Upload
phamduong
View
214
Download
2
Embed Size (px)
Citation preview
9/20/2015
1
CELLULAR DIVISION
1
CELL DIVISION Two genetically identical daughter cells are formed from one parent cell
2
• Asexual reproduction
• One parent duplicates its CHROMOSOMES and divides
• Occurs in multicellular and unicellular organisms
• Multicellular: Human cells, sea star fragments, plant clippings
• Unicellular: protists, bacteria
9/20/2015
2
3
Prokaryotic cell Chromosome (DNA + proteins)
Duplicate chromosome and move to opposite ends of cell
Cell elongates and copies continueto move to opposite ends
Division intotwo daughter cells
1
2
3
BINARY FISSION Asexual reproductionin single‐celled Bacteria and archaea(PROKARYOTES)
EUKARYOTIC CELL DIVISION Eukaryotes have 100s to 1000s of genes held in each chromosome
4
• Chromosomes are made of chromatin
• Chromatin ‐ 1 long strand of DNA surrounded by proteins
• DNA ‐ an organic molecule made of nucleic acids
Chromosomemade of chromatin
DNAmolecule
Chromatin in nucleus of a
eukaryotic cell
9/20/2015
3
5
EUKARYOTIC CELL DIVISION Chromosomes duplicate to form sister chromatids
Chromosome DNA
Identical sister
chromatids
Identical copies of initial
Chromosome and DNA
Sister chromatids under a microscope
IdenticalDNA
Sister chromatids tightly attached at centromere
6
EUKARYOTIC CELL DIVISION Duplicated chromosomes condense when a cell prepares to divide
• Individual chromosomes are only visible just before cell division
• How many would you expect to see in a human cell that is about to divide?
9/20/2015
4
7
THE CELL CYCLEThe process that occurs from birth to reproduction of a cell
• INTERPHASE – growth and synthesis of organelles and DNA to prep for dividing into two cells
• MITOTIC PHASE – dividing up all of the duplicates and splitting into two cells
G1
G2
S(DNA synthesis)
8
INTERPHASEGrowth and prep for dividing: includes G1 Phase, S Phase and G2 Phase
• G1 Phase– cell grows and duplicates organelles; checkpoint to proceed with division
• Phase ‐ DNA synthesis –duplicate chromosomes
• G2 Phase – cell continues growing in preparation for division.
9/20/2015
5
9
INTERPHASEGrowth and prep for dividing: includes G1 Phase, S Phase and G2 PhaseNEXT UP: MITOSIS!
Centrosomes
Centrosome – an animal organelle located near the nucleus where microtubules (for structural support) originate. (CH 4)
PROPHASE OF MITOSIS Mitosis: The equal division of 1 nucleus to 2 genetically identical daughter nuclei
10
• Mass of chromatin condenses into sister chromatids
• Centrosomes form a mitotic spindle of microtubules
CentrosomeMitotic Spindle
Sister Chromatids
Prophase
9/20/2015
6
PROMETAPHASE Mitosis: The equal division of 1 nucleus to 2 genetically identical daughter nuclei
11
• Nuclear envelope breaks into fragments
• Mitotic spindle microtubules reach sister chromatids and attach to their centromeres (at kinetochores)
• Mitotic spindle microtubules move sister chromatids towards the center
Prometaphase
Kinetochore(on centromere)
METAPHASE Mitosis: The equal division of 1 nucleus to 2 genetically identical daughter nuclei
12
• Mitotic spindle fully formed
• Sister chromatids are attached to spindle (at kinetochore) and lined up with chromatids in center of cell
Metaphase
9/20/2015
7
ANAPHASE Mitosis: The equal division of 1 nucleus to 2 genetically identical daughter nuclei
13
• Centromeres of sister chromatids break
• Kinetochores “walk” along microtubules (motor proteins + ATP)
• Parts of spindle attached to kinetochores shorten
• Other parts of spindle lengthen and elongate cell
Anaphase
Nuclearenvelopeforming
TELOPHASE Mitosis: The equal division of 1 nucleus to 2 genetically identical daughter nuclei
14
Telophase• Cell elongation continues
• Nuclear envelopes begin to form around chromosomes
• Chromatin fibers begin to unravel
• Mitotic Spindle Disappears
9/20/2015
8
CYTOKINESIS Division of the cytoplasm; overlaps with telophase; different in plants vs. animals
15
ANIMALS• Cleavage furrow forms• Actin and myosin molecules
contract to close furrow
PLANTS• Cell plate is formed from cell
wall materials• Cell plate divides parental cell
into two daughter cells
CELL DIVISION
16
Interphase Prophase Prometaphase
Metaphase Anaphase Telophase / Cytokinesis
9/20/2015
9
CELL DIVISION
17
INTERPHASE – G1, S Phase G2 – grow and duplicate
MITOSIS – PPMAT – organization and division of “stuff”
1. Prophase – chromosome condense; begin mitotic spindle formation
2. Prometaphase – nuclear envelope breaks, sister chromatids move to center
3. Metaphase – mitotic spindle fully formed, sister chromatids lined up in center
4. Anaphase – sister chromatids split, “walk” to opposite poles, cell elongates
5. Telophase– two nuclei formed, chromosomes uncoil, mitotic spindle disappears
CYTOKINESIS – Splitting 1 cell into two genetically identical cells!
