Mitosis The Cell Cycle

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Mitosis The Cell Cycle Unit Cell
Reproduction Biology
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• How many cells do you think your body has?

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• Each of us began as a single cell,
• so one important question is
• How did that single cell develop into a body with
  more than a trillion cells?

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Cell Division

• The production of such a large number of body
  cells is accomplished by many, many repeats of a
  cycle of cell division in which one cell gives
  rise to two cells, each of which in turn gives
  rise to two cells, etc.
• Thus, cell division is needed for growth.

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• Even in a fully grown adult, cells still undergo
  cell division.
• Why is this useful?
• Think about your skin, for example.

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Cell Division

• The two cells that come from the division of one
  cell are called daughter cells.
• Each of the daughter cells needs to have a
  complete set of chromosomes.

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What are chromosomes?

• Chromosomes are
• compact
• spools
• of
• DNA

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Chromosomes

• The chromosome (left in the picture) was isolated
  from a dividing cell.
• Notice that the chromosome consists
  of two identical halves
• Each half is
  called a
  chromatid

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Chromosomes

• The point where the two chromatids touch and are
  held together is called a centromere

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Review chromosome structure
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Lets make some chromosomes

• Obtain 2 white pipe cleaners and 2 of another
  color.
• Cut white pipe cleaners into 2
• 4 inch long pieces
• 3 inch long
• 2 inch long
• 1½ inch long

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Lets make some chromosomes

• Pick two different colored beads. You will need
  8 of each color
• Put one of the colored beads on each of the white
  pipe cleaners and move them to the center of the
  pip cleaners.
• Repeat by putting one of the other colored beads
  on each of the colored pipe cleaners

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Chromosome Numbers

• Each species has a certain number of chromosomes
  in each cell.

46
78
52
18
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Sex chromosomes

• Chromosomes that determine the sex of the
  organism
• In humans, sex chromosomes are either X or Y

XY
XX
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Autosomes

• All the other chromosomes in an organism

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Unsorted Human Chromosomes
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Karyotype
Photomicrograph of the chromosomes in a dividing
cell found in a human
What is the sex of the person whose chromosomes
are shown here?
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Question

• What percent of your genes come from your mom?
• What percent of your genes come from your dad?

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Where did my chromosomes come from?

• We inherit one member of each chromosome pair
  from each parent. 

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Where did my chromosomes come from?

• The 46 chromosomes in our somatic cells are
  actually two sets of 23 chromosomesa maternal
  set (from our mother) and a paternal set (from
  our father.)

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Homologous chromosomes

• The two copies of each chromosome
• They are the same size and shape and carry genes
  for the same traits

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Diploid Cells

• Cells having two sets of chromosomes
• All normal human cells are diploid cells (except
  reproductive cells egg and sperm cells)
• Commonly abbreviated as 2n
• In humans the diploid number is

46
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Haploid Cells

• Human sperm cells and egg cells

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Haploid Cells

• Contain only 1 set of chromosomes
• Haploid cells have only 1 chromosome of each
  homologous pair and only 1 sex chromosome
• Abbreviated as 1n
• When a sperm (1n) and egg cell (1n) combine, the
  new cell will be diploid (2n)

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A comparison
Diploid
Haploid
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Cell Division

• How do you think each daughter cell gets a
  complete set of chromosomes?
• In each cycle of cell division, the cell first
  makes a copy of all of the DNA in each of the
  chromosomes.

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Cell Division

• After the DNA in each chromosome has been copied,
  the cell undergoes a type of cell division called
  mitosis, which carefully separates the two copies
  of each chromosome to opposite ends of the
  dividing cell, so each daughter cell ends up with
  a complete set of chromosomes.

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What is the cell cycle?

• The repeating set of events that make up the life
  of a cell
• Cell division is one phase of the cell cycle

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What is the cell cycle?

• Interphase
• G1, S, G2 phase
• Mitosis (M phase)
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis

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Interphase

• The time between cell divisions
• Divided into 3 phases (G1, S, G2 phases)

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G1 phase

• Offspring cells grow to mature size

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S phase

• Cells DNA is copied

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S phase

• Cells DNA is copied

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G2 phase

• The time to prepare for cell division

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G2 phase

• Centrosomes two pairs of dark spots it is the
  microtubule organizing center
• Centrioles - structures in the cytoplasm from
  which the spindle fibers form

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G0 phase

• Cells can exit the cell cycle and enter a state
  called the G0 phase
• Cells do not copy DNA and do not prepare for cell
  division

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Mitosis

• Division of the nucleus

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Prophase

• DNA tightens and coils into chromosomes
• Nuclear membrane breaks down and disappears

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Metaphase

• Chromosomes line up in the center of the cell

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Anaphase

• The chromatids of each chromosome separate at the
  centromere

• chromatids move to opposite poles of
  cell

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Telophase

• Chromosomes return to chromatin state
• A nuclear membrane forms around each set of
  chromosomes

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Cytokinesis

• The cytoplasm of the cell divides
• The area of the cell membrane that pinches in and
  eventually separates the dividing cell into two
  cells is called the cleavage furrow.

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Cytokinesis
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Cytokinesis

• Vesicles formed by the Golgi apparatus fuse at
  the midline of the dividing cell, forming a
  membrane-bound cell wall called the cell plate.

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Plant cells in various stages of mitosis
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Cell Cycle
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Cancer cells
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Cancer cells
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Cancer cells
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Cancer cells