Transcript Telophase I and Cytokinesis

Chapter 10: Cell Growth, Division, and Reproduction
Why must a cell divide?
a) a large cell places a large demand on the DNA… “info overload”
b) a large cell has a low surface area to volume ratio – cell is less efficient at
moving materials in and out
c) a smaller cell has it’s own DNA – (not overworked anymore) AND a
HIGH surface area to volume ratio. Can manage cell needs better
Cell Division: 2 Types: Asexual and Sexual
Asexual Reproduction:
* Offspring are produced by a single parent,
without the participation of sperm and egg
* offspring are genetic copies of the parent
and of each other
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Sexual Reproduction:
• Fertilization of sperm and egg
produces genetically different
offspring
• Creates a variety of offspring
Why is cell division necessary?
• growth
• cell replacement
• wound repair
• asexual reproduction
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Prokaryotes reproduce by binary fission: asexual
• As the cell replicates its
single chromosome, the
copies move apart
• The growing membrane
then divides the cells
Prokaryotic chromosomes
Figure 8.3B
Colorized
TEM
32,500
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THE EUKARYOTIC CELL CYCLE AND MITOSIS
The large, complex chromosomes of
eukaryotes duplicate with each cell
division
LM 600
•A eukaryote has many more genes
(and chromosomes) than a prokaryote
• Genes are grouped into multiple
chromosomes in the nucleus
•Each chromosome contains a very long
DNA chain with attached histone
proteins
•Chromosomes are ONLY visible during
cell division
•If a cell is not undergoing division,
chromosomes unwind into loosely
packed fibers called chromatin
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46 chromosomes unwound = 2 meters!
The Cell Cycle: Interphase and Mitosis
1. 1. Interphase: All DNA is
duplicated and cell parts are made. 3
stages:
•G (gap)1: normal cell growth
•S (synthesis): all DNA is copied (new
set of chromatin is synthesized)
•G (gap)2: organelles replicated
2.Mitosis: Duplicated
chromosomes are evenly
distributed into two daughter
nuclei. 4 phases:
• Prophase
• Metaphase
• Anaphase
• Telophase Cytokinesis
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The Stages of Mitosis:
=
centromere
Sister chromatids
Interphase: G1, S, and G2
Prophase: chromatin condenses, sister chromatids join, nucleolus disappears,
centrosomes (centrioles) start to produce spindle fibers and begin migrating to poles,
nuclear envelope breaks down, spindles attach to chromosomes, and start moving them
to the middle
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The Stages of Mitosis: cont’d
Mitosis
video
Metaphase: chromosome pairs and centromeres are lined up at middle
Anaphase: centromeres split, spindles which are attached to chromosomes recoil and split sister
chromatids apart, other spindles get longer and poles are pulled farther apart…cell is stretched
Telophase and Cytokinesis: chromosomes unwind into chromatin, nuclear envelope and nucleolus
form, spindles disappear, microfilaments pinch at center  cytokinesis…cytoplasm completely
divides (in plants a cell plate is formed)... 2 new cells
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SUMMARY:
Putting it
all together
Drawings
AND
Real Pictures
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Cytokinesis differs for plant and animal cells
•In animals, cytokinesis occurs by a constriction of the cell (cleavage)
•In plants, cell membrane can’t pinch b/c of cell wall. A cell plate forms instead
Figure 8.7A
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Do all cells divide at the same rate?? NO
Fast dividing: intestinal lining, bone marrow, skin, follicle cells
Slow dividing: liver, pancreas
Non-dividing: nerve and muscle (after about 5 years of age)
Q: How is the cell cycle regulated in each type of cell?
A: Physical boundaries, Cyclins, and Regulatory Proteins
1. Physical Boundaries
Most cells stop dividing once they TOUCH each other
ex) cells in a petri dish grow in a single layer
and stop once whole surface is covered. Remove
some cells, and border cells will divide again to fill
the gap.
ex) wound boundary cells are stimulated to divide until
the space (wound) is healed.
