Lecture 13 Flashcards
Types of RNA
- messenger
- Ribosomal
- transfer
- RNAi (interference (with gene expression))
- mi RNA
- si RNA (small interfering)
Messenger RNA
formed during transcription from a DNA template
Ribosomal RNA
rRNA and protein combine to form ribosomes
Transfer RNA
- carries amino acids to the ribosome in translation
- can be uncharged or charged (has amino acid)
- anticodon matches with codon of mRNA
- specific amino acid for each anticodon attached to the 3’ end
Transcription stages
- initiation (promoter recognition)
- elongation
- termination
Occurs in nucleus for eukaryotes and cytoplasm in prokaryotes
Initiation (Transcription)
- RNA polymerase binds to promotor regions (DNA denatured in this region) and this determines where RNA synthesis begins (genes get switched on and off)
- DNA strands separate
- First RNA nucleotide triphosphate is placed at the site
Positive and Negative Regulation
In initiation: Binding of repressor protein blocks transcription
Binding of activator protein stimulates transcription
Elongation (Transcription)
addition of complementary nucleotides to 3’ end, growing RNA strand until termination sequence
Termination (transcription)
RNA polymerase reaches a chain termination sequence, this is a sequence which can form a loop!
Difference between transcription in eukaryotes and prokaryotes
Eukaryotes go through intermediate step of “primary transcript” (heterogeneous RNA) before processed into mRNA
RNA splicing/ alternative splicing
Removing the introns and exons joined to make the final transcript
alternative splicing name primary transcript can lead to different polypeptides from the same DNA sequence
DNA vs RNA
DNA sequences may be transcribed but not translated, mRNA is the only RNA to be translated into a polypeptide
Translation stages
Initiation - Ribosome binding site (small ribosome subunit moves along until start codon) –> Large ribosome subunit (A and P sites)
Elongation
Termination
