Lecture One - Transcription and Translation Flashcards
What is the basic structure of DNA?
The DNA and RNA strands run in the 5’ -> 3’ direction.
In RNA, T is replaced by U.
Cytosine, Thymine and Uracil are Pyrimidines.
Adenine and Guanine are Purines.
The two stands are reverse compliments of one another - antiparallel bonding.
What is the central dogma of biology?
DNA -> RNA -> Protein.
Note that not all genes make proteins.
Some genes create functional RNA, which is not translated into a protein.
How does transcription work?
Initiation -> elongation -> termination.
transcription unit = the area being transcribed.
Occurs in the nucleus.
RNA polymerase unzips the DNA strands in the 5’ -> 3’ direction.
RNA polymerase binds to the DNA in a promoter region.
The new RNA is made using the template strand of DNA (note that the actual sequence of the non-template strand is the sequence of the gene).
In Eukaryotes (as opposed to prokaryotes):
The promoter has a TATA box.
Transcription factors bind first (transcription factors recruit RNA polymerase).
Termination is a bit different too.
There is modification to the pre-mRNA - addition of the PolyA tail and the 5’ cap, as well as the splicing out of introns, to leave only exons.
How does splicing work in eukaryotes?
There is base pairing between the snRNPs (linear RNA molecule) and the mRNA.
The snRNPs find the regions where an intron switches to an exon.
Alternative splicing:
Different splicing of the same gene creates different mature mRNAs and therefore different proteins with different functions.
Some introns may be spliced out depending on how the RNA is spliced.
How does translation work?
The mRNA leaves the nucleus and enters the cytoplasm.
It attaches to a ribosome (with a small and large subunit).
The mRNA is fed through the ribosome in the 5’ 3’ direction.
There are three binding sites on the ribosome, the EPA sites, where the codons and anticodons join together.
Codon = three base pairs on the mRNA.
Anticodon = three base pairs on the tRNA.
As the codon and anticodon bind, this causes an amino acid, attached to the tRNA to be jointed to the polypeptide chain.
mRNA can often be translated by many ribosomes at once.
Signal peptides on polypeptide causes the ribosome mRNA polypeptide to be taken to the surface of the ER. This protein is processes in the ER and the golgi body. After this it is extruded into the lumen.
What is the sequence that occurs at the EPA sites on the ribosome?
The three binding sites on the ribosome:
E = exit site.
P = peptidyl-tRNA binding site.
A = aminoacyl-tRNA binding site.
The tRNA leaves the ribosome from the E site.
The tRNA is attached initially to the A site, and then moved to the P site to have its aminoacid joined to the polypeptide chain.
How is translation stopped?
With a stop codon.
A release factor binds the stop codon, and the polypeptide chain is released from the ribosome.
The release factor:
A very similar shape to a tRNA.
It adds a water molecule instead of an amino acid - thus ending the polypeptide chain.
