Unit 5 Study Guide
Cell Cycle
Name _________________________________________
1. I can describe the stages of the cell cycle.
pg. 1
Test Date: ________________
Interphase = period in between division
G1 = growth phase
S = DNA replication
G2 = Preparation for division (extra copies of
organelles are made, etc.)
M Phase = Cell Division
Mitosis = Division of the Nucleus:
(Prophase  Metaphase  Anaphase  Telophase)
Cytokinesis = Division of the Cytoplasm
NOTE: Cytokinesis is different in a plant cell vs. an animal cell
because of the cell wall. Animal cells form a cleavage furrow
(cell membrane pinches in) whereas plant cells form a cell plate
(the beginning foundation of a cell wall)
Mitosis is nuclear division plus cytokinesis, and produces
two identical daughter cells during prophase,
prometaphase, metaphase, anaphase, and telophase.
Interphase is often included in discussions of mitosis, but
interphase is technically not part of mitosis, but rather
encompasses stages G1, S, and G2 of the cell cycle.
2. I can describe the structure and function of DNA.
DNA is deoxyribonucleic acid. It is the genetic code because it
transmits the information needed to build proteins for the cell.
Each section of DNA that codes for a protein is called a gene.
DNA wrapped around histones (a type of protein) is called
Chromatin. A Chromosome is made up of 2 identical sister
chromatids (produced during DNA replication) made of
chromatin. Chromatin is DNA that is tightly wound around
histones. The DNA exists as unraveled Chromatin during most
of the cell cycle. It only condenses to form Chromosomes
during cell division.
Unit 5 Study Guide
Cell Cycle
Name _________________________________________
pg. 2
Test Date: ________________
DNA is a double helix. This means it is a double-stranded molecule that is twisted like a spiral staircase.
A DNA molecule is made of monomers (subunits) called nucleotides. Each nucleotide contains a
phosphate group, a sugar (deoxyribose), and 1 of 4 nitrogenous bases (Guanine, Adenine, Cytosine, or
Thymine). These nucleotides align so that the sugar and phosphate groups make up the side
(backbone) and alternate (S – P – S – P – S – P). Strong phosphodiester (covalent) bonds hold the
phosphates and sugars together. The nitrogen bases are perpendicular to the sugar and form the
“rungs” of the ladder. The nitrogen bases form hydrogen bonds with the complimentary strand of DNA
in order to hold the separate strands of the double helix together.
The Rule of Base Pairing states that Adenine only
bonds with Thymine (A = T) and Guanine only
bonds with Cytosine (G = C).
Guanine and Adenine are purines, which means
that they have a double-ringed structure. Cytosine
and Thymine are pyrimidines, which means that
they have a single-ringed structure. A pyrimidine
(C or T) always bonds with a purine (G or A). The
DNA strands run antiparallel to each other, which
means that the strands are facing opposite
directions. This means that one strand has the 5’
end of the sugar at the “top” of the molecule and
the other strand has the 3’ end of the sugar at the
top. Hydrogen bonds form to create the twisted
structure of DNA.
Additional Resource: http://www.dnalc.org/view/15524-Explaining-the-DNA-structure-3D-animationwith-basic-narration.html or http://tinyurl.com/7xk2w7q
Unit 5 Study Guide
Cell Cycle
pg. 3
Name _________________________________________
Test Date: ________________
3. I can explain how DNA is replicated.
DNA is replicated during S phase of the cell cycle. The DNA is unwound and replicated in sections called
replication bubbles; multiple
replication bubbles occur
simultaneously in order to speed
up the process. Replication is
finished when all of the bubbles
connect forming two complete
identical copies.
The process begins at the Point
of Origin and proceeds in both directions to form the bubble.
• GETTING STARTED = Helicase breaks the hydrogen bonds
between the strands and unwinds and separates the 2 DNA
strands. Where Helicase is breaking bonds is called the
Replication Fork. One strand begins with the 5’ end of the sugar
(5’ to 3’ = Lagging Strand). The other strand begins with the 3’
end of the sugar (3’ to 5’ = Leading Strand). Single-Strand
Binding proteins attach to the DNA strands to keep the strands
from twisting. Topoisomerase (another protein) attaches to the
strands to relieve stress and keep the strands from breaking
during replication.
