Since cells can’t continue to grow larger,
they must split, or divide at some point.
Cell Cycle
2 parts:
• Interphase – period of growth & DNA synthesis (copying)
• Mitotic phase – period of cell division (1 cell divides into 2
cells)
I love cells,
baby!
Interphase – time of cell growth & copying of
DNA
3 phases of interphase:
• G1 – growing & ribosomes making
proteins
• S – synthesis (or copying) of DNA
(sister chromatids formed)
• G2 – growing & getting ready to divide
Cells spend most of their time in interphase.
DNA is in chromatin (stringy) form.
Mitotic Phase – time of cell division
Consists of 2 main phases:
1. Mitosis – division of nucleus
2. Cytokinesis – division of cytoplasm
Sister Chromatids
• Identical copies of chromosomes attached by
a centromere.
Mitosis
4 phases:
• Prophase
• Metaphase
• Anaphase
• Telophase
http://www.cellsalive.com/mitosis.htm
Prophase
• DNA condenses
into chromosomes
• Nuclear
membrane
disappears
• Centrioles move
toward poles
• Spindle fibers
form & attach to
chromosomes
Metaphase
• Sister chromatids lined up on metaphase plate
with spindle fibers attached to them.
Anaphase
• Sister chromatids get pulled apart to poles as
spindle fibers shorten.
Telophase
• New nuclear membrane forms around chromosomes at
each pole
• Chromosomes “unpack” into chromatin
• Cell membrane begins to pinch in (animals cells) or cell
plate develops (plant cells)
Cytokinesis – division of the cytoplasm
Cell plate
Cleavage furrow
Control of the Cell
Cycle
• Enzymes control
cell cycle so cells
divide at the
right times
• Cancer –
uncontrolled cell
division caused
by a change in
the DNA that
codes for the
making of the
control enzymes
Cell Cycle Control
•
http://wps.prenhall.com/esm_freeman_biosci_
1/7/1948/498717.cw/index.html
Internal Vs external signals
• Internal – the
checkpoints
• External – growth
factors, density
dependent
inhibition, anchorage
dependence
Cell cycle checkpoints
• length varies depending on cell type
cell cycle checkpoints control the cell’s progression.
Check points determine if a cell is ready to progress to the
next stage.
G1 – mostly controlled by growth factors
G2 - determines if cell will enter the M phase & requires
proper completion of DNA synthesis.
M - b/t metaphase & anaphase; requires the proper
attachment of all chromosomes to spindle apparatus.
MPF = mitotic cyclin dependent kinase
complex
How MPFs work to
control the cell cycle
Once bound to cyclin, the mitotic cyclin
depdendent kinase complex (or
MPF) phosphorylates proteins
involved in the early stages of
mitosis.
The active MPF stimulates the
following:
• breakdown of the nuclear envelope
• chromosome condensation,
• mitotic spindle formation
• degradation of key proteins.
• activating the anaphase promoting
complex
To sum up…
• CDKs are only active when bound to cyclin.
• When working, they cause the cell to go
through the mechanics of mitosis.
• The cell doesn’t continually go through mitosis
b/c the cyclin gets destroyed when the MPF
complex reaches a certain concentration.
cancer
•
•
•
•
•
Tumor
Begign
Malignant
Metastasis
Radiation & chemo
Cancer
• Forms tumors &
can spread
through body metastasize
Causes of Cancer
• Environmental
factors
• UV radiation
from sun
• Tobacco
• Viral
infections
• Genetic
How to prevent cancer:
• Low fat, high fiber
diet
• Vitamins
• Exercise
• Don’t smoke
• Use sunscreen
• Regular doctor
appointments
Pitt Develops Possible Colon Cancer
Vaccine – 1/8/2013
• Watch the news video:
http://www.wtae.com/news/local/allegheny/Colon-Cancer-VaccineDeveloped-in-Pittsburgh/-/10927008/18057340/-/nfkl29//index.html
• Read the article from Pitt
http://www.upmc.com/media/NewsReleases/2012/Pages/PittVaccine-Prevent-Colon-Cancer.aspx
• Watch colonoscopy to detect/remove polyps:
http://www.youtube.com/watch?v=vVqgtUHP2z8
Removal of colon polyps
• http://www.gihealth.com/flashvideo/flash.html
Review of
the cell
cycle
• http://www.c
ellsalive.com
/mitosis.htm
Samples of Stop Motion Cell Cycle
Videos
Shyanne & Jake
http://www.youtube.com/watch?v=2NFF7hJSSy
4
2 Basic Modes of
Reproduction:
1.
