Transcription Flashcards
(54 cards)
1
Q
RNA polymerase action in prokaryotes
A
- begins transcription without a primer
- reads the template strand 3’ to 5’
- synthesizes the RNA transcript 5’ to 3’ using ribonucleotides
- recognizes termination signals
2
Q
What does transcription begin with?
A
- RNA polymerase identifying a genes promoter region
- interacts with DNA template strand
- initiates synthesis of a complementary, antiparallel RNA transcript
3
Q
When does transcription end?
A
-when a termination signal is reached
4
Q
what strand is read during synthesis?
A
-genes are described by the sequence of the CODING STRAND, but the TEMPLATE STRAND is the one read during synthesis by RNA polymerase
5
Q
Coding strand of DNA and RNA transcript sequence
A
- they are the exact same, but there are U’s instead of T’s in the RNA transcript
- both are 5’ to 3’
6
Q
numbering and base sequence
A
- the first base to be transcribed is +1
- downstream(to the right in the 3’ direction) goes up in plus direction
- upstream(to the left in the 5’ direction) goes down in the negative direction
7
Q
promoter
A
-always upstream of the +1 position
8
Q
what direction does the template strand run?
A
3’ to 5’
9
Q
holoenzyme
A
- core enzyme+sigma factor
- prokaryotic RNA polymerase construction
- scanning and recognition or promoter sequence cues by holoenzyme initiate RNA transcription
10
Q
core enzyme subunits
A
- 2 alpha subunits
- 1 beta subunit
- 1 beta’ subunit
11
Q
core enzyme
A
-has RNA polymerase activity for nucleotide elongation
12
Q
sigma factor
A
- required for recognizing and binding promoter sequences
- different sigma factors recognize different promoter sequences
- recruits core enzyme to DNA promoter
- dissociates from core enzyme after transcription begins
13
Q
prokaryotic promoters
A
- 2 consensus sequences
- TATA box
- -35 sequence
14
Q
prokaryotic TATA box
A
- prinbnow box
- sequence of 6 nucleotides
- 7 nucleotides upstream from the +1 transcriptional start site
15
Q
-35 sequence
A
- consensus sequence in prokaryotes
- 35 bases upstream from +1 transcriptional start site
16
Q
elongation in prokaryote RNA synthesis
A
- transcription begins at the +1 start site
- sigma factor must be released first, then core enzyme continues
- generated in the 5’ to 3’ direction
- creates a temporary “melt” of dsDNA to form transcription bubble
- results in supercoiling
17
Q
Net reaction of prokaryote RNA synthesis
A
- addition of a ribonucleotide to the growing RNA chain
- release of a pyrophosphate
18
Q
what do DNA polymerases and RNA polymerases have in common?
A
- both release a pyrophosphate which is further cleaved by pyrophosphatase
- provides energy to drive reaction
- makes reaction irreversible
19
Q
What are the two termination mechanisms for prokaryotic RNA sequences?
A
- Rho-dependent termination
- Rho-independent termination
20
Q
rho
A
-displaces the DNA template strand from RNA polymerase
21
Q
rho-dependent termination
A
-requires an additional protein to displace DNA template from RNA pol
22
Q
rho-independent termination
A
- requires a G-C rich stem loop followed by a poly-U stretch
- causes RNA pol to dissociate
23
Q
Shine-dalgarno sequence
A
- translation
- right before a gene
- tells ribosome to begin at that point to start translation
- the next time you see a start codon, you should start translation
- new shine-dalgarno sequence right before each new gene
24
Q
polycistronic
A
- only prokaryotes
- one mRNA codes for several proteins(multiple genes on one transcript
- code for multiple enzymes in the same biosynthetic pathway
25
rifampin
- antibiotic
- binds to prokaryotic RNA pol to prevent transcription
- used to treat TB
- interact with core enzyme and cause conformational change so it cannot read template strand
- ONLY PROKARYOTIC
26
prokaryotic RNA polymerase
-RNA pol I produces ALL types of RNA
27
Euchromatin
- less condensed DNA
| - more accessible to RNA polymerase for transcription
28
Acetylation of histone H1
-causes chromatin to revert to nucleosomes,beads on a string, so it is more exposed
29
Heterochromatin
- appears more dense DNA
- DNA is relatively inaccessible due to its highly condensed structure
- highly methylated which determines epigenetics/phenotype
30
Eukaryotic RNA polymerase I
-transcribes precursors to rRNA in the nucleolus
31
RNA polymerase II
- transcribes precursor to hnRNA in nucleoplasm
| - eventually hnRNA becomes mRNA
32
RNA polymerase III
-transcribes tRNA precursors
33
Eukaryotic consensus sequences
- TATA box
| - CAAT box
34
Eukaryotic TATA box
- Hogness box
- 25 nucleotides UPstream from start site
- recognized by RNA pol II
35
CAAT box
- 70 nucleotides UP stream from start site
| - recognized by RNA pol II
36
rRNA synthesis in Eukaryotes
- three rRNAs are transcribed as a single large precursor
- large precursor cut to three by RNA pol I
- individual rRNA are cleaved apart by RNases
37
tRNA synthesis in Eukaryotes
- RNA pol III
- removal of intron loops
- trimming of 5' and 3' ends
- base modifications at 3' end
- addition of 3'CCA sequence(important for adding amino acids)
38
where does eukaryotic transcription take place?
nucleus
39
Where does eukaryotic translation take place?
cytoplasm
40
Eukaryotic mRNA and prokarotic mRNA
Eukaryotic: extensively processed from hnRNA to mRNA
Prokaryotic: begin mRNA translation before transcription is over
41
5' capping
- addition of 7-methylguanosine to 5' end of eukaryotic mRNA
| - ribosome recognition signal AND protect from nuclease degradation
42
3' poly-A tail
- 3' terminus of eukaryotic mRNA contains a polyadenylation signal
- site for addition of adenine residues
- the additional A's are not encoded in the gene
- serves are a signal for transport out of the nucleus and stabilizes mRNA from nuclease degradation
43
introns
intervening sequences
44
exons
expressed sequences
45
Why must introns be removed?
-they are not exressed, so they must be removed for proper translation
46
Splicing
-the removal of introns and the joining of exons by snRNPs
47
snRNPs
- composed of snRNA and a group of proteins
| - form lariot, clip it out, join exons
48
lariat
-the excised intron
49
alternative splicing
- joining of different exons together to form different mRNAs
- produces proteins with SOME common domains, but the overall function is different
50
Who is primarily affected by systemic lupus erythematosus?
-onset is in late-teen females
51
systemic lupus erythematosus
- produce antibodies that recognize host proteins, including snRNPs
- results in butterfly rash
52
where is mature mRNA transported after processing events are complete?
cytoplasm
53
Amanita phalloides
- death cap mushroom
| - contains alpha-amanitin
54
alpha amanitin
-binds to RNA pol II and inhibits mRNA synthesis
