Bio 105 – Guide 05
http://microbiology.ucdavis.edu/sklab/images/DNA%20repair%20cartoon.jpg
http://curriculum.calstatela.edu/courses/builders/lessons/less/les4/genes/eut_and_pro.gif
http://www.sp.uconn.edu/~terry/images/other/pro_eu.GIF
Amount of DNA/cell is larger in eucaryotes
Only 2% of the Human Genome codes for
proteins – this compares with > 90% of viral or
bacterial genomes!!
Genes are not organized in the same manor as in
procaryotes - no operons and more importantly
genes are in pieces!!
Gene expression is different
Histones
Help solve the “packing problem”
Are involved in gene regulation
http://www.mun.ca/biology/scarr/MGA2-02-45.jpg
In eucaryotic cells, genes are found in pieces.
http://faculty.ircc.edu/faculty/tfischer/images/introns-exons.jpg
http://biology200.gsu.edu/houghton/4564%20'04/figures/lecture%2012/introns1.jpg
Introns open a window in to the
Evolutionary “Chicken – Egg”
Problem
Which came first DNA, RNA or
protein?
An answer was suggested by the
mechanism of intron splicing
http://www.ncbi.nlm.nih.gov/books/bookres.fcgi/cell/ch8f58.gif
Introns/Exons in Eucaryotes
(RNA – self splicing) – 1  7
different proteins
Alternative RNA splicing in
Eucaryotes
http://138.192.68.68/bio/Courses/biochem2/GeneIntro/GeneIntroResources/IntronsAndExons.gif
Having a poly-A Tail on
eukaryotic m-RNA is very
useful in helping to isolate
m-RNA. It is the key to
separating this RNA from
the bulk of isolated RNA
(r-RNA) and can be used to
isolate the active genes from
a cell.
http://www.invitrogen.com/imgLibrary/rna_isolation.gif
The control of gene expression is more
complex in multicellular eucaryotes than in
bacteria because:
a. Eucaryotes are much smaller
b. In eucaryotes, different cells are specialized
for different functions
c. Unlike eucaryotes, procaryotes live in
unstable environments
d. Eucaryotes have fewer genes.
e. The genes of eucaryotes are information for
making proteins.
If Eucaryotes do not have many
“operons”, then how are “groups”
of genes turned on and off at the
same time?
http://info.med.yale.edu/chldstdy/plomdevelop/development/images/reguprotein.gif
Regulation in Eucaryotes - Many Different Levels
•Packing and unpacking of chromosomal DNA
Gene Activation
Chromosome silencing
•Transcription
All use proteins to bind DNA for regulation
Prokaryotes – few lac operon as an example
Eucaryotes – many proteins Activators
important – transcription factors
•Lifetime of Message
Gene Regulation in Eucaryotes
is at Many Different Levels (cont.)
•Translation
Regulation of initiation
• Movement of m-RNA out of the Nucleus
•Post Translation
Protein Activation
•Protein Breakdown
RNA Interference
A mechanism for RNA-guided
regulation of gene expression
in which double-stranded
ribonucleic acid inhibits the
expression of genes with
complementary nucleotide
sequences. Conserved in most
eukaryotic organisms, the
RNAi pathway is thought to
have evolved as a form of
innate immunity against
viruses and also plays a major
role in regulating development
and genome maintenance.
http://hades1.bioquant.uni-heidelberg.de/rnai.html
http://www.scq.ubc.ca/wp-content/uploads/2006/07/transduction.gif
http://www.uic.edu/classes/bios/bios100/mike/spring2003/signaltrans03.jpg
Rhodopsin Cascade
http://papoian.chem.unc.edu/Projects/RhodopsinCascade-web.jpg
The End