Asexual – one parent
–
–
–
Produces offspring ID to parent
Ex: sponges, some worms, some plants,
bacteria, some fungi
Variation occurs through mutation
2. Sexual – two parents
–
Genetic variation occurs
Meiosis
• The making of
gametes
• Reduces
chromosome #
by ½ so the 2
halves can come
together & make
a whole.
• Creates genetic
variation.
Terms you need to
know:
• Somatic cell – all cells
other than sperm &
egg. Humans = 46
chromosomes;
diploid ( 2n)
• Gametes – sperm &
egg. Humans = 23
haploid (n)
• Gene – seg of DNA
that codes for the
making of a
polypeptide
• An ordered
picture of an
individuals
chromosomes
used to detect
abnormal
chromosome #
Karyotype
Trisomy 21 karyotype
More terms you need to know:
• Homologous
chromosomes –
paired
chromosomes that
contain genes that
code for the same
traits.
Homologous Chromosomes
Meiosis has
2 parts:
• Meiosis produces
4 non – identical
haploid gametes.
• Meiosis I –
separates
homologous pairs
of chromosomes.
• Meiosis II –
separates sister
chromatids – just
like mitosis.
•http://www.cellsalive.c
om/meiosis.htm
Meiosis I & II
2 Notable events in meiosis I that cause
genetic variation in gametes:
1.
Random
assortment of
homologous
chromosomes there are 2
possible
arrangement of
maternal &
paternal
chromosomes on
the metaphase
plate.
2n –
humans = 8 million
possible
combinations
2 Notable events in meiosis I that cause genetic
variation in gametes …
2. Crossing over –
occurs when
nonsister
chromatids of
homologous
chromosomes
exchange genes.
Can happen at up
to 3 different
locations along the
pair.
http://www.csuchico.edu/~jbell/B
iol207/animations/recombination
.html
A third notable event that causes variation in
offspring, not gametes, & occurs after meiosis if
sperm & egg meet:
• Random
fertilizaiton –
chance determines
which sperm (all of
which are
different)
fertilizes which
egg (all of which
are different).
Meiosis & Mitosis compared:
• http://www.pbs.org/wg
bh/nova/baby/divi_flas
h.html
Mistakes in Meiosis
• Nondisjunction – when chromosomes don’t
separate during meiosis.
• Results in:
• Trisomy – 3 of a chromosome
– Ex: Down Syndrome
– Ex: Klinefeltersyndrome xxy
• Monosomy – 1 of a particular chromosome
– Ex: Turner syn
http://www.tokyomed.ac.jp/genet/anm/domov.gif
Trisomy 21
Some terms
• Autosomes – chromosomes other than the
sex chromosomes
• Tetrad
• synapsis
• chiasmata
Evolutionary adaptation
depends on a population’s
genetic variation.
• Those individuals best adapted to their env
will live longer & therefore reproduce more,
passing on their well adapted genes.
• More variation means a greater chance of
individuals being better adapted, allowing
for the survival of the species.
Errors & Exceptions in Chromosomal Inheritance:
There can be alterations in chromosome number as well as
structure.
• Number: Aneuploidy & Polyploidy
– Caused by nondisjunction
Alterations of chromosome structure:
4 types…
Human Disorders Due to Chromosome Alterations:
• Down Syndrome: Trisomy 21
• Klinefelters syndrome: XXY
• Turners syndrome: XO
The phenotypic effects of some genes depend
on whether they were inherited from the
mother or the father (imprinting)
Extranuclear genes exhibit a non-Mendelian
pattern of inheritance
Trisomy 21
Incidence
• In the U.S. is about 1 in 1,000 births.
• No association between Down syndrome and culture,
ethnic group, socioeconomic status or geographic
region.
Age-Related Risks
• at age 35 are about 1 in 350.
• Under age 25, about 1 in 1,400.
• At age 40, about 1 in 100.
Klinefelter Syndrome
•
•
One of the most common genetic abnormalities.
Affects b/t 1 in 500 and 1 in 1,000 males
Turner Syndrome
• Symptoms
• Incidence: Approximately 1 in 2000 live-born female
infants. As many as 15% of spontaneous abortions have a
45,X karyotype.
Turner Syndrome