• LAYING THE FOUNDATION = DNA nucleotides cannot bond to “empty” space, so an RNA Primer is used.
Primase is the enzyme responsible for adding the RNA Primer. Primase attaches a short sequence of
complementary RNA nucleotides to the original strand. Primase adds one RNA primer at the Point of Origin on
the Leading Strand (3’ – 5’). Primase has to add multiple RNA Primers on the Lagging Strand (5’ – 3’).
• ADDING DNA NUCLEOTIDES = DNA polymerase III is the main enzyme responsible for replication. DNA
polymerase III adds DNA nucleotides to the RNA Primer. DNA polymerase III can only move 3’ to 5’ on the
original strand. This means that the NEW strand is built in the opposite direction (5’ to 3’). The Leading Strand
(3’ – 5’) is built continuously. DNA polymerase makes one long strand of complementary DNA. Because DNA
polymerase can only move 3’ to 5’, the Lagging Strand is built DISCONTINUOUSLY. Many RNA Primers are laid
and DNA polymerase III works from primer to primer. These short segments are called Okazaki Fragments.
Another enzyme, DNA polymerase I, removes the RNA primer and replaces it with DNA nucleotides. Next, the
enzyme DNA Ligase seals the gap between these fragments by adding a phosphodiester bond.
• PROOFREADING = DNA polymerase II proofreads and corrects mistakes, which are called mutations.
RESULT = DNA replication results in 2 identical molecules of DNA, each with one new strand and one original
strand. Because only one new strand is made for each molecule, it is called Semi-Conservative replication.
DNA polymerase adds complimentary
nucleotides to build the new strands of
DNA. It also proofreads the DNA for
mutations (mistakes).
G=C, A=T (complimentary nucleotides)
Unit 5 Study Guide
Cell Cycle
pg. 4
Name _________________________________________
Test Date: ________________
4. I can explain what occurs during each phase of mitosis. This means that I can tell the difference between
prophase, metaphase, anaphase, and telophase.
Prophase = SET UP: Chromatin in the nucleus begins to
condense and becomes visible in the light microscope as
Spindle
forms;
nuclear
membrane
chromosomes. The
nucleolus
disappears.
Centrioles
begin
disappears
moving to opposite
ends of the cell and fibers extend from
the centromeres. Some fibers cross the cell to form the
mitotic spindle. Late Prophase = The nuclear membrane
dissolves, marking the beginning of late prophase
(sometimes called prometaphase). Proteins attach to the
centromeres creating the kinetochores. Microtubules attach
at the kinetochores and the chromosomes begin moving.
Metaphase = MIDDLE: Spindle fibers align the chromosomes
along the middle of the cell nucleus. This line is referred to as
the metaphase plate. This organization helps to ensure that
in the next phase, when the chromosomes are separated,
each new nucleus will receive one copy of each chromosome.
Anaphase = APART: The paired chromosomes separate at
the kinetochores and move to opposite sides of the cell.
Motion results from a combination of kinetochore movement
along the spindle microtubules and through the physical
interaction of polar microtubules.
TELOPHASE = TWO NUCLEI: Chromatids arrive at opposite poles of cell, and new membranes form around the
Spindle breaks down; nuclear membrane reappears;
daughter nuclei. The chromosomes disperse and are no longer visible under the light microscope. The spindle
chromosomes
unwind
into
fibers disperse, and cytokinesis
or the partitioning
of the cell
maychromatin
also begin during this stage.
5. I can explain why DNA replication is important for the cell cycle.
DNA replication is important because it ensures that EVERY cell that is
produced through Mitosis has an exact copy of all of the original DNA.
Because the original DNA molecule is used as a template (rule of base
pairing), 2 identical molecules of DNA are produced through Mitosis.
Both copies of the DNA molecule have an original strand and a new
strand that was built following the rule of base pairing (A = T; G = C). This
means that all cells in the organism will have the same DNA, therefore
the same instructions for making proteins.
Unit 5 Study Guide
Cell Cycle
pg. 5
Name _________________________________________
Test Date: ________________
6. I can identify and label the phase of mitosis given a diagram, model, or using a microscope.
Unit 5 Study Guide
Cell Cycle
Name _________________________________________
pg. 6
Test Date: ________________