Lecture 12 Flashcards
What is a Promoter?
A DNA sequence that directs/regulates transcription
What is the Template Strand?
Strand of DNA that is used in transcription, it runs 3’ to 5’ away from promoter
What is elongation?
Adding RNA nucleotides in a 5’ to 3’ direction
What is RNA polymerase?
Initiates transcription at the +1 transcription factor
What happens at termination?
RNA disassociates
What is transcription?
DNA is transcribed into RNA
What happens after transcription in Eukaryotes?
MeG and a poly-A-tail are added
What is MeG? What does it do?
Methylated Guanine is added to the 5’ end of the RNA strand to prevent exonuclease from eating it
What is a poly-A-tail? What does it do?
A poly-A-tail is about 200 adenines added to the 3’ end of the RNA to prevent exonuclease from eating it
What is splicing?
Introns are removed from in-between exons with the enzyme spliceosome
What are introns?
They are non-coding sequences
What is a spliceosome?
A complex of snRNP’s which are protein/RNA complexes
How does splicing work?
snRNP’s bind to the intron/exon boundary and loop out the intron. It is cut at 5’ end and attaches to a “branch point A”
What is translation?
The genetic code carried by mRNA is translated into proteins
What is tRNA?
Transfer RNA is has an a.a. binding region and an anticodon, it carries the correct a.a to the ribosomes
What is Aminoacyl tRNA synthases?
It pairs the correct a.a to the tRNA based on the anticodon sequence
What is a ribosome and what are the subunits of prokaryotic ribosomes?
A ribosome catalyzes peptide bonds and in prokaryotic ribosomes the large subunit is 50s and the small subunit it 30s
What does the small subunit do?
Is used for recognition
What is in the large subunit?
Approach site, Polymerization site and Exit site
What happens in the large subunit?
The start codon (AUG) is positioned in the P site, the tRNA f-Met associates with the ribosomes so that it sits in the P site. The anticodon of the tRNA f-Met binds to the start codon of the mRNA
What are the steps of the elongation phase?
Bind, Bond, Shift
What happens during Bind?
A tRNA a.a. enters the A site and binds to the mRNA (anticodon to codon)
What happens during Bond?
Peptide bonds form between tRNA f-Met and tRNA a.a. and the growing chain moves from the f-Met to the a.a. in the A site
What happens during Shift?
The ribosome shifts down the ribosome towards the 3’ end in a one codon step. The first tRNA leaves through the exit site and the second tRNA is in the P site to continue the process
What is termination phase?
When a STOP codon is encountered the ribosome stalls until release factor comes, the release factors release the a.a. chain which will go on to fold
What are silent mutations?
A base pair is substituted but results in no change in the primary structure because of the redundancy of codons
What are missense mutations?
A base pair is substituted but codes for a different amino acid
What is a nonsense mutation?
A base pair is substituted and codes for a stop codon
What is a frameshift mutation?
A base is added or deleted resulting in all a.a. after being affected
