Review Sheet for Test 4 - Biology 1107Dr. Adams
Gene Expression - Transcription and Translation
Genes work by having information that ultimately codes for the structure of a protein; so . . .
genes code for proteins which in turn make YOU. Needs an intermediary between the DNA in
the nucleus and the making of proteins at the ribosomes in the cytoplasm.
RNA (ribonucleic acid): compared to DNA: ribose sugar, uracil instead of thymine, single
Transcription - making mRNA from DNA template; made in 5' - 3' direction from the sense strand.
Non-transcribed side of the DNA double helix is called antisense strand.
Involves the enzymes helicase and RNA polymerase, which binds to DNA to begin
transcription at the Promoter sequence (a sequence of DNA that says begin transcription here)
Translation - takes place at ribosomes; ribosomes have two binding sites (P and A) for tRNA=s.
Posttranscriptional modification and processing (covered much more thoroughly in Chap. 14)
Genetic code is virtually universal -- all organisms share the same
coding mechanism; exceptions:
some single-celled organisms and
Mutations: The ultimate "stuff" of evolution
CONTROL of Gene Expression
- Gene Regulation
Jacob & Monod -- Experiments with E. coli bacteria (prokaryotes) discovered that . . .
Prokaryotes: use operons -- groups of functionally related genes controlled by one promoter
have regulatory genes for regulatory (repressor) proteins that bind to the operator region of
the promoter to control transcription
Eukaryotes: Many more levels of control than prokaryotes; do
not appear to use operons
Pretranscriptional/Transcriptional - heterochromatinization (condensation) of specific DNA
sequences in different cells, Euchromatin, gene-specific promoter sequences, enhancing proteins,
generalized promoters ("TATA" box); multiple copy DNA
eukaryotic regulatory mechanisms:
(Chapter 15) -- Recombinant DNA and transgenic organisms
Restriction enzymes cut DNA, leaving "sticky" ends on both DNA for "desired" gene and bacterial
plasmid DNA; makes insertion of gene into plasmid possible. "Give" plasmid back to bacteria
and bacteria then make desired protein from inserted gene (remember, in prokaryotes, virtually
all DNA transcribed and, if transcribed, translated.)
If want to "give" a eukaryotic
gene to a prokaryote, as described above, have two problems:
1. Must have a prokaryotic promoter on the gene
2. Must get rid of introns in eukaryotic gene. Made possible by discovery of . . .
Reverse transcriptase, used by retroviruses to turn their injected RNA
into DNA in the host cell.
So, to isolate a desired eukaryotic gene without introns: create copy (complementary) DNA,
called cDNA, from mRNA using
These problems are often not
problems when sticking a eukaryotic gene into another eukaryote,
particularly if the "donor" and "host" are closely related. This is because the regulatory mechanisms
for the gene are shared -- SO, not only do organisms share the same coding mechanism but apparently
the regulatory mechanisms as well.
Uses: monoclonial antibodies, oil-eating bacteria (genes for metabolism of unusual food sources),
resistant crops, hormone manufacture (eg., insulin)
EVOLUTION (Chapter 17) -- for FINAL EXAM
Change in the genetic makeup (allele frequencies) of populations of species from one generation
to the next. Requires time.
Evolutionary Theory: Important historical figures
For natural selection to occur:
1. Must be overproduction of offspring.
2. Variation (through sexual reproduction and mutation, the ultimate source)
3. Limits on population growth -- Competition for resources, predation, etc.
4. Differential reproductive success -- Survival to reproductive age, followed by reproduction
"Survival of the fittest"
Fitness - the success an organism has at getting its genes into the next generation.
The evidence for evolution
1. Artificial Selection
2. Fossils (there are some intermediates ["missing links"] in the fossil record)
3. Comparative Anatomy - must use Homologous structures for analysis
analogous structures indicate convergent evolution
4. Comparative Embryology/Development (eg., humans have tails/gill slits in the embryo)
5. Comparative Biochemistry - Molecular (DNA, proteins) similarities suggest close relationships
(eg., chimpanzee and human DNA=s are >99% identical
6. Biogeography - Distribution of organisms of the earth
Phylogeny - trees of relationships between species indicates close relationships based on recent