Cellular Division 1
Cell Division All cells are derived from pre-
existing cells New cells are produced for growth and to replace damaged or old cells Differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals) 2
Keeping Cells Identical The instructions for making cell parts are encoded in the DNA, so each new cell must get a complete set of the DNA molecules 3
DNA Replication
DNA must be Original DNA copied or strand replicated before cell division Two new, identical DNA Each new cell strands will then have an identical copy of the DNA
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Identical Daughter Cells
Two identical daughter cells Parent Cell 5
Chromosomes
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Prokaryotic Chromosome The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane
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Eukaryotic Chromosomes
All eukaryotic cells store genetic information in chromosomes
Most eukaryotes have between 10 and 50 chromosomes in their body cells Human body cells have 46 chromosomes or 23 identical pairs
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Eukaryotic Chromosomes
Each chromosome is composed of a single, tightly coiled DNA molecule Chromosomes can’t be seen when cells aren’t dividing and are called chromatin
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Compacting DNA into Chromosomes DNA is tightly coiled around proteins called histones 10
Chromosomes in Dividing Cells Duplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids
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Karyotype A picture of the chromosomes from a human cell arranged in pairs by size First 22 pairs are called autosomes Last pair are the sex chromosomes XX female or XY male 12
Boy or Girl? The Y Chromosome Decides
Y - Chromosome
X - Chromosome 13
Cell Reproduction
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Types of Cell Reproduction
Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells Mitosis & binary fission are examples of asexual reproduction Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells Meiosis is an example 15
Cell Division in Prokaryotes
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Cell Division in Prokaryotes Prokaryotes such as bacteria divide into 2 Parent cell identical cells by the process of binary fission Chromosome Single chromosome doubles makes a copy of itself Cell wall forms Cell splits between the chromosomes dividing the cell 2 identical daughter cells
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Prokaryotic Cell Undergoing Binary Fission
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Animation of Binary Fission
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The Cell Cycle 20
Five Phases of the Cell Cycle G1 - primary growth phase S – synthesis; DNA replicated G2 - secondary growth phase
collectively these 3 stages are called interphase
M - mitosis C - cytokinesis
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Cell Cycle
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Interphase - G1 Stage 1st growth stage after cell division Cells mature by making more cytoplasm & organelles Cell carries on its normal metabolic activities
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Interphase – S Stage
Synthesis stage DNA is copied or replicated
Two identical copies of DNA
Original DNA 24
Interphase – G2 Stage 2nd Growth Stage Occurs after DNA has been copied All cell structures needed for division are made (e.g. centrioles) Both organelles & proteins are synthesized
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What’s Happening in Interphase? What the cell looks like
Animal Cell
What’s occurring 26
Sketch the Cell Cycle DNA Copied Cells Mature
Daughter Cells
Cells prepare for Division
Cell Divides into Identical cells 27
Mitosis 28
Mitosis
Division of the nucleus Also called karyokinesis Only occurs in eukaryotes Has four stages Doesn’t occur in some cells such as brain cells
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Four Mitotic Stages
Prophase Metaphase Anaphase Telophase