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Regulation of Cell Cycle: Cyclins and Regulatory Proteins
2. Cyclins: proteins present in cells ONLY when dividing
3. Regulatory Proteins: used IN and OUT of the cell
to stimulate division
ex) INternal regulatory proteins:
* one type makes sure all chromosomes are made before going further
* another type makes sure all spindles are formed before going further
ex) EXternal regulatory proteins: direct cells to increase OR decrease
RATE of cell division
* growth factors – outside chemical signal for cell to start division: vital
in embryo development and wound healing
* others work as “red lights” to slow down cell division – preventing
tumor development
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Cancer: Uncontrolled Cell Division
Cancer cells divide excessively; no control system
• produce malignant tumors which invade normal cell space, robbing
them of nutrients and blood supply
• produce own growth factors constant divide signal
• divide and live longer than normal cells
•Tumor: benign (cells stay put) OR malignant (cells metastasize)
•Carcinomas (covering and linings): skin, intestine (colon)
•Sarcomas (support tissue): muscle, bone
•Leukemia and Lymphoma: blood tissue
•Chemotherapy: side effects felt most by fast-dividing cells
•ex: hair follicles, intestinal lining, immune cells
•Anti-Cancer drugs: all botanical extracts
* Taxol: freezes mitotic spindle no division
* Vinblastin and Colchicine: stop spindle formation  no division
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Q: What causes cancer cell growth ?
A: defects (mutations) in the DNA (genes) which code for
regulatory proteins
How do these defects happen??
1. chemical exposure (ex: tobacco and cigarette smoke)
2. radiation exposure (ex: x-rays, uv light rays from sun)
3. viruses can disrupt DNA (ex: HPV, HIV)
** Many cancer cells have a mutation in gene “P53”
“P53” gene codes for an internal regulatory cell cycle
protein at the S of Interphase.
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Normal, Programmed, Cell Death??
Apoptosis: pre-programmed, deliberate cell death
Process:
1. cell looses fluid and shrinks
2. chromatin breaks down
3. cell membrane distintegrates
4. cell’s neighbors clean up debris and re-use materials
Why needed?
1. This is a key role in embryonic development (ie; shape changes)
ex: paddle  hand
ex: tadpole  frog
** Too much cell death is linked to certain diseases (Parkinson’s, AIDS)
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CHROMOSOMES
Chromosomes: coiled DNA (chromatin)
•
in humans: 23 pairs  46 in ea. body cell
(23 from mom, 23 from dad)
• Homologous chromosomes: same #, size,
shape, gene location, centromere location
(ex: chromosome #1 from mom is
homologous to chromosome #1 from dad,
etc.)
• haploid # = (n) half (23 total): sex cells (egg and sperm)
• diploid # = (2n) double (46 total): body (somatic) cells
• Sex cells (23, haploid): 22 autosomes (#1 #22), 1 sex chromosome (#23)
• Body cells (46, diploid): 22 pairs of autosomes… (44 total)
1 pair of sex chromosomes (XX) or (XY)
• Q: Which cell determines the sex of the offspring; egg or sperm?
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MEIOSIS: a.k.a. “reduction division”
Summary:
• Diploid (2n) cell (germ cell)
Phases:
• Interphase (G1, S, G2)
forms cells with (n) nuclei
• Two divisions
• Used for gamete
formation only
• Takes much longer
than mitosis
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I & Cytokinesis
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II
& Cytokinesis
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Unique features
animation
Stages of Meiosis
Interphase: G1, S, G2
Prophase I:
•chromatin condenses
•sister chromatids join at centromere
•homologous pairs of sister chromatids join
to make tetrads
• crossing over occurs to shuffle genes
• nuclear envelope and nucleolus disappear
• centrioles migrate, grow spindles, attach to tetrads
•tetrads start to move to middle of cell
Metaphase I: tetrads lined up at metaphase plate
Anaphase I:
•spindles recoil
•homologous pairs pulled apart
•each pair of sister chromatids move to opposite pole.
