2. The Cell Cycle

Why do cells divide

1. To grow

2. To reproduce

3. to repair damage

solute

the dissolved substance

solvent

what substances are dissolved into (usually water)

diffusion

the movement of a solute from high to low concentration

osmosis

the movement of a solvent across a semi-permeable membrane

the cell cycle

1. interphase

2. mitosis

3. cytokinesis

   the length of the cycle depends on the type of cell
   

interphase

• the longest period of the cell cycle

• DNA replicates because each new cell will need to have a copy of it

G1

cell grows

synthesis

DNA replicates

G2

cell prepares to divide

cell division

• occurs in

  • mitosis (the division of cell nucleus and its contents)

  • cytokinesis (the division of the cell)

• one parent cell will split into two genetically identical cells known as daughter cells

mitosis 4 stages

1. prophase

2. metaphase

3. anaphase

4. telophase

prophase

• nuclear membrane and nucleolus breaks down

• chromatin condenses to form chromosomes (composed of a pair of chromatids)

• centrosomes (duplicated during G2 phase) move to opposite ends of the cell

• microtubules extend from centrosomes to form spindle fibres (these are the same microtubules that are part of the cytoskeleton)

metaphase

• chromosomes line up in the middle of the cell

• spindle fibres from each centrosome are attached to the centromere regions of the chromosomes

anaphase

• chromatids get separated

• pulled towards the centrosomes at opposite poles by spindle fibres

• cell elongates

telophase

• nuclear membrane reforms around the chromatids (now called daughter chromosomes)

• daughter chromosomes begin to stretch out back into chromatin

• spindle fibres break down

• two nuclei observable

• cell has pinched shape

cytokinesis

• final phase of the cell cycle and the final stage of cell division

• cell splits into two daughter cells

• contractile ring pinches off the cytoplasm in the middle

• cell enter interphase after this phase

mitosis in plant cells

• the nuclear membrane helps signal spindle development (spindle fibres also have self-organization capabilities)

• during telophase, plant cells divide by producing a cell plate down the middle instead of pinching, which develops into a new cell wall