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Early Prophase
Chromatin in nucleus condenses to form visible chromosomes Mitotic spindle forms from fibers in cytoskeleton or centrioles (animal) Nucleolus
Cytoplasm
Nuclear Membrane Chromosomes
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Late Prophase Nuclear membrane & nucleolus are broken down Chromosomes continue condensing & are clearly visible Spindle fibers called kinetochores attach to the centromere of each chromosome Spindle finishes forming between the poles of the cell 32
Late Prophase Chromosomes
Nucleus & Nucleolus have disintegrated 33
Spindle Fiber attached to Chromosome Kinetochore Fiber
Chromosome 34
Review of Prophase What the cell looks like
What’s happening
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Spindle Fibers
The mitotic spindle form from the microtubules in plants and centrioles in animal cells Polar fibers extend from one pole of the cell to the opposite pole Kinetochore fibers extend from the pole to the centromere of the chromosome to which they attach Asters are short fibers radiating from centrioles 36
Sketch The Spindle
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Metaphase Chromosomes, attached to the kinetochore fibers, move to the center of the cell Chromosomes are now lined up at the equator Equator of Cell Pole of the Cell
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Metaphase Asters at the poles
Spindle Fibers
Chromosomes lined at the Equator 39
Metaphase
Aster
Chromosomes at Equator 40
Review of Metaphase What the cell looks like
What’s occurring 41
Anaphase Occurs rapidly Sister chromatids are pulled apart to opposite poles of the cell by kinetochore fibers 42
Anaphase
Sister Chromatids being separated
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Anaphase Review What the cell looks like
What’s occurring 44
Telophase
Sister chromatids at opposite poles Spindle disassembles Nuclear envelope forms around each set of sister chromatids Nucleolus reappears CYTOKINESIS occurs Chromosomes reappear as chromatin 45
Comparison of Anaphase & Telophase
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Cytokinesis
Means division of the cytoplasm Division of cell into two, identical halves called daughter cells In plant cells, cell plate forms at the equator to divide cell In animal cells, cleavage furrow forms to split cell 47
Cytokinesis Cleavage furrow in animal cell
Cell plate in plant cell
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Mitotic Stages
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Daughter Cells of Mitosis Have the same number of chromosomes as each other and as the parent cell from which they were formed Identical to each other, but smaller than parent cell Must grow in size to become mature cells (G1 of Interphase) 50
Identical Daughter Cells What is the 2n or diploid number?
2
Chromosome number the same, but cells smaller than parent cell 51
Review of Mitosis 52
Draw & Learn these Stages
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Draw & Learn these Stages
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Name the Mitotic Stages: Interphase
Name this? Prophase
Telophase Name this?
Metaphase Anaphase 55
Eukaryotic Cell Division Used for growth and repair Produce two new cells identical to the original cell Cells are diploid (2n)
Prophase
Metaphase
Chromosomes during Metaphase of mitosis
Anaphase Telophase Cytokinesis 56
Mitosis Animation Name each stage as you see it occur?
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Mitosis in Onion Root Tips Do you see any stages of mitosis?
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Test Yourself over Mitosis 59
Mitosis Quiz
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Mitosis Quiz
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Name the Stages of Mitosis: Early Anaphase
Early prophase
Metaphase
Interphase
Late Prophase
Late telophase, Mid-Prophase Advanced cytokinesis
Early Telophase, Begin cytokinesis
Late Anaphase 62
Identify the Stages ? Early, Middle, & Late Prophase
?
? Metaphase
Late Prophase
Late Anaphase
Anaphase
?
? Telophase
?
