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Lecture 15

BIOL 1201 Lecture Notes - Lecture 15: Phenylalanine, Deoxyribose, RibosePremium

Biological Sciences
Course Code
BIOL 1201
Moroney, James

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BIOL 1201- Lecture 15- RNA
Differences between DNA and RNA
1.Deoxyribose is replaced by the 5 carbon sugar, ribose.
In DNA the pyrimidines are C and T. In RNA the pyrimidines are C and U . In RNA
U pairs with a.
DNA is really stable
Deciphering the Code:
In vitro protein synthesis: enzymes, ribosomes,
PLUS synthetic mRNA
First synthetic mRNA was UUUUUUUU, a repeat of the triplet UUU
Produced polypeptide made up of only phenylalanine (UUU codes for phenylalanine )
All combinations decoded by the mid ’60s
FEATURES of mRNA codons
AUGcodes for Met and START
3 codons give stops: UGA, UAA, UAG
Virtually universal
Fig. 17.5
Universal Code
oFirefly gene for luciferase causes “glow”
oGene identified and inserted into tobacco plant DNA
oTobacco recognizes firefly DNA
Tobacco plant “glows”
TRANSCRIPTION (synthesis of RNA)
1. Initiation
RNA polymerase binds to specific location on DNA (the promoter region)
RNA polymerase catalyzes separation of DNA strands
One DNA strand serves as template
Transcription unit on DNA template includes more bases than specific DNA code for
Fig. 17.7
2. Elongation
RNA polymerase works “downstream” from the promoter on the DNA
Polymerase reads DNA in the direction 3’ to 5’
Proper RNA sequence grows from 5’ to 3’ by addition of nucleotides
3. Termination
RNA polymerase transcribes terminator nucleotides, signaling end of transcription
Completed RNA transcript released
Prokaryotic transcript ready for translation
Eukaryotic transcript undergoes processing before translation
PROCESSING of Eukaryotic RNA (nucleus)
1. Addition of 5’ cap and poly(A) tail
Protects mRNA from degradation
Facilitates export of RNA from nucleus
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