Transcription 1
What is the central dogma and how does it relate to gene expression?
DNA-> RNA -> Proteins
DNA->mRNA (transcription)
mRNA->Proteins (translation and folding)
What is the key enzyme in transcription? What does it synthesize and in what direction?
Where does translation occur in prokaryotes versus eukaryotes?
The polypeptide that is synthesized in translation is synthesized in what direction?
N terminus to C terminus
Explain where transcription occurs in prokaryotes vs eukaryotes
Prokaryotes: cytoplasm
Eukaryotes: nucleus
Given this coding strand of DNA, what would be the sequence of the mRNA produced in transcription?
5' ACCTTCGGATCGA 3'
5' ACCUUCGGAUCGA 3'
What is a codon? What is an anticodon? Where are both found and what is their function?
Codon: 3 base sequence on mRNA, codes for specific amino acids
Anticodon: found on anticodon loop on tRNA, complementary to mRNA codons
What is the genetic code? What are 3 characteristics of the genetic code?
Unambiguous- a single codon never codes for more than 1 amino acid
Conservative: the first 2 phases in codons usually code for the same amino acid
Redundant: more than 1 codon specifies one amino acid
What is a gene? What are the different regions on a gene that are important signals in transcription?
A gene is a functional segment of DNA that codes for traits
Promotor and terminator regions
What is RNA processing? What happens in this process? In what cell type does this process occur?
Modifications are made to mRNA in eukaryotic cells after transcription and before translation
Introns removed, 5' cap & 3' tail added
Describe the structure and function of tRNA
3' end: CCA sequence, amino acid attachment site
Anticodon loop complementary to codon on mRNA
Function: bring amino acids to the ribosome
What is the 'wobble position'? What does this mean?
The 3rd base in anticodons in tRNA may not have standard base pairing with the codons in mRNA
ex: anticodon AGG can pair with codon UCU but serine is still coded for
In transcription, what are the 2 names of the DNA strands and what is the function of each?
Template/noncoding strand: used as a template for the complementary mRNA
Coding/nontemplate strand: identical to the mRNA (minus swap T and U bases)
Given this template strand of DNA, what is the sequence of the mRNA strand that is produced in transcription? What is the sequence of the coding strand?
3' ACGACCAAATGTG 5'
mRNA: 5' UGCUGGUUUACAC 3'
Coding: 5' TGCTGGTTTACAC 3'
Explain how tRNA becomes "charged"
Aminoacyl-tRNA synthetase activity
Amino acid+ATP bind to aminoacyl....
Breaking of ATP
tRNA binds to the synthetase and the amino acid is attached
Given this template strand, give the codon and amino acid sequence
3' ACCGATTCG 5'
mRNA: 5' UGG CUA AGC 3'
a.a: Trp-Leu-Ser
The process of creating RNA from DNA is called ____ and is done by the enzyme ______
Reverse transcription
Reverse transcriptase
Viruses contain this enzyme and perform this process
Explain the sequence of events of transcription (in prokaryotes)
(Hint: initiation, elongation, termination)
Initiation: sigma factor binds to RNA polymerase and guides RNA poly to the promotor sequence on the gene
Elongation: RNA polymerase transcribes DNA and synthesizes mRNA in the 5' to 3' direction
Termination: The terminator sequence is transcribed and a hairpin loop forms in mRNA. Transcription ends.
Explain the structure of the ribosome
(Hint: What are the functions of the different sites within the ribosome?)
Composed of rRNA and proteins
E site: exit site
P site: holds growing polypeptide chain
A site: where new tRNA enters
Explain the steps of translation.
(Hint: initiation, elongation, termination)
Initiation: mRNA binds to small subunit of ribosome, initiator tRNA binds to start codon, large subunit binds
Elongation: Charged tRNA enters A cite, translocation, etc etc
Termination: stop codon reached, release factor (a protein) binds to stop codon. Translation ends.