Chapter 10: Cell Division and Growth

Chromosomes When cells are NOT dividing, DNA is found in the nucleus in the form of uncoiled chromatin. What does this look like?

Chromosomes When the cell is getting ready to divide, chromosomes form as the DNA wraps and coils tightly around histones.

Chromosomes Chromosomes: carriers of genetic information that is copied and passed to new cells Genes: section of DNA that controls production of a protein; found on a chromosome

Chromosomes Structure of Chromosomes Sister Chromatids: two identical halves of the chromosome (made when DNA copies itself) Centromere: middle area where two chromatids are joined

Non-replicated Replicated Centromere ONE chromosome chromosomes Sister chromatids ONE chromosome

Chromosomes Chromosome Numbers Each species have a characteristic number of chromosomes Fruit Flies = 8 chromosomes (4 pairs) Adder’s Tongue Fern = 1, 263 chromosomes (631 pairs) Humans = 46 chromosomes (23 pairs)

Chromosomes - Karyotype

Chromosomes TWO Types of Chromosomes 1. Sex Chromosomes: determine the sex of an organism Humans have 2 of these chromosomes (1 pair) Males: XY Females XX

Chromosomes TWO Types of Chromosomes 2. Autosomes: remaining body chromosomes Humans have 44 of these chromosomes (22 pairs) that “travel” in pairs

Chromosomes Homologous chromosomes: two chromosomes in a pair; 1 copy from each parent You have 2 of every chromosome that carry genes for the same trait, but they are NOT identical Ex: Chromosome 19 contains genes for hair color Mom’s #19 could have the “blonde” hair gene Dad’s #19 could have the “brown” hair gene

b B C D E F a A c d e f The letters are the genes Upper case and lower case letters are versions of the genes

Chromosomes Chromosomes in each cell Diploid: a cell containing two copies of each chromosomes (both chromosomes in the homologous pair) Abbreviated: 2N Human Ex: skin cell, muscle cell (any BODY cell) 2N = 46

Chromosomes Chromosomes in each cell Haploid: a cell containing one copy of each chromosomes Abbreviated: N Human Ex: Sperm & Egg cells (any SEX/gamete cell); N =23

Cell Size Limits Organisms grow by producing more cells Cell size is usually comparable between a young and old animal; the older animal just has MORE of them

Cell Size Limits Why can’t cells continually grow larger? DNA “Overload”: it can’t meet all the cells needs/demands

Cell Size Limits Why can’t cells continually grow larger? Exchanging Materials: Rate at which materials are exchanged depends on the cell membrane (surface area of the cell) Rate at which materials are used (oxygen, water) or produced (waste) depends on the volume of the cell

Cell Size Limits As the length of the cell increases, the volume increases faster than the surface area Hard for cells to keep up with moving materials and wastes in and out so the cell divides

Cell Division in Eukaryotes TWO types of cell division 1. Mitosis: Cell division that produced body cells identical to the original parent cell (diploid) Examples of cells that do this: skin, muscle, heart 2. Meiosis: Cell division that produces gametes with half the number of chromosomes as the parent cell (haploid) Ex of cells that do this: sperm and egg; GAMETES ONLY

Cell Division in Eukaryotes Cell Cycle: sequences of growth and division of the cell THREE STEPS OF THE CELL CYCLE 1. Interphase (most time spent here) 2. Mitosis 3. Cytokinesis

Cell Division in Eukaryotes How long does it take for a cell to go through one cell cycle? It all depends on the cell. A human liver cell, for example, completes one cell cycle in about 22 hours, as shown in the graph.

Cell Division in Eukaryotes 1. Interphase: time when the cell is NOT dividing THREE PHASES OF INTERPHASE 1. G1 = cell grows, makes organelles 2. S = DNA copied 3. G2 = cell makes centrioles; normal metabolism preparing to divide

Cell Division in Eukaryotes 2. Mitosis: dividing of the cell’s nucleus FOUR PHASES OF MITOSIS 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Cell Division in Eukaryotes 1. Prophase: longest phase of mitosis Chromatin coils into visible chromosomes (sister chromatids) Nuclear envelope/membrane starts to disappear Spindle fibers appear from centrioles (animal cells only)

Cell Division in Eukaryotes 2. Metaphase: shortest phase of mitosis Spindles attach and move chromosomes to line up along the equator (middle) of the cell

Cell Division in Eukaryotes 3. Anaphase: Chromosomes are pulled apart at the centromere by spindles and separated into sister chromatids

Cell Division in Eukaryotes 4. Telophase Sister chromatids reach opposite poles (sides of the cell) Spindles disappear Nuclear envelopes/membranes reappears Cell begins to split into 2 new cells

Cell Division in Eukaryotes 3. Cytokinesis: dividing of the cell’s cytoplasm, forming two new cells Animal cells: 2 new cells are separated by the cytoplasm “pinching in”

Cell Division in Eukaryotes 3. Cytokinesis: Plant cells: 2 new cells cell plate separated by a cell plate that helps form the cell walls

Cell Division in Eukaryotes 3. Cytokinesis:

Cell Division in Eukaryotes Meiosis: Cell division that produces gametes with half the number of chromosomes as the parent cell (haploid) 2 separate cell divisions: meiosis I and meiosis II Interphase and Cytokinesis occur with both divisions

Cell Division in Eukaryotes Meiosis starts with 1 diploid cell and ends with 4 haploid cells Each gamete has half the number of chromosomes as a diploid cell 1 diploid cell with 4 chromosomes 4 haploid cells with 2 chromosomes each

Cell Division in Eukaryotes MEIOSIS 1 Prophase I DNA coils into tetrads (pair of homologous chromosomes) Spindles appear Nuclear envelope/membrane disappears Crossing over occurs: DNA is swapped between chromosomes in a pair

Cell Division in Eukaryotes MEIOSIS 1 Metaphase I Tetrads are moved by the spindles and line up along the equator

Cell Division in Eukaryotes MEIOSIS 1 Anaphase I Tetrads pulled apart by the spindles and separated into chromosome Chromosomes begin moving to opposite ends of the cell

Cell Division in Eukaryotes MEIOSIS 1 Telophase I Chromosomes reach opposite sides of the cell Spindle disappears Nuclear envelope/membrane reappears Cytokinesis occurs after this step, forming 2 new cells, which then go through interphase again

Cell Division in Eukaryotes Meiosis II--has 4 stages, PMAT II Each stage--occurs just like the stages of mitosis Prophase II Metaphase II Anaphase II Telophase II

Cell Division in Eukaryotes MEIOSIS II Prophase II Spindle appear in each of the 2 new cells Nuclear envelopes/membranes disappears

Cell Division in Eukaryotes MEIOSIS II Metaphase II Sister chromatids line up in the middle/equator of the cell.

Cell Division in Eukaryotes MEIOSIS II Anaphase II Spindles split centromeres and sister chromatids separate Chromatids start to move to opposite ends of the cell

Cell Division in Eukaryotes MEIOSIS II Telophase II Sister chromatids (haploid) reach opposite ends of the cell Spindles disappear Nuclear envelopes/membranes appear Cytokinesis follows this step forming 4 new cells

Cell Division in Eukaryotes Sooooo, what happens after meiosis? Sexual reproduction: production and combination of gametes Fertilization: fusion of male and female gametes to form zygote Zygote: diploid cell (2 of each chromosome) http://video.sciencemag.org/VideoLab/2127025888001/1/medicine

Comparison of Types of Division Mitosis Meiosis Occurs in most body cells Occurs only in sex cells One division Two divisions One cell makes 2 diploid cells One cell makes 4 haploid cells Identical to the parent Different from parent