Bio A/H
Activity 1. What is DNA (review)?
DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms.
Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where
it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is
called mitochondrial DNA or mtDNA).
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G),
cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent
of those bases are the same in all people. The order, or sequence, of these bases determines the
information available for building and maintaining an organism, similar to the way in which letters of
the alphabet appear in a certain order to form words and sentences.
DNA bases pair up with each other, A with T and C with G, to
form units called base pairs. Each base is also attached to a
sugar molecule and a phosphate molecule. Together, a base,
sugar, and phosphate are called a nucleotide. Nucleotides are
arranged in two long strands that form a spiral called a double
helix. The structure of the double helix is somewhat like a
ladder, with the base pairs forming the ladder’s rungs and the
sugar and phosphate molecules forming the vertical sidepieces
of the ladder.
An important property of DNA is that it can replicate, or make
copies of itself. Each strand of DNA in the double helix can
serve as a pattern for duplicating the sequence of bases. This is
critical when cells divide because each new cell needs to have
an exact copy of the DNA present in the old cell.
2. What is a chromosome and a karyotype?
TEXT: Chapter 8, section 1: page 151-153
In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called
chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called
histones that support its structure.
Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not
dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell
division and is then visible under a microscope. Most of what researchers know about chromosomes was
learned by observing chromosomes during cell division.
Each chromosome has a constriction point called the centromere, which divides the chromosome into
two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the
chromosome is labeled the “q arm.” The location of the centromere on each chromosome gives the
chromosome its characteristic shape, and can be used to help describe the location of specific genes.
1
Bio A/H
CHROMOSOME DURING MITOSIS METAPHASE (2 chromatids, duplicated DNA)
The chromosome seen here is already
duplicated. It has two chromatids
(the left and right), and a centromere(
where the two chromatids are joined.
A chromosome can consist of either a
single copy of DNA , or a duplicated
copy of DNA. Both are considered to
be chromosomes.
If we unwind a chromosome, we will
see that a chromosome is made of
chromatin (threads of doublestranded DNA) that is tightly wound
up around circular proteins called
histone.
Define:
1. Chromosome
2. Chromatid
3. Centromere
4. Chromatin
5. Histone
The picture shown on the next page is called a karyotype. This is the karyotype of a human. A
karyotype is a picture of all the chromosomes that are in a single human cell. The X and Y chromosomes
2
Bio A/H
determine the gender of the person and are called sex chromosomes (XX is female and XY is male). All
other chromosomes (pairs 1-22) are called autosomes. You have one copy from your mother and one
from your father. These “matched pairs” are called homologous chromosomes.
This is a pair of
chromosomes that has
already been
duplicated (notice that
each chromosome
looks like an X, which
means it is already
duplicated.
Autosomes come in different shapes and sizes but each autosome has another chromosome (its
homologue) that contains the same genes. Autosomes contain genes that are not associated with
gender, such as eye color, height, hair color , etc.
A diploid cell contains a pair of each autosome and a pair of sex chromosomes. A haploid cell
contains only one of each autosome and one sex chromosome. Haploid cells are eggs and sperm and
must combine with another haploid cell during fertilization to produce offspring (sexual reproduction)
1. What is an Autosome?
2. What is a Sex Chromosome
X
Y
3. What is a Homologous pair?
4. Haploid (which karyotype on the next page is haploid? What does it mean to be haploid?)
a. Diploid (which karyotypes are diploid? _______ which is diploid AND duplicated? _____
5. Can you have a karyotype that is haploid? What type of cell has only “half the chromosomes “
(haploid).
What type of cells in your body are diploid?
3
Bio A/H
Here are images of homologous pairs of chromosomes that have not duplicated their DNA (left) and
homologous pairs that have duplicated their DNA (right). Both of these sets are diploid (2 homologous
chromosomes). However , the set on the right has duplicated DNA as well (it is in metaphase).
Karyotype A
Karyotype B
Karyotype C
4
Bio A/H
Activity 3. Introduction to Cell Division (book):
- Read the chapter in your book on Mitosis (pg154 – 159) and answer the following questions
1. All cells come from pre-existing cells. What is the division of prokaryotic cells called? How many
chromosomes does a bacteria have and what is it’s shape?
