Download Energy in the Cell

Cell Growth and Division
Ch. 8
Cell Size and Limitation
• Cells come in a variety • What is diffusion?
of sizes.
– Diffusion limits cell
size
– DNA content limits
size
Diffusion and DNA limit cell size
because…
• Cells rely on diffusion
to carry on proper
functions
– Cells require a constant
supply of glucose and
oxygen
– Cells must constantly
get rid of waste.
• DNA is found in all
cells.
– The larger the cell, the
greater number of
enzymes
– DNA makes enzymes
needed for the cell
Is bigger better?
• Surface Area to
Volume Ratio
– As the cell size
increases, its volume
increases 2x
faster….why is this a
problem?
Other ways to solve
the problem
• If cell size doubled, it
would be an 8 fold
increase in volume, but
the surface area would
only increase 4 fold.
Therefore, there is not
enough membrane for
nutrients to flow through
to keep the cell alive.
How do cells overcome this
problem?
• What do you think?
– How will you get more
membrane to
compensate for the
volume?
• They divide into 2
cells allowing for
twice as much
membrane to be
formed.
1.7a Cell growth and division are caused by complex
interactions between the different kinds of molecules in
the cell.
3 purposes of cell division
1. Growth
• 1.8a All growth and
development within a
2. Repair
cell is a consequence
3. Reproduction
of an increase in cell
a. Asexual- offspring
number, size and/or
produced only by one
products.
parent. (bacteria)
b. Sexual- produces offspring
that have a combination of
genetic material from two
parent organisms.
Rate of Cell Division
• The Pituitary gland
secretes a growth
hormone that tells
cells when to divide
and how much. If you
lack this hormone,
dwarfism may occur.
1.7b Molecules from different parts of the cells, such
as hormones, can affect cell behavior.
Structure of eukaryotic
chromosomes
• Before cell division, each
chromosome is replicated.
• Each chromosome consists
of 2 identical sister
chromatids.
• Each sister chromatid will
separate from each other
during cell division and go
into its new cell.
• Centromere region also
called kinetochore.
• When chromatin coils
it becomes
______________?
Chromosome Structure
Histones are proteins that are wrapped up by DNA in the
chromosome structure consisting of chromatin. This is
then coiled many times within the chromosome.
1.1a All of the cells in your body come from a single cell
that differentiates into many different cells, but they all
essentially have the same genetic instructions.
• 1.11 All organisms
begin their life cycles
as a single cell, and in
multicellular
organisms, new
generations of
embryonic cells form
by cell division.
1.8b Cells differentiate from each other because of
gene expression and/or environmental influences.
• Certain genes can be
turned off or on at
certain time.
(Expresses or not
expressed).
• The environment can
influence what cells
are expressed or not.
This also causes cells
to differentiate.
The Cell Cycle
• The cell cycle is the
repeated sequence of
cell growth
(interphase) followed
by cell division
(mitosis)
• 5 phases
–
–
–
–
–
Interphase
Prophase
Metaphase
Anaphase
Telophase
Mitosis
Mitosis- process of nuclear division followed by cytoplasmic division.
SOMATIC CELLS (body cells)
Mitosis vs. Meiosis
• Mitosis
– Somatic cells
– 1 cell division
– 2 daughter identical to
parent
• Meiosis
– Gametes
– 2 divisions
– Daughter cells have
half of genetic info as
parent.
Interphase…a busy time (90% of
cell cycle)
• Cell activities during
interphase:
–
–
–
–
–
–
–
–
–
Make ATP
Repairing themselves
Excreting wastes
Making proteins
Producing new organelles
Duplicating DNA
Chromatin duplicates
Metabolism
Cell growth in size
• 3 phases:
– G1: normal growth
phase (9 hours)
– S: DNA is replicating
(10 hours)
– G2: final growth in
preparation for mitosis
(2 hours)
Structure of the Chromosome
• Each chromosome has
two identical partssister chromatids that
are held together by a
centromere.
