TRANSCRIPTION Flashcards
Synthesis of RNA using DNA as a template
TRANSCRIPTION
possible products of transcription
mRNA
rRNA
tRNA
Addtnl RNA molecules (noncoding)
for structural, catalytic and regulatory functions
noncoding RNAs
sequences of amino acids
mRNA
mRNA is ____% of the entire RNA
⁓2%
TRANSCRIPTION | FEATURES
only particular genes or group of genes are transcribed at any one time
MORE SELECTIVE
TRANSCRIPTION | FEATURES
phases of transcription
initiation
elongation
termination
some includes activation
TRANSCRIPTION | DIFFERENCE W DNA REPLI
primer needed?
no primer needed
TRANSCRIPTION | DIFFERENCE W DNA REPLI
involves ____ of DNA molecules
limited segments
TRANSCRIPTION | DIFFERENCE W DNA REPLI
Within transcribed segments, only ____ serves as a template for a particular RNA molecule
only 1 DNA strand
% of rRNA in the entire RNA
⁓80%
- smallest
- ⁓15% in the entire rna
- Has extensive intrachain base-pairing
- Serves as an adapter molecule that carries its specific amino acid
tRNA
how many species of tRNA is involved during translation or protein synthesis
20
each tRNA correspond to 1 amino acid
tRNA
There is at least ____ of tRNA molecule for each of the 20 amino acids found in proteins
one specific type
smaller rRNA
prokar or eukar
prokaryotic
what do you call the part that the amino acid binds to
acceptor arm
amino acids will be attached to the ____ end
3’
a tRNA that carries an amino acid
active / charged tRNA
smallest component of RNA
mRNA
Most heterogeneous based on size and base sequence
mRNA
carries genetic information from DNA -> protein
coding RNA
SYNTHESIS OF RNA
- Reads DNA template strand in 3’ -> 5’ direction
- Hence: 5’ -> 3’ polymerase action
- Lacks a separate proofreading 3’ -> 5’ exonuclease active site
DNA DEPENDENT RNA POLYMERASE
DdRP
SYNTHESIS OF RNA
requirements for DNA DEPENDENT RNA POLYMERASE
DNA template
Substrates: ATP GTP UTP CTP
Mg2+, Zn2+
RNA POLYMERASE | CORE ENZYME
required for enzyme assembly
α, Ω
RNA POLYMERASE | CORE ENZYME
needed for template binding
has polymerase activity 5’ -> 3’
β
RNA POLYMERASE
- 2 α, 1 β, 1 β′, and 1 Ω
- lacks specificity (that is, it cannot recognize the promoter region on the DNA template).
core enzyme
RNA POLYMERASE
- **sigma subunit (sigma factor) **
- enables RNA polymerase to recognize promoter regions on the DNA
holoenzyme
DIRECTION
DNA template strand
3’ - 5’
DIRECTION
DNA nontemplate / Coding strand
5’ - 3’
DIRECTION
RNA transcript
5’ - 3’
Each nucleotide in the newly formed RNA undergoes ____
base pairing
PROKARYOTIC gene transcription
initiation
elongation
termination
PROKARYOTIC GENE TRANSCRIPTION
product
primary transcript
PROKARYOTIC GENE TRANSCRIPTION
RNA polymerase ____ a primer to initiate synthesis
does not require
PROKARYOTIC GENE TRANSCRIPTION
binds to a promoter region of the DNA
holoenzyme portion
PROKARYOTIC GENE TRANSCRIPTION
directs the transcription of adjacent segments of DNA (genes)
promoter
PROKARYOTIC GENE TRANSCRIPTION
promoter region
-35 sequence
pribnow box
EUKARYOTIC GENE TRANSCRIPTION
promoter region
TATA or Hogness box, -25
CAAT box, -70 to 80
- Local unwinding of the DNA continues mediated by the polymerase
- RNA polymerase synthesizes RNA using nucleoside monophosphates, releasing pyrophosphate each time
- Direction of the product: 5’ - 3’ RNA transcript
