Set 9 Flashcards
List and briefly explain different mechanisms of post-transcriptional control of gene expression (think about examples)? *
● Localization of mRNA: results in uneven distribution of proteins in cytoplasm eg. axial polarity to the embryo - Bicoid gene expressed in the anterior part
● RNA editing (not including splicing) alters mRNA sequence eg. deamination of A to I (inosine)
● Gene silencing by small RNA, either inhibit or degrade mRNA (example is the control of the LIN14 gene through lin4 (codes for miRNA))
● Translational control/ riboswitch, turns On/Off depending on conditions eg. coordinate & opposite translation regulation of ferritin and transferrin receptor
● Alterations to stability + longevity
Explain the role of mRNA stability (or editing, or iRNA, or translational control switch or mRNA localization – five different questions possible) in control of gene expression.
● Localization of mRNA: ZBP1 finds ZIP code sequence on mRNA, used to shuttle to correct part of cell using cytoplasm as guide.
● RNA editing: guide RNA can add or delete long sections of U, single nucleotide changes include deamination of A to I (which is recognized as G) and C to U
○ If in 5’UTR, alters translational efficiency, may create new or alter original reading frame, may create a new start codon, extend N terminus
○ If in coding sequence, may produce aa substitutions, or new STOP codon
○ If in 3’UTR, alters stability and ZIP code trafficking properties
● Gene silencing by small RNA: Dicer cuts introns into miRNA and siRNA for RNA interference. These are incorporated into RISC, which binds to complementary sequences on mRNA and either cleaves, inhibits, or silences it
● Riboswitch: secondary or tertiary structure within the UTR determines whether or not translation will occur (see example of ferritin/ transferin genes)
● Alterations to stability/ longevity: elements in 3’UTR contribute to stability, certain sequences will result in rapid degradation (these are instability elements). AU rich elements and related binding proteins can cause degradation to occur from either end, or can control how available the mRNA is to ribosomes.
Explain the connection between pre m-RNA splicing and transport of mRNA from the nucleus.
The cell will prevent unspliced or improperly spliced mRNA from exiting the nucleus. This selective export allows for regulation of specific biological processes
What is trans-splicing? Give an example.
Trans splicing is splicing that joins exons from different RNA’s.
Example: Trypanosoma: leader sequences get spliced into 39nt mini exons. These will splice with the 5’ ends of all coding genes and will trigger the addition of a poly A tail at the 3’ end.
What does S in 16S stand for? What is the numerical value of this constant?
S stands for the sedimentation rate of centrifugation. S stands for svedberg units. The numerical value is 1S=10^-13 seconds.
What are the roles of three major RNAs in protein synthesis?
mRNA - primary transcript that carries genetic information from DNA in the form of codons
tRNA - translates mRNA code - each a.a. Has its own tRNA which then binds to mRNA due to codon-anticodon complementarity
rRNA - associates w/ proteins to form ribosomes which catalyzes the assembly of protein chains
What is the name of the region of tRNA molecule which attaches to an amino acid?
Acceptor Stem
How many different tRNAs are there in an eukaryotic cell? How many different aminoacyl tRNA synthetases are there in an eukaryotic cell?
50 different tRNAs in animals and plants
20 different aminoacyl tRNA synthetase (one for each aa)
What are the roles of tRNA in translation?
tRNA will be linked to and transport a particular aa
tRNA anticodon will recognize and bind an mRNA codon
What is the wobble position for an anticodon? For a codon?
Anticodon - at the 1st position codon (5’)
Codon - at the 3rd position codon (3’)
Explain what does it mean when we say that the code is degenerate? Codons are
synonymous?
Degenerate = redundancy of genetic code→more than 1 codon for every amino acid Synonymous = 2 codons for the same a.a.→codons that code for same amino acid