Chromosome number
• Somatic Cells (body cells) of a particular
species have the same number of
chromosomes (humans have 46 or 23 pairs).
• Chromosome number (n) tells how many of
each type of chromosome is in the cell.
– 1n (haploid), 2n (diploid)
Other structures used..
• Centrioles are a pair of
cylindrical structures made of
microtubules that are only found
in animal cells and found just
outside the nucleus.
• Spindles are cagelike structures
that are made of microtubules
and used to separate sister
chromatids.
• Spindle fibers are the individual
microtubules of the spindle.
Prophase- the first phase
• Chromatin coils and becomes
chromosomes.
• The nucleus disappears.
• Centrioles migrate to opposite
poles of the cell. Made of
microtubules.
• The spindle forms and attaches
to the centrioles and
centromere.
• Centrosome is where
microtubules originate.
Metaphase- the
• Chromosomes line up
along the equator
• Spindle fibers attach
to the centromeres.
nd
2
phase
Anaphase- the
• Sister chromatids
separate and
centromeres split
apart.
rd
3
phase
Telophase- the
• The “reverse” of
prophase
– Chromosomes uncoil
to make chromatin
– Spindle fibers
disappear
– Nucleus forms
– Plasma membrane
begins to from between
2 nuclei.
th
4
phase
The final step
• Cytokinesis- the division of the
cytoplasm that results in two
new daughter cells.
• CELL CLEAVAGE- split in two
• In plants, a cell plate forms
across the equator, so the
membrane doesn’t have to pinch
in.
• ** Centrioles are not found in
plant cells during cell division.
Mitosis in motion
The result
• Each new daughter cell will have complete set of genetic
material.
Apply Chromosome number
•
•
•
•
•
•
•
•
Human somatic cell (46 or 23 pairs)
G1
S
G2
P
M
A
T
Cell Cycle Regulators
• Cyclins are proteins that
regulate the timing of the cell
cycle in eukaryotic cells.
– Ex. Kinases end DNA
replication.
• Internal Regulators- proteins
that respond to events inside
the cell.
• External Regulators- direct
cells to speed up or slow
down cell cycle.
External or Internal?
– Make sure cell doesn’t
enter mitosis until all its
chromosomes have been
replicated.
– Growth factors.
– Prevents cell from entering
anaphase until all of its
chromosomes are attached
to mitotic spindle.
Enzymes control the cell
• Some control progression
from one phase to another.
• Come inhibit progression.
• If too much or not enough
is produced it can lead to
cell death or cancer.
• Genes control enzyme
production.
• Contact inhibition is
another way the cell
cycle is controlled.
Cells normally stop
dividing when they
come into contact with
each other.
1.7a Cell growth and division are caused by
complex interactions between the different
kinds of molecules in the cell.
Cancer..A Mistake in the Cycle
• Cancer is thought to be due to
•
changes in genes that make enzymes
involved in the cell cycle.
• Cells divide when they shouldn’t.
• Cancer cells do not respond to the •
signals that regulate the growth of
most cells.
• Oncogenes
• Malignant vs. Benign
• Neoplasm- abnormal masses of cells
that have lost control over growth
and cell division.
Cancer cells can break away
from a tumor (large mass) and
travel through the blood to
other areas in the body.
Gene p53 normally stops the
cell cycle until all
chromosomes have been
replicated, but if there is a
defect, growth is not controlled.
Characteristics of cancer
1. Grow and divide abnormally
2. Cell membrane is leaky, cytoskeleton is
disorganized.
3. Cells have a weakened capacity for
adhesion and may break away to move to
other sites in the body (metastasis).
4. Cancer cells can have lethal effects.
Other causes of cancer
•
•
•
•
Cigarette smoke
Air and water pollution
UV radiation
Certain viruses
– Cervical cancer -HPV
– Mesothemioma
– Liver cancer- Hep B
• Some people may be born
with genetic mistakes
which may cause cancer.
