Lab 10
Mitosis
Background
Reproduction means producing a new
organism from an existing organism. The new
offspring must receive hereditary information
and enough cytoplasmic material to maintain
its own metabolism. The process of mitosis is
responsible for ensuring that both cells receive
the correct genetic information and cytoplasm.
Prokaryotic fission
Prokaryotic cells do not contain organelles.
Therefore, their genetic chromosome is
located in the cytoplasm. First the chromosome is replicated so the cell then contains
two exact copies of all the genetic material.
Each chromosome is attached at one point to a
protein located in the cell membrane. This
attachment ensures that each daughter cell will
contain a copy of the chromosome as the cell
splits into two.
Eukaryotic cell division
Cells that contain organelles, eukaryotic
cells, exhibit a much more complex process
during cell division. Not only do eukaryotic
cells, have to contend with their genetic material locked in the nucleus, but they also have
multiple chromosomes that need to be separated to each daughter cell.
G2 phase the cell will prepare for mitosis by
translating the necessary proteins. This is the
shortest phase of interphase.
Mitosis
Mitosis is responsible for ensuring that the
genetic material is equally divided between
the daughter cells. While mitosis is divided
up into four phases, to the cell all the phases
blend together.
Prophase During prophase, the chromatin
condenses into visible structures called
chromosomes. In animal cells, the centrioles, which replicated during interphase, move
to opposite sides of the cell. (The centrioles
are too small to be seen with a light microscope.) However, you can identify their
location by the star burst pattern of microtubules that surround the centrioles. The
microtubules located between the centrioles
produce a structure called the spindle. Some
of these microtubules attach to the chromosomes. Simultaneously, the nuclear envelope
begins to disappear. Prophase is the longest
phase of mitosis. Therefore when you are
looking at rapidly dividing cells you will see
many cells in prophase.
Metaphase As the microtubules grow they
Cell division involves two processes: mitosis (nuclear division) and cytokinesis
(cytoplasmic division). Mitosis ensures that
the genetic material is evenly divided.
Cytokinesis ensures that each new cell contains enough of the cytoplasmic components
required to sustain cellular metabolism.
push against each other. This “tug-of-war”
places the chromosomes in a line along the
center of the microtubule spindle. This line of
visible chromosomes is called the metaphase
plate. This is the most recognizable phase of
mitosis.
Cell Cycle
licated chromosomes split apart. The
microtubules begin to pull the chromosomes
in opposite directions. The key to identifying
this phase if that the moving chromosomes
look like Vs. You can also see the poles of the
cell pushed apart. This is the shortest phase of
mitosis so you will have to look longer to find
a cell in anaphase.
Cells pass through a sequence of events call
the cell cycle. The cell cycle is composed of
two stages the interphase and mitotic phase.
A cell will spend 95% or more of its life cycle
in interphase. Interphase is further subdivided
into three phases called: G1, S, and G2. During
the G1 phase, the cell increases in volume. G1
is the longest phase in the cell cycle. Indeed,
some cells may opt out of the cell cycle during
G1 and enter a stationary phase called G0.
Cells continuing in the cell cycle will, after
G1, enter the S phase. During the S phase the
chromosomal DNA (the genetic material) is
replicated. Following the S phase, during the
Lab 10
Anaphase During anaphase the paired rep-
Telophase This phase of mitosis begins as
soon as the chromosomes stop moving. Now
it looks like prophase in reverse. The chromosomes uncoil, two nuclear envelopes
re-form, nucleoli reappear, and the microtubules breakdown.
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Cytokinesis While the first part of the
mitotic phase, mitosis, is broken up into sub
sub phases, the second part of the mitotic
phase, cytokinesis has no sub phases. Mitosis
ensures that the daughter cells obtain equal
amounts of the genetic material. Cytokinesis,
on the other hand, is responsible for separating
the cytoplasm and begins in late anaphase. In
animal cells, microfilaments attached to the
cell membrane constrict in a ring around the
middle of the cell and pinch the cell into two
cells. Each new cell contains a new nucleus
from mitosis. This invagination is called
cleavage furrowing. Do not underestimate
the importance of cytokinesis. It is important
for the daughter cells to receive enough cytoplasm and organelles to maintain metabolism
until more cytoplasm and organelles can be
produced.
Exercise 10.1 Animal Cell Mitosis
1. Under high power in your microscope identify and draw below all four phases of mitosis from the
White Fish blastula.
