Transcription Flashcards
DNA always occurs as a ______ while RNA is _______, although RNA can fold into different shapes.
DNA-Double Helix
RNA- single stranded
RNA chemically differs from DNA in the fact that …..
RNA contains the sugar ribose (x=OH) instead of deoxyribose (x=H) and the base uracil (U) instead of thymine (base pairing with adenine)
DNA Coding Strand 5’- A T G C C A - 3’
DNA Template Strand 3’- T A C G G T - 5’
mRNA 5’- A U G C C A -3’
Protein N- Met- Pro - C
SUPER IMPORTANT.
Note similarity between coding strand and mRNA plus the one difference (TU)
Prokaryotic mRNA versus eukaryotic mRNA (structurally)
P- multiple proteins from one mRNA
E- 5’cap, PolyA tail, one protein after splicing.
Transcription differs from replication…
- RNA does not remain H-bonded to DNA template but is displaced and the DNA helix reforms
- RNA is ____than DNA
shorter
The main enzymes in transcription are ______, similar to DNA polymerases, moving in the _____ direction to create an RNA chain in the _____ orientation
RNA polymerase; moves 3’ to 5’, creates 5’ to 3’
** ALSO employs hydrolysis of high-energy bonds to drive reaction AQ
Unlike DNA poly, RNA poly CAN start…
start transcription/growing without a primer
The non-template strand is called the ______ strand and is similar in sequence to the RNA transcript with the exception of TU
CODING strand
RNA poly recognizes startpoints for transcription and is sensitive to signals to increase or decrease production of gene product dependent on need.
Interesting.
A regulatory protein sequence called the _______ is upstream(5’) of start site and controls….
Promoter: controls binding of RNA poly to DNA
Frequency of transcription is controlled by _____ within the promoter
cis regulatory sequences
RNA poly has a ____ subunit that recognizes promoter DNA sequences that determine the start point and frequency of transcription
sigma
Eukaryotes have 3 RNA polys
I–>
II–>
III–>
I–> produces rRNA
II–> produces mRNA
III–> produces small RNAs such as tRNAs and 5S rRNA
In E. Coli, the ______sequence is in the promoter and helps mediate poly binding
TATA box/ Pribnow box
Elongation continues until RNA poly encounters termination signals such as _____ or ______
Hairpin loop or Rho protein
A cistron is a….
region of DNA that encodes for a single polypeptide chain
***just prokaryotes?
Prokaryotic transcript products are not modified or spliced like eukaryotes.
Answer.
A polycistronic transcript is capable of…
making a number of different proteins from one mRNA
BASIC transcription cycle (prokaryotic)
1)
2)
3)
1) Initiation:sigma subunit of RNA poly binds promoter sequence of DNA
2) elongation: 5’ to 3’ polymerization
3) termination: (sigma falls off )RNA forms hairpin or else runs into Rho protein
-
-
- Addition of 5’ cap in leader sequence
- splicing out introns (non coding)
- addition of Poly-A tail in 3’ trailer sequence
Prokaryotic RNA poly requires ______ but Eukaryotic RNA poly requires…….
P- sigma
E- lots of proteins
What complicates eukaryotic transcription?
nucleosomes
In eukaryotes, _____ relieve tension while in prokaryotes _______ does so
E- topoisomerases
P- gyrase
Capping of mRNA occurs at ____ end and is necessary to …..
5’ end
Protects transcript form degradation and is necessary to be recognized by small ribosomal subunit for translation
A complex structure known as ______ ensure that exons are accurately spliced; small ribonucleoproteins called _____ are involved in spliceosome formation
spliceosomes; snRNPs
Only the ____ at the start of an intron and the ____ at its end are considered INVARIANT nucleoties
GU; AG
AG is also at end of exon?(3’)
1-Adenine in intron attacks 5’ splice site (AG)and cuts backbone of RNA
2-the cut 5’ of intron (GU) covalently attaches to self at original A= loop
3-released 3’- OH end of exon (AG) reacts with start of next exon joining two exons together
4- exon (lariat) is released
THIS IS Slicing.
RNA splicing is performed by the _____
spliceosome
______splicing is a common means to regulate gene expression
Alternative splicing
Two types of slicing errors:
1) exon skipping (exon 1 + exon 3, forgetting exon 2)
2) cryptic splice site selection: not the AG,GU signal
Poly-A tail is created at the _____ end of the mRNA. A _______ signals cleavage site for polymerase to numerous Adenines to…
3’ end. polyadenylation sequence
-this slide was confusing
microRNAS are involved in ……
regulation of gene expression
HIV has the enzyme ______ that produces….
reverse transcriptase that produces dsDNA from viral RNA and then incorporates dsDNA into host genome for expression
common antibiotic drugs target bacterial _____
RNA polymerase
