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CHAPTER 8
Cellular Reproduction:
Cells from Cells
Chapter overview
• Reproduction
•
Cells vs. organisms
•
Reproduction and proliferation
• Non-sexual reproduction
•
Mitosis and the cell cycle
•
Cancer
• Sexual reproduction
•
Meiosis and sex
•
Chromosomal abnormalities
•
The advantages of diploidy and sex
Today
• Reproduction
•
Cells vs. organisms
•
Reproduction and proliferation
• Non-sexual reproduction
•
Mitosis and the cell cycle
•
Cancer
• Sexual reproduction
•
Meiosis and sex
•
Chromosomal abnormalities
•
The advantages of diploidy and sex
REPRODUCTION
•
Is the creation of new organisms by organisms
•
Can refer to single cells and multicellular organisms
•
Can be asexual and sexual
Reproduction of Organisms
• Asexual reproduction (reproduction from one parent) is based on “simple” cell division
– Single cell organisms
(example: amoeba)
– Some multi-cellular organisms
– Lower animals (example:
hydra)
– Plants can
•
Sexual reproduction (reproduction from two parents) is based on a cycle of
fertilization & reduction of chromosome number
–
More complex than asexual reproduction
–
Second half of this lecture plus next lecture
“SIMPLE” CELL DIVISION
AND
THE CELL CYCLE
• Each minute, ~109 cells die in our body
• Each day, ~1012 cells are formed in our body
Cell division plays a role in
•
The replacement of lost or damaged cells
•
Wound healing
•
Growth
•
Reproduction
•
Cancer
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Physical organization of genetic information
• The central event of cell division
is the distribution of genetic
information between daughter
cells
• Cell division requires equal
distribution of genetic information
•
•
The complete set of all genetic
information in an organism is
called genome
Chromosomes
Human genome contains ~20,000
protein-encoding genes
This cell is dead, because it was killed by the staining procedure
•
The genome is physically
organized in pieces called
chromosomes
Structure of chromosomes
•
Chromosomes are large continuous pieces of DNA in
complex with packaging proteins
(DNA + packaging proteins = chromatin)
•
DNA in chromosomes is highly compacted
•
Completely unfolded human chromosomes would be 16 –
85 mm long
DNA double helix
Histones
“Beads
on a
string”
1
The DNA is packed by coiling and folding:
Nucleosome
• 1st level: beads-on-a-string (nucleosome); each bead
consists of DNA wound around a protein core of 8 histones
• 2nd level: the beaded string is wrapped into a helical fiber
• 3rd level: a thick supercoil.
• 4th level: the supercoil is folded (this maximum folding only
2
Tight helical fiber
during cell division)
Supercoil
4
Sister
chromatids
Centromere
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3
Number of chromosomes
Chromosomes may be small or large
 The number of chromosomes does not
inform about the amount of DNA
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Cell cycle
centromere
• The cell cycle produces two daughter
1 chromosome =
1 chromatid
cells from a parent cell
• The central event of the cell cycle is the
chromosome cycle
• A chromosome is the genetic
information that is physically connected
into one unit.
Duplication
Sister
chromatids
1 chromosome
= 2 chromatids
• 1 Chromosome consists of one
chromatid or two chromatids (sister
chromatids) that are connected at the
centromere
Cell
division
• When the cell divides, the two sister
chromatids separate from each other
1 chromosome
= 1 chromatid
•All eukaryotic cells that divide
repeatedly undergo a cell cycle
•The cell cycle consists of two
phases:
•Interphase
•Mitotic phase
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Interphase
(90% of time)
Mitotic
phase (M)
(10% of time)
Interphase
S phase
•The interphase consists of three parts:
Interphase
•G1 (Gap 1): Cell growth
•S phase (DNA synthesis)
G2
G1
•G2 (Gap 2): Cell growth and
preparation of mitotic phase
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Mitotic
phase
Mitosis and Cytokinesis
Interphase
• Mitosis = division of nucleus
• Cytokinesis = division of the cytoplasm
• Mitosis and cytokinesis are different
processes, but occur in a coordinated
manner
• Cytokinesis starts in the final subphase of
mitosis.
Cytokinesis
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Mitosis
The four stages of mitosis
Prophase
1.Prophase
• Condensation of the chromatin
 sister chromatids become
visible in light microscope
• Centrosomes double, move
apart, and produce spindle
fibers (microtubules)
• Nuclear envelope dissolves
Early Centrosome
mitotic
spindle
Centromere Fragments of
nuclear envelope
Chromosome, consisting
of two sister chromatids
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Spindle
microtubules
2. Metaphase
Metaphase
Prophase
•
Chromosomes convene on an imaginary plate equidistant from the two poles of the
spindle
•
The centromeres of all chromosomes are lined up at this plate.
•
Spindle fibers from both poles attach to a centromere of each chromosome
Spindle
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
3. Anaphase
•
Each chromatid is now an independent
daughter chromosome.