– Gene p53.
• Cancer is the 2nd
leading cause of death
in the U.S. Heart
disease is #1.
Stem Cells
• Stem cells are unspecialized
• Neurons are noncells that have the potential to
replaceable.
differentiate to become
specialized in structure and
• Embryonic stem cell
function into a wide variety of
research is very
cell types.
controversial because the
• In early embryonic development,
cells are taken from a
stem cells produce every type of
human embryo.
tissue in the body.
• Transplants fail- different
• Stem cells in bone marrow can
genetic info.
make more than a dozen types of
blood cells.
3 kinds of stem cells
1. Totiopotent- the egg and the cells that result
from early cell division. Human fertilized egg
has the potential to form a whole organism.
2. Pluripotent- forms five days after fertilization
(blastocyst- outer layer of cells and inner cell
mass). Inner cells form tissue of human.
3. Mulitpotent- pluripotent cells specialize further
to give rise to specialized cells. Present in adults.
Which type of cells do you think are used for
medical therapies? Why?
Pluripotent
Cell Cycle Review
• Click on the following link, then click on
your book and go to Ch. 10 and take the
Self-Test and do the Active Art.
• Ch. 10 Review
Meiosis and Sexual Reproduction
Ch. 9
Meiosis….Some terms to know
• Haploid (1n)- a cell
with only one
complete set of
chromosomes
(gametes or sex cells).
Diploid (2n)- a cell
that contains two
complete sets of
chromosomes. (all
other cells)
Which are diploid and which are haploid?
How do you know sex cells (eggs and sperm) are only haploid?
Homologous Chromosomes
come from a Tetrad
• Homologous
chromosomes are
pairs of chromosomes
where each one is
identical to the other.
• A tetrad is a structure
containing 4 strands of
DNA tightly paired
together.
Meiosis
• There is a meiosis I and II.
Each are the same steps as
mitosis.
• You begin with one diploid
cell and produce 4 haploid.
• This gives you many
different combinations of
genes to be passed on. It’s all
chance on the ones you get.
Crossing Over
• Occurs during
prophase 1 when
homologous
chromosomes pair up
and form tetrads and
exchange portions of
chromatids.
Meiosis Provides for Genetic
Recombination
• 1.28a Sorting and
recombination of
genes in sexual
reproduction, allows
for a great variety of
possible gene
combinations.
• That is why no two
people are alike.
(Besides identical
twins- why?)
1.46 A great diversity of species increases the chance
that at least some living things will survive in the
face of large changes in the environment.
• Why is this?
• So, is diversity good?
Give an example.
The Steps…Let’s review.
•
•
•
•
•
•
•
•
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
TelophaseII
• What occurs during
each step?
Terms to know
• Zygote- diploid cell resulting from fusion of
egg and sperm: a fertilized egg.
• Embryo- early developmental stage of an
organism that takes place within an egg,
see, or body of its mother. From time of
conception to eighth week of pregnancy.
Gamete Formation in Plants
• Plant spores- 1n
• Originate in
sporophytes (sporeproducing bodies).
• Germinate and form
gametophytes (gamete
producing haploid
bodies)
Gamete formation in Animals
• Germ cells  gametes
• Males: spermatocyte
enters meiosis and
cytoplasmic division
making 4 haploid
spermatids that
develop into sperm.
Females
• Germ cell 
oocyte
(immature
egg). Makes
3 polar
bodies and
an ovum
(egg) that
receives most
of the
cytoplasm.
1.8c Mitosis vs. Meiosis
• Mitosis
– Somatic cells
– One cell division
– Two daughter cells
with same number
of chromosomes as
parent.
– Daughter cells are
identical to parent.
• Meiosis
– Sex Cells
– Two cell divisions
– Four daughter cells
with half
chromosomes as
parent
– Daughter cells not
identical to parents.