Final Unit: Transcription and RNA Processing Flashcards
What is the central dogma of molecular biology?
DNA –> mRNA –> Protein
What is a simple summary of transcription?
Transcribe an RNA copy of the DNA instruction
Where does transcription occur in Eukaryotes? Prokaryotes?
Nucleus. Cytoplasm.
What are four key differences between RNA Synthesis and DNA Synthesis?
- rNTP (ribonucleoside triphosphate) instead of dNTP (deoxyribonucleoside triphosphate)
- Only one template strand of DNA is used for RNA synthesis
- No primer is needed in RNA synthesis
- RNA is much more unstable and short-lived
Is RNA from transcription single or double stranded?
Single
Is the RNA from transcription complementary or non-complementary to the DNA template strand?
Complementary
What are the 5 types of RNA?
- Messenger RNA (mRNA)
- Small nuclear RNA (snRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
- Micro RNA (miRNA)
What is mRNA’s role?
To specify polypeptides
What is snRNA’s role?
Key component of a spliceosome
What is tRNA’s role?
Deliver amino acids
What is rRNA’s role?
Involved with ribosomes
What is miRNA’s role?
Block expression of mRNAs
The RNA produced from transcription is identical to the DNA _______ strand with the exception of what:
DNA nontemplate strand, T replaced with U
Which enzyme is the workhorse of transcription?
RNA Polymerase
What direction does RNA polymerase work in?
5’ to 3’
How many RNA Polymerases are in bacteria?
1
How many RNA Polymerases are in eukaryotes?
3 (I, II, III)
What part of DNA does RNA synthesis occur in?
A locally unwound segment of DNA
What is a gene?
A unit of genetic information that controls the synthesis of one protein/structural RNA molecule
What is a transcriptional unit?
The stretch of DNA that is transcribed into RNA
In addition to a segment of DNA, what are the components of a transcriptional unit?
Promotor, Introns, Exons, and Terminator
What does +1 refer to?
Transcription site
Before the initiation site is referred to…
Upstream
Is upstream + or -? 5’ or 3’?
(-) and 5’
After the initiation site is referred to…
Downstream
Is downstream + or -? 5’ or 3’?
+ and 3’
What is the name for the strand read by RNA polymerase?
Template strand
What are three names for the strand read by RNA polymerase?
Template, non-coding, antisense
What are three names for the strand not read by RNA polymerase?
Non-template, coding, sense
Why is coding strand an appropriate name for the strand that is not read by RNA polymerase?
The sequence of the coding strand matches the sequence of the RNA that is transcribed from the template strand (except T is replaced with U)
What are the three stages of transcription in prokaryotes?
Initiation, Elongation, Termination
PROKARYOTES: In initiation, what is the role of sigma?
Helps place RNA polymerase onto DNA template
PROKARYOTES: In initiation, sigma and RNA polymerase together form a …
Holoenzyme
PROKARYOTES: In initiation, after how many ribonucleotides is sigma no longer needed?
About 9
PROKARYOTES: What are the two important parts of the promoter?
-10 box and -35 box
PROKARYOTES: Where is the -10 box found?
10 bases upstream from the transcription start site
PROKARYOTES: What is the sequence of the -10 box?
TATAAT
PROKARYOTES: Where is the -35 box found?
35 base pairs upstream from the transcription start site
PROKARYOTES: What is the sequence of the -35 box?
TTGACA
PROKARYOTES: What four key things happen in initiation?
- Sigma factor recognizes the promoter region
- RNA polymerase attaches
- DNA strands separate to form open complex
- Polymerization begins
PROKARYOTES: How long is the new RNA strand associated with the template strand?
Only temporarily
PROKARYOTES: Does elongation need sigma factor?
No
PROKARYOTES: What are the two key events in elongation?
- SIgma factor released
- RNA polymerase synthesizes RNA using the template strand
PROKARYOTES: When does termination occur?
When RNA polymerase reaches the termination sequence
PROKARYOTES: What happens when the termination sequence is reached?
RNA polymerase and newly-made mRNA dissociate from DNA
PROKARYOTES: What happens when the termination sequence is transcribed?
A hairpin structure is formed
EUKARYOTES: Why is everything more complicated in eukaryotes?
mRNA has to leave the nucleus
EUKARYOTES: What features of eukaryotic transcription are identical to prokaryotes?
Basic features
EUKARYOTES: Which form of RNA polymerase transcribes mRNA?
RNA Polymerase II
EUKARYOTES: How many basal transcription factors are needed to initiate transcription?
5
EUKARYOTES: Many eukaryotic promoters include a unique sequence called the ______
TATA box
EUKARYOTES: Where is the TATA box located?
About 30 basepairs upstream of the transcription start site
EUKARYOTES: Do eukaryotes use sigma proteins?
No
What is the main difference between the RNA product of bacteria vs the RNA product of eukaryotes?
In bacteria, DNA is converted to mRNA directly. In eukaryotes, the product is transcription is called pre-mRNA. It needs further processing before translation.
EUKARYOTES: What are the three steps of RNA Processing?
Capping, Splicing, Tailing
EUKARYOTES: The protein-coding regions of eukaryotic genes are interrupted by _______ regions
Non-coding
EUKARYOTES: What are the coding regions of eukaryotic genes called?
Exons
EUKARYOTES: What are the intervening noncoding sequences of eukaryotic genes called?
Introns
EUKARYOTES: Are exons or introns in the final mRNA?
Exons
EUKARYOTES: What is the process that removes introns?
Splicing
EUKARYOTES: What splices the RNA?
Small nuclear ribonucleoproteins (snRNPs)
EUKARYOTES: What do the snRNPs form in splicing?
Spliceosome
EUKARYOTES: What are the 4 steps of RNA Splicing?
- snRNPs bind to intron
- snRNPs assemble to form the spliceosome
- Intron is cut
- Intron is released and exons are joined together
EUKARYOTES: What is alternative splicing?
Making different mRNA transcripts from different combinations of exons
EUKARYOTES: What is added to the 5’ end of pre-mRNA?
5’ cap
EUKARYOTES: What does the 5’ cap consist of?
A modified Guanine nucleotide
EUKARYOTES: What is the role of the 5’ cap?
Serves as a recognition signal for translation
EUKARYOTES: What is added to the 3’ end of pre-mRNA?
Poly(A) tail
EUKARYOTES: What does the Poly(A) tail consist of?
A bunch of As
EUKARYOTES: What is the role of the Poly(A) tail?
Protects mRNA from degradation