The Cell Cycle
Dec 27, 2015
The Cell Cycle
Genetic Information Genome: cell’s genetic
information DNA organized into
chromosomes• Diploid (2n): 2 sets of
chromosomes … somatic (body) cells
• Haploid (1n): 1 set of chromosomes… gametes (sex cells]
Sex Chromosomes – determine the sex of an organism
Autosomes- carry traits; not linked to sex
Chromosomes
Before cells divide, their DNA coils up tightly into chromosomes
Chromatin: DNA-protein complex that makes up chromosomes
Chromatids: replicated strands of a chromosome
Centromere: narrowing “waist” of sister chromatids
Functions of Cell Division
Unicellular reproduction Growth/Development Renewal/Repair
The Cell Cycle
Interphase (90% of
cycle) • G1 phase~ growth
• S phase~ synthesis
of DNA • G2 phase~
preparation for cell division
Mitotic phase• Mitosis~ nuclear
division • Cytokinesis~
cytoplasm division
Interphase
Growth 1 (G1)• Cell grows
Synthesis (S)• DNA replicates
Growth 2 (G2)• Cell grows and
prepares to divide
Mitotic Spindle
Spindle fibers (microtubules) originate from the centrosome• Some animal cells contain
centrioles Aster- short array of
microtubules that extend from centrosome
Kinetochore- protein structure on chromosomes that microtubules attach to
Mitosis
Prophase Prometaphase Metaphase Anaphase Telophase
Prophase
Chromosomes visible
Nucleoli disappear
Sister chromatids Mitotic spindle
forms Centrosomes
move to opposite ends of cell
QuickTime™ and aCinepak decompressor
are needed to see this picture.
Prometaphase
Nuclear membrane fragments
Spindle interaction with chromosomes
Kinetochore develops
QuickTime™ and aCinepak decompressor
are needed to see this picture.
Metaphase
Centrosomes at opposite poles
Centromeres are aligned
Kinetochores of sister chromatids attached to microtubules (spindle)
QuickTime™ and aCinepak decompressor
are needed to see this picture.
Anaphase
Paired centromeres separate; sister chromatids liberated
Spindle fibers shorten at the kinetochore end
Chromosomes move to opposite poles
Each pole now has a complete set of chromosomes
QuickTime™ and aCinepak decompressor
are needed to see this picture.
Telophase/Cytokinesis
Telophase• Daughter nuclei form• Nuclear envelopes
arise• Chromatin becomes
less coiled• Two new nuclei
complete mitosis Cytokinesis
• Cytoplasmic division
Plant and Animal Cytokinesis
Plant Mitosis
Bacteria Division
Prokaryotes divide by binary fission• Chromosome
duplicates• Cell grows• Membrane
pinches inward• Two identical
cells result
Evolution of Mitosis
The “missing links” between prokayrotic binary fission and eukaryotic mitosis
How do they know when to split?
Cell cycle has a control system
Cells pass through “checkpoints” • “Go-ahead” signal
cell continues to copy DNA and divide
• No signal cell leaves cell cycle and enters into G0 phase (no growth occurs)
Chemical Controls
Protein kinases activate or deactivate cells• “Stop” and “go”
signals To be active,
kinases must be attached to a cyclin (Cdks)• MPF (maturation –
promoting factor)~ triggers M-phase
Keeping Division in Check
Growth factors• Protein that
stimulates cells to divide
Density-dependent inhibition• Crowded cells stop
dividing Anchorage
dependence• Cells must attach
to a substrate to divide
Dividing Cells Gone Wild Transformation of single cell
• If not destroyed, will reproduce and form a mass of cells (tumor)
Benign or malignant• If cells don’t spread benign• Malignant tumors spread and/or damage major
organs Metastasis
• Spread of cells from original site • Through lymph and blood vessels