CHAPTER 10

CELL GROWTH & DIVISION

10-1 Cell GrowthHow do we grow?

Our cells divide!

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

Metaphase

Chromosomes line up on metaphase plateCentromeres attach to the spindle

AnaphaseCentromeres split- 2 sister chromatids become

individual chromosomesMove along spindle to opposite ends of cell

TelophaseNuclear envelope forms at each endSpindle disappearsNucleolus forms

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

Controls on Cell DivisionCan be turned on/off

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)

Causes of uncontrolled cell growth:

Failure to respond to internal or external regulators (cyclins)

Ex: P53- gene that normally stops cell cycle until all DNA is copied Defect causes uncontrolled cell division