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Chapter 2
Cellular Reproduction
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Chapter Outline
Cells and Chromosomes
Mitosis
Meiosis
Life Cycles of Some Model Genetic
Organisms
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Cells and Chromosomes
In both prokaryotic and
eukaryotic cells, the genetic
material is organized into
chromosomes.
Eukaryotic: 23, non-circular, linear
Prokaryotic: 1, circular
Viruses: 1, DNA circular; 1, RNA linear
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The Cellular Environment
Cytoplasm / cytosol / Nucleus/ …the inside of a
cell….. Plasma membrane….the outside of the cell…
Water ( 70-80 %)
Hydrophilic and Hydrophobic Molecules;
Amphiphatic
Carbohydrates (Glucose and Glycogen)
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Lipids (Cholesterol, ©phospholipids
and fatty acids)
The Cellular Environment
Proteins (amino acids to polypeptide), including
enzymes
Ribonucleoproteins, including RNAse as an enzyme
Membrane—made of lipids and proteins
Cell Wall: cellulose [murein-(sugars and amino acid)in bacteria)
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Animal and Plant Cells
Organelles:
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Animal and Plant Cells
No Organelles:
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Animal and Plant Cells
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Chromosomes
 Double-stranded DNA with
associated proteins and
sometimes RNA
 Prokaryotic cells contain one
circular chromosome plus
smaller plasmids ( ?)
 Most eukaryotic cells contain
several large linear
chromosomes plus a
circular mitochondrial DNA
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Vocabulary for Chromosomes
Diploid: cells with 2 copies of each chromosomes
Haploid: cells with one copy of each chromosomes
Somatic cells: any cells of an organism, diploid and
go under mitosis.
Germ line: reproductive cells that give rise to
gametes
Gametes: specialized cells (sperm and ova)
Centromere: point of interaction of each
chromosomes; region of chromosomes required for its
movement.
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Cell Division in Prokaryotes:
Fission
 A mother cell divides to produce two daughter cells.
 The mother cell’s chromosome is duplicated prior to fission.
 Each daughter cell receives one copy of the chromosome and
more or less the rest of the content.
 Clone—a population of genetically identical cells.
 Colony—a visible mass of cells (1 to 250 cells).
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Division time?
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Cell Division in Eukaryotes:
Inter (I) Phase and Mitosis (M) Phase
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30 min to
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 Cells, the basic units of all living things, are enclosed by
membranes.
 Chromosomes, the cellular structures that carry the genes,
are composed of DNA and protein.
 In eukaryotes, chromosomes are contained within a
membrane-bounded nucleus; in prokaryotes they are not.
 Eukaryotic cells possess complex systems of internal
membranes as well as membranous organelles such as
mitochondria, chloroplasts, and the endoplasmic reticulum.
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Haploid eukaryotic cells possess one copy of each
chromosome; diploid cells possess two copies.
Prokaryotic cells divide by fission (binary)
Eukaryotic cells divide by mitosis and meiosis.
Eukaryotic chromosomes duplicate when a cell’s
DNA is synthesized; this event is characteristic of
the S phase of the cell cycle.
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Mitosis
When eukaryotic cells divide, they
distribute their genetic material
equally and exactly to their
offspring.
Inter-phase:
Chromatin---Heterochromatin
---Eurochromatin
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M-phase:
Chromosomes
Mitosis in Animal Cells
mechanical force?
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Microtubules, Centrosomes and
Centrioles.
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Centrosome duplicates (S phase)
Centrosomes move to opposite sides of nucleus
during prophase.
Mitotic spindle assembles (microtubules=MT)
Microtubule organizing centers (MTOCs)
Spindle MTs make contact with chromosomes
---centromere
(sequence repeated DNA sequence=heterochromatin
=CEN sequences)
---kinetochore
(protein-like containing structure)
Cytokinesis in
Animal and Plant Cells
Cleavage furrow associated with the contractile ring (Actin and Myosin)
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As a cell enters mitosis, its duplicated chromosomes
condense into rod-shaped bodies (prophase).
As mitosis progresses, the chromosomes migrate to
the equatorial plane of the cell (metaphase).
Later in mitosis, the centromere that holds the sister
chromatids of a duplicated chromosome together
splits, and the sisters chromatids separate (or disjoin)
from each other (anaphase)
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As mitosis comes to an end, the chromosomes
decondense and a nuclear membrane reforms
around them (telophase).
Each daughter cell produced by mitosis and
cytokinesis has the same set of chromosomes; thus,
daughter cells are genetically identical.
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Meiosis
Sexual reproduction involves a
mechanism that reduces the
number of chromosomes by
half.
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Homologues
Xx or Xy
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Comparison of
Mitosis and Meiosis
Non-reduction
Reduction
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Prophase I: Leptonema
Chromosomes
condense
Each chromosome has
two sister chromatids
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Prophase I: Zygonema
Synapsis (pairing) of
homologous chromosomes
Synaptonemal complex
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The Synaptonemal Complex
Function ?
