Cell Growth and Division Notes

Cell Growth & Division (Mitosis)

Cell Theory Review

  • All living things are made of cells.
  • Cells are the basic unit of life.
  • Cells come from pre-existing cells.

Cells Need Nutrients to Grow

  • Cells grow when they can take in more nutrients through their plasma membrane than they can use.
  • When cells reach a certain size, they need to divide.
  • These steps are part of the cell cycle.

Cell Division: Prokaryotes vs Eukaryotes

  • Prokaryotes:
    • Binary Fission: A cell grows, increases in size, then divides into two new cells.
  • Eukaryotes:
    • Must divide their Nucleus (mitosis).

Cell Cycle

  • The cell goes through a set of phases:
    • Growth, preparation, division.
    • Only a small portion of the cycle is actually spent dividing.

Phase 1: Interphase

  • The cell spends about 90% of the cycle in this phase.
  • Made up of 3 stages:
    • G1 - Gap 1
    • S - Synthesis
    • G2 – Gap 2

G1: Cell Growth

  • Increase in size and synthesize new proteins and organelles.

S Phase (Synthesis)

  • When DNA replication takes place.
  • Chromosomes duplicate and form sister chromatids.
  • Each of the 46 chromosomes is duplicated by the cell.

G2 Phase

  • Cell grows more and makes organelles and molecules for division.
  • Example: centrioles.
  • Shortest stage of interphase.

Cell Division Prokaryotes vs. Eukaryotes (body cells)

  • Prokaryotes: Binary fission
    • Once a cell grows twice its size, it divides into two.
  • Eukaryotes: must divide their nucleus (mitosis)

M Phase = Mitosis

  • Human diploid cell divides (46 chromosomes).
  • After G2, the cell is ready to divide.
  • Eukaryotes go through Mitosis.
  • Mitosis = division of the nucleus.

What is contained in the nucleus?

  • Cell Nucleus:
    • Where chromosomes "live".
  • Chromosomes:
    • Contain all genetic material.
  • DNA:
    • The material from which chromosomes are constructed.
  • Gene:
    • A segment of a chromosome (made up of DNA).

What parts of the cell are involved?

  • Chromosomes (in nucleus):
    • Made up of tightly wound DNA.
    • DNA is replicated before it divides so that new cells have identical DNA.

Eukaryotic Nuclear Division: Mitosis

  • There are 4 phases of mitosis to create 2 identical daughter cells:
    • Prophase
    • Metaphase
    • Anaphase
    • Telophase

Prophase

  • Chromosomes condense and become visible.
  • Centrioles move to opposite sides.
  • Spindle forms.
  • Nuclear envelope breaks down.

Metaphase

  • Sister chromatids (chromosomes) line up at the center of the cell.
  • Microtubules connect to the poles.

Anaphase

  • Sister chromatids move away from the center towards the poles.

Telophase

  • Chromosomes disperse.
  • Nuclear envelope reforms.
  • Spindle breaks.
  • Two cells begin forming.

Cytokinesis - last step!

  • Divides the cytoplasm of the parent cell into two identical diploid daughter cells.

Plant cell vs. Animal cell

  • A plant cell forms a cell plate during cytokinesis that becomes the cell wall.
  • An animal cell forms a cleavage furrow.

Mitotic Division of an Animal Cell

  • G2 of Interphase
  • Prophase
  • Prometaphase
    • Centrosomes (with centriole pairs)
    • Chromatin (duplicated)
    • Chromosome, consisting of two sister chromatids
  • Metaphase
  • Anaphase
  • Telophase and Cytokinesis
    • Metaphase plate
    • Cleavage furrow
    • Nuclear envelope forming
    • Daughter chromosomes

Mitosis in a plant cell

  • Late interphase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
    • Cell plate forms (not pinching in)