Unit 5: Cell Division

Mitosis & Meiosis

•Cell division is

•Why do cells divide rather than grow larger?

  • As a cell becomes too big
  • There is not a sufficient amount of surface area available for

•Cell Cycle

  • 2 Major Divisions
  • Interphase –
  • G1 (Gap 1) –

Cell grows

Number of organelles increase – double

Cell structures are synthesized

  • S (Synthesis) –
  • G2 (Gap 2) –
  • Mitosis
  • Cell division that occurs in ( ).
  • Each daughter cell contains the
  • Usually involved in

•After replication, DNA wraps around proteins called histones that help organize and condense DNA to form .

  • The chromatin further condenses to form
  • Chromosomes are
  • Chromosomes consist of
  • Sister chromatids are identical because of

•Phases of Mitosis

  • Prophase
  • DNA in the form of chromatin (DNA loose in the nucleus) condenses to form chromosomes
  • Nucleolus disappear
  • Nuclear envelope breaks down
  • Centrioles migrate to the poles of the cell – assist in moving chromosomes
  • mitotic spindle begins to form – made of protein fibers called microtubules from the cytoskeleton – move chromosomes during cell division
  • Metaphase
  • Chromosomes migrate and line up single file at the equator of the cell
  • Microtubules of mitotic spindle attach to chromosomes at the centromere
  • Anaphase
  • sister chromatids separate toward the poles of the cell – pulled by microtubules
  • Telophase
  • separated chromatids arrive at the poles of the cell
  • cytokinesis begins - cytoplasm begins to divide into two separate cells
  • mitotic spindle breaks down
  • nuclear membrane and nucleoli reappear, chromosomes uncoil and become chromatin
  • Cytokinesis
  • During cytokinesis in animal cells & other cells lacking cell walls

•Mitosis in Plants:

  • plant cells do not have centrioles although they do have a mitotic spindle
  • plant cells do not divide by cytokinesis –
  • Cell plate is a

•Cell growth and division is regulated

  • The cell cycle is regulated by
  • Example: Contact Inhibition
  • Why is cell growth regulated so carefully?
  • Uncontrolled cell growth can lead to.
  • Cancer is a disorder in which
  • Cells continue to divide until they form tumors that can damage surrounding tissues.

•Human chromosomes

  • Humans have (or total of 46 chromosomes)
  • Each organism must inherit a single copy of every gene from each of its “parents.”
  • Gametes are formed by a process that .
  • The two sets of chromosomes are homologous.
  • Each of the chromosomes that come from the male have a corresponding chromosome from the female parent.
  • A cell that
  • The number of chromosomes in a diploid cell is sometimes represented by the symbol .
  • For humans, the diploid number is 46, which can be written as

.

  • Gametes contain only a single set of chromosomes, and therefore only a single set of genes. These cells are .
  • Haploid cells are represented by the symbol .
  • For humans, the haploid number is 23, which can be written as

.

  • Fertilization

•Meiosis

  • Meiosis:
  • These cells have– haploid(1n); ex: 46  23
  • When the gametes join at conception the full number of chromosomes is restored – diploid (2n)
  • Meiosis involves two cell divisions, meiosis I and meiosis II.
  • meiosis starts with

•Interphase I

  • DNA is replicated forming duplicate chromosomes

•Meiosis I

  • Prophase I
  • Nuclear membrane breaks down
  • Centrioles begin to move
  • Spindle fibers form
  • Chromosomes condense
  • Homologous chromosomes begin to pair up to form a tetrad.
  • Metaphase I
  • tetrads migrate to the equator and line up
  • spindle fibers are formed attach to centromeres
  • Crossing-over may occur =
  • Crossing-over
  • Anaphase I
  • homologous chromosomes are pulled apart from one another (tetrad is pulled apart)
  • the joined sister chromatids move together toward the poles (in mitosis, sister chromatids are pulled apart)
  • Telophase I & Cytokinesis
  • Spindle fiber disentigrates.
  • Nuclear membranes form. The cell separates into two cells. 1st Cell Division!

•Meiosis II: Unlike meiosis I, neither cell goes through chromosome replication.

  • Prophase II
  • Centrioles move to opposite sides of the cell
  • Spindle fibers start to assemble
  • Metaphase II
  • Spindle fibers align the chromosomes along the cell equator
  • Anaphase II
  • The sister chromatids separate and move toward opposite ends of the cell
  • Telophase II & Cytokinesis
  • Nuclear membrane forms
  • Spindle fibers disentigrate
  • Cells divide to produce four haploid daughter cells. 2nd Cell Division!

•Meiosis in Males

  • Spermatogenesis –

•Meiosis in Females

  • Oogenesis –

•Venn Diagram