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Cell Division & Mitosis
RUSSELL BIOLOGY
RHODES AP BIO
Multicellular organisms are made of cells and cell products
Multicellular organisms have divided from a single cell
Most cells are specialized
Regeneration is a limited property
Cells must form 3-D organism with specialized tissues in specific locations
Zebra fish (Danio rerio) grows new fin when attacked by Knifefish (Notopterus
notopterus)
10.1 Overview: The Cycle of Cell Growth and Division
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STEPS
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Cell growth and everyday activity like making proteins from accessible DNA
regions called genes and making of new organelles and structures
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DNA replication
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DNA (chromosomes) segregated into equal parts; even distribution
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DNA moved into two new nuclear regions
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Cytoplasm divided; fairly even distribution
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2 new cells; genetically identical to each other and the parent
PURPOSES
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Growth
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Maintenance
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Repair
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Reproduce
Concepts
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DNA is chemical that stores information
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Genes are regions of chromosomes that code for proteins
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A-T, C-G (Purines and pyrimidines)
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Double helix
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Chromosomes are individual and linear
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Replication
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Chromosomes that have replicated are called sister chromatids and are
joined at kinetochores by centromeres, forming arms
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Cell division is used for
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Growth = larger organisms
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Replacement = due to wear and tear
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Repair = to fix wounds
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Reproduction of single celled eukaryotes
Duplicates
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Chromosomes are replicated
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Cells produced are identical genetically to each other AND to the cell produced
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In meiosis cells generated have potential to be genetically different and contain ½ the DNA of the
parent cell = gametes
Partitioning of Chromosomes
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2 copies of each chromosome = Diploid;
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These are homologous meaning they have the same genes in the same positions and sequences
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1 copy of each chromosome = haploid
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“ploidy “ refers to chromosome sets
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Chromosomes replicate into sister chromatids ( for a phase there are 4 of each)
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Sister chromatids move apart in Segregation
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Each cell gets one of each set of chromatids; pairs of homologous chromosomes creating CLONES
10.2 Overview: The Mitotic Cell Cycle
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Cell Cycle = Interphase + Mitosis + Cytokinesis
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Interphase
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Between NUCLEAR divisions
Phases of Mitosis
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Prophase
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Prometaphase
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Metaphase
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Anaphase
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Telophase
Cytokinesis
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Animal cells “furrow” with a band of microfilaments pinching the cell into two
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Plant cells deposit material for new cell wall starting at midpoint
Concepts
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Chromatid
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Kinetochore
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Spindle
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Centrosome
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centriole
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Microtubules
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Metaphase plate (plane)
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Segregation
Page 207
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Interphase = between divisions
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G1 = chromosomes as chromatin, dark nucleus, everyday protein synthesis; cell growth
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S= synthesis or REPLICATION of DNA; chromosomes are sister chromatids
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G2 = cohesions; centrosomes have replicated; new organelles
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G0 = sometimes cells are suspended and won’t divide again (not the typical scenario)
Mitosis= division of eukaryotic nucleus
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Prophase= chromosomes visible (chromatids); nucleus disintegrating;
centrosomes moving and creation of spindle occurring
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Prometaphase= nucleus gone, spindle formed; kinetochores attached to spindle; tugging starts
to move chromosomes to metaphase plane
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Metaphase= chromosomes aligned at spindle midpoint
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Anaphase= kinetochores separate and chromatids/ now chromosomes move toward poles
along the spindle microtubules; cohesions are cut
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Telophase= two separate nuclei (piles of chromosomes at the poles) now begin to uncoil and
become chromatin, nuclei are rebuilt; cytokinesis has started; clones will be created
Cytokinesis= physical division of cytoplasm
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Animal = cleavage furrow
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Plant= cell plate
10.3 Overview: Formation and Action of the Spindle
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Plant cells
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No centrosomes – spindle forms around nucleus
Animal cells
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Centrosomes divide and two parts move apart
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Microtubules form creating the spindle
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Kinetochore microtubules
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Pole to kinetochore of chromosome
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Motor proteins of kinetochore WALK chromosome along microtubule
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Motor proteins at poles pull kinetochore microtubules
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Movement is species and cell-type specific
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Anaphase
Non-kinetochore microtubules
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Pole to overlap region at metaphase plane without chromosomes
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Overlap region is reduced and cell lengthens
10.4 Overview: Cell Cycle Regulation
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Check points for starting critical phases
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Internal check points
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Cyclin and cyclin dependent protein kinases (Cdk)
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Cyclin + phosphate (phosphorylation) = Cdk
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Initiate or regulate 4 key events
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External check points
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Surface receptors and binding sites for proteins
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G1, G1/S, S and M
Growth hormones, peptide hormones, surface groups, matrix
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Speed/ slow/ stop
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Contact inhibition
Cancer
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Control of cell cycle is lost, continuous and uncontrolled growth of cells = mass
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oncogenes
SEE PAGE 217
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Control proteins called Cyclins regulate function of many checkpoints
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Cyclins are proteins (work based on concentration) and Cdk are enzymes (function
when phosphorylated and connected to cyclin) and cause action to occur
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1. G1/S checkpoint
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Cell is stopped ; waiting for extracellular signals, checking for DNA damage; needs growth factor
to procede.
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MAIN check point; once past G1/ S committed to mitosis
2. G2/M checkpoint
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Stopped before Mitosis if DNA didn’t replicate
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Insure identical daughter cells
3. Mitotic Spindle checkpoint
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Check at metaphase to see if chromosomes and kinetochores attached to spindle; insures even
distribution of DNA
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MPF Maturation Promoting Factor
10.5 Overview: Cell Division in Prokaryotes
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Replication of DNA caused by enzymes
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Two circles of DNA migrate to opposite ends of cell
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Move as they are attached to CM and cell is elongating
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CW grows inward to create two cells
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“ Theta replication”
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“Binary fission”