Download Chapter 10

Chapter 10
Cell Growth and Division
10-1 Cell Growth
• Objectives:
– Explain the problems that growth causes for cells
– Describe how cell division solves the problems of
cell growth
Limits to Cell Growth
• Cells are small for a reason
• As cells grow
1. Greater demand is placed on the DNA
-DNA is responsible for all cell
functions, so a larger cell means
more cellular reactions that need to
take place
2. Moving materials in and out of the cell
becomes more difficult
Ration of Surface Area to Volume
Cell Size
5 cm
10 cm
Surface
Area
(l×w×6)
Volume
(l×w×h)
SA to
Volume
Ratio
150 cm2
600 cm2
125 cm3
1000 cm3
150/125
= 6:5
600/1000
= 6:10
• Volume increases more rapidly than surface area
• Becomes difficult for cells to bring in necessary
nutrients and eliminate waste produced
Division of the Cell
• Process by which a cell divides in two
• Reasons:
–
–
–
–
Growth (multicellular organism)
Repair (multicellular)
Reproduction (unicellular, asexual)
Maintenance
• Before cells can divide, DNA must be copied
– Each daughter cell receives a complete copy of the cell’s
genetic information
• Resulting cells are small enough (increased ratio of
surface area to volume) to allow for efficient materials
exchange with environment
10-2 Cell Division
• Objectives:
– List and explain the main events of the cell cycle
– Describe the 4 stages of mitosis
Cell Division in Prokaryotes vs.
Eukaryotes
• Prokaryotes- copy the single chromosome and
split contents into two cells
– Called binary fission
• Eukaryotes, more complex process
– Mitosis-division of nucleus, followed by
– Cytokinesis- division of cytoplasm
Chromosomes
• Chromosomes are made of DNA that is highly
organized
Chromosome Structure
• You are looking at a chromosome and
its copy
• The result is identical sister chromatids
attached by a centromere
• One chromatid goes to each of the
daughter cells
• A human body cell entering cell
division contains 46 chromosomes,
each of which contains 2 sister
chromatids
chromosome
(condensed form)
How many chromosomes do we have
now?
Fight the urge. This is still considered a
SINGLE chromosome since they are
identical and attached. After replication of
the chromosome, it is still considered one
chromosome!
Diploid Number
• Each organism has a specific number of
chromosomes, for humans it is 46
– 23 pairs of homologous chromosomes
• The total number is referred to as the diploid
number (2n)
Chromosome Numbers
The Cell Cycle
• The Cell Cycle is a series of events that cells go
through as they grow and divide
• It’s a combination of 2 main phases
• Interphase- the period of growth between
divisions
– Includes 3 subphases G1, S, and G2
– (accounts for ~90% of time spent in cell cycle)
• M phase- consisting of mitosis and cytokinesis
Cell Cycle
• Actively dividing cells take
about 24 hours to
complete this cycle
• Cells that don’t divide are
“stuck” in G1
M phase
Interphase
Interphase
• Consists of
– G1 phase (growth, really gap)
– S phase (synthesis of DNA)
– G2 phase (growth, really gap)
G1 Phase
• Cell grows in size
• Protein and organelle production increased
• Gather and synthesize nutrients
– ex. Make the 6 billion nucleotides needed to
replicate the DNA. Acquire/synthesize enough
amino acids to build all the required proteins to
divide the cell, etc…
Cells can hang in this subphase for a very
long time like certain muscle cells or
forever like cardiac (heart) muscle or
neurons, which do not divide at all…
S phase
• Enzymes make an exact copy of
the DNA
– Every chromosome has a copy,
DNA has doubled, but there are
still only 46 chromosomes
– Why?? Remember that sister
chromatids (original DNA and the
copy) only equal one
chromosome
• Centrosomes replicate
• Centrosomes, also called
asters, hold the centriole pair
Centrosome Structure
• Microtubules from the centrioles are what pull sister chromatids apart
during mitosis
G2 phase
• More growth and organelle production
– Shortest of the Interphase subphases
– Once finished, mitosis begins
M phase
Mitosis
• Four Stages:
– Prophase (pro- means first)
– Metaphase (meta- means middle/after)
– Anaphase (ana- means apart)
– Telophase (telo- means far away/end)
Prophase
• Longest phase of mitosis
• Chromosomes become visible
• Centrioles (animal cells only)
migrate to opposite ends of the
cell
• Mitotic spindle starts to form
– Spindle fibers form in foot ball
shape across cell
• Spindle attaches to each
chromosome near the
centromere
• Chromosomes coil more tightly
• Nuclear envelope and nucleolus
disintegrate
Prophase
Chromatin condenses into
chromosomes
Metaphase
• Chromosomes line up
in the middle
(equator) of the cell
• Spindle fibers attach
to centromeres
Metaphase
Anaphase
• Centromere holding sister
chromatids together splits
separating chromosomes
• Spindle fibers shorten,
pulling chromatids apart to
opposite ends of cell
• Animal cells begin to pinch
in
• Plant cells begin to form
cell plate in the middle
Anaphase
Telophase
• Nuclear membrane built
from ER around each
set of chromosomes
• Nucleolus reforms in
each nucleus
• Spindle breaks down
• Chromosomes become
mass of chromatin again
Telophase
Two cells dividing into
four
Cleavage
furrow
forming
(animal cells)
Cytokinesis
• Final division of cytoplasm resulting in two
daughter cells
– Animals – cell membrane pinches together
– Plants – cell plate forms new cell membrane
dividing the daughter cells
• Often happens at the same time as telophase