3C- Transcription: Synthesis of RNA Flashcards
What is transcription?
process of creating a complementary RNA copy of a sequence of DNA
What are the steps of transcription?
- RNA polymerase moves the transcription bubble, like the slider of a zipper, to split the double helix DNA molecule into two strands of unpaired DNA nucleotides, by breaking the hydrogen bonds between complementary DNA nucleotides.
- RNA polymerase adds matching RNA nucleotides that are paired with complementary DNA nucleotides of one DNA strand.
- RNA sugar-phosphate backbone forms with assistance from RNA polymerase to form an RNA strand.
- Hydrogen bonds of the untwisted RNA + DNA helix break, freeing the newly synthesized RNA strand.
- If the cell has a nucleus, the RNA is further processed (addition of a 3’UTR poly-A tail and a 5’UTR cap) and exits through to the cytoplasm through the nuclear pore complex.
What is the coding strand?
This is the strand of DNA that the RNA will make the replica copy of. It will complement with the template strand to make a direct copy of the coding strand.
The only difference is that there are U’ s instead of T’s in the RNA
What is the promotor sequence?
Promoters are regions of DNA that promote transcription and, in eukaryotes, are found at -30, -75, and -90 base pairs upstream from the transcription start site
The TATA box, as a core promoter, is the binding site for a transcription factor known as TATA-binding protein (TBP)
What is the primary transcript?
A primary transcript is an RNA molecule that has not yet undergone any modification after its synthesis such as methylation, or the addition of a Poly-A tail
What is the difference between upsteam and downstream?
In molecular biology and genetics, upstream and downstream both refer to a relative position in DNA or RNA. Each strand of DNA or RNA has a 5’ end and a 3’ end, so named for the carbons on the deoxyribose (or ribose) ring. Relative to the position on the strand, downstream is the region towards the 3’ end of the strand. Since DNA strands run in opposite directions, downstream on one strand is upstream on the other strand.
Give a general features of the differences between the coding strand, template strand, mRNA produced and the amino acid sequence produced
What is added to the 5’ end of the hnRNA? It’s function?
A methylated guanosine cap
it’s a pyrimidine with 3 phosphate groups attahced to the 5’ hydroxyl of the ribose
the cap seals the 5’ end of the primary transcrips and decreases the rate of degredation. it also serves as a recognition site for the binding of mature mRNA to a ribosome at the initiation of protein synthesis
What is added to the 3’ end of the hnRNA? It’s function?
after the RNA polymerase transcribes the stop codon, it adds a AAUAA, which is a polyadenylation signal
with the help of ATP–>AMP + PPi, poly(A) polymerase adds on sections of adenine nucleotides, 1 at a time
the poly(A) tail is a protein binding site that protects the mRNA from degredation
What is the general sequence of intron excision?
the intron/exon boundaries are AGGU. THe introls almost all begin with a 5’-GU and end with a 3’-AG
a splicosome is formed by snRNP’s binding to the and forming a loop –> U1 and U2 cleave before the 5’-GU –> U5 cleaves after the 3’AG –> Exon 1 and 2 linked together –> lariat shaped splicosome with the intron leave and get degraded
What are the 5 different RNA polymerases in eukaryotes?
- RNA polymerase I synthesizes a pre-rRNA 45S (35S in yeast), which matures into 28S, 18S and 5.8S rRNAs which will form the major RNA sections of the ribosome.[6]
- RNA polymerase II synthesizes precursors of mRNAs and most snRNA and microRNAs.[7] This is the most studied type, and, due to the high level of control required over transcription, a range of transcription factors are required for its binding to promoters.
- RNA polymerase III synthesizes tRNAs, rRNA 5S and other small RNAs found in the nucleus and cytosol.[8]
What are the 4 different subunits of the prokaryotic RNA polymerase?
- β’: The β’ subunit is the largest subunit. The β’ subunit contains part of the active center responsible for RNA synthesis and contains some of the determinants for non-sequence-specific interactions with DNA and nascent RNA.
- β: The β subunit is the second-largest subunit. The β subunit contains the rest of the active center responsible for RNA synthesis and contains the rest of the determinants for non-sequence-specific interactions with DNA and nascent RNA.
- αI and αII: The α subunit is the third-largest subunit and is present in two copies per molecule of RNAP, αI and αII. Each α subunit contains two domains: αNTD (N-Terminal domain) and αCTD (C-terminal domain). αNTD contains determinants for assembly of RNAP. αCTD (C-terminal domain) contains determinants for interaction with promoter DNA, making non-sequence-non-specific interactions at most promoters and sequence-specific interactions at upstream-element-containing promoters, and contains determinants for interactions with regulatory factors.
- ω: The ω subunit is the smallest subunit. The ω subunit facilitates assembly of RNAP and stabilizes assembled RNAP.
What is the whole binding process at the promotor, including all the TF’s?
the TATA box is located at -25 and is recognized by the TATA-binding protein (a part of TFIID) –> TFIIA and B bind to TBP –> RNA polymerase bind –> E, F, and H bind to the RNA pol –> txn can begin at a basal level
coactivators bind to enhancer regions upstream of the TATA box –> activate TBP and enchance txn
What are sigma factors?
They are small units which bind to the promotor region of a prokaryotic genome
the RNA polymerase bind to the sigma factor and begins txn
they are released when the growing RNA chain is ~10 nucleotides long
How is rRNA synthesized and packed into ribosomes?
How is tRNA made?
