Lab Manual - eScience Labs

Lab 11: Mitosis
•S: DNA replicates
•G 2 : the second growth phase in which cellular organelles (mitochondria, ribosomes, and centrioles)
are replicated.
•M: mitoc division (prophase, metaphase, anaphase and telophase)
A cell normally completes the cycle in 18-24 hours, with mitosis occupying 1-2
hours of that me (Figure 2). Each stage is regulated by specialized proteins
that coordinate the division and cell growth. Certain types of cancer are associated
with the failure of these proteins.
Figure 3: Two chromads
are joined together by a
centromere to form a
chromosome pair.
Chromosomes are joined as a four-arm structure by a centromere (Figure 3).
During cell division (both meiosis and mitosis) each chromosome is duplicated,
resulng in two idencal chromads. For a short while the cell contains four
copies of each chromosome (two from your mother and two from your father).
The chromads are then pulled apart and divided into daughter cells.
In mitosis, the division of the parent cell produces two cells, each having two sets of chromosomes
(diploid (2n)). Thus, somac cells can replicate and maintain the right number of chromosomes.
Mitosis (Figure 4):
• Interphase: The longest period of the cell cycle was named Interphase because it was the
“in-between” period between cell cycles. It is the phase where the cell grows, its DNA replicates
and it prepares for division. The replicated chromosomes pair up as sister chroma-
ds (exact copies of each other).
• Prophase: The nuclear membrane breaks down and the chromosomes separate. Structures
which will serve as anchors in the cell (centrioles) during the division process appear.
• Metaphase: The chromosomes line up in the middle of the cell. Microtubules aach to the
chromosomes. The orientaon of each pair of homologous chromosomes is independent
from all other chromosomes. This means they can “flip flop” as they line up, effecvely
shuffling their genec informaon into new combinaons. Microtubules (long strands)
grow from each centriole and link together while also aaching to each pair of homologous
chromosomes.
• Anaphase: The microtubules pull the sister chromads apart.
• Telophase: One set of chromosomes arrives at each centriole, at which me a nucleus
122