Mitosis in Plant Cells
Plants grow at the ends of their stems and
roots by adding new cells. These special
regions are called meristems and are the sites
of very active nuclear and cell division In
addition, plants will increase their girth
through cell division growth. In animals, cell
division occurs continually throughout the
body.
Besides location plant cells exhibit a few
more differences in mitosis. Plant cells do not
contain centrioles. Instead, the microtubule
bundle is anchored on opposing cell walls.
Since plant cells contain a hard cell wall, they
do not form a cleavage furrow. Instead plant
cell cytokinesis involves the formation of a
cell plate. Vesicles originating from the Golgi
apparatus migrate to the spindle equator and
fuse with each other. The contents of the
vesicles include material for making new the
cell wall (cellulose) and new cell membrane
components. The vesicles fuse to from the
cell plate which will divide the two daughter
cells.
Exercise 10.2 Plant Cell Mitosis
1. Under high power in your microscope identify and draw below all four phases of mitosis from the
meristem of the Allium root tip.
Meiosis
The chromosomes in eukaryotic cells exist
in pairs of homologous chromosomes. They
contain similar, but not identical genetic
information. One homologue is inherited
from your dad and the other from your mom.
Therefore your cells are diploid (2n) since
they have both homologues in the same
nucleus. For sexual reproduction the germ
cells must contain only one of the homologues
Exercise 10.3
and are called haploid (1n). To obtain a haploid state cells under go meiosis which
resembles the mitotic phase done twice
(meiosis I and meiosis II). Since meiosis follows the S phase, there are essentially four
copies of each chromosome. Unlike mitosis,
in meiosis prophase I the duplicated homologous chromosomes attach to each other until
metaphase I where they separate.
Meiosis
1. Using four different colors depict two pairs of condensed homologous chromosome through each
stage of meiosis.
Lab 10
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Exercise 10.1 Report Animal Cell Mitosis
Name _________________________
Prophase
Anaphase
Metaphase
Telophase
Exercise 10.2 Report Plant Cell Mitosis
Prophase
Anaphase
Metaphase
Telophase
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Exercise 10.3 Report
Name __________________________
Meiosis I
Meiosis II
Prophase II
Prophase I
Metaphase II
Metaphase I
Anaphase II
Anaphase I
Telophase II
Telophase I
Exercise 10.4 Report
DNA sequence name:
Species DNA matches to:
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BLAST
The comparison of nucleotide or protein
amino acid sequences from the same or different organisms is a very powerful tool in
molecular biology. By finding similarities
between sequences, scientists can infer the
function of newly sequenced genes, predict
new members of gene families, and explore
relationships between genes and organisms.
Now that whole genomes are being sequenced,
sequence similarity searching can be used to
predict the chromosomal location and function
of protein-coding and transcription-regulation
regions in genomic DNA.
BLAST is an anagram that stands for Basic
Local Alignment Search Tool. BLAST is a
computer program that takes a user submitted
sequence and finds a related sequence from a
database. The researcher or student can submit either DNA/RNA nucleotide or protein
amino acid sequence. This process allows a
user to identify the gene and species of an
unknown sequence providing the sequence is
in the database. Currently one of the largest
data bases is located at the National Center for
Biotechnology Information (NCBI, check the
URL (address) you must type in the exercise
below.) which is part of the National Institute
of Health (NIH) which is funded by the Federal Government.
Exercise 10.4
Using a computer that is connected to the internet and open a browser.
Navigate to Dr. Engle’s web page (DrEngle.net) and make your way to the Biology I web page.
Scroll down the page to the “Additional Resources” section. Click on the “Week 10 Laboratory
DNA sequence list” link. Scroll down and randomly click on any link on the page. Be sure to copy
the name of the file you are clicking on to the report on page 4 of this lab.
You should now see a DNA sequence on your screen. Select the entire sequence and copy it to
the clipboard (Edit -> Copy)
Open a new tab or window and point a browser to: www.ncbi.nlm.nih.gov/BLAST. Under the
“Basic BLAST” section click on the “nucleotide blast” link.
Paste your DNA sequence into the first entry box labeled “Enter Query Sequence: Enter
accession number(s), gi(s), or FASTA sequence(s)”
In the next section of that same page titled “Choose Search Set” selects which data base to
search. We don’t want to search the Human genomic database so click on the radio button labeled
“Others (nr etc.)”
Now click on the blue “BLAST” button near the bottom of the page.
When the results page comes up (you may have to wait a few seconds) scroll down to find the
first identifiable species in the list and report that organism in the lab report on page 4.
Lab 10
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