RNA-Reynolds Flashcards
How is RNA different than DNA
3
- T in DNA
- DNA 2’ H
- double stranded DNA
- U in RNA
- RNA 2’ OH
- single stranded RNA
rRNA
- Ribosome 65% rRNA and 35% protein
- very stable, most abundant
- catalytic site/ structural part of ribosome
- Assembled in nucleolus
mRNA
- Messenger
- genome transcribed from DNA to mRNA
- template for protein sysnthesis
- structure:
- 3’ Poly-A tail
- 5’ cap of 7-methyl guanosine
- monocistronic (euk)
tRNA
structure
- Transfer
- translation of genetic info from mRNA into proteins
- carries a specific aa
- stable structure
- Acceptor stem: site where a specific aa is linked
- Anticodon loop: base pairs with the codon on mRNA
- Unique nucleotide bases
- stable structure
Roles of RNA
- transmission of genetic info
- storage of genetic info (retrovirus)
- catalysis/structural (rRNA and snRNA)
- Gene regulation (miRNA/siRNA)
Naming of strands
non-template strand 5’ to 3’
template strand 3’ to 5’
what are the promoting portion of the prokaryote gene
- -35 box and -10 box
- binding sites in DNA where transcription begins
Codons
- nucleotide triplets in mRNA
- pair with tRNA to code for specific aa
Polycistronic
- prokaryotic mRNA
- contains info for more than one polypeptide chain
monocistronic
- Eukaryotic mRNA
- contanis info for only one polypeptide chain
Transcription
- DNA→mRNA
- transcribed regions contains the protein coding sequence
- can occur in either direction depending on which strand is the template strand
In transcription what is released for each nucleotide added
PPi (pyrophospate) cleavage of PPi helps drive reaction
Prokaryotic RNA polymerase
- make RNA using the template strand of DNA
- make RNA 5’ to 3’ (no pimer needed in prok and euk)
- No proof reading (3’ to 5’ exonuclease activity)
- No 5’ to 3’ exonuclease activity
core enzyme
maded of alpha and beta
(prok RNA polymerase)
Haloenzymes is
core enzyme (RNA polymerase), and sigma
sigma subunits
- confer promoter specificity
- guides RNA polymerase to specific promoter sequeces on the DNA template strand
TATA Box
-10 Box
sequences in the prok promoter region recognized by RNA polymerase
Initiation of RNA polymerase cannot initiate transcription on its own it needs…
- Sigma= protein subunit that bind to prok DNA
- Sigma + RNA polymerase =holoenzyme
- (made of core enzyme and other proteins)
Promoter in transcription
- regulatoy region of DNA
- located upstream of coding sequence
- Contains DNA consensus recognized by RNA polymerase (-35,-10)
Consensus Sequence
is a sequence that is most commonly found in a giver region when multiple sequences are aligned
Transcription steps in prok
Initiation
- Sigma binds to promoter region of DNA (-35 and -10 box)
- RNA polymerase attaches
- Hollow enzyme now formed
- +1 site is where new molecule is generating
- Sigma opens DNA helix
- Initiation complete
- Sigma releases
Elongation
- mRNA synthesis continues
- transcription termination signal
- Hairpin loop forms
Eukaryotic transcription
- Transcription factors rather than sigma factors
- Complex promoters and regulatory regions
- tissue specific
Euk transcription RNA polymerase II
mRNAs
(make the message)
Eukaryotic RNA processing
rRNA, tRNA, mRNA
includes (3)
- occurs in nucleus before mRNA translation in cytoplasm
- Includes
- 5’ capping
- Intron splicing
- 3’ polyadenylation
what prok RNA is not generally processed ?
mRNA
euk rRNA processing
preribosomal RNA cleaved by ribonucleases→ small sized pieces of rRNA
Introns splicing
you want to keep extons and cut out the introns
Introns: non-coding intervening sequences, more introns than exons
5’ mRNA capping
- modified Guanosine 5’ capping of mRNA
- stabilitiy of message
- more stable than hairpin
- help exit from the nucleus
Polyadenylation
- Poly A tailing (polyadenylation) to 3’ end
- confirms mRNA stability
- Cleavage signal sequence (AAUAAA)
need for:
- transcription termination
- translation
- nuclear export mRNA
Enzyme that splices out introns
- spliceosome enzyme
- Made of small nuclear RNAs (snRNAs) and small nuclear ribonucleoproteins (snRNP)
Alternative Splicing
- Production of two/more proteins vary in aa sequence from one gene
- most individual genes express multiple mRNAs (multiple proteins)
Reverse transcriptase
- Make DNA from viral RNA
- makes complementary DNA resulting in dsDNA
- high mutation rate/ error prone (leads to drug resistance)