Transcript Cell Growth and Cell Division Powerpoint

How do we get more cells:
Mitosis vs. Meiosis and What’s
going on the rest of the time
DNA has two forms:
• Chromatin: unwound and stringy;
information is accessible but difficult
to move
• Chromosomes: folded up chromatin;
information is NOT accessible, but
easy to move
• DNA SPENDS MOST OF THE TIME
AS CHROMATIN!!!
Chromosome structure:
Telomeres (ends)
Centromere
(middle)
During replication each
chromosome is duplicated
Sister chromatids – two identical
copies of chromosomes attached
at the center
There are different types of
chromosomes
• Each type has a different set of
GENES on them.
• Chromosomes that are the same
type are called HOMOLOGOUS
chromosomes
Homologous chromosomes
• Have the same set of genes but
may have different ALLELES
• An allele is a variation of a
gene.
Homologous chromosomes
Gene: Hair color
- allele: brown hair
Gene: Hair color
- allele: blonde hair
Gene: Eye color
- allele: brown eyes
Gene: Eye color
- allele: blue eyes
What do we need to do before the
cell can split?
• Make another copy of DNA
• Make more organelles (cell parts)
• Cells Grow
Cell Cycle
Cell Cycle
G1(Gap 1) – Cell growth and protein
synth.
S – DNA replication (copying)
G2 (Gap 2) – growth, prepare for cell
division
M – Mitosis (nuclear division) and
cytokinesis (cell division)
Why do cells need to divide?
• When we grow • To repair damage
• Replace cells when they die
Mitosis
• Process by which body cells
duplicate and split their nucleus
• 4 stages
• Followed immediately by
cytokinesis
1. Prophase
Duplicated chromatin folds up into
chromosomes
1. Prophase
• Centrosomes separate and move
toward opposite poles
1. Prophase
• Centrosomes start to form the
Mitotic spindle
–Made of microtubules (cytoskeleton)
1. Prophase
• Nuclear membrane breaks down
• Nucleolus disappears
2. Metaphase
• Chromosomes line up along the
middle of the cell  metaphase plate
• Spindle fibers attach to the
centromeres of each chromosome
3. Anaphase
• Sister chromatids separate and one
chromatid of each chromosome
moves toward opposite poles
4. Telophase
•
•
•
•
Chromosomes unwind to chromatin
Nuclear Envelope reforms
Spindle breaks down
Nucleolus reappears
Cell Division is not yet Done!!
• What have we made?
– One Cell with Two complete
Nuclei
What is left to do?
- Cytokinesis: Divide the
cytoplasm and separate the cells
Cytokinesis
• Animal cells:
Membrane
pinches inward
until it divides the
cytoplasm into two
equal parts
–Cleavage Furrow
Cytokinesis
• Plant cell: Cell plate
forms in the middle
of the cytoplasm
• Made of cellulose
• Becomes cell wall
NOW Cell division is done!
• Now you have Two Identical
daughter cells (also identical to
parent!)
Controlling Cell Division
• Cells know when they need to
divide
–Complicated series of “stop”
and “go” signals make sure cells
only divide when needed
Controlling Cell Division
• Cells know when they don’t need
to divide
Loss of control
• What happens?!?
– cells divide uncontrollably
–Pile up on top of each other
–Form big balls of cells called?????
»TUMORS!!!
Tumors
• Tumor cells do not respond to (or
do not have) the body’s control
signals
–missing a “stop” signal
–Hyperactive “go” signal
Tumor vs. Cancer
• Cells that grow out of control for
tumors.
• BUT tumors aren’t necessarily
cancerous
Tumor vs. Cancer
• Benign tumors: grow out of
control, but are isolated and
don’t interfere with healthy cells.
• Malignant tumors: grow out of
control AND interfere with
healthy cells.
Tumor vs. Cancer
• Malignant tumors are cancerous.
Spreading Cancer
• What if 1 cancer cell breaks off and
enters the blood stream?
–When it “lands” it will form a new
tumor there
–This is called metastasis
Sexual vs. Asexual Reproduction
DNA from
how many
parents?
Asexual
Sexual
Offspring
Example
Chromosome Terms
• Diploid: two of each type of
chromosome (one from each parent)
• Haploid: one of each chromosome
• Most human cells are Diploid
–We have 46 chromosomes
• 22 pairs of body chromosomes
• 2 sex chromosomes (XX or XY)
• What would happen if we made
Egg and Sperm cells through
mitosis?
– Fertilized egg would have 92
chromosomes!
• What do we have to do when
forming these cells?
–Divide the DNA in half!
Major differences between
Mitosis and Meiosis
• one cell goes through two divisions to
make a total of 4 cells
• cells created at the end are different
from the cell they came from because
of crossing over
Meiosis
• After the first division, cells are
haploid and no longer diploid
• Happens only in reproductive cells
Genetic Variation:
- diversity between individuals
- created by crossing over and
meiosis and sexual reproduction!
Meiosis I: 1st division
1.Homologous chromosomes pair
up to form tetrads
2.Crossing over occurs:
homologous chromosomes
swap info (blonde allele for
brown allele)
Meiosis I: 1st division
Similar steps to mitosis but:
3. Cells end up haploid but
chromosomes are still duplicated
Meiosis II: 2nd division
Just like mitosis
- each cell from Meiosis 1 divides
- Creates 4 cells total
- all are different because of
crossing over
- all have ½ the original
chromosomes
Compare and Contrast Mitosis and
Meiosis