Download unit vi – cell cycle

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Test Date ______________
UNIT VI – CELL CYCLE
The third statement of the Cell Theory states that all cells come from ____________________________. The continuity of life is based on
the reproduction of cells or __________________________________. In most organisms, cells increase to a certain size and then divide
into two cells. This cycle of growth and cell division is known as the ________________________. The cell cycle is defined as the period
of time from the beginning of one __________________________ to the _______________________________________. This type of
cell division is __________________________ reproduction. In asexual reproduction, the genome, or total endowment of ___________ of
the cell is exactly replicated resulting in ____________________________________.
I. IMPORTANCE OF ASEXUAL REPRODUCTION
A. Single-celled Organisms
Single-celled organisms belonging to kingdoms _____________________________, ________________________________,
_____________________, and ___________________, use asexual reproduction to _________________________________.
B. Multicellular Organisms
1. Growth & Development - Organisms grow through _____________________________, rather than unlimited growth of a cell.
 Surface Area to Volume Ratio – As the size of an object increases, the ____________________ increases at a much faster
rate than the ________________; therefore, the surface area to volume ratio becomes a _____________________ number.
 In a cell, the ______________________________ represents the surface area and the ______________________________
represents the volume. At a certain point, a cell can no longer meets its needs and maintain _________________________;
therefore, cells only grow to a certain size.
2. Renewal & Repair -Cell division is used to replace cells that die from normal wear & tear; for example, ____________________
and _____________________________. Other types of cells maintain the ability to divide, but keep it in reserve unless severely
damaged; for example, ________________________________. Other cells do not appear to divide at all in a mature human; for
example, ________________________________ & ______________________________________.
II. CELL CYCLE IN PROKARYOTES
All ____________________ undergo a type of cell division known as ________________________. Binary fission is a less complex,
faster process than eukaryotic cell division because bacteria lack a _____________________, _______________________________
and have only ____________ chromosome. Draw in the appearance of the DNA during binary fission.
III. CELL CYCLE IN EUKARYOTES - AN OVERVIEW
There are two main parts to the eukaryotic cell cycle:
A. Interphase - Accounts for about ________ of cell cycle.
This is the period of time in which a cell is carrying out
__________________________________________,
__________________________________________.
_________________________________ synthesis is
occurring at a high rate. The cell’s DNA is in the form of
_________________________, long, fine strands of DNA
wrapped in __________________________________.
B. M-Phase – Period of time in which cell division occurs.
Consists of two main events:
 Mitosis – Division of the
______________________________________

Cytokinesis – Division of the
______________________________________
IV. A CLOSER LOOK AT INTERPHASE
There are three stages to interphase:
1. G1 - Cell grows, carries out normal cell activities such as ___________________________________________. Organelles are
replaced if needed. ____________________________ production is very high.
2. S - ____________________. Replication of _____________ takes place. Known as the “Point of No Return”. Replication takes
place in the ____________________________ of the cell.
3. G2 - Preparation for _________________________. _______________________ and _____________________________ are
replicated.
Cell at the END of interphase…
Protein microtubules that
will form spindle fibers
Cell membrane
Nuclear envelope
Chromatin
Centrioles (replicated)
1. ____________________ has been replicated – still in
chromatin form.
2. ________________________ have been replicated in
______________________ cells only. This replication
results in 2 pairs of centrioles, composed
of ________________________________________.
3. The ________________________________________
and __________________________________ are still
present.
V. A CLOSER LOOK AT MITOSIS
Mitosis, also known as the _________________________, is described in four stages, but it is a continuous process.
1. PROPHASE – This is the ___________________________ phase of ___________________________.
Microtubules form Spindle fibers –
some are kinetochore and some are
non-kinetochore microtubules
Sister chromatids attach
at the centromere
Centrioles
Nuclear envelope disintegrates
1. __________________ and ____________________
_______________________________ disassemble.
2. Replicated DNA thickens & condenses  results in
__________________________________ made up
of 2 ___________________________________held
together by the _____________________________.
3. _____________________________________ begin
moving to opposite sides of the cell.
4. _____________________________extend to form
Spindle fibers from centriole to centriole. Some of
these fibers, known as kinetochore microtubules,
begin to attach at the kinetochore of each chromatid.
(located at the centromere). Other fibers, known as
non-kinetochore microtubules span the cell to aid
in support and structure.
2. METAPHASE – This is the _________________ phase of mitosis.
Kinetochore microtubules
1. __________________________________________
network is fully formed with ____________________
at opposite ends.
2. Each ___________________________________ is
Attached by their kinetochore (at the centromere) to a
spindle fiber from each pole.
3. Sister chromatids align in ______________________
(middle)__ of cell.
Centrioles
Spindle fiber network
Sister
chromatids
3. ANAPHASE
Centromeres
Kinetochore microtubules
Non-kinetochore microtubules
4. TELOPHASE – By the end of telophase . . .
Chromosomes
uncoil to
Chromatin
1. _________________________________ split.
2. Sister ________________________ are pulled
apart by _kinetochore microtubules_ to
opposite ends of the cell.
3. Genetic material is now known as daughter
_____________________________________.
4. Cell is elongating; preparing for two new nuclei.
1. Complete set of ____________________________ at each pole of
the cell.
2. __________________________________ _ disassemble.
3. New ______________________________________ forms around
nucleus.
4. _chromosomes_ uncoil  ______________________________.
5. _nucleolus_ reforms  _____________________________ are
produced ____________________________ synthesis resumes
 cell ______________________________________ resumes
Nuclear envelope reforms
5. CYTOKINESIS – This is the final step, which begins during __________________________. Cytokinesis differs in plant and animal
cells because plant cells have a ______________________________.
a. Animal Cell – In the final stages of telophase, the ___________________________________________ pinches in. This is
referred to as a _________________________________. This cleavage furrow deepens until the parent cell is pinched in two,
producing two separate, identical ________________________________________.
b. Plant Cell – There is no cleavage furrow in plant cells. Instead, during late telophase, ______________________ from the Golgi
apparatus move to the center of the cell where cellulose and other materials they contain come together to form a
___________________________________
VI. CONTROL OF THE CELL CYCLE
A. Timing of the Cell Cycle
The timing of the cell cycle is regulated by proteins known as ____________________________ that bind with enzymes known as
_____________________ to form a complex called ______________________________________ or ______________. These
______________________________ are responsible for monitoring checkpoints in the cell cycle.
 If the progression of the cell cycle is too slow, ____________________________________________________________.
 If the cell cycle progresses too quickly, the result is uncontrolled cell growth or _________________________. This is harmful
for many reasons
o If a cell spends all of its time dividing, _________________________________________________
o The rapidly- dividing, nonfunctional cells steal __________________________________ from healthy, functioning cells
causing ____________________________________.
o The rapid replication of _________________________ results in a greater risk of __________________________.
B. Stem Cells
Stem cells are ____________________________ cells that have the ability to _______________________________. Stem cells
that can give rise to many types of cells are said to be ___________________________. Although stem cells are found in certain
locations in adults, most research involves the use of _________________________________ stem cells, due to the fact they are
considered to be “_________________________” and capable of unlimited specialization. Scientists hope that stem cells may be
used as implants to replace __________________________________________, but there are many ___________________ and
______________________________ concerns.
C. Number of Cell Divisions per Cell
Each cell is programmed to divide a certain number of times, and then it will not divide again. This is monitored by
_______________________, a series of DNA ________________________ found at the tips of each ______________________.
As DNA is ________________________ in _________ of the cell cycle, the telomeres shorten. Once they reach a critical length,
the DNA does not replicate again, and the cell does not __________________. _____________________ and ______________
produce an enzyme known as _______________________, which restores the chromosomes back to their original length, thereby
theoretically making the cell capable of ___________________________________ cell division.