2. What is the cell cycle and in what type of cells does the cell cycle occur? ?
3. What two processes need to happen for one cell to divide into 2 completely separate cells?
4. Draw a picture of a chromosome and label the centromere and chromatid.
5. How many total chromosomes does a human cell have?
a. How many are autosomes?
b. How many are sex chromosomes?
c. What sex chromosomes do Males have?
d. What sex chromosomes do Females have?
5
Bio A/H
6. Define the terms Haploid and Diploid. Then provide examples of each type of cell.
7. What is mitosis?
8. List the 4 phases of mitosis and briefly describe what happens in each phase.
9. How is cancer related to the cell cycle?
10. What kind of molecules control the cell cycle?
6
Bio A/H
Activity 4. THE CELL CYCLE (Online, reading, questions)
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html
Be sure to watch the animation above. It will help you to visualize how the cell cycle works.
Cell Cycle and Mitosis
Summary:
The cell cycle, or cell-division cycle is:


A series of events that takes place in a eukaryotic (with a nucleus) cell leading to its
division and replication.
The cell cycle can be divided into two MAJOR periods:
o Interphase — during which the cell grows, accumulating nutrients needed for
mitosis and duplicating its DNA
 G1, S, G2
o M phase, during which the cell splits itself into two distinct cells, often called
"daughter cells. This involves both
 Mitosis replication of the chromosomes formation of two nuclei AND
 Cytokinesis involves actually splitting the single cell into two distinct
daughter cells.
The cell-division cycle is a vital process by which a single-cell fertilized egg develops into a mature
organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed.
Learning Objectives:
1. Describe the phases of the cell cycle
2. Describe the phases of mitosis
3. Define cytokinesis
Study Guide:
After cell division, each of the daughter cells begin the interphase of a new cycle. Although the various
stages of interphase are not usually morphologically distinguishable, each phase of the cell cycle has a
distinct set of specialized biochemical processes that prepare the cell for initiation of cell division.
The Cell Cycle:
The cell cycle consists of four distinct phases:
G1 phase, S phase (synthesis), G2 phase (collectively known as interphase)
M phase (mitosis and cytokinesis).
7
Bio A/H
Activation of each phase is dependent on the proper progression and completion of the previous one.
Cells that have temporarily or reversibly stopped dividing are said to have entered a state of quiescence
called G0 phase.
G1 phase.
Metabolic changes prepare the cell for division (cellular contents are duplicated). At a certain point - the
restriction point - the cell is committed to division and moves into the S phase.
S phase.
DNA synthesis replicates the genetic material. Each chromosome now consists of two sister chromatids.
G2 phase.
Metabolic changes assemble the cytoplasmic materials necessary for mitosis and cytokinesis. DNA is
“proofread” for accuracy
M phase.
A nuclear division (mitosis) followed by a cell division (cytokinesis or division of the cytoplasm).
The period between mitotic divisions - that is, G1, S and G2 - is known as interphase.
G0
Many times a cell will leave the cell cycle, temporarily or permanently. It exits the cycle at G1 and
enters a stage designated G0 (G zero). A G0 cell is often called "quiescent". Many G0 cells are anything
but quiescent. They are busy carrying out their functions in the organism. e.g., secretion, attacking
pathogens.
Often G0 cells are terminally differentiated: they will never reenter the cell cycle but instead will carry
out their function in the organism until they die. For other cells, G0 can be followed by reentry into the
8
Bio A/H
cell cycle. Most of the lymphocytes in human blood are in G0. However, with proper stimulation, such
as encountering the appropriate antigen, they can be stimulated to reenter the cell cycle (at G1) and
proceed on to new rounds of alternating S phases and mitosis.
G0 represents not simply the absence of signals for mitosis but an active repression of the genes needed
for mitosis. Cancer cells cannot enter G0 and are destined to repeat the cell cycle indefinitely.
Mitosis:
During mitosis replicated chromosomes become positioned near the middle of the cytoplasm and then
segregated so that each daughter cell receives one of the chromatids from each chromosome (one copy
of the original DNA (if you start with 46 in the parent cell, you should end up with 46 chromosomes in
each daughter cell).
Prophase
Prophase is the first stage of mitosis proper. Chromatin condenses (the chromatin/DNA replicate during
Interphase, so it is now “coiling into chromosomes), the nuclear envelope dissolves, centrioles (if
present) divide and migrate and the spindle forms.
Metaphase
Metaphase follows Prophase. The chromosomes (which at this point consist of 2 identical chromatids
held together by a centromere) migrate to the equator of the spindle, where the spindles attach to the
kinetochore fibers.
Anaphase
Anaphase begins with the separation of the centromeres, and the pulling of chromosomes (we call them
chromosomes after the centromeres are separated) to opposite poles of the spindle. To do this cells
9
Bio A/H
utilize microtubules (referred to as the spindle apparatus) to "pull" chromosomes into each "cell".
Animal cells (except for a group of worms known as nematodes) have a centriole. Cells that contain
centrioles also have a series of smaller microtubules, the aster, that extend from the centrioles to the cell
membrane. The aster is thought to serve as a brace for the functioning of the spindle fibers.
Telophase
Telophase is when the chromosomes reach the poles of their respective spindles, the nuclear envelope
reforms, chromosomes uncoil into chromatin form, and the nucleolus (which had disappeared during
Prophase) reform. Where there was one cell there are now two smaller cells each with exactly the same
genetic information. These cells may then develop into different adult forms via the processes of
development.
Cytokinesis
Cytokinesis is the process of splitting the daughter cells apart. Whereas mitosis is the division of the
nucleus, cytokinesis is the splitting of the cytoplasm and allocation of the organelles and cytoplasm into
each new cell.
1. Diagram the cell cycle. Identify all phases of interphase and the M phase, and briefly identify what takes
place in each phase.
2. What is the G0 phase? What types of cells might go through a G0 phase? Why?
3.
Which cells never go through a G0 phase? What is the result?
4. What is the key event in mitosis? How does the cell ensure that each daughter cell gets exact copies of
the DNA (all chromosomes).
5. How would you differentiate mitosis and cytokinesis?
10
Bio A/H
Activity 5. MODELING MITOSIS (LAB ACTIVITY)
Modeling Mitosis
Directions: Read below before beginning. This lab has two parts:
1. Demonstrating how mitosis and meiosis work with model chromosomes
2. Computer analysis of Karyotyping. You must complete part I first BUT to save time, get your laptop set
up so you can work on the models while it is booting.
Step 1: Building chromosomes –
For this activity you’ll need to make 6 duplicated chromosomes.
-
-
Step 1: build 2 red chromosomes each with 3 beads on either side of the magnetic centromere. Then build
2 YELLOW chromosomes exactly the same way.
Step 2: Now build 2 RED chromosomes each with 2 beads on either side, followed by 2 YELLOW
chromosomes with 2 beads on either side.
Step 3: Finally build 2 RED chromosomes with 1 bead on either side, followed by 2 YELLOW chromosomes
with 1 bead on either side.
In total you should have three pairs of Red chromosomes and three pairs of YELLOW chromosomes.
The two colors represent the mother’s and father’s chromosomes.
The different SIZES represent different types of chromosomes.
Step 2: modeling the phases
Use the white board and marker to draw the outlines of the cell, centrosomes, nucleus and spindle fibers. Then
position the chromosomes in the proper place to demonstrate each phase below. I must check off each phase
for you to get credit.
_____________Phase 1: Use your board to accurately demonstrate PROPHASE. Once we check you are correct,
draw a diagram of your model in the space below.
_____________Phase 2: Use your board to accurately demonstrate METAPHASE. Once we check you are
correct, draw a diagram of your model in the space below.
_____________Phase 3: Use your board to accurately demonstrate ANAPHASE. Once we check you are correct,
draw a diagram of your model in the space below.
_____________Phase 4: Use your board to accurately demonstrate Telophase. Once we check you are correct,
draw a diagram of your model in the space below.
11