FACTORS THAT AFFECT CELL DIVISIONLab studies have shown that cells divide based on environmental cues
18
• Anchorage Dependence – cells will not divide if they are not in contact with a solid surface
• Density Dependent Inhibition –cells will only grow in a single layer
• Environment Chemistry – cells will only divide if all important nutrients are available and growth factors are present.
Grow cells in culture
No growth factor
No cell division
Add growth factor
Cells divide
9/20/2015
10
GROWTH FACTORS Signal the cell cycle control system to divide
19
G2
G1S
M
G1
checkpoint
Plasma membrane
Controlsystem
Growthfactor
Relay proteins
Receptorprotein
Cytoplasm
• Growth factors are molecules released in the bloodstream that notify a cell to divide.
• Cell division is regulated by the cell cycle control system’s series of checkpoints
CANCER CELLS DIVIDE EXCESSIVELYCancer cells have mutations(s) on genes that affect cell cycle control system proteins
20
• Tumor – a mass of abnormally dividing cells within normal tissue
• Malignant tumors invade other parts of the body (cancer)
• Metastasis – the spread of cancer cells beyond their original site
• Immortal – HeLa cells have been dividing since 1951
Metastasis
Tumor Growth to neighboring tissue
9/20/2015
11
SOMATIC CELLSA typical body cell with two sets of chromosomes
21
• Diploid organisms have homologous chromosomes called autosomes
• Homologous chromosomes carry genes for the same characteristics
• Locus – Gene location on a chromosome
• Sex chromosomes (X & Y)
Locus
Pair of homologousduplicated chromosomes
One duplicated chromosome
Centromere
Sisterchromatids
HUMAN LIFE CYCLEDiploid adults produce haploid gametes that create a diploid zygote. The zygote cells replicate through mitosis as it grows to adulthood.
22
n
n
Sperm cell
Egg cell
Haploid gametes (n = 23)
Ovary Testis
Multicellulardiploid adults(2n = 46)
Diploidzygote(2n = 46)
n
Meiosis
n
Haploid stage (n)Diploid stage (2n)
Key
Fertilization
Mitosis anddevelopment
2n
• Gametes are the only human cells not produced by mitosis
9/20/2015
12
MEIOSIS Cell division that produces haploid gamete cells for sexual reproduction in diploid organisms
23
• Two steps: Meiosis I / Meiosis II
• Working with pairs of homologous chromosomes
• Steps are similar to mitosis
Mitosis deals with one chromosome at a time
Meiosis deals with chromosomes in pairs
MEIOSIS I (PMAT)Duplicated chromosome pairs “cross over” and result in 2 diploid cells
24
Prophase I
Sites ofcrossing over
Sisterchromatids
Sister chromatidsremain attached
Metaphase I Anaphase I
MEIOSIS I: Homologous chromosomes separate
Homologouschromosomesseparate
Tetrad
Telophase I andCytokinesis
Tetrad – four chromatids aligned gene by gene through the process of synapsis
Crossing Over – During synapsis, chromatids exchange segments of genetic
material. This rearranges genetic information. Tetrads are held together at sites of cros
Result: haploid set of chromosomes with sister chromatids still attached
9/20/2015
13
MEIOSIS II (PMAT again)Haploid cells divide again to separate sister chromatids
25
Sister chromatidsseparate
Prophase II
MEIOSIS II: Sister chromatids separate
Metaphase IITelophase I and
Cytokinesis Anaphase IITelophase II
and Cytokinesis
Haploiddaughtercells forming
Cleavagefurrow
MEIOSIS I
Independent orientation at Metaphase II lead to lots of variation in offspring. Possibilities for each gamete = 2n where n = haploid number
26
MITOSIS VS. MEIOSIS