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22 Cards in this Set
- Front
- Back
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What were the Three key sets of experiments definedthe relationship between nuclear DNAand protein expression? |
– A messenger exists that transmitsinformation from the nucleus to thecytoplasm (Brenner, 1960) – The genetic code is read in triplets (Crick,1961, Nirenberg, 1961, Khorana, 1960’s) – The amino acid sequence is linearly relatedto the DNA sequence (Yanofsky, 1967). |
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What are the main features of RNA transcription? |
• RNA polymeraseenzymes make RNA • Addition of nucleotidesin a 5’ → 3’ direction • Requires a template,the two strands ofDNA need to beseparated |
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How are the nucleotides joined in RNA? |
Like in DNA, thenucleotides in RNAare joined by covalentphosphodiester bonds |
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What are the 3 main steps in transcription? |
• Initiation• Elongation• Termination |
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What happens in initiation in E.coli Prokaryotic Transcription? |
RNA polymerase isdirected to the start siteof transcription on thedouble stranded DNA.Enzyme findstranscriptional start site |
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What is the Sigmafactor? |
A sigma factor (σ factor) is a protein needed only for initiation of RNA synthesis. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase to gene promoters |
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What is a pribnow box? |
The Pribnow box (also known as the Pribnow-Schaller box) is the sequence TATAAT of six nucleotides (thymine-adenine-thymine-etc.) that is an essential part of a promoter site on DNA for transcription to occur in bacteria |
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What happens to the sigma factor shortly after transcription starts? |
RNA polymerase is a protein complex aabb’Sigma factor (s) dissociates shortly aftertranscription initiation starts |
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What happens in the elongation step of transcription? |
ELONGATION Reading of DNAsequence on templateand synthesis of amessenger RNA approx. 50nt/sec |
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What happens at termination? |
TERMINATION Reaching of transcriptionaltermination site, mRNAsynthesis finishes |
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What is termination controlled by? |
Termination controlled by STOP sequences inDNA These are GC rich regions that mean theRNA transcript forms a hairpin loop Termination sometimes requires assistance ofa protein, rho () |
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What is mRNA detachement from DNA template facilitated by? |
Weak A-U pairing to DNA |
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How is prokaryotic transcription different to eukaryotic transcription? |
Eukaryotic: • More complex --> more Proteins involved – Polymerases – Initiation factors – Elongation factors – Other helper proteins • Additional mRNA Processing |
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Eukaryotic genes are “split” . What are exons? |
Exons: regions of DNA within a gene unit that arefound in mature mRNA = “expressed” regions. |
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What are introns? |
Introns: regions of DNA within a gene unit that are notfound in mature mRNA = “intervening” regions. Do not code for any amino acids in mature protein |
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What is capping in Eukaryotic Transcription: mRNA processing? |
Capping: formation of 7-methylguanosine cap at 5’ end GTP “reacts” with 5’ end ofmRNA resulting in addition to 5’phosphate group (5’ – 5’ bond) The guanine is methylated at 7’position |
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What is splicing in Eukaryotic Transcription: mRNA processing? |
Splicing: removal of intronic segments |
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What is Polyadenylation? |
Polyadenylation: addition of tail to 3’ end of RNA Complex processEssentially adds 50 – 250 adenosineresidues to end of RNA chainAdded to 3’ end, as normal. |
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In eukaryotes which mRNA can leave the nucleus? |
In eukaryotes, only fully processed mRNA canbe exported from the nucleus and is madeavailable for translation |
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How can some hnRNAs be spliced? |
Some hnRNAs can be spliced in differentways, resulting in different protein productfrom a single gene |
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What does mRNA carry the code for? |
mRNA carries the code for protein production |
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What is a visual representation of transcription? |
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