Download Pre-lab Homework Lab 2: Mitosis and the Cell Cycle

Biology 102
PCC - Cascade
Pre-lab Homework Lab 2: Mitosis and the Cell Cycle
Name: _______________________________________
Date/Lab time: ___________________
1. Label the figure with the following phases
of the cell cycle (note the position of interphase
and mitosis):
•
•
•
•
•
•
•
•
G1
G2
S
Anaphase
Metaphase
Telophase
Prophase
Cytokinesis
2. Briefly describe the main occurrences in the
four phases of mitosis. Include what
happens to the nucleus, spindle fibers and
chromosomes.
•
Prophase:
•
Metaphase:
•
Anaphase:
•
Telophase:
3. On the back of this sheet, briefly describe how we will estimate the length of time a growing onion
root tip cell spends in each of the phases of the cell cycle (hint: read lab exercise 3).
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Biology 102
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Name: _______________________________________
Date/Lab time: ___________________
Lab 2: Mitosis and the Cell Cycle
LAB SYNOPSIS:
• You will model the process of the cell cycle using pop-beads.
• You will identify the phase of the cell cycle in micrographs of plant and animal cells.
• You will estimate the amount of time cells spend in each of the phases of the cell cycle.
OBJECTIVES: After successfully completing this lab, a student will be able to:
• Describe the major events of the cell cycle.
• Illustrate the process of nuclear division with models, words, and diagrams.
• Recognize cells in the various phases of the cell cycle given micrographs or descriptions.
Overview:
The cell cycle is the process in which one parent cell becomes two new daughter cells. The resulting two
cells are genetically identical to each other and genetically identical to the parent cell. Most of your contain
46 chromosomes, 23 inherited from your mom, 23 inherited from your dad. The goal of the cell cycle is to
make exact copies of each of these chromosomes.
Exercise 1: Modeling the Cell Cycle with Pop Beads
To understand the mechanism of the cell cycle, we are going to use pop beads to model the each of the
phases.
Procedure: Constructing Chromosomes Using Pop Beads.
1. Using figure 1 as a guide, construct chromosomes for a pretend cell containing 4 chromosomes
(2 red chromosomes originally inherited from its mother and 2 yellow chromosomes from its
father). This is a diploid cell.
Diploid cell (2n)- A cell containing 2 sets of chromosomes. One set from mom,
one set from dad.
Diploid cells contain homologous pairs of chromosomes.
Homologous chromosomes- are similar in size, the order of genes and
centromere position (represented in fig. 1 by the white magnetic links).
Homologous chromosomes are not however identical because one was
inherited from mom and the other from dad.
Sets and Pairs
For figure 1 understand;
Which set of chromosomes were inherited from the father?
Which set of chromosomes were inherited from the mother?
Which chromosomes are homologous pairs?
Confirm your understanding of this with your instructor before continuing.
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Figure 1. Pop bead chromosomes
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The goal of this exercise is to go through
the phases of the cell cycle to make two new
cells that are an exact copy of the cell in
figure 1.
The Cell Cycle- The sequence of phases that
occurs as a cell divides (one parent cell
becomes two genetically identical daughter
cells). Fig 2.
The phases of the cell cycle were first
identified by how they appear under the light
microscope. Three major events are noted
under the microscope; interphase, mitosis &
cytokinesis.
Figure 2. The Cell Cycle (one cell becomes two)
Interphase- Phase of the cell cycle when the nucleus of the cell does not appear to be doing much.
Interphase is divided into 3 main parts; Gap 1, Synthesis Phase & Gap 2. For this activity we will
focus on what happens to the chromosomes during the Synthesis Phase. See your textbook and lecture
for details of the Gap 1 and Gap 2 phases.
• Gap 1 (G1)- Phase in which the cell grows and functions normally. If the cell does not divide, it
enters what is called the G0 phase, otherwise it will continue into the synthesis phase.
• Synthesis Phase (S-Phase)- Phase in which the cell duplicates its DNA.
During the S-phase of interphase each chromosome goes through the process of DNA replication.
Following DNA replication, each chromosome is composed of 2 identical
sister chromatids attached at the centromere.
Procedure cont.
2. Although in real cells you cannot see individual chromosomes, to
demonstrate the results of the S-phase, construct exact copies of each
of your chromosomes and link them via their magnets.
Note: Following the S-phase, you still have 4 chromosomes, but each
chromosome is made up of two sister chromatids. Fig. 3.
Figure 3. After DNA Replication
Label each of the following in figure 3. Chromosome, Sister Chromatid & Centromere
• Gap 2 (G2)- Phase in which the cell resumes its growth in preparation for mitosis.
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Mitosis- Phase of the cell cycle that separates the sister chromatids (nuclear division). We will focus on
what is happening to the chromosomes. See your textbook for additional details. Mitosis is separated
into 4 parts; prophase, metaphase, anaphase and telophase.
• Prophase- chromosomes become visible under the light microscope.
Prior to prophase, chromosomes are not visible. During prophase the chromosome’s DNA begins to
super-coil or condense into visible chromosomes. Also during prophase the nucleolus disappears and the
nuclear envelope breaks down. Microtubules extend from centrioles at either pole of the cell forming the
spindle apparatus.
