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DO ARE YOU READY? PAGE 554-555,
#1, 2, 3
Identify the cell
Cell wall structures shown in
Figure 1 and explain
Mitochondria the importance
or function of each.
Cell Membrane
Nucleus
Chromosome
2. (a) Organize the following structures from largest to smallest:
organ,chromosome,organism,nucleus,tissue, DNA molecule,cell,gene,
Smallest - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - > Largest
(b) Use the listed structures in (a) as labels for the diagram.
organ
cell
chromosome
diaper
organism
nucleus
gene
3. If a human muscle cell contains 46 chromosomes, indicate the
number of chromosomes that you would expect to find in the cells
shown in Figures 3, 4, 5, and 6.
46
23
23+23=46
23
5. Many single-cell organisms divide by a process called binary fission.
One cell divides into two cells identical to each other and identical
to the original cell. More complex organisms form specialized sex
cells. When sex cells combine from two different organisms, they
form a fertilized egg or zygote.
(a) Identify one advantage of binary fission as a means of
reproduction. faster, only one parent is needed, and
the offspring are the same as the parent.
(b) Identify and explain an advantage of reproduction by the union of
sex cells from different individuals.
New traits are possible; Each sex cell will have a different
combination of genes. Variation allows for adaptability to the
environment and, thus, greater survival.
7. Table 1 shows the events in a typical cell cycle. Draw and label
a circle graph to represent the data.
Rapid Growth
Grow & DNA
Replication
Prep. For
Division
Mitosis
ASEXUAL CELL REPRODUCTION
– Pg. 558 – Ch. 17.1
•Asexual reproduction:
• One cell divides to produce two cells
• Both cells are identical to each other
• Both cells are identical to the original
WHY DO CELLS NEED TO DIVIDE?
- EFFICIENCY: big cells are less efficient (lower sa/v ratio).
Cells divide to increase surface area.
- GROWTH - Cells divide to increase the size of an organism.
- DIFFERENTIATION - Cells have different jobs. They divide
to produce cells that do different things in complex organisms.
CELLS GROW AND DIVIDE IN WHAT IS CALLED THE
CELL CYCLE.
Cell Cycle has 2
major phases:
•Interphase
•Division Phase
(Mitosis)
CELL CYCLE
INTERPHASE – when cell is not actively dividing, and
they are carrying out their specific function (majority of
cell’s lives)
Interphase is divided
into 3 parts:
(G1  S  G2)
G1 = GAP 1
= GROWTH
(G0=STATIONARY)
CELL CYCLE
S = SYNTHESIS = DNA DOUBLES (COPIES ITSELF)
- Single chromosomes in the nucleus of a cell form
double chromosomes
CELL CYCLE
G2 = Gap 2 = Growth and preparation for cell
division
CELL CYCLE
G1 = Gap 1 = Growth and normal cell function
S = Synthesis = DNA Doubles (copies itself)
•Normally 46 chromosomes in the nucleus of each
human body cell = doubles
G2 = Gap 2 = Growth and preparation for cell division
INTERPHASE
S – PHASE
In the S-phase (part of interphase) DNA is
replicated and chromosomes become
double chromosomes.
CHROMATIDS
DNA
DOUBLES
CENTROMERE
Chromosome Structure
• Chromatin = DNA + proteins that makes up
chromosome
• Chromosome = condensed (wound) DNA with a
centromere
• Sister chromatids = a chromosome and its duplicate
attached to one another by a centromere
Chromatid
Centromere
Chromatin
Chromosome
Chromosome
(Double)
(DNA Coiling clip)
Mitosis
• Division phase of mitosis
• Composed of 4
phases:
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
MITOSIS
INTERPHASE
PROPHASE
– Chromosomes begin to
condense (become
visible)
– Spindle fibers form
– Centrioles (animal cells)
move to opposite poles
– Nuclear envelope
disappears
PROPHASE
Centrioles
PROPHASE
Spindle fibers
Chromosomes
become visible
METAPHASE
MITOSIS
METAPHASE
– Chromosomes line
up in the middle of
the cell.
METAPHASE
MITOSIS
ANAPHASE
– Centromeres split
– Sister chromatids
move apart towards
opposite ends of the
cell. They are now
each individual
chromosomes.
ANAPHASE
MITOSIS
TELOPHASE
– Spindle fibres disappear.
– Chromosomes at
opposite ends, loosen
– Cytoplasm starts to pinch
off (cleavage furrow; Cell
plate)
– Nuclear envelope reform.
TELOPHASE
MITOSIS
CYTOKINESIS
– Cells separate
– Splitting of cytoplasm
CYTOKINESIS
Review: MITOSIS
DNA doubles in S-phase (INTERPHASE)
prior to mitosis
ONE cell becomes TWO. Each resulting
(daughter) cell is identical and the same
as the original cell (same genetic
information, same number of
chromosomes)
FOR: growth, multiplication
Mitosis in action
Biology Project
Microscope images of onion root tips
Cells Alive
Cell clips
CLONING
CLONING is the process in which identical offspring
are formed from a single cell or tissue.
