Transcription/Translation Flashcards
How many chromosomes do prokaryotes have?
1 pair
Transcriptional differences
prokaryotes have operons, polycistronic mRNA, no hnRNA (introns), no histones, circular DNA
- and translation and transcription happen at the same time in the cytosol
- NO mRNA processing
How is Eukaryotic DNA packed
alpha helix - histones - nucleosomes - chromosomes
less than 2% of the DNA in the chromosome is actually coding DNA, extrons
tRNA role
brings the AAs to ribosome for protein synthesis
name for the strand of DNA that gets transcribed
template strand
name for the strand of DNA that is identical to the mRNA synthesized, except with T replaced by U
coding strand
Are promoters found in Prokaryotic or Eukaryotic DNA?
both! you mother fucker
-TATA box is an essential component of the promoter region. It helps the transcription machinery find the right start site
RNA polymerases
–Don’t need a primer
-have no 3’ to 5’ exonuclease capability (higher error rate than DNA)
Name the RNA polymerases in Eukaryotes and their function.
RNA pol I - synthesizes the most RNA - rRNA
RNA pol II - makes the second most amount - mRNA
RNA pol III - makes the least amount of RNA - tRNA
What happens when RNA pol I, II, or III is not working
I - less protein synthesized (no fucking ribosomes)
II- less protein synthesized (no fucking directions)
III - no protein synthesized (no AA are retrieved for syn)
Prokaryotic RNA pol
only one, that makes all 3 types of RNA
requires a sigma factor
What the hell is alpha amanitin?
its a toxin from mushrooms that blocks RNA pol II
decreasing mRNA in cell (especially GI cells, because new ones cant make mRNA without RNA pol II)
no cure so you could die in a few days if you get a big dose
Prokaryotic transcription
RNA polymerase, template DNA, sigma factor, Rho factor, nucleotides (A, U, C, G)
sigma factor
helps get RNA pol to the start site
Rho factor
required for termination
Don’t forget about differential splicing, euk or prok?
Allows *Eukaryotes to form many different gene products
What is mature mRNA
spliced + cap and tail
-occurs in nucleus before leaving for cytosol
purpose of 5’ cap and polyA tail
- protects 5’ end and allows for ribosome binding
- prevents degradation
Key differences in Eukaryotic transcription (that you dont already know)
no sigma factor, instead requires multiple general transcription factors
Its moncistronic: 1 mRNA = 1 protein
requires this polyadenylation signal (AAUAAA)
*and of course stuff to cut DNA for splicing (endonuclease) - prokaryotic DNA is not spliced
Beta-thalassemia
decreased number of Hb molecules due to a mutation causing decreased transcription of the gene
miRNA?
miRNA regulate mRNA transcript stability.
A patient is found to have deficiency in a chloride channel, CFTR, that is traced to a mutation in the 3′ end of the gene, where the sequence AATAAA is found mutated to AAGAAA. What effect will this have?
The mRNA will not be able to leave the nucleus (needs cap/poly A tail/needs splices – if its mutated wont get a poly A tail) – mutation is affecting the transcript (if you cant get transcript into cytoplasm wont make the protein)
Many antibiotics work by inhibiting bacterial mRNA synthesis. Rifamycin, for example, blocks transcription in E. coli. How is it possible that this drug is such a potent antibiotic to E. coli, yet does not cause harm to the person taking it?
- Could be due to difference in RNA polymerase
- Or Ribosome has different subunits in prok and eukary
- Could block the sigma factor
- **Sigma factor, polymerases are different, and ribosomes are different (anything that targets the difference in bacteria and us)
What would prevent the production of a normal transcript in bacteria?
Bacteria: Lack of sigma factor, lack of Rho factor, problem with RNA polymerase,
Both: (TATA box or promoter, lack of nuceotides, lack of ATP
What would prevent the production of a normal transcript in humans (eukaryotes)?
Euk: failure to splice, poly A tail or cap failure, problem unwinding DNA (issue with histones), lack of specific transcription factors (ones that enhance transcription)
4 letter alphabet
3 letter code
how many possible combinations/codons?
4x4x4 = 64 (we dont have this many - its redundant, BUT not ambiguous)
Name the start codon and stop codons
start codon = AUG (ATG if asked for coding DNA sequence)
Stop: UAA, UAG, UGA
Types of mutations?
point mutation - single base change
silent mutation - change results in same AA
missense mutation - specifies a different amino acid
non-sense mutation - produces a stop codon
insertion/deletion - results in frameshift mutation unless an entire codon is inserted or deleted