Chapter 8
Cell Growth
In most cases, a living
thing grows because it
produces more and more
cells
Limits of Cell Growth
Number 1
Cell membrane- food oxygen
and water enter and wastes
leave
How fast things enter and
leave depends on the
surface area
How fast products are used
up and waste is produced
depends on the volume
Fig 8-2
Surface Area and volume
do not increase at the same
rate so this is a problem
Number 2
All the information a cell
needs to survive and
function is stored in the
DNA
When a cell is small
enough RNA is made to
make all the proteins a cell
needs
As a cell gets bigger it
does not make more RNA so
there is an information
crisis
As the cell grows there is
not enough RNA to support
its growth
The cell becomes
inefficient
The Solution: Cell
Division
The process where by the
cell divides into two
daughter cells
Draw picture in notes
Rates of Cell Growth
E. coli – divides every 30 minutes
1 day – 14kg mass
3 days – mass of earth
Ideal conditions do not last long
Controls on Cell Growth
Cell behavior – cell growth
and cell division are
carefully controlled
Heart and nervous system
– cells rarely divide
Skin and digestive tract –
cells divide through life
When cells come in
contact with other cells
they stop growing
Scientists are still working
on why this is true
Cell growth can be turned on
Example – a cut, broken bone
Cell growth stops when fixed
Uncontrolled Cell Growth
Results are severe
Cancer – disorder where
cells have lost the ability to
control their own growth
8-2 Cell Division: Mitosis and
Cytokinesis
Eukaryotic Cells
Nucleus and membrane bound
organelles
Eukaryotic cells divide in two steps
1.
Mitosis – the process by which the
nucleus of a cell is divided into 2
nuclei, each with the same number and
kinds of chromosomes as the parent
cell
2. Cytokinesis – process of
the cytoplasm dividing to
form 2 new cells
The process is complex
1.
2.
Large amounts of DNA
need to be separated.
Each cell needs one
copy of a chromosome
Chromosomes
Structures in the cell that
contain the genetic
information that is passed
from one generation to the
next
The cells of different
organisms contain different
numbers of chromosomes
Humans – 46
Goldfish – 94
Dog – 78
Cat – 32
Chromosomes are made of
chromatin.
Chromatin is made of DNA
and proteins.
When a cell is not dividing chromatin is
lose and spread out
When a cell is going to divide
chromatin condenses and chromosomes
become visible
The proteins in chromatin
help in the folding of DNA.
Helps it fit and keeps it
organized.
Total length of DNA
10,000x the length of a
chromosome
Histones
Circular proteins that the
DNA is wrapped around
Nucleosome
Bead like structures of DNA wrapped
around a few histones
Chromosome Structure
Ready to divide
DNA replicated
Chromosomes become visible by
condensing
The structure of eukaryotic chromosomes
Centromere
Sister
chromatids
Supercoil within
chromosome
Chromosome
Continued coiling
within supercoil
Histone H1
Nucleosome
DNA
The chromosome has two
identical parts – 2
Chromatids
The two chromatids are
often called sister
chromatids
Centromere – holds sister
chromatids together
The Cell Cycle
The period of time from
one mitosis to the next
A cell grows, prepares for
division, and divides to
form two daughter cells
Includes mitosis
`
Mitosis – M phase
Interphase
G1 – growth and activity
S- DNA replication
G2 – growth and activity
Some cells in the body go
through the cell cycle every
6 hours
Some cells never do
(nerve and muscle)
Interphase
Long
Period between cell
divisions
3 phases – G1, S, G2
G1 – (gap1) – growth and
development
S (DNA synthesis phase) –
replication
Proteins associated with
chromosomes are also made
G2- gap 2 – shortest phase
Synthesis of materials
needed for cell division
During interphase the cell
is active
Proteins are made
DNA is copied
ATP is made and used
Cells that are specialized
do their thing
Example - secretion
Do Now
What are the 2 phases of the cell cycle?
What happens in g1?
What happens in S phase?
What happens in the g2 phase?
What is chromatin?
What are histones and nucleosomes?
What do uncopied chromosome s look like?
What do copied chromosomes look like?
How many chromosomes do humans have?
Mitosis is divided into 4 stages.
Prophase (Ready)
Metaphase (Middle)
Anaphase (away)
Telophase (two)
Prophase
Longest phase
50-60% of total mitosis
time
Chromosomes become
visible – coil tightly
Centrioles separate and
move to opposite sides
Chromosomes attach to
the spindle
Nucleolus disappears
Nuclear envelope breaks
down
Spindle
Meshlike structure that
develops from the
centrioles
Helps chromosomes move
Metaphase
Shortest – few minutes
Chromosomes line up at
the center of the cell
Anaphase
Centromeres that join sister
chromatids split
Sister chromatids separates into
individual chromosomes
Chromosomes separate into two groups
near the poles
Over when chromosomes
separate
Telophase
Chromosomes loosen up –
go back to chromatin
Occurs in the area where
the nucleus will form
Nuclear envelope reforms
Nucleolus becomes visible
Mitosis is over
Cytokinesis
Last step in cell division
Two nuclei form – each
with a set of chromosomes
Cytokinesis – division of
the cytoplasm
Animal Cells – cell
membrane pinches in
Plant cells – cell plate
forms down the middle
The cell wall forms in the
cell plate
Plant Cell undergoing
Mitosis
Mitosis Movie
9-3 Meiosis
A type of cell division that gametes (eggs and
sperm) undergo
A cell has two copies of each chromosome.
Humans have 46 chromosomes or 23 pairs.
Homologous Chromosomes
Two chromosomes that make up a pair
Carry the same types of information
One originally came from mom and one
originally came from dad
Diploid
A cell with pairs of chromosomes
One from mom and one from dad
2N
Diploid number for humans is 46
Haploid
A single set of chromosomes
1N
Autosomes
Body cell chromosomes
Humans have 22 pairs
Sex Chromosomes
X and Y
Humans have two
Females have 2 X chromosomes
Males have an X and Y chromosome
Karyotype
A picture of all of the chromosomes found in
one cell.
Can be used to determine gender and genetic
diseases.
Meiosis
2N produces 1N
Process of reduction division in which
the number of chromosomes per cell is
cut in half
2 rounds of cell division
Meiosis I and Meiosis II
Produces gametes (eggs and sperm)
Meiosis I
Prophase I
Metaphse I
Anaphase I
Telophase I
Tetrad
`
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Telophase II produces gametes (IN)
(eggs or sperm)