•
Motor proteins (= kinetochore) at the
centromeres “walk” the daughter
chromosomes along their microtubules
toward opposite poles of the cell
•
Meanwhile, these microtubules shorten
•
The microtubules that are not attached to
chromosomes lengthen, pushing the poles
farther apart
Anaphase
Daughter
chromosomes
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
4. Telophase
•
Produces two daughter cells
•
The reverse of prophase
•
Nuclear envelopes form
•
The chromosomes uncoil
•
Nucleoli reappear
•
Spindle disappears
Telophase and Cytokinesis
Nucleolus
forming
Cleavage
furrow
Nuclear
envelope
forming
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Cytokinesis (= division of cytoplasm)
•
In animals, cytokinesis is caused by a ring of cytoskeletal proteins (microfilaments)
•
In plants, membrane vesicles that contain cell wall material accumulate in the middle
of the cell and gradually fuse
Cleavage furrow
Contracting ring of
microfilaments
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Vesicles containing New cell wall
cell wall material
Cell plate
Cell wall
Mitosis animations:
http://www.maxanim.com/genetics/Mitosis/Mitosis.htm
http://www.johnkyrk.com/mitosis.html
Mitosis movies:
http://www.youtube.com/watch?v=aDAw2Zg4IgE
http://www.youtube.com/watch?v=DD3IQknCEdc
•This is actually not very precise: In the human body, 3x109 cells
form every minute  30,000 errors occur each minute.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Normal plant and animal cells have a cell cycle control system that consists of special proteins
•
These proteins generate “stop” and “go ahead” signals at certain key points during the cell cycle
•
The cell cycle normally halts at the G1 phase unless the cell receives a go-ahead signal
•
If that signal never arrives, the cell will switch into a permanently non-dividing state called G0
(for example, nerve and muscle cells)
•
If the go-ahead signal is received and the G1 checkpoint is passed, the cell will usually complete
the rest of cycle
G1
checkpoint
S phase
Interphase
G1
Go
Muscle and
nerve cells
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
G2
Mitotic
phase
(M)
In Cancer Cells the Cell Cycle is Out of Control
•More than 500,000 people die of cancer in the USA each year
•1/3 of all cancers in men are prostate cancer
•¼ of all cancers in women are breast cancer
Summary – Nonsexual reproduction
Nature of nonsexual reproduction
•
Creation of a new organism from a single parent, and the offspring is genetically
identical to the parent.
Mechanism
•
“Simple” cell division (mitosis). Repeatedly dividing cells go through cell cycles.
Each cycle produces an exact copy of the genetic information of the parent cell.
Role
•
Enables the continued existence of many species (single cells and multicellular
organisms).
•
Enables the maintenance and repair of organs.
•
Loss of cell cycle regulation can lead to cancer.
Most important words to know
•
Genome, chromosome, chromatid, chromatin
•
Cell cycle, mitosis, interphase, cytokinesis
요약- 무성생식
무성생식의 특징
• 단일 부모로부터 새로운 유기체를 생산하며, 그 자손은 부모와 유전적으로
동일하다.
기작
• “단순한” 세포분열 (체세포분열, mitosis). 세포주기를 통해 반복적으로 세
포가 분열함. 각 주기는 부모 세포의 유전정보를 정확하게 복사한다.
역할
• 많은 종 (단세포와 다세포 유기체)들의 존재를 지속시킨다.
• 장기의 유지와 보수를 가능하게 한다.
• 세포주기를 조절할 수 없는 세포는 암세포가 될 수 있다.
가장 중요한 단어들
• Genome, chromosome, chromatid, chromatin
• Cell cycle, mitosis, interphase, cytokinesis
SEXUAL REPRODUCTION
AND MEIOSIS
(Introduction)
Sexual reproduction
–
A new cell is created by “mixing” the chromosomes of two parent
cells  number of chromosomes is doubled
–
The cell with the doubled chromosome set can exist a long time and
even divide and create a multicellular organism
–
Eventually, a special cell division reduces the chromosome number
back to the original level.
–
The mixing step that doubles chromosome number is called fertilization
–
The division that reduces the chromosome number is called meiosis.
–
Therefore sexual reproduction involves a cycle of fertilization & meiosis
The sexual life style is usually a cycle between a haploid and a diploid karyotype
•
The karyotype
–
is the ordered set of chromosomes
characteristic for each eukaryotic species
–
The simple set of chromosomes (before
fertilization) is called haploid
–
The karyotype resulting from fertilization is
diploid: The chromosomes exist in two copies
–
The two copies are called
homologous chromosomes
–
The homologous chromosomes are
almost identical: Same order of genes
•
The human karyotype
–
1 haploid set = 22 autosomes + X or Y
–
1 diploid set = 22 pairs of autosomes + XX (♀) or XY (♂)
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Haploid stage (1n) of life cycle
Diploid stage (2n) of life cycle
http://en.wikipedia.org/wiki/Sex
In some organisms both the haploid (1n) and the diploid (2n) stages can multiply
Life cycles of yeast
http://en.wikipedia.org/wiki/Yeast
In multicellular organisms, either the haploid or the diploid stage dominates
1n
Main stage in lower plants
(mosses)
2n
Main stage in
•Higher plants (flowering plants) – only
pollen and eggs are haploid;
•Animals – only sperm and eggs are
haploid
Multicellular sexual organisms have two principally different kinds of cells
•
In higher multicellular
sexual organisms (higher
plants and animals):
– Somatic cells  do not
transmit their genetic material
to the next generation  are
mortal
(Somatic cells are diploid)
– Germ cells (egg, sperm) 
transmit their genetic material
to the next generation  are
immortal
(Germ cells are haploid
and generated by meiosis)
•
Hence, sex is the reason that
we are mortal
In this chicken, the eggs and
their precursors in the ovary
are the germ line cells All other cells are somatic cells
Gametes and the life cycle of humans
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings