Chapter 7 and 8 Flashcards
Extrons
encode proteins
Introns
separate proteins
Introns are spliced from preRNA via the
spliceosome
Name a couple properties of RNA
- RNA has ribose instead of deoxyribose
- RNA is single stranded
- RNA has A, G, C, and Uracil which is a pyrimidine
U can pair with A and G only during folding but not during transcription - RNA can catalyze biological reactions
Name two classes of RNA
mRNA is the intermediate between DNA and protein, while functional RNA functions by itself
tRNA…
brings amino acids to mRNA in translation
snRNA
unite with protein subunits to form the spliceosome that removes introns from mRNA
RNA transcription goes in the
5’ to 3’ direction (pairs are added to the 3’ end)
For any gene, how many strands of DNA are used?
Just one, no matter how many times the gene is replicated
What happens in initiation stage for prokaryotes
RNA Polymerase binds to a promoter located close to the start of the 5’ to 3’ direction
RNA polymerase scans for DNA promoter sequence
mRNA is usually the same as the
nontemplate strand except T is replaced with U
What is the sigma factor?
a protein binding to the RNA polymerase, which “promotes” the expression of specific genes of the DNA, by binding or not to their promoter site(s). The sigma factor is usually released after transcription is complete
TTG and TATAAT box: what are those?
promoter sequences that usually attract the RNA Polymerase II
How does transcription terminate?
Transcription goes beyond protein segment of the gene, creating a 3’ untranslated region at the end of the transcript
What are the two termination mechanisms?
Intrinsic and rho dependent: In intrinsic, the termination sequences are abundant in G and C which form a hairpin loop (3 H bonds between G and C as opposed to A and T’s 2 H bonds) which RNA stops after U to backtrack, but hairpin loop prompts whole sequence to snap off DNA template strand; rho factor is when RNA has a upstream segment called rut rich in C but poor in G; Rho binds to rut pauses polymerase, and breaks off RNA from RNA polymerase
Three different type of polymerase molecules in eukaryotes. Name them
RNA polymerase I transcribes an RNA gene RNA Polymerase II transcribes all protein encoding genes from which mRNA is the result RNA Polymerase III transcribes small functional RNA genes (tRNA snRNA)
Why is mRNA in eukaryotes cotranscriptional
5’ undergoes processing while 3’ is still being synthesized
How does RNA polymerase III recognize promoter sequences
Requires general transcription factors to bind to regions in the promoter before binding of the core enzyme
What’s the function of a general transcription factor
GTF’s find and bind to sequences in promoters or other GTFs and serve to attract the RNA polymerase II to position and start transcription
Explain the TATA box
Usually the site of the first event, where the TBP or TATA binding protein attracts otehr GTFs and RNA Polymerase III to the promoter to start the preinitiation complex
Explain the 3 stages of pre-mRNA processing
Adding a cap at the 5’ end, splicing to eliminate introns, and AAUAAA and a poly(A) tail is added to the mRNA
CTD (Carboxy Terminal Domain)
Part of RNA Polymerase II near the site at which new pre mRNA emerges and helps bind with proteins to help with pre-mRNA processing
Introns usually have
GU at the 5’ end and AG at the 3’ end
How does intron removal work?
One end’s G attaches to an A in the middle of the intron, in which then the two exons are joined together, leaving the intron as free-floating.
Spliceosomes operate with the help of
snRNAs (small nuclear RNAS)
What molecule helps synthesize RNA primers
Primase
DNA Polymerase I
Revomes the small primase fragments on the lagging strand
Eukaryotes have how many genes per mRNA
Just one while prokaryotes have > 1 per mRNA
