The Flow of Genetic Information Flashcards
Three ways that genetic information flows
- Expression (DNA to Proteins)
- Recombination (DNA shared with other cells)
- Replication (DNA given to new generation of cells)
rRNA
Ribosomal RNA
- 5S, 16S, 23S
- Catalytic role
- 70% of cellular RNA
mRNA
Messenger RNA
- Informational role
- 10% of cellular RNA
tRNA
Transfer RNA
- Functional role
- 20% of cellular RNA
RNA Polymerase structure
- (in E.coli) has 5 subunits: α, β, β’, ω and σ
- α, β, and β’ synthesize RNA
- ω helps with enzyme assembly
- σ factor recognizes promotor region to initiate transcription (adds specificity)
- catalyzes phosphodiester bond formation between ribonucleotides
- DNA dependent, no primers needed
Protein Encoding Sequence Structure (DNA)
Promoter - RNA-coding sequence - Terminator
Protein Encoding Sequence Structure (mRNA)
Leader - Protein-coding sequence - Trailer
Promoter Structure
-35 sequence - variable sequence - Pribnow box (-10) - +1 (start transcription)
Terminator Structure
Contains A-U pairs with weak bonding
Initiation
RNA Polymerase binds to promoter sequence assisted by σ factor
Elongation
RNA Polymerase moves along template strand (antisense), opening a transcription bubble and ribonucleotides are added to 3’ -OH of preceding nucleotide
Termination
RNA Polymerase reaches a terminator sequence:
- Self determining/intrinsic/Rho independent: stem loop forms from transcribed RNA, pulling polymerase apart
- Enzyme/Rho dependent: terminator protein binds to terminator sequence on mRNA and yanks mRNA through it to push polymerase off
Why use operons?
Allows for related genes to be expressed and regulated together
Polycistronic mRNA arises from…
…transcription of operon genes that are on a single mRNA
AUG codes for…
N-formylmethionine
Nonsense codons:
UGA, UAG, UAA
There are __ sense codons
64 (4 bases^3 per codon)
The code is degenerate because…
…different codons code for the same amino acid
Wobble Effect
3rd base in codon is flexible for matching
G pairs with U, I pairs with everything but G
Shine-Dalgarno Box
- AGGA
- Upstream of start codon
Translation Initiation
- 30S subunit binds to SD box
- fMet tRNA binds to AUG
- 50S subunit binds
Important sites on 50S subunit
A site: site where new tRNA attaches
P site: site where growing polypeptide is held
E site: site where tRNA is released
Translation Elongation
50S subunit catalyzes formation of peptide bond between amino acids
Translation Translocation
Ribosome advances one codon down, leaving empty tRNA in E site and the new peptide tRNA in the P site
Translation Termination
As the stop codon is reached, release factor proteins are recruited and bind in the A site, causing the polypeptide to release and ribosome to fall apart
