Week 2 - Transcription and Translation Flashcards
DNA
Deoxyribose sugar + nitrogenous base + phosphate
RNA
Ribose sugar + nitrogenous base + phosphate
Nucleotide
Sugar + base + phosphate
Nucleoside
Sugar + base
DNA pyramidines
Thymine + Cytosine
DNA purines
Adenine + Guanine
How many rings are in purines?
2
How many rings are in pyramidines?
1
Functions of DNA
Storage of genetic information, Replication + inheritance, Expression of genetic messages into proteins
Three forms of RNA
rRNA, tRNA, mRNA
What is rRNA?
75% to 80% of cellular DNA, form ribosomes and produced in nucleus
What is tRNA?
RNA transcribed by RNAP III
Define transcription
Formation of RNA from DNA
General steps of transcription
Initiation, Elongation and Termination
How is transcription initiated?
RNA polymerase II attaches itself onto the TATA-binding protein (TBP) which is a subunit of TFIID
What is the TATA box?
Promoter sequence, 24-32 bases upstream of the initiator
How is the RNA strand elongated?
Elongation is the addition of nucleotides to the mRNA strand. RNA polymerase reads the unwound DNA strand and builds the mRNA molecule, using complementary base pairs.
What is termination?
Termination includes cleavage of messenger RNA.
Coding strand vs template strand
Coding strand: the RNA should be a RNA version of the coding strand, with uracil present instead of thymine
Template strand: the RNA is formed complementary to the template strand
How is mRNA modified after transcription?
- Addition of a methylated guanosine cap at 5’ end
a) prevention of 5’ digestion by exonucleases
b) allow for the transport of mRNA out of the nucleus + aid in translation - Addition of poly a tail at 3’ end
a) protection from premature degradation by exonuclease - Removing of exons from the mRNA
Note: mRNA contains non-coding segments called untranslated regions at ends 5′ and 3′ which play regulatory roles
What is the wobble hypothesis?
States that the steric requirement between anticodon (tRNA) and codon (mRNA) is very strict for the first two positions and more flexible for the 3rd
Initiation of translation
Ribosome attaches itself to the initiation codon (AUG) of the mRNA, the codon will be read 5’ to 3’ (in triplets)
Elongation of translation
The amino acid chain will lengthen as the codon moves from the A, P to E site
Termination of translation
Release factors enter the A site, which leads to the hydrolysis of ester bonds linking polypeptide to tRNA
Three types of release factors: RF1 (UAA/UAG), RF2 (UAA/UGA), RF3 (non-codon specific)
