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Chapter 8
Cellular Reproduction
Cells from Cells
Part 1 - Mitosis
Bellwork Week 14 – November 9th
1. Why can’t we all be just one giant cell? In other words why do
cells have to divide?
2. Which of the following facts interests you most and why?
Cell Size Limitations
1. Diffusion limits cell size (REVIEW!)
Slow and inefficient over large areas
2. Surface area to volume ratio limits cell size (NEW!)
Volume increases faster than surface area
Requires more nutrients, get rid of more wastes
but through a relatively smaller surface area –
it is more difficult for things to get in and out!
3. DNA limits cell size (NEW!)
Limit to how quickly DNA can be read
Limit to # of proteins built / period of time.
Surface to Volume Ratio
Remember the cell races?
This explains why some teams did well and others did not...
Question
Which of these has the best ratio of
surface to cell volume?
What Cell Reproduction Accomplishes
• Reproduction
– Is defined as the birth of new organisms.
– Occurs much more often at the cellular level.
– Cell Division has roles in:
• The replacement of lost or damaged cells.
• Cell reproduction and growth.
Passing On Genes from Cell to Cell
• Before a parent cell divides, it duplicates its
chromosomes.
• The two resulting “daughter” cells are
genetically identical.
The Reproduction of Organisms
Asexual in Single Celled Organisms
• In asexual reproduction, single-celled
organisms reproduce by simple cell division.
Hydra Budding
The Reproduction of Organisms
Asexual in Multicellular Organisms
– Some multicellular organisms can divide into
pieces that then grow into new individuals.
The Reproduction of Organisms
Sexual Reproduction
• Sexual reproduction is different.
– It requires fertilization of an egg by a sperm.
– Production of egg and sperm is called
meiosis. We will discuss this later in the
PowerPoint.
Remember Cell Theory?
– Last last part of cell theory states that all cells
in the world today come from preexisting cells.
How does this happen?
The Cell Cycle
The Cell Cycle and Mitosis
• Almost all of the genes of a eukaryotic cell
– Are located on chromosomes in the cell
nucleus.
– Let’s look at Chromosomes before we start
on our discussion of the cell cycle…
Eukaryotic Chromosomes
• Each eukaryotic chromosome contains one
very long DNA molecule,
– Typically bearing thousands of genes.
• The number of chromosomes in a eukaryotic
cell
– Depends on the species.
Chromosomes
– Note that the number of
chromosomes has no
bearing on the
complexity of an
organism.
– Ophioglossum
reticulatum, a species
of fern, has the largest
number of
chromosomes with
more than1,260!!
How many pairs of chromosomes do humans have?
Chromosomes
– Are made of chromatin, a combination of
DNA and protein molecules.
– Are not visible in a cell until cell division
occurs.
Chromosomes
• The DNA in a cell is
packed into an
elaborate, multilevel
system of coiling and
folding.
• Note: We will discuss
the details of protein
synthesis in a later
chapter.
DNA Packing
Chromosomes
• Before a cell divides, it
duplicates all of its
chromosomes, resulting in two
copies called sister chromatids.
• When the cell divides, the sister
chromatids separate from each
other.
Can You Memorize This Word?
InProMATeC
Keep this word in mind for helping you to
remember all phases of the cell cycle.
The Cell Cycle
• Eukaryotic cells that divide undergo an orderly
sequence of events called the cell cycle.
• The cell cycle consists of two distinct phases:
1. Interphase
2. Mitotic phase
The Cell Cycle
The Cell Cycle
Interphase
• G1: Growth…
• S: Copy the DNA...
• G2: Growth…
Mitosis & Cytokinesis
• Process which forms
two daughter cells.
Mitosis Overview
Interphase
• “Normal time”
• Cells spend MOST of their
time in this phase
• NOT part of mitosis!
Plant Cell
Animal Cell
Late Interphase
Mitosis and Cytokinesis
• Mitosis
– Is the division of the chromosomes.
– Is preceded by interphase.
