body cells copyright cmassengale

DNA chromosome – wound DNAp (like DNA suitcases) chromatin- unpackaged unwound DNA Each cell has 46 chromosomes (23 from mom and 23 from dad). Diploid – a cell with 2 set of chromosomes. (somatic cells)

copyright cmassengale Karyotype A picture of the chromosomes First 22 pairs are called autosomes Last pair are the sex chromosomes copyright cmassengale

Mitosis 1 diploid parent cell splits into 2 identical diploid daughter cells. Copied chromosomes made in synthesis are called sister chromatids… held together by centromeres. chromosomes Parent cell Sister chromatids identical daughter cells

Prophase the chromosomes coil up and become visible while the nuclear envelope disappears. Sister chromatids are present. A centriole forms at each pole and spindle fibers made of microtubules grow out. Short microtubules stick out from the centriole in a star shape known as an aster.

Metaphase Early in metaphase (prometaphase) spindle fibers attach to each of the chromatids at a sight called the kinetochore. The spindle fibers line the chromatids up at the equator of the cell called the metaphase plate. Kinetochore

Microtubules Chromosomes Fig. 12-7 Aster Centrosome Sister chromatids Microtubules Chromosomes Metaphase plate Kinetochores Centrosome 1 µm Figure 12.7 The mitotic spindle at metaphase Overlapping nonkinetochore microtubules Kinetochore microtubules 0.5 µm

Anaphase Anaphase- During this phase, the kinetochores “reel in” or “gobble up” the spindle fibers to pull the sister chromatids apart by splitting their centromere. The split chromatids are pulled towards opposite poles of the cell

Telophase Once the chromatids have reached the opposite sides the spindle fibers disappear, the chromosomes unravel, and the nuclear envelope reappears on the two new nuclei. In cytokinesis, the cytoplasm then forms a cleavage furrow at the equator to split the cytoplasm. (in plants a cell plate forms at the equator.)** Two identical daughter cells are formed

Mitosis Vid Mitosis

copyright cmassengale Identify the Stages ? Early, Middle, & Late Prophase ? ? ? Metaphase Anaphase Late Prophase ? ? ? Telophase & Cytokinesis Late Anaphase Telophase copyright cmassengale

copyright cmassengale Mitosis Quiz copyright cmassengale

Why mitosis? Somatic cells divide for growth or maintenance. What about reproduction?

Meiosis 1 diploid parent cell divides twice into 4 haploid unidentical daughter cells Haploid – 1 set of chromosomes. meiosis forms sperm or eggs called gametes . (gametes are haploid…1 set of 23 chromosomes)

Meiosis Forms Haploid Gametes Meiosis must reduce the chromosome number by half Fertilization then restores the 2n number from mom from dad child too much! meiosis reduces genetic content The right number! copyright cmassengale

Prophase I Homologous Chromosomes- a pair of chromosomes that have genes for the same trait (one from mom, one from dad) During prophase I, Tetrads form. A tetrad is two homologous chromosomes made of sister chromatids linked together. Homologous chromosomes Sister chromatids tetrad

Crossing over These tetrads will trade genetic information in a process called crossing over. (new gene combinations form)

Metaphase I During metaphase I tetrads are lined up at the equator of the cell. Independent assortment- mom and dad’s chromosomes line up in any order.

Anaphase I, Telophase 1 During anaphase I, the tetrads are split into chromatids and pulled to opposite sides of the cell. During telophase I the cell is split into two diploid cells.

Meiosis II 2nd Stage Meiosis II (P II, M II, A II, T II) Prophase, metaphase, anaphase, telophase are repeated just like mitosis to split the chromatids into chromosomes.

copyright cmassengale Meiosis Animation copyright cmassengale

copyright cmassengale Spermatogenesis Occurs in the testes produce 4 spermatids Spermatids mature into sperm Men produce about 250,000,000 sperm per day copyright cmassengale

Spermatogenesis in the Testes Spermatid copyright cmassengale

copyright cmassengale Spermatogenesis copyright cmassengale

copyright cmassengale Oogenesis Occurs in the ovaries Makes 3 polar bodies that die and 1 egg Immature egg called oocyte one oocyte matures into an ovum (egg) every 28 days copyright cmassengale

Oogenesis in the Ovaries copyright cmassengale

copyright cmassengale Oogenesis Oogonium (diploid) Mitosis Primary oocyte Meiosis I Secondary (haploid) Meiosis II (if fertilization occurs) First polar body may divide Polar bodies die Ovum (egg) Second polar body a A X Mature egg copyright cmassengale

Why go through the Trouble? Each parent produces new combinations of genes through crossing over, independent assortment and random fertilization.

Cancer Cancer is when cells divide uncontrollably. They usually stop dividing when they touch other cells.