elongation
ELONGATION
direction of the product
5’ - 3’
Elongation of RNA continues until a ____ is reached
terminal signal
TERMINATION
occurs without additional proteins
INTRINSIC
TERMINATION | INTRINSIC
p-independent - requires formation of a ____
HAIRPIN LOOP[
TERMINATION
requires p protein to release RNA from DNA (signaling that there is already termination)
p-dependent
TERMINATION
with helicase activity: separates the RNA-DNA hybrid helix, causing release of the RNA
p protein
EUKARYUOTIC GENE TRANSCRIPTION
found in rRNA (nucleolus)
Pol I
EUKARYUOTIC GENE TRANSCRIPTION
important in the synthesis of mRNA, and noncoding RNAs (lncRNA, miRNA, snRNA)
POL II
EUKARYUOTIC GENE TRANSCRIPTION
tRNA, 5S rRNA, some snRNA and snoRNA
POL III
EUKARYUOTIC GENE TRANSCRIPTION
Resembles the bacterial RNA pol
RNA POLYMERASES (mitochondria)
EUKARYUOTIC GENE TRANSCRIPTION
Required for the assembly of a transcription initiation complex at the promoter and the determination of which genes are to be transcribed
transcription factors
POST-TRANSCRIPTIONAL MODIFICATIONS
Modification of the primary transcript (pre-rRNA to different intermediate-sized pieces of rRNAs)
rRNA
post transcriptional modificatons happen via
ribonucleases
POST-TRANSCRIPTIONAL MODIFICATIONS
Sequences at both ends of the molecule are removed, and, if present, an intron is removed from the anticodon loop by nucleases.
tRNA
POST-TRANSCRIPTIONAL MODIFICATIONS
a. Addition of a 5’ cap
b. Addition of a 3’-poly-A tail
c. RNA Splicing
mRNA
POST-TRANSCRIPTIONAL MODIFICATIONS
ADDITION OF A 5’ CAP:
The cap is a ____ attached to the 5′- terminal end of the mRNA through an unusual 5′→5′-triphosphate linkage that is resistant to most nucleases
7-METHYLGUANOSINE
POST-TRANSCRIPTIONAL MODIFICATIONS
ADDITION OF A 5’ CAP:
The cap is a 7-methylguanosine attached to the ____ of the mRNA through an unusual 5′→5′-triphosphate linkage that is resistant to most nucleases
5’ TERMINAL END
**POST-TRANSCRIPTIONAL MODIFICATIONS
ADDITION OF A 5’ CAP:
The cap is a 7-methylguanosine attached to the 5′- terminal end of the mRNA through an unusual ____ that is resistant to most nucleases
5’ - 5’ TRIPHOSPHATE LINKAGE
POST TRANSCRIPTIONAL MODIFCATIONS
ADDITION OF A 5’ CAP:
The cap is a 7-methylguanosine attached to the 5′- terminal end of the mRNA through an unusual 5′→5′-triphosphate linkage that is resistant to ____
MOST NUCLEASES
POST TRASNCRITPIONAL MDOFICATOOIN
- a chain of 40–250 adenylates (adenosine monophosphates) attached to the 3′-end
- not transcribed from the DNA
- added by the nuclear enzyme, polyadenylate polymerase
- Purpose
- To terminate transcription
- Tails help stabilize the mRNA, facilitate its exit from the nucleus, and aid in translation
- After the mRNA enters the cytosol, the poly-A tail is gradually shortened.
ADDITION OF A 3’-POLY-A TAIL
POST TRANSCRIP MODIF | ADDITION OF 3’-POLY-A TAIL
a chain of ____ adenylates attached to 3’ end
40 - 250
POST TRANSCRIP MODIF | ADDITION OF 3’-POLY-A TAIL
added by the nuclear enzyme ____
polyadenylate polymerase
POST TRANSCRIP MODIF
removal of introns (intervening sequence) from the primary transcript and joining of exons to form a continuous sequence that specifies a functional polypeptide
RNA splicing
intervening sequence
introns
molecular complex that facilitates splicing
spliceosome
