Biochem - Molecular (Transcription & Translation Part 1) Flashcards
Pg. 72-73 in First Aid 2014 Sections include: -DNA/RNA/Protein synthesis direction -Start and stop codons -Functional organization of a eukaryotic gene -Regulation of gene expression -RNA polymerases -RNA processing (eukaryotes) -Splicing of pre-mRNA
In what direction is DNA synthesized? What about RNA?
DNA and RNA are both synthesized 5’ => 3’
What is the energy source for bonding of DNA/RNA, and where on the DNA/RNA is it located?
The 5’ end of the incoming nucleotide bears the triphosphate (energy source for bond).
In what direction does protein synthesis occur?
Protein synthesis is N-terminus to C-terminus
In what direction is mRNA read?
mRNA is read 5’ to 3’
Explain 3’ hydroxyl attack, particularly by drugs.
The triphosphate bond is the target of the 3’ hydroxyl attack. Drugs blocking DNA replication often have modified 3’ OH, preventing addition of the next nucleotide (“chain termination”).
What are the mRNA start codons?
AUG (or rarely GUG); Think: “AUG inAUGurates protein synthesis”
What amino acids do mRNA start codons code in eukaryotes versus prokaryotes? What may be the fate of this amino acid in eukaryotes?
EUKARYOTES - Codes for methionine, which may be removed before translation is completed; PROKARYOTES - Codes for formylmethionine (f-met).
What are the mRNA stop codons?
UGA, UAA, UAG; Think: “UGA = U Go Away, UAA = U Are Away, UAG = U Are Gone”
Draw the functional organization of a eukaryotic gene, including and labeling the following: (1) Enhancer (2) Exon (3) Promoter (4) 5’ ends (5) 3’ ends (6) Intron (7) Sense/Coding strand (8) Template strand (9) Start of transcription (+1) (10) TATA box (11) Transcribed region (12) Termination signals.
See p. 73 in First aid 2014 for visual
What characterizes the promoter, and what function does it serve?
Site where RNA polymerase and multiple other transcription factors bind to DNA upstream from gene locus (AT-rich upstream sequence with TATA and CAAT boxes)
What commonly results from promoter mutation?
Promoter mutation commonly results in dramatic decrease in level of gene transcription
What is an Enhancer, and what is its function?
Stretch of DNA that alters gene expression by binding transcription factors
What defines a Silencer?
Site where negative regulators (repressors) bind
Where are Enhancers/Silencers located in relation to the gene whose expression they regulate?
Enhancers and Silencers may be located close to, far from, or even within (in an intron) the gene whose expression it regulates
Name the types of RNA polymerases in eukaryotes and the type of RNA made by each.
(1) RNA polymerase I makes rRNA (Think: “most numerous RNA, Rampant” (2) RNA polymerase II makes mRNA (Think: “largest RNA, Massive”) (3) RNA polymerase III makes tRNA (Think: “smallest RNA, Tiny”); Think: “I, II, and II are numbered as their products are used in protein synthesis”
Besides making the different types of RNA, what functions do eukaryotic RNA polymerases serve?
No proofreading function, but can initiate chains. RNA polymerase II opens DNA at promoter site.
What kind of RNA polymerase do prokaryotes make, and what does it do?
1 RNA polymerase (multisubunit complex) makes all 3 kinds of RNA
What is the initial transcript (i.e., made from transcription ) called? In general, what happens to it?
Initial transcript is called heterogeneous nuclear RNA (hnRNA). hnRNA is then modified and becomes mRNA.
What are the 3 major processes that occur following transcription, and where? What product results from them?
The following processes occur in the nucleus following transcription: (1) Capping of 5’ end (addition of 7-methylguanosine cap) (2) Polyadenylation of 3’ end (~ 200 A’s) (3) Splicing out of introns; Capped, tailed, and spliced transcript is called mRNA
What occurs following RNA processing in eukaryotes?
mRNA is transported out of the nucleus into the cytosol, where it is translated
Where is alpha-amantin found, and what is its mechanism? What clinical finding does it cause, and in what context?
Alpha-amantin, found in Amanita phalloides (death cap mushrooms), inhibits RNA polymerase II. Causes severe hepatotoxicity if ingested.
Where are P-bodies found, and what is their purpose?
mRNA quality control occurs at cytoplasmic P-bodies, which contain exonucleases, decapping enzymes, and microRNAs; mRNAs may be stored here for future translation
Does Poly-A polymerase require a template? What is the polyadenylation signal?
Poly-A polymerase does not require a template; AAUAAA = polyadenylation signal
What are the 3 major steps in splicing of pre-mRNA?
(1) Primary transcript combines with small nuclear ribonucleoproteins (snRNPs) and other proteins to form spliceosome (2) Lariat-shaped (looped) intermediate is generated (3) Lariat is released to precisely remove intron and join 2 exons
For which condition are antibodies to spliceosomal snRNPs (anti-Smith antibodies) highly specific?
Antibodies to spliceosomal snRNPs (anti-Smith antibodies) are highly specific for SLE
With what disease are Anti-U1 RNP antibodies highly associated?
Anti-U1 RNP antibodies are highly associated with mixed connective tissue disease
