Cellular reproduction depends on the cell cycle
• “All cells come from preexisting cells.”
8-1
8-2
8.1 Cellular reproduction depends on the cell
cycle
• Cell cycle:
– Interphase, G1 or G0, S – DNA synthesis, G2 – preparation
for division, M-phase/division, and cytokinesis
8-3
Figure 8.1C
8-4
The Cell Cycle and Chromosomes
A. The cell cycle can be divided
into two main parts: 1)
Interphase and 2) Cell division
1. Cells spend most of their
lives in interphase—growing (G1),
S phase, and G2 (preparing for
division).
http://www.cellsalive.com/cell_cycle.htm
The Cell Cycle and Chromosomes
http://www.cellsalive.com/cell_cycle.htm
a. Cells that do not “plan” on
dividing go into a stalled state
called G0 (gap 0)-examplebrain neurons & muscle cells
Some cells will stay in G0
until they need to divideexample-white blood cells
The Cell Cycle and Chromosomes
b. Cells replicate/copy
their DNA during S phase
(DNA synthesis). Why?
Duplicate DNA is needed
because the cell nucleus is
divided and each new cell
needs a complete set.
The Cell Cycle and Chromosomes
c. G2 –Cells prepare for division
1-by growing more
2- by repairing DNA damaged
during replication/S phase.
3-Producing proteins that control
when the cell enters mitosis.
4-IF the cell has too much damaged
DNA or isn’t functioning correctly, it
will be “killed” off (apoptosis) by a
protein called p53—division will
never occur in these cells.
http://www.bioinformatics.org/p53/introduction.html
Loose chromosomes
• During interphase and early
prophase notice-DNA forms
long stranded chromosomes,
but still is not in condensed
chromosome form. Why?
• It would be much harder to
correct DNA duplication errors
if it was condensed and
wrapped around histones and
protein synthesis could not
occur during G2.
Extremely condensed
and shortened during
later mitosis stages
2. Cell Division is an important function performed by
cells after their “growth or G1 and G2” phases
-Permits growth and repair
-Is necessary for the zygote (fertilized egg) to develop into
a newborn
For example, skin cells need
to divide frequently to
provide a protective layer
for our body.
B. Draw and label the cell
cycle (be sure to include the
two main parts: interphase
and cell division):
II. DNA and Chromosomes-After Gap 1
and S phase of interphase, DNA forms
chromosomes
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II. DNA and Chromosomes
A. In prokaryotic cells, DNA is located in the cytoplasm.
1. Most prokaryotes have a single DNA
molecule/chromosome containing most of the cell’s
genetic information.
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2. Prokaryotes have “extra” circular pieces of DNA
called “plasmids”. Fill in the term plasmid in your
bacterial cell diagram on your notes.
tic cells also have “extra” circular pieces of
DNA called “plasmids” that function and
replicate independent of the cell’s main
DNA or may become a part of the main
DNA. Label the “plasmid DNA” on the
prokaryote diagram:
II. DNA and Chromosomes
B. A picture of
chromosomes during
meiosis is called a
karyotype. A karyotype
can be used to
determine genetic
abnormalities.
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II. DNA and Chromosomes
C. Many eukaryotes have 1000
times the amount of DNA as
prokaryotes.
1. Eukaryotic DNA is stored as
chromatin in the nucleus.
DNA chromatin forms
chromosomes during cell
division.
2. The number of
chromosomes varies widely
from one species to
another.
II. DNA and Chromosomes
C. Many eukaryotes have 1000 times the amount of
•
DNA as prokaryotes.
3. Most species have 2 sets of chromosomes-one
from each parent (humans have 23 pairs for a
total of 46 chromosomes).
a. Species with 2 genders (humans) have 2
sex chromosomes that don’t match (X,Y). So,
the total matching homologous pairs for
humans is really only 22.
b. The chromosomes that are homologous
are called autosomes. Humans have 44
autosomal chromosomes and 2 sex
chromosomes.
4. Cells with a copy of chromosomes from each
parent are called Diploid or 2n
– Pairs of chromosomes
– The diploid number of chromosomes for humans is 46
•
Haploid or n cells only contain half from each parent
– Unpaired chromosomes
– The haploid number of chromosomes for humans is 23
D. Chromosome Structure
1. Eukaryotic chromosomes contain DNA and protein, tightly packed
together to form chromatin.
a. Chromatin consists of DNA tightly coiled around proteins called
histones.
b. DNA and histone molecules form nucleosomes.
c. Nucleosomes pack together, forming a thick fiber.
d. Each cell contains about 2 meters worth of DNA, a single person
as enough DNA to stretch from the Earth to the Sun more than
400 times. (150 billion meters)
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Chromatin vs. Chromosome
Chromatin
Chromosomes
Unwound DNA
Found throughout
interphase of cell cycle
DNA is being used for
protein synthesis (strands
are more accessible)
Tightly packaged/condensed
DNA
Condensed form only during
cell division after replication
DNA is not being used for
protein synthesis
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8.3 Mitosis has a set series of phases
PMAT-memorize an mnemonic  Please make
me a taco
• Mitosis phases:
– Prophase
– Metaphase
– Anaphase
– Telophase
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Figure 8.3A
8-21
Figure 8.3A
continued
8-22
Cytokinesis: Division of Cytoplasm
8-23
8.4 Cytokinesis follows mitosis
• Cytokinesis –
division of
cytoplasm
– Follows mitosis in
most cells
8-24
Cell Cycle Control and Cancer
8-25
8.5 Cell cycle control depends on checkpoints
• In order for the body to remain healthy, the cell
cycle must be controlled.
• G1, S, G2, and M stages occur in order and only
when the previous stage has been successfully
completed.
• Checkpoints can delay the cycle until all is well.
– G1 checkpoint
• Apoptosis (programmed cell death) may be signaled.
– G2 checkpoint
– M checkpoint
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Figure 8.5
8-27
8.6 Cancer cells are distinctly abnormal
• Development of cancer
– Mutations (DNA changes) due to environmental
assaults can result in abnormal growth of cells and
eventually cancer.
– Any tissue with a high rate of cell division is more
susceptible to carcinogenesis (development of
cancer).
– Characteristics of cancer cells:
•
•
•
•
Lack differentiation
Have abnormal nuclei
Form tumors
Undergo angiogenesis and metastasis
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Figure 8.6
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HOW BIOLOGY IMPACTS OUR LIVES
8C Protective Behaviors and Diet Help Prevent
Cancer
• Protective behaviors:
–
–
–
–
–
–
Don’t smoke.
Use sunscreen.
Avoid radiation.
Be tested for cancer.
Be aware of occupational hazards.
Carefully consider hormonal therapy.
• Right diet:
–
–
–
–
–
Increase consumption of foods rich in vitamins A and C.
Limit consumption of salt-cured, smoked, or nitrite-cured foods.
Include vegetables from the cabbage family in the diet.
Be moderate in the consumption of alcohol.
Maintain a healthy weight.
8-30
Connecting the Concepts:
Chapter 8
• All cells receive DNA from preexisting cells
through the process of cell division.
• The cell cycle has checkpoints that determine if
the DNA is normal and capable of functioning
properly.
• Mitosis is part of the cell cycle, and there are
negative consequences if the cell cycle comes out
of synchronization.
• Separation of the chromatids during mitosis
ensures that daughter nuclei have the same
number of chromosomes as the parent cell.
8-31
Cell Cycle and Chromosomes
Name that species!
Instructions: Groups of two students will be assigned a random species. You will need to
find the answers from ch. 5.2 (p. 138-139) and ch. 6.1 (p. 168) and from the species
information provided on your handout.
1.
What are chromosomes and how many does your species have (notes and p.
138)?
2.
Explain Fig. 5-5 in terms of size---when is DNA most visible? Arrange the DNA
descriptions from least visible to most visible (there are 5 headings/descriptions to
arrange).
3.
Is your species a eukaryotic organism or prokaryote? If it is a prokaryote, how is the
DNA/chromosome different from eukaryotes? (p. 556)
4.
Draw and label an example chromosome of your species (see figure 5.5)
5.
6.1 (p. 168) What are sex chromosomes and How many sex chromosomes do most
organisms have?
6.
What are autosomes and how many does your organism have?
7.
What are homologous chromosomes and how many does your organism have?
8.
What is the difference between diploid and haploid cells? Which cells of most
organisms are diploid? Which are haploid? Why?
9.
Be ready to present your findings.