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Chapter 19
Organization and Control of
Eukaryotic Genomes
 (here are at least 6 different modes
of eukaryotic gene control…)
 (Remember: the example of operons is only
seen in prokaryotic cells)
Use this as a note
taking guide…
Copy this and add to
it with the following
slides
 Eukaryotes have
many different modes
of control over gene
expression
AT ALL STEPS IN
THE DIAGRAM
 Until the last step…
degradation
 Packing of
chromatin
 Areas of tightly coiled DNA
are not easily transcribed.

Histones, nucleosomes
 Each specialized cell
only translates a small
fraction of its genes,
for example, the
pancreas makes insulin
and glucagon where as
the liver,brain,skin etc. do not.
 (use your CD to view an
animation on these)
 Other chromatin modifications for gene
transcription:

Methylation= low expression (can be
imprinting as well- Ch.15) M = MUTED

Histone Acetylation = more transcription
(A = ACCESS)

Histone Deacetylation = less transcription
Controlling
when and for
how long a
gene is
transcribed is
“transcriptional
control”.
TRANSCRIPTION: Enhancers
Transcription
Initiation Complex
is another type of
transcription factor
control. But still the
same idea as the last
chapters 16-17)
A Eukaryotic Gene and its mRNA
NEW
Post transcriptional control
involves cutting out the
introns.
Sometimes different introns
are cut out. See the picture
of fetal vs adult hemoglobin
production.
Evolution of human α & β-globin
 ~ 97 % of human DNA does not encode for
proteins or RNA
 Regions of telomeres and centromeres have
many tandemly repeating sequences /
satellite DNA … WHY?
Post-translational
control, means after
transcription and
translation, the mRNA
and the protein can be
degraded/stopped.
Degradation of proteins:
past Nobel Prize in Chemistry!
 Ubiquitin tags proteins which need to be
degraded and proteasomes (the orange
structure) degrade/recycle them.
Cancer can be caused by mutations of
healthy genes (proto-oncogenes) which
normally control the cell cycle, like ras, or
which suppress tumors, like p53.
If the cell cycle is out of control and/or if
tumors are no longer suppressed, these are
changes which can lead to cancer.
How do proto-oncogenes
become oncogenes? 3 examples
 What is a proto-oncogene?
 A normal gene, that usually is involved in
some control of cell growth and division.
These genes are not cancerous, but if
mutated, could lead to cancer.
 What is an oncogene?
 A mutated proto-oncogene which causes too
much growth or loss of control over the cell
cycle in some way.
Over-stimulated
to divide (see
fig. a) or not
inhibited (fig b)
when it does
divide, both
result in
increased cell
division =
cancer
predisposition
Ras
p53
Cancer usually results
from multiple genetic
changes.
But, inheriting an
oncogene puts a person
a step closer to a
potentially cancerous
state.
Chapter 20
Genetic/DNA technology
Different uses and
techniques
This is the only slide of the CH 20
concept map
Ch 20 cDNA
 This means Complementary DNA
 Can be used to make DNA from a finished
(introns already cut out) piece of mRNA.
 This would be important for the insertion of
eukaryotic genes into bacteria (as in lab 6A,
the pGLO gene)
 Since prokaryotes do not recognize introns,
the DNA which is complementary to the
mRNA must be used.
Ch 20 Nucleic acid probes
 Used to identify which colonies or samples of
DNA contain a desired gene.
 A radioactive DNA Hybird is made (a single
strand of a portion of DNA that is the desired
gene, or part of it)
 If it binds to a sample of denatured (untwisted
and unwound) DNA then you know the gene
is in that sample. (fig 20.4)
Ch 20
PCR, polymerase chain reaction
 Used to make more DNA if only a small sample is
obtained. (many times this technique is used for crime
scene DNA evidence)
 The DNA is carefully heated, to make it separate
into single strands, then it is cooled
 Special DNA Primers are added to the solution
and the corresponding bases align with the help
of DNA polymerase = copying of the DNA. Done
over & over to get a larger sample.
Ch 20 Restriction Enzymes
 Are used to cut DNA at specific sites (at palindromes like MOM or
A MAN, A PLAN, A CANAL, PANAMA or RACECAR)
 These are used in Gel Electrophoresis and also in
cloning, inserting genes into plasmids or bacterial
chromosomes—since you get “sticky ends”
 These were first discovered in bacteria, bac. used them to
cut up foreign DNA from viruses or other bacteria.
Ch 20 Gel Electrophoresis
 A solution of DNA pieces (which were cut by restriction





enzymes) is carefully pipetted into a thick gel layer.
An electric current is passed through the gel.
DNA is negatively charged (because of the phosphate
groups), it is attracted to the + electrode.
The fragments separate based upon their size.
Small fragments move further than the long fragments.
RFLP: restriction fragment length polymorphisms, the
analysis of the various lengths of DNA in a gel, this is the
DNA fingerprint = (RFLP).