? Telophase & Cytokinesis
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Locate the Four Mitotic Stages in Plants Anaphase Telophase Metaphase
Prophase 64
Uncontrolled Mitosis If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell
Cancer cells 65
Abnormal Cell Division • Tumor – Mass of undifferentiated cells not normally found in a certain part of the body a. Benign tumor – cell mass that does not fragment and spread beyond its original area of growth; can become harmful by growing large enough to interfere with normal body functions
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b. Malignant tumor - nonencapsulated growth of tumor cells that are harmful; they may spread or invade other parts of the body •
cells of these tumors move from the original site (metastasize) and establish new colonies in other regions of the body
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Cancer term used to refer to refer to any abnormal growth of cells that has a malignant potential Carcinogens agents responsible for causing cancer
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Factors associated with cancer • Radiation – X rays and gamma rays – UV light (UV-B)
• Sources of carcinogen – Tobacco – Nickel – Arsenic – Benzene – Dioxin – Asbestos
- uranium - tar - cadmium - chromium - polyvinyl chloride (PVC)
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• Diet – Alcohol – Smoked meats and fish – Food containing nitrates (e.g. bacon)
• Viruses – Hepatitis B virus (HBV) and liver cancer – Herpes simplex (HSV) type II and uterine cancer – Epstein – Barr virus and Burkitt’s lymphona – Human Y-cell lymphotropic virus (HTLV-1) and lymphomas and leukemias 70
• Hormonal imbalances – Diethylstilbestrol – Oral contraceptives
• Types of genetic and familial cancers – Chronic myelogenous leukemia – Acute leukemias – Retinoblastomas – Certain skin cancers – Breast, endometrial, colorectal, stomach, prostate, lung 71
Treatments of cancer • Surgery • Chemotherapy • Radiation
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Chemotherapy • Uses various types of chemicals to destroy mitotically dividing cancer cell • Types of chemotherapeutic drugs a. Antimetabolites – compounds interfering fatally with the cell’s metabolic pathways – methotrexate (prevents the synthesis of new DNA)
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b. Toposiomerase inhibitors – prevent the”unzipping” of DNA (doxorubicin) c. Alkylating agents – form chemical bonds within the DNA of cancer cells resulting in breaks and other damage not easily repaired (cyclophosphamide & chlorambucil) d. Plant alkaloids – disrupt the spindle apparatus, thus disrupting the normal separation of chromatics at the time of anaphase (vinblastine) 74
Radiation Therapy • Uses powerful X rays or gamma rays • From outside • Implanting radioactive “seeds” into the tumor
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p53 • Guardian of the genome • Tumor-suppressor p53 gene • Stops a damaged cell just before the S phase so that it can be repaired • Directly involved with the DNA repair process • Gives a cell the ability to be genetically healthy
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Radiation • Destroys cancer cells • Apoptosis – Programmed cell death (death that has a genetic basis) – Occurs in many cells of the body because they might be harmful or it takes too much energy to maintain them
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• When p53 initiates apoptosis, the cell’s DNA is cut into pieces and the cytoplasm and nucleus shrinks; this is followed by engulfment by phagocytes
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Meiosis
Formation of Gametes (Eggs & Sperm)
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Facts About Meiosis Preceded by interphase which includes chromosome replication Two meiotic divisions --- Meiosis I and Meiosis II Called Reduction- division Original cell is diploid (2n) Four daughter cells produced that are monoploid (1n) 80
Facts About Meiosis Daughter cells contain half the number of chromosomes as the original cell Produces gametes (eggs & sperm) Occurs in the testes in males (Spermatogenesis) Occurs in the ovaries in females (Oogenesis) 81
More Meiosis Facts Start
with 46 double stranded chromosomes (2n) After 1 division - 23 double stranded chromosomes (n) After 2nd division - 23 single stranded chromosomes (n) Occurs in our germ cells that produce gametes 82
Why Do we Need Meiosis? It is the fundamental basis of sexual reproduction Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote
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Fertilization – “Putting it all together” 2n = 6 1n =3
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Replication of Chromosomes Replication is the process of duplicating a chromosome Occurs prior to division Replicated copies are called sister chromatids Held together at centromere
Occurs in Interphase
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A Replicated Chromosome Gene X
Homologs
(same genes, different alleles)
Sister Chromatids (same genes, same alleles)
Homologs separate in meiosis I and therefore different alleles separate. 86
Meiosis Forms Haploid Gametes Meiosis must reduce the chromosome number by half Fertilization then restores the 2n number from mom
from dad
child
too much! meiosis reduces genetic content The right number! 87
Meiosis: Two Part Cell Division Sister chromatids separate
Homologs separate Meiosis I
Meiosis II
Diploid Diploid
Haploid 88
Meiosis I: Reduction Division
Spindle fibers
Nucleus Early Prophase I (Chromosome number doubled)
Late Prophase I
Nuclear envelope
Metaphase Anaphase Telophase I I I (diploid) 89
Prophase I
Early prophase Homologs pair. Crossing over occurs.
