DNA
Double helix
Strands run antiparallel
A-T
G-C
DNA replication DNA from DNA
Transcription RNA from DNA
Initial step in transcription makes “pre mRNA”
p199
Pre mRNA “edited” to make mRNA
Two ways to control DNA expression
1) which genes are expressed
2) what introns are edited out
The Genetic Code
What translates RNA into proteins
mRNA has codons
tRNA has one anticodon
1) initiation (small subunit of ribosome and
mRNA and initiator tRNA join) ends with large
subunit of ribosome joining
2) elongation (second tRNA binds, second amino
acid bonds with first amino acid, continues with
more tRNAs/amino acids)
3) termination (stop codon, release factor)
Sickle cell anemia
Ricin: Which of the following would be affected
by ricin?
DNA
mRNA
tRNA
rRNA yes
replication
transcription
translation ricin
Chapter 14 Regulation of Gene Expression
All cells contain the same DNA
How do cells know what to develop into?
Gene regulation
Only a small portion of a cell’s genome is actually
expressed.
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1) DNA (transcribed into RNA)
Controlled by physical access to genes
Expression can be amplified by making
extra copies of chromosomes
2) new transcript RNA
Regulation of introns (alternative splicing)
3) RNA transport
When and where RNA leaves nucleus
controlled by proteins in nuclear envelope pores
and proteins bound to mRNA
4) Translation
mRNA varies in lifespan (long lifespan means
more polypeptide)
translation can be inhibited by proteins
binding with the ribosomes
RNAs can regulate mRNA lifespans
5) Protein processing
New protein may be deactivated by enzymemediated modifications
Master genes that control other genes
Homeotic genes control body plan, major
body feature