WHY our cells divide…Why don’t our cells just get bigger?1. increased demands on DNA
Like a library…
2. harder to move nutrients/wastes in/outSurface area to volume ratioVolume increases faster Like a street…
vs.
What do we call this? Cell division: the process by which a cell divides into 2
daughter cells First, must copy DNA
Why? So each daughter cell gets their own set
Smaller size cells = better surface area to volume ratio
10-2 Cell Division
Two main parts:Mitosis- division of nucleusCytokinesis- division of the cytoplasm
MitosisCan be…Reproduction (asexual)- unicellular organismsGrowth + development- multicellular organisms
Occurs right after egg is fertilized (embryo)
ChromosomesChromosomes- carry genetic information (DNA)Condense at the beginning of cell divisionChromosomes replicate forming sister
chromatidsCentromere- area where chromatids attachOrganisms have a specific # of chromosomes
Humans = 46
The Cell CycleSeries of events cells go thru as they grow + divideGrow, prepare for division, divide, grow again…
Cell Cycle Phases
4 phases:1. M phase- mitosis and cytokinesis2. G1 phase- most of growing3. S phase- chromosome replication4. G2 phase- prepare for mitosis
G1, S and G2 = “interphase”
MitosisDivision of nucleusMajor part of M phase of cell cycle4 parts (PMAT)
1. Prophase 2. Metaphase 3. Anaphase 4. Telophase
Prophase
LongestChromosomes condenseCentrioles move to opposite sides of cell
form spindlesNucleolus gone/ nuclear envelope disappears
AnaphaseCentromeres split- 2 sister chromatids become
individual chromosomesMove along spindle to opposite ends of cell
CytokinesisDivision of the cytoplasmUsually occurs at the same time as telophaseAnimals- cell membrane draws in + pinches offPlants- cell plate forms
Followed by cell membrane then cell wall
10-3 Regulating the Cell Cycle
Specific cell types are highly controlled Muscle + nerve cells- don’t divide once fully
developed Skin cells + bone marrow- constantly divide to
replace old cells
Cell Cycle Regulators
Cyclin- protein that regulates timing of cell cycleWhen injected into non-dividing cell, cell would
then divideCyclin protein family- several proteins
Cyclins2 main types:1. internal regulators- respond to events inside cell
Ex: cell wont enter mitosis if all DNA is not copied
2. external regulators- respond to events outside cell Direct cell to speed up/slow down division Ex: growth factors- speed up during embryo
development/ slow down when they contact another cell
Uncontrolled Cell GrowthCan have severe/deadly consequencesCancer- when cells do not respond to signals to
regulate growth and divisionCause masses (tumors)