3. Use figure 4 to guide you through the process. Fig. 4A represents
prophase. Your moving of the chromosomes with your hands is equivalent
to the work the spindle microtubules are doing.
• Metaphase- chromosomes line up in the middle of the cell (along the
metaphase plate).
4. Line chromosomes up single-file so sister chromatids are facing either
side of the cell (Fig. 4B).
• Anaphase- sister chromatids begin to separate and move to either side of the
cell.
5. Separate sister chromatids and pull them to either side of the cell (Fig.
4C).
• Telophase- sister chromatids, now considered individual chromosomes, are
pulled all the way to ether side of the cell. The nuclear envelope reforms
around the chromosomes, the chromosomes de-condense and the nucleolus
reforms.
6. Pull chromosomes further away from one another (Fig. 4D).
----------------------------------------------------------Cytokinesis- This is the process of cell division, dividing one cell into two new
daughter cells.
7. Pull chromosomes yet further away from each other. Note: each “new
cell” should have identical chromosomes to each other and to the original
parent cell (Fig. 4E).
Practice the phases of the cell cycle again without the aid of the figures.
If this were a human skin cell;
How many total chromosomes would there be prior to the cell cycle? _______
How many sets of chromosomes would there be? _______
How many chromosomes would there be in each set? _______
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Figure 4. Phase of the Cell Cycle
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Exercise 2: Identifying Cells in Mitosis
The phases of the cell cycle (interphase, mitotic phases and cytokinesis) can be identified from
micrographs (photos of microscope images). Use the provided micrographs (onion root tip and/or white
fish blastula cells) and identify the phases of the cell cycle. In these micrographs, plant cells tend to be
square, while animal cells tend to be circular.
Procedure:
1. Nucleus: The nucleus is often the most obvious structure within a cell. Identify the nucleus in the
provided micrographs. Changes to the structure of the nucleus will help you distinguish cells
undergoing mitosis from those still in interphase.
2. Interphase: Find a cell that has a nucleus with no visible chromosomes (visible chromosomes
would appear as thick strands, almost wormlike). Not being able to see the chromosomes is
characteristic of a cell’s nucleus in interphase. Sketch a cell in the “interphase” box on the
following table. Label any visible structures, and list the main events happening at this phase.
3. Prophase: Find a cell whose nucleus appears to be in prophase. Review the phases from your
modeling activity above with the pop beads. Sketch a cell in prophase, label any structures you
can see, and list the main things that are happening in this phase.
4. Continue on finding cells in metaphase, anaphase, and telophase. Sketch each cell, label your
sketch, and list what is happening during each phase.
Labeled sketch of cell
Interphase
Main events of phase
Prophase
Metaphase
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Anaphase
Telophase
Exercise 3: Estimating the Time Spent in the Phases of Mitosis
Cells in your body reproduce at different rates. Skin cells reproduce frequently (about once per day);
liver cells reproduce rarely (about once per year); after initially formed nerve and muscle cells almost
never reproduce. The whole process of mitosis, prophase to telophase, takes ~ 90 min. The following
exercise will allow you to estimate how long each phase lasts.
Procedure:
1. Each team of two will need one of the provided onion root tip micrographs. This area of the root is
undergoing rapid cell reproduction.
2. Identify the phases of the cell cycle for 25 randomly chosen cells. Record this information in table 1
below. It is important that you choose cells randomly so as not to bias your data.
3. Once you have identified 25 cells, trade jobs with your lab partner. Record total data in Table 1.
Table 1: Number of cells in each phase of the cell cycle counted by self and lab partner.
Phase Interphase
Prophase
Metaphase
Anaphase
Telophase
Total
Your 25
Partners 25
TOTALS
4. After identifying a total of 50 cells, trade data with 3 other groups so that you have a total of 200
cells identified. Record this data in Table 2.
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Table 2: Number of cells in each phase of the cell cycle counted by four lab pairs.
Phase Interphase
Prophase
Metaphase
Anaphase
Telophase
Total
Your Total
Other #1
Other #2
Other #3
TOTALS
5. Now you are ready to estimate the amount of time these cells spend in each different phase. In an
onion root tip, the entire cell cycle takes about 12 hours (depending on the plant’s health and where
you are looking in the root). We will use 12 hours (720 minutes) as a rough estimate.
6. Calculate the percentage of time spent in each phase by counting the total number of cells in each
phase (total in interphase, in prophase … and so on) and dividing each by the total number of cells
you counted (this should be 200 if you have compared with 3 other groups). Record this data in
Table 3.
7. Multiply the percentage of time in each phase by the total time of the cell cycle (720 minutes) and
this gives you an estimate of the time spent in each phase. Record this data in Table 3.
Table 3: Estimate of time spent in each phase of the cell cycle.
Phase Interphase
Prophase
Metaphase
Anaphase
Telophase
Total
% of cells in
each phase
100%
Time
estimate
720
minutes
8. Most of the cells in your body are not dividing as quickly as onion root tips; however, the amount of
time spent in the various phases of mitosis is about the same as you have calculated.
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