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Collin College BIOL 1408 Unit 11 Cell Division Packet
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- BIOL 1408
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- Collin College
Collin College BIOL 1408 Unit 11 Cell Division Packet
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Unit 11Cell Division
Abstract
Cellular division is a process needed to guarantee the survival of an organism.
Complex eukaryote cells are constantly exposed to various environmental stresses,
which can lead to cell death. This cellular death would eventually result in the failure
of a vital organ in the organism if the cells were not capable of dividing and replacing
themselves. It is not desirable for cells to constantly be dividing either, however, as this
would result in the production of an excessive amount of cells. Because of this delicate
balance that exists in the maintenance of an organism’s homeostasis, it is crucial that
cell division be a strictly regulated process. The cell cycle is a cycle that consists of
multiple steps and checkpoints that exist to ensure 1) that the integrity of a cell’s
genetic material is maintained through each division and 2) that the cell is properly
prepared for the overall process of cell division. If a problem arises, processes in the
cycle exist to either correct the problem, or terminate the cell so that the complications
are not carried over into the daughter cells.
11.1 Observation of Animal Cells Undergoing Mitosis
Introduction
Mitotic cell division is the regulated division of somatic (body) cells. The stages of the
cell cycle are Interphase and M-phase. M-phase includes Prophase, Prometaphase,
Metaphase, Anaphase, and Telophase.
Interphase includes the following stages:
G1: Synthesis of enzymes and proteins needed in S phase occurs; time length varies even
in cells of the same organism.
S: The genetic material (DNA) of the cell is replicated. In humans, 46 chromosomes are
replicated into 46 pairs of sister chromatids.
G2: Synthesis of proteins and enzymes needed for cell division (i.e. microtubules).
G0: Cells are not in a dividing state. Cells can exit active growth/division in the cell
cycle and transition to G0. The cells are not dividing at this part of the cell cycle. This can
be a natural, normal transition as a part of an organisms growth and development (for
instance, nerve and muscle cells are in G0), or can be due to either a shortage of nutrients
or another environmental or internal stress is affecting the cells’ ability to enter the cell
cycle.
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, M Phase is where cell division occurs. This phase is divided into several stages:
Prophase, Prometaphase, Metaphase, Anaphase, and Telophase:
Prophase: Chromosomes condense and become visible; spindle apparatus begins to
form as centrioles migrate to opposite poles of the cell.
Prometaphase: Chromosomes are fully condensed, spindle apparatus has formed, the
nuclear envelope breaks down, chromosomes are becoming attached to microtubules at
the kinetochores located at the centromere.
Metaphase: Attachment to microtubules results in movement of the chromosomes to the
metaphase plate; kinetochores of each chromosome must be bound to microtubules
bundle before advancing through M phase checkpoint.
Anaphase: Centromeres split, and each chromatid becomes a chromosome; chromosome
separation occurs and cytokinesis (cleavage of the cell membrane) begins at the end of
this stage
Telophase: Nuclear envelopes reform around the chromosomes in each daughter cell at
the poles of the spindle; cytokinesis continues and is completed so that two daughter
cells are formed.
In this experiment you will be observing whitefish blastula. This will familiarize you with
the appearance of the different stages of mitosis.
Materials and Methods – Observation of Animal Cells Undergoing
Mitosis
1. Obtain a slide from your slide box labeled “white fish blastula.” What objective
are you going to use initially to scan this slide? ________ Scan the slide with
the appropriate objective, and look for circles on the slide. These circles contain a
plethora of blastula cells within them.
2. Once you have found a circle, switch to a higher objective. If you need to focus
when using this higher objective, which focus adjustment knob are you going to
use? ________.
3. Working in pairs, find a cell or cells that represent each stage of mitosis and
diagram them in figure 1. Check your answers with your instructor.
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