Late prophase
Chromosomes condense. Spindle forms. Nuclear envelope fragments. 90
Tetrads Form in Prophase I Homologous chromosomes (each with sister chromatids)
Join to form a TETRAD
Called Synapsis 91
Crossing-Over Homologous chromosomes in a tetrad cross over each other Pieces of chromosomes or genes are exchanged Produces Genetic recombination in the offspring 92
Homologous Chromosomes During Crossing-Over
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Crossing-Over
Crossing-over multiplies the already huge number of different gamete types produced by independent assortment 94
Metaphase I Homologous pairs of chromosomes align along the equator of the cell
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Anaphase I
Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres. 96
Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two.
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Meiosis II Gene X
Only one homolog of each chromosome is present in the cell. Sister chromatids carry identical genetic information.
Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. 98
Meiosis II: Reducing Chromosome Number
Prophase II
Metaphase Telophase II Anaphase 4 Identical II II haploid cells 99
Prophase II Nuclear envelope fragments. Spindle forms.
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Metaphase II
Chromosomes align along equator of cell.
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Anaphase II Equator
Pole
Sister chromatids separate and move to opposite poles.
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Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two. 103
Results of Meiosis Gametes (egg & sperm) form
Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome 104
Gametogenesis Oogenesis or Spermatogenesis 105
Spermatogenesis Occurs in the testes Two divisions produce 4 spermatids Spermatids mature into sperm Men produce about 250,000,000 sperm per day 106
Spermatogenesis in the Testes Spermatid
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Spermatogenesis
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Oogenesis Occurs in the ovaries Two divisions produce 3 polar bodies that die and 1 egg Polar bodies die because of unequal division of cytoplasm Immature egg called oocyte Starting at puberty, one oocyte matures into an ovum (egg) every 28 days 109
Oogenesis in the Ovaries
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Oogenesis First polar body may divide (haploid) a
Mitosis Oogonium (diploid)
X
A
X
Primary oocyte (diploid)
X a
X a
a
Polar bodies die
X
Meiosis I Meiosis II (if fertilization A occurs) X A
X
Secondary oocyte (haploid)
Ovum (egg) Mature egg A X
Second polar body (haploid) 111
Comparing Mitosis and Meiosis 112
Comparison of Divisions Mitosis
Meiosis 2
Number of divisions
1
Number of daughter cells
2
4
Yes
No
Same as parent
Half of parent
Where
Somatic cells
Germ cells
When
Throughout life
At sexual maturity
Growth and repair
Sexual reproduction
Genetically identical? Chromosome #
Role
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Sources of Variation • Mutation • Crossing-over • Segregation • Independent assortment • Fertilization
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Mutation • Point mutation – Change in a DNA nucleotide results in the production of a different protein
• Chromosomal mutation – Genes are rearranged
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Crossing-over • Occurs during Meiosis I • Is the exchange of a part of a chromatid from one homologous chromosome with an equivalent part of a chromatid from the other homologous chromosome • Explains why a child can show a mixture of family characteristics
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Segregation • Involves the separation and movement of homologous chromosomes to the poles • During anaphase 1 • Characteristics of both parents
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Independent Assortment • Combination of chromosomes • 2n where n is the number of pairs of chromosomes • Variation is possible because each pair of homologous chromosome assorts independently of the other pairs of homologous chromosomes
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Fertilization • Offsprings
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Nondisjunction • A pair of homologous chromosomes does not segregate properly during gametogenesis and both chromosomes of a pair end up in the same gamete • The cells usually die • If not, trisomy or monosomy occurs
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Translocation • The transfer of a piece of one nonhomologous chromosome to another – 14/21 translocation is monosomic and has only 45 chromosomes; one 14 and one 21 are missing and replaced by the translocated 14/21 – 15% of the children of carrier mothers inherit the 14/21 chromosome and have DS – Children born to fathers with 14/21 are Downic
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