Download Study Guide_DNA and Cell Cycle

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STUDY GUIDE – Model 7 - DNA Structure & Function & Cell Division Study Guide
Read to Learn
DNA Structure
As proposed by Watson and Crick, deoxyribonucleic acid (DNA) consists of two long
nucleotide chains. The two nucleotide chains twist around one another to form a double
helix, a shape resembling a spiral staircase. Weak chemical bonds between the chains hold
the two chains of nucleotides to one another. A nucleotide in the DNA chain consists of
three parts: a nitrogenous base, a phosphate group, and a molecule of deoxyribose. The
possible nitrogenous bases of each nucleotide chain are adenine (A), guanine (G), cytosine
(C), and thymine (T). The bases are opposite one another on the two nucleotide chains and
are held together by weak hydrogen bonds. Adenine is always opposite thymine and binds to
thymine. Guanine is always opposite cytosine and binds to cytosine. Adenine and thymine
are said to be complementary, as are guanine and cytosine. This is known as the principle of
complementary base pairing.
DNA Replication
Before a cell enters the process of mitosis, its DNA replicates itself. Equal copies of the DNA
pass into the daughter cells at the end of mitosis. In human cells, th is means that 46
chromosomes (or molecules of DNA) must be copied.
The process of DNA replication begins when specialized enzymes called helicases pull apart,
or “unzip,” the DNA double helix. As the two strands separate, the exposed bases then
attract their complementary bases. The enzyme DNA polymerase joins all the matching
bases, forming a long strand of nucleotides. Thus, the old strand of DNA directs the
synthesis (creation) of a new strand of DNA through complementary base pairing. The old
strand then unites with the new strand to reform a double helix. This process is called
semiconservative replication because one of the old strands is conserved in the new DNA
double helix.
DNA replication occurs during the S phase of the cell cycle. After
replication has taken place, the chromosomal material shortens and
thickens. The chromatids appear in the prophase of the next mitosis.
The process then continues, and eventually two daughter cells form,
each with the identical amount and kind of DNA as the parent cell.
Show what you know
1.
Label the following diagram of a nucleotide.
2.
Write the complementary strand of DNA for the base sequence below:
A
T
T
G
G
G
A
A
C
G
C
T
T
A
A
A
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3.
Sequence the following events that occur during DNA replication.
_____ Helicase breaks hydrogen bonds
_____Cell gets a signal to divide
_____Polymerase reads the genetic code
_____Chromosomes form and become visible in the nucleus
_____Following base pair rules, polymerase attaches free nucleotides to form a new
complementary strand.
_____the old strands and the new strands re-twist into two helixes.
_____Helix unzips
4. If one strand of DNA has a base sequence containing 250 adenine bases, how many
thymines are present? _______________
5. If a gene on a chromosome is 3000 base pairs long, how many nucleotides does the
gene contain? ______________
6. A student stated, “The process of Replication uses an original DNA helix to create two brand-new
copies of DNA so cells can divide.” Explain how this student’s response is partially true and partially
false.
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Name:______________________________ Date: _____________ Period: _____
MODEL 8 – Cell Cycle, Mitosis & Meiosis
I will be able to do…
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Describe similarities and differences between mitosis and meiosis including replication and
separation of DNA and cellular material, changes in chromosome number, number of cell
divisions, and number of cells produced in complete cycle
Recognize mitosis as a part of asexual reproduction
Outline the cell cycle in terms of interphase, mitosis, and cytokinesis
Place mitosis diagrams in order and describe what is occurring throughout the process.
(Students are not expected to memorize the names of the steps or the order of the step
names.)
Read to Learn
The cell cycle involves many repetitions of cellular growth and reproduction. With few exceptions (for
example, red blood cells), all the cells of living things undergo a cell cycle.
The cell cycle is generally divided into two phases: interphase and cellular division. During interphase,
the cell spends most of its time performing the daily functions that make it unique. Mitosis is the 1 st part
of cellular division during which the cell’s nucleus divides into two new nuclei with the same genetic
material in each. After the second part of Cellular Division, Cytokinesis, two new daughter cells are
formed. These two new daughter cells are genetically identical and are therefore clones!
Interphase
The interphase stage of the cell cycle includes three distinctive parts in which certain functions are
carried out. During interphase the following processes and events are carried out:
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In the G1 phase, proteins are synthesized and cells carry out their functions in order for their
survival. For example, a pancreas cell in will produce and secrete insulin, a muscle cell will
undergo the contractions that permit movement, and a salivary gland cell will secrete salivary
enzymes to assist digestion.
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Right before mitosis begins the cell prepared for replication and division. During the S
(Synthesis) phase of interphase the DNA within the nucleus replicates. During this process, the
cell’s entire DNA is faithfully copied, so two DNA molecules exist for each one formerly present.
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During the G2 phase of Interphase, proteins organize themselves to form a series of fibers called
spindles, which assist chromosome movement during mitosis. The spindle is constructed from
amino acids for each mitotic division, and then taken apart at the conclusion of the process.
Mitosis
During mitosis, the nuclear material becomes visible as threadlike chromosomes. The chromosomes
organize in the center of the cell, and then they separate, and 46 chromosomes move into each new cell
that forms.
Mitosis is a continuous process, but for convenience in denoting which portion of the process is taking
place, scientists divide mitosis into a series of phases: prophase, metaphase, anaphase, telophase.
1. Prophase: Mitosis begins with the condensation of the chromosomes to form visible threads in
the phase called prophase. Two copies of each chromosome exist; each one is a chromatid. Two
chromatids are joined to one another at a region called the centromere. As prophase unfolds,
the chromatids become visible in pairs, the spindle fibers form, and the nuclear envelope
dissolves.
2. Metaphase: Metaphase is the stage of mitosis in which chromosomes line up on the equatorial
plate or equator.
3. Anaphase: At the beginning of anaphase, the chromatids move apart from one another. Each
chromosome is attached to a spindle fiber, and each half of the chromosomes are drawn to
opposite poles of the cell by the spindle fibers.
4. Telophase: In telophase, the chromosomes finally arrive at the opposite poles of the cell. The
distinct chromosomes begin to fade from sight as masses of chromatin are formed again. The
events of telophase are essentially the reverse of those in prophase. The spindle is dismantled
and its amino acids are recycled and the nuclear envelope is reformed.
Cytokinesis: Cytokinesis is the process in which the cytoplasm divides and two separate cells form.
In animal cells, cytokinesis begins with the formation of a furrow in the center of the cell. With the
formation of the furrow, the cell membrane begins to pinch into the cytoplasm, and the formation of
two cells begins.
In plant cells, cytokinesis occurs by a different process because a rigid cell wall is involved.
Cleavage does not take place in plant cells. Rather, a new cell wall is assembled at the center of
the cell which we call the cell plate. The cell plate separates the two daughter cells.
THE PURPOSE: Mitosis serves
several functions in living cells.
In many simple organisms, it is
the method for asexual
reproduction (for example, a
bacterium divides into two during
Binary fission). In multicellular
organisms, mitosis allows the
entire organism to grow by
forming new cells and replacing
older cells. In certain species,
mitosis is used to heal wounds or
regenerate body parts. It is the
universal process for making new
cells!
Show what you know (mitosis):
1. Put the following stages of mitosis (cell division) in order and
label each stage.
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2. Not including cell division, what are the other phases of the
cell cycle? Name them in sequence.
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3.
What happens during cytokinesis? Is it a part of Mitosis?
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Classifying
On the line provided, label each event with one of the four phases
of mitosis in which it occurs. A phase may be used more than once.
5. The chromosomes line up across the middle of the cell.
6. Chromosomes become visible.
7. Centrioles separate.
8. Sister chromatids separate into individual chromosomes.
9. Two new nuclear envelopes form.
10. The nucleolus disappears and the nuclear envelope
breaks down.
11. Each chromosome is connected to a spindle fiber.
12. The individual chromosomes move apart.
Comparing and Contrasting How does cell division differ in a plant cell versus an animal cell?
The cell in the diagram below illustrates a stage of mitotic cell division. Base your answers
to questions 13-15 on the diagram.
13. What is indicated by letter B?
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14. What is indicated by the dashed lines? ___________________________
15. How do these structures work together during mitosis and why is their
job so important? _______________________________________________
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16. Explain the relationship between replication and cellular division. Be sure to address how these
processes affect the survival of organisms.
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