-Many plants and some animals can reproduce in this
way.
CLONING
-Cells to be cloned must be TOTIPOTENT (or
multipotent).
-This means the cell has not yet specialized. It may
become any type of tissue.
CLONING
This can be done by using stem cells or by somehow
turning differentiated cells become totipotent.
STEM CELLS
CLONING
This can be done by using stem cells or by
somehow turning differentiated cells
totipotent.
DIFFERENTIATED CELLS CAN ALSO BE “TRICKED”
INTO BECOMING TOTIPOTENT WITH CHEMICALS
OR ELECTRIC SHOCK.
HOW TO CLONE:
MITOSIS
IMPLANTED INTO
SURROGATE MOTHER
Click & Clone
HOW TO CLONE:
HOW TO CLONE DOLLY:
Telomere shortening
There might be a few reasons why Dolly
died far too young
Telomere shortening:
•Telomeres are the ends of a chromosome.
•As each cell replicates, the telomeres
grow progressively shorter.
•Scientists believe cells stop replicating when the
telomeres reach some critical length.
•Dolly's telomeres were found to be approximately
80% of the length they should be for a sheep her age.
There might be a few reasons why Dolly
died far too young
•It might be for the shortening of telomeres of a
cloned animal, you have to count the years of the
clone &their mother to get a correct age for it's
telomere length.
•Research is in progress to determine if this
phenomenon is seen in other
organisms and whether
or not it is important.
There might be a few reasons why Dolly
died far too young
•DNA damaging:
•Over an organism's lifetime, the DNA
within its cells deteriorates, and
unrepaired damage causes
some diseases, including cancer.
•Scientists are concerned that this accumulated damage
may be carried along during the cloning process. If so, it
would give the clone a "head start" on developing some
diseases and cancer.
CLONING
Identical twins are natural clones caused by the
blastula splitting before differentiation and each
separate ball of cells becoming a separate embryo =>
baby.
INCOMPLETE SPLITTING
2
3
INCOMPLETE SPLITTING
2
CLONING
Let’s clone a mouse!!
AGING
Cells seem to have a limited life span.
•Ex. Heart cells only undergo 50 mitotic
divisions.
Maybe due to:
-Increased number of mistakes
-ends of the chromosome ,called telomeres “shortens”
(like a candle wick) and when its gone it can’t divide.
- telomerase enzyme seems to have some influence
in slowing the loss of the telomeres….
Science Now – Biology of Aging
CANCER
CANCER IS: Cells growing and dividing out of
control.
Causes could be: Smoking, diet, radiation, genetic
predisposition
Treatments?
1) Radiation - has to be localized
2) Chemotherapy – chemicals stop mitosis
3) Surgery – removes benign tumors. If the tumor is
malignant it can go through metastasis – it can
move around the body.
Cancer vs. Normal cells
Normal cell have a number of characteristics.
They can:
• Reproduce themselves exactly
• Stop reproducing at the right time
• Stick together in the right place
• Self destruct if they are damaged
• Become specialized or ‘mature’
Cancer vs. Normal cells
Cancer cells are different to normal cells in
several ways.
• They carry on reproducing
• They don’t obey signals from neighbouring cells
• They don’t stick together
• They don’t specialize but stay immature
• They don’t die if moved to a different part of the
body
Cancer cells don't stop
reproducing
Unlike normal cells, cancer cells do not stop
reproducing after they have doubled 50 or 60 times.
This means that a cancer cell will go on and on and on
doubling. So one cell becomes two, then four, then
eight, then sixteen....
Cancer cells don't stop
reproducing…contd
They may be more resistant to self destruction than
normal cells, or they may self destruct more slowly
than they reproduce. Eventually a tumour is formed
that is made up of billions of copies of the original
cancerous cell. Scientists describe cancer cells as
being 'immortal'.
Cancer cells do not obey
signals
Something in the cancer cells overrides the normal
signaling system. This may be because the genes that
tell the cell to reproduce keep on and on firing. Or
because the genes that normally tell the cell to stop
reproducing have been damaged or lost. So the cancer
cell keeps on doubling up regardless of the damage it
causes to the part of the body where it is growing.
Cancer cells do not stick
together
Cancer cells can lose the molecules on their surface
that keep normal cells in the right place. So they can
become detached from their neighbours. This partly
explains how cancer cells spread to other parts of the
body.
Cancer cells do not become
specialized
Unlike normal cells, cancer cells do not carry on
maturing once they have been made. In fact, the cells in
a cancer can become even less mature over time. With
all the reproducing, it is not surprising that more of the
genetic information in the cell can become lost. So the
cells become more and more primitive and tend to
reproduce more quickly and even more haphazardly.
Work on…
- Mitosis Quiz Tomorrow
- 17.2 Review Questions #1-6, p. 571