Notes on the Cell Cycle

Prokaryotes: Organelles without a nucleus

Binary Fission: Make 2 cells from one

  • In bacteria, a copy of the chromosome (DNA) must be made before binary fission can occur.
  • We now have 2 bacteria each with it’s own chromosome.
  • Before this can happen again, each little bacterium must first grow.

The Cell Cycle has 2 phases: Interphase and M phase

Eukaryotic Cell Cycle (refer to the coloring worksheet)

  • G1 Phase:

-Cell increases in size

-synthesizes (creates/produces) new proteins and organelles

  • Synthesis Phase (S phase):

-DNA is copied/replicated

  • G2 Phase

-Growth, copying of organelles, preparation for Mitosis

**Mitosis: division of the nucleus

**Cytokinesis: Division of everything else in the cell

-All 3 phases G1, S, and G2 together are called INTERPHASE

Mitosis and Cytokinesis together are called M Phase

Interphase comes before cell division

**Cytokinesis-division of the cytoplasm/cell splitting

Mitosis Notes
Mitosis: 4 stages

Aka: Nuclear Division—The division of the nucleus and DNA

1)Prophase-Nuclear membrane disappears

-Chromatin shortens and condenses and forms pairs of chromatids

-2 chromatids are held together by the centromere and form 1 chromosome

-centrioles ( which are only in animal cells) appear; made of microtubules; always present as pairs; cylindrical in shape; aligned at a 90 degree angle

-spindle fibers appear

2) Metaphase-the chromatids move to middle of cell and line up in a straight line; the centrioles (think of them as fishing rod) move to opposite side of cell; the spindle (the line that is thrown out) is formed; easiest stage to locate because chromosomes are lined up so neatly.

3) Anaphase-The centromere splits so chromatids are now chromosomes, which move to opposite poles of cell towards centrioles moving along spindle fibers.
4) Telophase-Need to reverse what happened in prophase. Have 2 sets of genetic material, form a nucleus in each half of cell; nuclear membrane reforms; centrioles disappear; cell gets ready for cytokinesis; chromosomes elongate, get thinner and look like chromatin again; cell looks more oval—end of mitosis, ready for cytokinesis

Notes on Eukaryotic Chromosomes

  • Rod-shaped structures
  • Made of DNA
  • DNA is coiled around “histones” (special proteins)
  • Made of 1000’s of genes
  • Each chromosome is made up of DNA-shaped as a double helix and carries our genetic information encoded or prearranged in the genes---it’s also a nucleic acid.
  • DNA comes in various forms, but it’s still the same substance:

-It can be strung out like thread

-It can be crumpled up and called Chromatin

-It can be coiled = Chromosome

  • Chromosomes exist as very long thin strands that coil into a tight supercoil
  • The DNA is known as chromatin during the resting stage of the cell division.

-The DNA molecule makes a copy of itself

-This makes them more visible with a microscope

  • Chromosomes get denser and thicker, coil more, before cell division
  • The copies are called chromatid
  • They are held together by a centromere
  • The 2 chromatids (the left and right sides) are held together by a centromere are called a chromosome.