Cell Division & Mitosis RUSSELL BIOLOGY RHODES AP BIO
Dec 27, 2015
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
STEPS
Cell growth and everyday activity like making proteins from accessible DNA regions called genes and making of new organelles and structures
DNA replication
DNA (chromosomes) segregated into equal parts; even distribution
DNA moved into two new nuclear regions
Cytoplasm divided; fairly even distribution
2 new cells; genetically identical to each other and the parent
PURPOSES
Growth
Maintenance
Repair
Reproduce
Concepts DNA is chemical that stores information
Genes are regions of chromosomes that code for proteins
A-T, C-G (Purines and pyrimidines)
Double helix
Chromosomes are individual and linear
Replication
Chromosomes that have replicated are called sister chromatids and are joined at kinetochores by centromeres, forming arms
Cell division is used for
Growth = larger organisms
Replacement = due to wear and tear
Repair = to fix wounds
Reproduction of single celled eukaryotes
Duplicates
Chromosomes are replicated
Cells produced are identical genetically to each other AND to the cell produced
In meiosis cells generated have potential to be genetically different and contain ½ the DNA of the parent cell = gametes
Partitioning of Chromosomes
2 copies of each chromosome = Diploid;
These are homologous meaning they have the same genes in the same positions and sequences
1 copy of each chromosome = haploid
“ploidy “ refers to chromosome sets
Chromosomes replicate into sister chromatids ( for a phase there are 4 of each)
Sister chromatids move apart in Segregation
Each cell gets one of each set of chromatids; pairs of homologous chromosomes creating CLONES
10.2 Overview: The Mitotic Cell Cycle Cell Cycle = Interphase + Mitosis + Cytokinesis
Interphase
Between NUCLEAR divisions
Phases of Mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Animal cells “furrow” with a band of microfilaments pinching the cell into two
Plant cells deposit material for new cell wall starting at midpoint
Concepts
Chromatid
Kinetochore
Spindle
Centrosome
centriole
Microtubules
Metaphase plate (plane)
Segregation
Page 207
Interphase = between divisions G1 = chromosomes as chromatin, dark nucleus, everyday protein synthesis; cell growth
S= synthesis or REPLICATION of DNA; chromosomes are sister chromatids
G2 = cohesions; centrosomes have replicated; new organelles
G0 = sometimes cells are suspended and won’t divide again (not the typical scenario)
Mitosis= division of eukaryotic nucleus Prophase= chromosomes visible (chromatids); nucleus disintegrating;
centrosomes moving and creation of spindle occurring Prometaphase= nucleus gone, spindle formed; kinetochores attached to spindle; tugging starts to
move chromosomes to metaphase plane
Metaphase= chromosomes aligned at spindle midpoint
Anaphase= kinetochores separate and chromatids/ now chromosomes move toward poles along the spindle microtubules; cohesions are cut
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 Animal = cleavage furrow
Plant= cell plate
10.3 Overview: Formation and Action of the Spindle
Plant cells
No centrosomes – spindle forms around nucleus
Animal cells
Centrosomes divide and two parts move apart
Microtubules form creating the spindle
Kinetochore microtubules
Pole to kinetochore of chromosome
Motor proteins of kinetochore WALK chromosome along microtubule
Motor proteins at poles pull kinetochore microtubules
Movement is species and cell-type specific
Anaphase
Non-kinetochore microtubules
Pole to overlap region at metaphase plane without chromosomes
Overlap region is reduced and cell lengthens
10.4 Overview: Cell Cycle Regulation Check points for starting critical phases
Internal check points
Cyclin and cyclin dependent protein kinases (Cdk)
Cyclin + phosphate (phosphorylation) = Cdk
Initiate or regulate 4 key events
G1, G1/S, S and M
External check points
Surface receptors and binding sites for proteins
Growth hormones, peptide hormones, surface groups, matrix
Speed/ slow/ stop
Contact inhibition
Cancer
Control of cell cycle is lost, continuous and uncontrolled growth of cells = mass
oncogenes
SEE PAGE 217 Control proteins called Cyclins regulate function of many checkpoints
Cyclins are proteins (work based on concentration) and Cdk are enzymes (function when phosphorylated and connected to cyclin) and cause action to occur
1. G1/S checkpoint
Cell is stopped ; waiting for extracellular signals, checking for DNA damage; needs growth factor to procede.
MAIN check point; once past G1/ S committed to mitosis
2. G2/M checkpoint
Stopped before Mitosis if DNA didn’t replicate
Insure identical daughter cells
3. Mitotic Spindle checkpoint
Check at metaphase to see if chromosomes and kinetochores attached to spindle; insures even distribution of DNA
MPF Maturation Promoting Factor
10.5 Overview: Cell Division in Prokaryotes
Replication of DNA caused by enzymes
Two circles of DNA migrate to opposite ends of cell
Move as they are attached to CM and cell is elongating
CW grows inward to create two cells
“ Theta replication”
“Binary fission”