DLA 3a- Transcription Flashcards
What is the central dogma?
The information that is contained in the DNA is transcribed to mRNA by RNA polymerase
mRNA is translated to protein by ribosomes
Outline RNA transcription in Prokaryotes and Eukaryotes
- DNA transcribed via RNA polymerase to mRNA
- mRNA translated to proteins via ribosomes
NB: tRNA and rRNA are involved in the processing in the mRNA
How is the catalytic activity of RNA polymerase similar to that of DNA synthesis?
- Phosphodiester bond formation between nucleotides and pyrophosphate is released
- DNA is used as the template
What are the differences between Catalytic Activity of RNA polymerase and DNA synthesis?
-RNA polymerase has helicase activity
-the nucleotide triphosphate (NTP) used as substrate are different
Thymine base in DNA is replaced with Uracil to be complementary to Adenine in RNA synthesis
The sugar of RNA is ribose sugar and not deoxyribose
No primer is required to initiate synthesis
In bacteria, a single RNA polymerase is composed of…
The core polymerase and sigma factor
What is the sigma factor in RNA polymerase?
It enables the RNA polymerase to recognize promoters
Describe the 3 different RNA polymerases in Eukaryotes
- RNA polymerase 1: 5.8S, 18S, and 28S rRNA genes
- RNA polymerases 2: all protein-coding genes (mRNA), lnc -RNAs and some snRNAs
- RNA polymerase 3: tRNA genes and some snRNAs
What does the r in rRNA mean?
Ribosomal
What does the t mean in tRNA?
Transfer
What does “lnc” mean in lnc-RNA?
Long non-coding
What does the “Sn” mean in snRNA?
Small nuclear
What is the -10 region in prokaryotic gene?
The pribnow box
What region does RNA polymerase bind to for a prokaryotic gene?
The promoter region
Describe where the ignition and termination of RNA synthesis occurs
- Initiation of RNA synthesis at the beginning of the gene at +1
- RNA polymerase releases the RNA transcript after the terminal signal
What is the -35 region in prokaryotic genes?
The -35 region
Where does mRNA transcription begin?
At +1 base pair
Where is the promoter region in the prokaryotic genes?
The conserved regions at -35 and -10 base pairs
What are the subunits of RNA polymerase?
The core enzyme and the sigma subunit
What is the function of Holoenzyme RNA polymerase for prokaryotic RNA polymerase?
It binds to prokaryotic DNA and scans till it recognizes the promoter sequence
Describe the functioning of prokaryotic RNA polymerase
- At the promoter sequence, RNA pol. unwinds the helix to expose the template strand
- Requires all 4 NTOs as substrate( A,U,C,G)
- RNA polymerase will then synthesize in the 5’ to 3’ direction reading the template strand from 3’ to 5’
- Elongation of the RNA occurs
- RNA pol. will stop at the termination signal
Which DNA strand serves as the template for RNA ?(both prokaryotes and eukaryotes)
Template strand/ anti-sense strand / non-coding strand
How can the template/ antisense strand be identified?(both prokaryotes and eukaryotes)
Read in 5’ to 3’ direction
What is the Un-used/ non transcribed DNA strand called ? (both eukaryotes and prokaryotes)
Non-template strand/sense strand/ coding strand
Why does the RNA polymerase have helicase activity?
RNA pol. has helicase activity to open up a double helix
A DNA strand is as follows:
3’. TACCGACGGT 5’
What will be the resulting RNA strand of transcription?
5’ AUGGCUGCCA’3
Explain the termination of Prokaryotic Transcriotion
- DNA sequence at the end of the gene contains inverted repeats
- When the DNA is transcribed to single stranded RNA, it will form complimentary bond to itself and then firm a hairpin loop
- At the end of the hairpin loop are many consecutive U pairs on the RNA(weak A-U pairing)
- Energy of making the hairpin loop will dissociate the RNA from the DNA template
What is the purpose of Rho proteins?
Sometimes these specific proteins assist the RNA to dissociate from the DNA template
What is a ORF(Open reading frame)?
This is DNA information that will first be transcribed to RNA and next directly translated in to protein
Most times a single gene on the prokaryotic mRNA is …
Transcribed to a single mRNA
When a single gene of a prokaryote being transcribed to a single mRNA it has…
One open reading frame / one ORF
Explain the function of the information comprising an open reading frame/ ORF
- the information comes 3 base pairs at a time, called a codon
- Each codon will be translated to an amino acid by the ribosome, to be discussed later
- Starting from start codon AUG, 3 base pairs at a time, all the way to the stop codon
- There is one universal start codon but three universal stop codons
What are polycistronic genes?
When there are multiple genes expressed from one promoter region
Sometimes mRNA have …
Polycistronic genes under the control of one promoter