TYPES OF

RNA

1. mRNA
2. rRNA
3. tRNA

DEFINE

mRNA

• "messenger"
• contains genetic info that is transcibed into proteins

DEFINE

rRNA

• "ribosomal"
• components of ribosome and involved in translation

DEFINE

tRNA

• "transfer"
• involved in translation
• directly responsible for converting codons in to AA

PATHWAY

transcription

• small portion of DNA double helix is opened and unwound
• one of exposed strands acts as template for synthesis of RNA
• incoming rNTPs incorporated into growing RNA chain
• resultant RNA transcript elongated one base at time
• sequence complentary to that of DNA template strand

DEFINE

sense strand

DEFINE

non-template DNA strand

coding/sense strand

contains same info as mRNA

DEFINE

template strand

non-coding/antisense strand

complementary to mRNA

• similar polymerase enzymes
• product made 5' to 3'
• anchored to ssDNA template
• must unwind DNA double helix
• processive enzymes
• add one nucleotide at a time

1. initiation
2. elongation
3. termination

DEFINE

initiation

• slower
• recognition of initiation sequence on DNA call promoter
• unwinding of region to expose the DNA template
• synthesis of 1st few bases in RNA

DEFINE

elongation

• faster
• rapid incorporation of rNTPs to finish RNA chain

DEFINE

termination

DEFINE

sigma factor

• detachable
• necessary to initiate transcription
• specific contacts w/ promoter bases

DEFINE

holoenzyme

• RNA pol bound to sigma factor
• normally slides along DNA until it encounters a promoter sequence

DEFINE

promoter

• nucleotide sequence in DNA to which RNA pol binds to transciption
• "consensus sequence"

DEFINE

TATA box

eukaryotic

main DNA sequnce that signals transcription inititation

recognized by TBP

AFFECT OF

binding TFIID to TATA box

AFFECT OF

TFIIH

helicase activity

kinase:  phosphorylates RNA pol

DEFINE

enhancers

DNA sequences acting to stabilize that transcription initiation complex

increases about of transcripts made

QUESTION

Where does regulation of transciption frequently occur?

EFFECT OF

elongation

ACTIONS OF

RNA pol

• transcription
• carries pre-mRNA processing proteins on C-terminal tail to transfer to mRNA at appropriate time

DEFINE

prokaryotic transcription termination

DEFINE

Rifampin

• antibiotic
• binds to prokaryotic RNA pol but not eukaryotic
• slows bacterial growth

ASPECTS OF

rRNA processing

ASPECTS OF

tRNA processing

• RNAase P:  cleaves tRNA 5' end
• UU at 3' end replaced by CCA
• modification of several key bases

ASPECTS OF

pre-mRNA processing to mRNA

• cap added to 5'
• poly A tail added to 3'
• introns spliced

DEFINE

5' cap

• 1st processing event on pre-mRNAs
• cap 5' end w/ 7-methyl guanosine (m7G)
• stabilizes mRNA
• binds CBC protein:  aids in export of mRNA into cytosol and aligns mRNA on ribosome during translation

DEFINE

splicing

• removes 1 intron
• removed as "lariat"
• transesterifications

DEFINE

trans-esterificatinos

DEFINE

differential splicing

DEFINE

snRNA

small nuclear RNA

binds to snRNPs

carry out RNA spilcing

DEFINE

snRNP

• small ribonuclear protein
• recognize splice sites and facilitate catalysis

DEFINE

spliceosome

assembly of snRNPs

large complex performs RNA splicing

DEFINE

poly A tail

• polyadenylation
• 3' end of eukaryotic mRNAs are modified by addition of tail w/ several hundred A bases
• kept ss for poly-A-binding protein
• helps stamilze mature mRNA

ASPECT OF

mRNA transport to cytoplasm

• selective
• only "export-ready" mRNAs transported through nuclear pore complexes
• "export-ready" bind appropriate set of proteins

DEFINE

"export-ready"

• presence of CAP binding complex
• absence of snRNPs
• RNA export factors often bound