Biology Lecture 3 Notes (Cell Division)
Mitosis serves as a way to divide DNA equally and precisely; Mitosis occurs due to three systems
that work together:
o One ‘system’ is the timing and programming to ensure that DNA can divide; ‘an
elaborate master program of molecular checks and balances that ensures an orderly and
timely progression through the cell cycle’.
o The second ‘system’ divides the DNA into two copies.
o The final system uses the cytoskeleton to separate the DNA into the two daughter cells.
Depending on the age, some cells would undergo a different type of division
called meiosis, creating daughter cells that only have half the normal amount of
Replication of DNA of each chromosome creates two molecules called sister chromatids.
o The equal distribution is called chromosomal segregation.
Steps of Mitosis:
Interphase is the longest phase is cell division as it prepares the cell of mitosis
Within the G 1ycle, the cell creates RNA, proteins and other types of cellular
molecules but not DNA.
G 1ycle stands for gap, where DNA is not being replicated.
After the G1cycle, the S cycle begins; duplicating chromosomal proteins as well
as DNA and continues synthesis of other molecules as well.
S cycle stands for synthesis, where DNA is being (duh) synthesized.
Once S cycle is completed, the cell enters2G cycle, where DNA synthesis stops,
but other molecules contain to be replicated.
After the end of the G2cycle, actual cell division beings.
During prophase, the chromatin condenses into chromosomes.
The nucleolus disappears in most species of cells, shutting own RNA
synthesis; rRNA is made in the nucleolus.
The mitotic spindle forms in between the two centrosomes as they start
heading towards the opposite ends of the cell to form the spindle poles.
o The spindles develop as microtubules come out from the
During prometaphase, the nuclear envelope starts to break down.
Kinetochores form on either side of the chromatid on the sides of the
Since microtubules attach to the kinetochores, the connections are
important as they divide the chromatids from each other. Microtubules attach to the kinetochores, and the ones that don’t attach overlap
the opposing side’s tubules.
The sister chromatids become aligned on the spindle midpoint (also known as