Structural...
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Prophase I: Pachynema
Chromosomes condense
further
Bivalent of chromosomes
Tetrad of chromatids
Crossing over occurs
(exchange material)
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Prophase I: Diplonema
Paired chromosomes
separate slightly but are
in contact as chiasmata
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Chiasmata
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Prophase I: Diakinesis
Nuclear envelope fragments
Spindle fibers (MT) attach to
kinetochores
Chromosomes move to central
plane in pairs
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Metaphase I
Paired chromosomes are
oriented toward opposite
poles
Terminalization: chiasmata
move toward telomeres
 Why?
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Anaphase I
Chromosome disjunction
(separation of paired
chromosomes)
Separated homologues
move toward opposite
poles
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Telophase I
 Chromosomes reach the poles; nuclei forms
 Spindle apparatus is disassembled
 Daughter cells separated by membranes
 Chromosomes decondense
 Each chromosome still has two sister
chromatids
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Prophase II
Chromosomes condense
Chromosomes attach to a
new spindle apparatus
Sister chromatids are
attached to spindle fibers
from opposite poles
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Metaphase II
Chromosomes align
at equatorial plane
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Anaphase II
Centromeres split
Chromatid disjunction—sister
chromatids move toward opposite
poles
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Telophase II
 Separated chromatids gather at
poles; daughter nuclei form
 Each chromatid is now called a
chromosome
 Each daughter nucleus contains
a haploid set of chromosomes
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Cytokinesis
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Daughter cells are NOT
genetically identical
Maternal and paternal homologues
synapse, then disjoin independently.
Homologous chromosomes exchange
material by crossing over
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 Diploid eukaryotic cells form haploid cells by meiosis, a
process involving one round of chromosome duplication
followed by two cell divisions (meiosis I and meiosis II).
 During meiosis I, homologous chromosomes pair
(synapse), exchange material (cross over), and separate
(disjoin) from each other.
 During meiosis II, chromatids disjoin from each other.
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Human
23
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3,200
20 to 25,000
Life Cycle of
Saccharomyces cerevisiae
(yeast).
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Arabidopsis thaliana, plant
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Spermatogenesis and
Oogenesis in Mammals
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In yeast, haploid cells with opposite mating types fuse
to form a diploid zygote, which then undergoes meiosis
to produce four haploid cells
Meiosis in the reproductive organs of Arabidopsis
produces microspores and megaspores, which
subsequently develop into male and female
gametophytes
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The double fertilization that occurs during
Arabidopsis reproduction creates a diploid
zygote, which develops into an embryo, and a
triploid endosperm, which develops into
nutritive tissue in the seed
In mice and other mammals, one cell from
female meiosis becomes the egg, whereas all
four cells from male meiosis become sperm
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Ribosome:is cell organelles that consist of RNA and proteins.
They are responsible for assembling the proteins of the cell.
Mitochondria: is the cell's power producers. They convert energy into forms that are usable
By the cell.
Golgi:is responsible for manufacturing, warehousing, and shipping certain cellular products.
Lysosome:is a membranous sacs of enzymes. These enzymes are typically hydrolytic
and can digest cellular macromolecules.
Endoplasmic Reticulum: is a network of tubules and
flattened sacs that serve a variety of functions in the cell. The rough endoplasmic
reticulum manufactures membranes and secretory proteins. The smooth ER has a wide range of
functions including carbohydrate and lipid synthesis.
Plasma membrane: is a thin semi-permeable membrane that surrounds the
cytoplasm of a cell, enclosing its contents. Its function is to protect the integrity of the interior of the
cell by allowing certain substances into the cell, while keeping other substances out.
Cilia and flagella:are protrusions from some cells that aid in cellular locomotion.
They are formed from specialized groupings of microtubules called basal bodies.
Nucleus:is a membrane bound structure that contains the cell's hereditary
information and controls the cell's growth and reproduction.
Nucleolus
contains nucleolar organizers which are parts of
chromosomes with the genes for ribosome synthesis on them
Nuclear envelope:is a double membrane that contains the nucleus. These membranes
separates the contents of the nucleus from the cytoplasm.
Nuclear pore: is a protein complex that helps to maintain the shape of the nucleus and assists
in regulating the flow of molecules into and out of the nucleus.
Microtubules:are hollow rods, functioning primarily to help support and shape the cell as well as
regulate cell cycle and division.
Microfilaments:or actin filaments are solid rods and are active in muscle contraction.
They are particularly prevalent in muscle cells.
Cell wall:Outer covering of most cells that protects the bacterial cell and gives it shape.
Pilus:is a protein tube structure. It transfers genes from one bacteria to other bacteria.
Chloroplast:is the organelle where photosynthesis occurs in photosynthetic eukaryotes.
The organelle is surrounded by a double membrane.
Vacuole:structure in a plant cell that provides support and participates in a variety of cellular
functions including storage, detoxification, protection, and growth.
Centriole:
cell division.
is found in animal cells and help to organize the assembly of microtubules during