Mitosis (All Phases)
Animal Mitosis
Sea Urchin (time lapse)
Phases of Mitosis
• Mitosis consists of four distinct phases:
1. Prophase
Prophase
Prometaphase
2. Metaphase
Metaphase
3. Anaphase
Anaphase
1. Telophase
Telophase
Step 1: Prophase
• Two halves called sister
chromatids
• Center region called
centromere
• Nucleus disappears
• Centrioles migrate to
opposite poles
• Spindle fibers made of
microtubules form
between centrioles
Step 2: Metaphase
• Chromosomes line up
• Chromosomes attached to spindle
fibers at centromeres
• Pulled to middle (equator) by
spindle fibers
• Each sister chromatid has own fiber
Step 3: Anaphase
• Chromosomes begin to
pull apart
Step 4: Telophase
•Chromosomes at opposite ends
•Reverse of Prophase
•Nucleus reforms
•Chromosomes unwind into chromatin
•Spindle breaks down
•Nucleolus reappears
Cytokinesis
• Typically occurs during
telophase.
• Is the division of the
cytoplasm.
• Is different in plant and
animal cells due to the
presence of a cell wall
in plants
• Animal cell to the right.
Cytokinesis
Cytokinesis in Plants
Figure 8.9b
Control of the Cell Cycle
Cellular Reproduction
Cells from Cells
Part 2 - Cancer
Cancer Cells
Growing Out of Control
• Normal plant and animal cells have a
cell cycle control system.
• Proteins called Cyclins interact with
enzymes to become activated
• These proteins control the cell cycle
What Is Cancer?
• Cancer can be defined as a malignant growth
resulting from uncontrolled cell division.
• Cancer is a disease of the cell cycle.
• Cancer cells do not respond normally to the cell
cycle control system.
• It is caused by a change in one or more genes
that produce Cyclins
• 2nd leading cause of death in US
• Affects any tissue in body
What Is Cancer?
• Cancer cells can form tumors,
– Abnormally growing masses of body cells.
• If a tumor is malignant,
– It can spread to other parts of the body.
What Is Cancer?
Figure 8.10
Causes of Cancer
• Environmental Conditions (carcinogens)
–
Affect Genes: segment of DNA responsible for production of
a protein
–
Failure to produce enzymes
–
Overproduction of enzymes
• Viral Infection
Some of the Many Cancers
Caused By Smoking
Some Cancers Associated With
Smoking Cigarettes
1.
Lung Cancer
7.
Stomach Cancer
2.
Head and Neck Cancer
8.
Bladder Cancer
3.
Mouth Cancer
9.
Cervical Cancer
4.
Esophageal Cancer and
Throat Cancer
10.
Breast Cancer
11.
Kidney Cancer
12.
Myeloid Leukemia
13.
Liver cancer
5.
Pancreatic Cancer
6.
Colorectal Cancer
Encyclopedia of Cancer by R.N. Tamara L. Brown
http://www.ash.org.uk/html/factsheets/html/fact04.html
Chemicals Included In
Tobacco Smoke
Cancer Prevention and Survival
• Cancer prevention includes changes in
lifestyle:
– Not smoking
– Exercising adequately
– Avoiding exposure to the sun
– Eating a high-fiber, low-fat diet
– Visiting the doctor regularly
– Performing regular self-examinations
Cancer Treatment
• Cancer treatment can involve
– Radiation therapy, which damages DNA and
disrupts cell division.
– Chemotherapy, which uses drugs that disrupt
cell division.
Cancer Treatment
• Cancer cells are often grown in culture for
study.
CHAPTER 8
Cellular Reproduction
Cells from Cells
Part 3 - Meiosis
Biology and Society: A $50,000 Egg!
• A few years ago, a sterile couple was willing to
pay $50,000 to a woman willing to donate her
eggs.
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings
Infertility
– Affects one in ten American couples.
•
In vitro fertilization (IVF) can help infertile
couples.
–
A sperm and an egg are joined in a petri
dish.
–
The embryo is implanted into the mother’s
uterus.
–
IVF is one of many reproductive
technologies.
Meiosis
The Basis of Sexual Reproduction
• Sexual reproduction depends on
– Meiosis.
– Fertilization.
Vocabulary
• Genes: Segments
of DNA on a
chromosome
• Code for a trait
Hair
Color
Eye
Color
Homologous Chromosomes
• Chromosomes for the same
trait, such as seed shape.
• Memory trick remember that
“homo” means same.
• Note, it does NOT mean that the
genes are identical, just that they
code for the same trait. So you
can have a gene for wrinkled
and a gene for smooth for
example, but both are genes for
seed texture.
Question
Every person has two chromosomes for each
trait. Where does each one come from?
Answer
One comes from the mother and the other from
the father
Homologous Chromosomes
Different organisms of the same species have
the same number and types of chromosomes.
Homologous
Chromosomes
are the sets of
each pair
1 half of the pair is from
the mother
1 half of the pair is from
the father
Humans=
23 pairs or 46 total
• A karyotype is an orderly arrangement of
chromosomes.
• Homologous chromosomes are matching pairs
of chromosomes.
Somatic Cell
• A somatic cell
– Is a typical human body cell.
– Has 46 chromosomes.
Sex Chromosomes
• Humans have
– Two different sex chromosomes, X and Y.
– Twenty-two pairs of matching chromosomes,
called autosomes.
Diploid
•A cell with TWO of each kind of chromosome.
• One from each parent
• Abbreviated 2n
•Memory trick: remember that “di” means two.
– Humans are diploid organisms.
• Their cells contain two sets of chromosomes.
• Their gametes are haploid, having only one
set of chromosomes.
Haploid
•A cell has half the normal number of
chromosomes, or one of each kind.
•Abbreviated n
•Memory trick: “ha” sounds a lot like
“half”
•Gametes are halploid
• Sperm & Eggs in humans
Gametes and the Life Cycle of a
Sexual Organism
• The life cycle of a multicellular organism is the
sequence of stages leading from the adults of
one generation to the adults of the next.
Figure 8.14
• Fertilization
– Is the fusion of sperm and egg.
– Creates a zygote, or fertilized egg.
• Sexual life cycles involve an alternation of
diploid and haploid stages.
Meiosis – Creating Gametes
The Process of Meiosis
• In meiosis,
– Haploid daughter cells are produced in diploid
organisms.
– Two consecutive divisions occur, meiosis I and
meiosis II, preceded by interphase.
– Crossing over occurs.
Meiosis Overview
Telophase I and Cytokinesis
Interphase
Prophase II
Prophase I
Metaphase II
Metaphase I
Anaphase II
Anaphase I
Telophase II and Cytokinesis
Figure 8.16.1
Figure 8.16.2
Figure 8.16.3
Comparing Mitosis and Meiosis
All the events
unique to
meiosis occur
during meiosis I.
Why do cells divide by Meiosis?
•To reduce
chromosome number
N egg
•Allows for
Chromosome Variety
N
Sperm
2N baby
Meiosis is how haploid gametes
are produced
•Mitosis = ASEXUAL reproduction
•Meiosis = SEXUAL reproduction
•Each gamete produced by meiosis is
genetically unique.
The Origins of Genetic Variation
• Offspring of sexual reproduction are
genetically different from their parents and
from one another.
Independent Assortment
of Chromosomes
• In independent assortment, every
chromosome pair orients independently of the
others during meiosis.
Genetic Variation
Random Fertilization
• The human egg cell is fertilized randomly by
one sperm, leading to genetic variety in the
zygote.
Crossing Over
• In crossing over,
– Homologous chromosomes exchange
genetic information.
– Genetic recombination occurs.
Crossing Over
Meiosis Provides Genetic Variation
7 pairs of chromosomes (Pea plant)
• 128 Possible sperm, 128 possible eggs
• 16,384 possible offspring
23 pairs of chromosomes (Human
• 8 million possible sperm, 8 million eggs
• 70 trillion different zygotes possible
When Meiosis Goes Awry
• What happens when errors occur in meiosis?
How Accidents During Meiosis
Can Alter Chromosome Number
• In nondisjunction,
– The members of a chromosome pair fail to
separate during anaphase.
– Gametes with an incorrect number of
chromosomes are produced.
• The result of nondisjunction
Down Syndrome
• Down Syndrome
– Is a condition where an individual has an
extra chromosome 21.
– Is also called trisomy 21.
• The incidence of Down Syndrome increases
with the age of the mother.
Abnormal Numbers of
Sex Chromosomes
• Nondisjunction
– Also affects the sex chromosomes.
Klinefelter’s XXY - Trisomy
•Male and female
characteristics
•Reduced fertility
Turner’s Syndrome X - Monosomy
XO sex chromosome
Instead of XX female
X
+
Empty
sperm
=
XO
Gene Linkage and Maps
Sometimes genes seem to be inherited
together
These genes lie very close on a
chromosome to each other – linked genes
Crossing over can separate these linked
genes – frequency of new gene
combinations help map genes
Evolution Connection
New Species from Errors
in Cell Division
• Errors in meiosis may have been instrumental
in the evolution of many species.
• Polyploids
– Are new species.
– Have more than two sets of homologous
chromosomes in each somatic cell.
Please take out the note card you were given
at the start of class. Please draw two
circles on each side of the card:
Mitosis
• Interphase

Pairs of Chromosomes
(one from each parent)
• Prophase
Each chromosome has replicated
(aka -chromatids – think “chromosome kids!”)

Meiosis
• Interphase
• Prophase 1
this time, the homologous pairs match-up
into a Tetrad
 (original and copy/original and copy)


Pairs of Chromosomes
(one from each parent)
Tumor-Busting Viruses
Current Issues in Biology, Volume 2
Scientific American
Tumor-Busting Viruses
Concept Review
• How can doctors kill cancer cells without harming healthy
ones? Such targeted treatment is one of the biggest
challenges in cancer care.
• This image shows how cancerous cells intermingle with
healthy ones. Melanoma, or skin cancer cells, are shown in
green amid healthy cells, shown in red.
Tumor-Busting Viruses
Concept Review
• A new answer may lie in virotherapy. This type of treatment
uses scientifically-engineered viruses to target cancer cells.
Tumor-Busting Viruses
Concept Review
• Some viruses, such as engineered adenoviruses, show
promise at selecting and destroying cancer cells.
• They kill tumor cells by invading through unique receptors
on the surface of cancer cells, and then burst the cells open
or make them more vulnerable to traditional chemotherapy.
Tumor-Busting Viruses
Concept Review
• Here are examples of cancer experiments involving
virotherapy.
Tumor-Busting Viruses
Concept Review
• But more research is needed to prevent engineered
adenovirus therapies from having dangerous side effects.
• Normal adenoviruses are common, causing illnesses such
as colds. Many people could have immune systems already
primed to fight adenoviruses, and suffer severe immune
reactions from engineered ones.
• In 1999, an 18-year-old patient died after suffering a severe
immune reaction in an adenovirus experiment.
Tumor-Busting Viruses
Testing Your Comprehension
What is virotherapy?
a)
b)
c)
d)
stimulating cancer tissue with sonic pulses
exposing patients to cold viruses to boost their immunity
applying engineered viruses to infect and kill cancer cells
putting patients in a pressure chamber during treatment
Tumor-Busting Viruses
Testing Your Comprehension
Which of these structures would you not find in a virus?
a)
b)
c)
d)
mitochondrion
ribosome
nucleus
all of the above
Tumor-Busting Viruses
Testing Your Comprehension
How do viruses selectively attach to target cells?
a)
b)
c)
d)
target cells display unique cell-surface receptors
target cells secrete unique identification proteins
viruses attach to specific materials engulfed by cells
viruses are not selective about target cells
Tumor-Busting Viruses
Testing Your Comprehension
What would be the purpose of giving patients immunosuppressive drugs during virotherapy with adenoviruses?
a)
b)
c)
d)
adenovirus can damage a normal immune system
to hold the immune system in reserve after therapy
to minimize side effects caused by immune response
none of the above is correct
Tumor-Busting Viruses
Biology and Society
If I were diagnosed with a deadly form of cancer, and were
offered the chance to join a virotherapy research trial, I’d be
willing to try this experimental therapy.
Strongly
Agree
A.
B.
C.
D.
E.
Strongly
Disagree
Tumor-Busting Viruses
Thinking about Science
What would be important medical safety steps to include in a
research trial studying whether a certain brain cancer could
be fought with engineered adenovirus?
Tumor-Busting Viruses
Interpreting Data and Graphs
Using this illustration
as a guide, describe
how an engineered
virus can infect and
kill a cancer cell,
while leaving a
healthy cell alone.