CHAPTER 10 CELL GROWTH & DIVISION

10-1 Cell Growth  How 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/out  Surface area to volume ratio  Volume 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 nucleus  Cytokinesis- division of the cytoplasm

Mitosis  Can be…  Reproduction (asexual)- unicellular organisms  Growth + development- multicellular organisms  Occurs right after egg is fertilized (embryo)

Chromosomes  Chromosomes- carry genetic information (DNA)  Condense at the beginning of cell division  Chromosomes replicate forming sister chromatids  Centromere- area where chromatids attach  Organisms have a specific # of chromosomes  Humans = 46

The Cell Cycle  Series of events cells go thru as they grow + divide  Grow, prepare for division, divide, grow again…

Cell Cycle Phases  4 phases:  1. M phase- mitosis and cytokinesis  2. G1 phase- most of growing  3. S phase- chromosome replication  4. G2 phase- prepare for mitosis  G1, S and G2 = “interphase”

Mitosis  Division of nucleus  Major part of M phase of cell cycle  4 parts (PMAT)  1. Prophase  2. Metaphase  3. Anaphase  4. Telophase

Prophase  Longest  Chromosomes condense  Centrioles move to opposite sides of cell  form spindles  Nucleolus gone/ nuclear envelope disappears

Metaphase  Chromosomes line up on metaphase plate  Centromeres attach to the spindle

Anaphase  Centromeres split- 2 sister chromatids become individual chromosomes  Move along spindle to opposite ends of cell

Telophase  Nuclear envelope forms at each end  Spindle disappears  Nucleolus forms

Cytokinesis  Division of the cytoplasm  Usually occurs at the same time as telophase  Animals- cell membrane draws in + pinches off  Plants- 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 Division  Can be turned on/off

Cell Cycle Regulators  Cyclin- protein that regulates timing of cell cycle  When injected into non-dividing cell, cell would then divide  Cyclin protein family- several proteins

Cyclins  2 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 Growth  Can have severe/deadly consequences  Cancer- when cells do not respond to signals to regulate growth and division  Cause 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