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Cell Reproduction
Notes Day 1
Warm Up
Where are your genes located?
http://people.na.infn.it/~nicodem/research/cell_genes.jpg
•DURING MOST OF THE CELL’S LIFE, DNA
FORMS A TANGLED MASS CALLED CHROMATIN.
•CHROMATIN LOOKS LIKE A PLATE OF
SPAGHETTI.
•RIGHT BEFORE A CELL DIVIDES, THE
CHROMATIN FORMS INTO CHROMOSOMES (XSHAPED).
CHROMATIN
MOST OF THE TIME
CHROMOSOMES
ONCE IN A WHILE
Cell Division
•
•
•
•
Chromosomes = Tightly coiled, rod-shaped DNA
Chromosomes are made of chromatin
Human body produces 2 trillion cells per day & 25
million per second
Cells are formed by cell division of older cells
1. When a cell divides, DNA is first copied & then
distributed
2. Each cell ends up with a complete set of DNA
Chromosome Number
• Each human somatic cell has 2 copies of 23
different chromosomes
– Total 46
– Somatic = any cell that is NOT a sex cell
– (also called body cells or autosomes)
Sets of Chromosomes
• Each pair is made up of 2 homologous chromosomes
– Homologous chromosomes = chromosomes that are similar
in size, shape, & genetic content
– Each homologue comes from one of the parents
• One from mom
• One from dad
Cells Can Be Diploid or Haploid
• Diploid = a cell that contains 2 sets of
chromosomes (2n)
• Haploid (monoploid) = a cell that contains
only 1 set of chromosomes (1n or n)
Chromosomes Determine Your
Gender
• Humans have 23 pairs of chromosomes
• 22 pairs are autosomes (chromosomes NOT
directly involved in determining sex)
• 1 pair are sex chromosomes (contain genes
that WILL determine the sex)
– X & Y chromosomes
X & Y Chromosomes
• Male = XY
• Female = XX
• Male (dad) can donate an X or a Y to
offspring
• Female (mom) can ONLY donate an X
So-Which parent determines the sex of the
baby?
MALE
XY
Gametes
• Gametes are reproductive cells
– Males = sperm (n = 23)
– Female = egg (n = 23)
• Combine in fertilization to make a:
– Zygote (n = 46)
Karyotype
• Karyotype = a photo of the chromosomes in a
dividing cell that shows the chromosomes
arranged by size.
Karyotype cont’d
• Each of an individual’s 46 chromosomes
has thousands of genes so the presence of
all chromosomes is essential for normal
functioning
– Humans who are missing a chromosome don’t
survive
– Humans with more than two copies of a
chromosome, called trisomy, may survive but
will not develop properly.
What is wrong?
The Cell Cycle
• Repeating sequence of cell growth and
division during an organism’s life
• 90% of cell life is spent in INTERPHASE
• Then it may go into MITOSIS &
CYTOKINESIS
INTERPHASE
(divided into mini-phases)
• G1(first growth) phase = Cell grows rapidly
• S (synthesis) phase = DNA copied
• G2 (2nd growth) phase = Nucleus prepares
to divide
http://publications.nigms.nih.gov/insidethecell/ch4_interphase_big.html
AFTER INTERPHASE
• Mitosis
• Cytokinesis
• http://www.cellsalive.com/cell_cycle.htm
Mitosis and Meiosis
WARM UP
Females are X___
Males are X___
Having 3 copies of a chromosome is
called a ______________
Mitosis and Meiosis
• Mitosis:
-division of somatic (body) cells
- results in two daughter cells that
are identical
• Meiosis
-division of gametes (sex cells)
Mitosis
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase
The Cell Cycle is Carefully
Controlled
• Key check points which feedback signals from the
cell will delay the next step
• Controlled by proteins!
1. Cell Growth CHECKPOINT (G1) – Start –
Nerve/muscle cells stop here
2. DNA Synthesis CHECKPOINT (G2) – Enzymes
3. Mitosis CHECKPOINT – Back to G1 phase
When Control is Lost -- Cancer
• Cancer = Cell growth is uncontrolled - does not
respond to control mechanisms.
• Causes: Mutations that cause over-production of
growth molecules – (accelerator) or by inactivating proteins that slow or stop the cell cycle
(brakes)
• Tobacco and UV radiation linked to increased
cancer risk.
Change in Chromosome Number
• Trisomy = humans with more than 2 copies of
chromosomes – improper development
• Karyotype = a photo of the chromosomes in a
dividing cell.
• Disjunction = when egg/sperm cells form – each
chromosome and homologue separate –
sometimes one or more chromosomes fail to
separate - unequal distribution.
• Down Syndrome - 3 copies of chromosome 21NONDISJUNCTION
Change in Chromosome Structure
• Mutation – A change in an organism’s
chromosomal structure.
• Deletion = piece of chromosome breaks off
completely – lacks of a set of genes – fatal
• Duplication = chromosome fragment attaches to
its homologous chromosome –two copies of a
gene set
• Inversion = chromosome piece reattaches
to original chromosome, but in reverse
orientation.
• Translocation = chromosome piece
reattaches to a nonhomologous
chromosome.
Interphase
• Interesting things happen!
1. Cell preparing to divide
2. Genetic material doubles
Prophase
• Chromosome pair up!
1. Chromosomes thicken and shorten
-become visible
-2 chromatids joined by a
centromere
2. Centrioles move to the opposite
sides of the nucleus
3. Nucleolus disappears
Metaphase
• Chromosomes meet in the middle!
1. Chromosomes arrange at equator of
cell
2. Become attached to spindle fibres
by centromeres
3. Homologous chromosomes do not
associate
Anaphase
• Chromosomes get pulled apart
1. Spindle fibres contract pulling
chromatids to the opposite poles of
the cell
Telophase
•
1.
2.
3.
Now there are almost two!
Chromosomes uncoil
Spindle fibres disintegrate
Centrioles replicate
Cytokinesis
• Cell splits
http://www.cellsalive.com/mitosis.h
tm
Metaphase
Telophase
Prophase
Anaphase