Telophase I and Cytokinesis:
•cell pinches in middle  divide cytoplasm.
•each cell (2) has 1 pair of sister chromatids
from each original tetrad
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Stages of Meiosis cont’d
Prophase II:
•spindles form again,
•spindles attach to and start moving sister
chromatid pairs to middle
Metaphase II:
•sister chromatid pairs lined up at
metaphase plate
Anaphase II:
•spindles recoil
•centromeres divide
•sister chromatids separate
Telophase II and Cytokinesis:
•nucleolus and nuclear envelope appear
•chromosomes unwind into chromatin
•cell pinches in middle
•divide cytoplasm…4 new daughter cells
• each with (n) number
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Meiosis stages video
Review: A comparison of mitosis and meiosis
comparison animation
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Gamete formation begins with a 2n body cell
Spermatogenesis: production
of sperm (spermatozoa)
Oogenesis: production of egg
(ovum)
Spermatogonia: male germ
cells (2n) which will undergo
meiosis to make 4 sperm (n)
cells each time
Oogonia: female germ cells
(2n) which will undergo
meiosis and make 1 egg (n)
and 3 polar bodies (n) each
time
s
s
s
s
EGG
3 polar bodies
Spermatozoa: small, very little
cytoplasm, flagella
• Head with nucleus, midpiece with
mitochondria, flagella
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Polar bodies: a waste of DNA in order
to get a large egg
conservation of cytoplasm:1 big egg with
lots of energy in it’s stored food
Q: Why is everyone different? (except identical twins)
• Random crossing over of
genes during prophase I
• Random orientation of
chromosomes at metaphase
plate
• Random fertilization
All this leads to many
different combinations
of chromosomes
in eggs and sperm
2 23 = 8 mill combo’s for egg/sperm
at fertilization: 8M x 8M = 64 trillion combo’s of
chromosomes…not including crossing over!!
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Orientation
animation
Alterations of chromosome number and structure
Karyotype: a photographic inventory of an
individual’s chromosomes
• used to detect abnormal chromosome
number or abnormal chromosome shape
non-disjunction: failure of chromosomes
to separate equally
•
Can lead to trisomy (2n + 1) individual
•
Trisomy 21 : Down’s Syndrome
( 1 in 700 births; most common)
•
Trisomy 18, 15, etc…
•
XYY: Super Male
•
XXX: Super female
•
XXY : Klienfelter’s Syndrome
•
XO: Turner’s Syndrome
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Trisomy 21
Non-disjunction in Meiosis I vs. Meiosis II
failure of homologous pairs to separate
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failure of sister chromatids to separate
Polyploidy: Extra Set(s) of Chromosomes
• Results when entire set (s) of chromosomes
fail to separate (nondisjunction) during meiosis
• 2n + n = 3n (Triploid)
• 2n + 2n = 4n (Tetraploid)
Miscarriage,
severe birth defects, or
early death
• Polyploidy is lethal in humans but is tolerated in
plants
• Plants can be forced into polyploidy with
colchicine
• ex. polyploid coffee beans provide more robust
flavor
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Alterations of chromosome structure: birth defects and cancer
• Deletions, duplications, inversions, and translocations
• Occurs during crossing over
example
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Bonus Questions: Pick any 2 of your choice
1. What is the full name of a sperm cell?
2. During which phase is non-disjunction of chromosomes
most problematic (Meiosis I or Meiosis II)?
3. When a karyotype is made, what is the “n” number of
that cell (n, 2n, 3n or 4n)?
4. Name a chemotherapy agent which prohibits spindle
formation.
5. What term describes the spread of malignant cancer to
other organs in the body?
6. Cancer of the tissues which function as coverings and
linings are collectively called?
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings