transcription I-lecture 25

mRNA

Carries genetic code from DNA to ribosome for protein synthesis

tRNA

Transfers amino acids to ribosome during translation

rRNA

Structural and catalytic RNA of ribosomes

snRNA

Small nuclear RNA involved in splicing

snoRNA

Processes and modifies rRNA

miRNA

Regulates gene expression by silencing mRNA

siRNA

Triggers mRNA degradation (RNA interference)

lncRNA

Long non-coding RNAs regulating transcription/chromatin

piRNA

Protects germline genome from transposons

RNA synthesis steps

Initiation, elongation, termination

Initiation

RNA polymerase binds promoter; sigma factor assists in bacteria

Elongation

RNA polymerase synthesizes RNA 5'->3'

Termination

Stops transcription; rho-dependent or rho-independent

Rho-independent termination

Hairpin loop + poly-U tail destabilizes complex

Rho-dependent termination

Rho protein binds RNA and terminates transcription

Sigma factor

Recognizes promoter (-10, -35); helps initiate transcription in bacteria

Transcription

Synthesis of RNA from a DNA template

Promoter

DNA sequence upstream where RNA polymerase binds

Coding region

DNA sequence transcribed into RNA

Sense strand

Strand with same sequence as RNA (except U for T)

Antisense strand

Template strand used for RNA synthesis

Polycistronic

One mRNA codes multiple proteins (prokaryotes)

Monocistronic

One mRNA codes one protein (eukaryotes)

Transcription bubble

Locally unwound DNA region during transcription