Transcript CHAPTER 10

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