02/18 translation Flashcards
what are the three post transcriptional modifications
5’ Capping, 3’ Poly A Tail, Intron splicing
why is it important that the spliceosome splices out the introns differently
this allows for different mature mRNA to be translated into different poly peptides
why is there a lesser amount of genes than originally thought
one gene can be spliced into many different types of polypeptides
what are constitutive exons
they are exons that are in all mature mRNAs
what are alternative exons
they are exons that may or may not be spliced out in a mRNA, this varies from cell to cell as it changes the function of the polypeptide for a specific need or function
describe the process of 5’ capping
a modified guanine cap is attached to the 5’ end of the RNA and this acts as a unique feature that cap-binding proteins will recognize and bind to, which forms the cap
what are the three primary roles of the cap-binding proteins
1) movement of RNA from the nucleus to the cytoplasm
2) initation of translation: the ribosome will find the cap and use it to locate the start codon
3) protections the 5’ end from 5’-3’ exonucleases
if we did not have the 5’ cap, what would occur
translation could not occur
what are the two primary roles of the poly-A SEQUENCE
they facilitate termination and the addition of the poly-A tail in post-transciption modifications
describe the mechanism of adding the poly A tail
an endonuclease recognizes the polyadenylation signal in the mRNA and will cleave the RNA 20 nucleotides downstream of the signal
polyA polymerase will then add the adenines
True or false, the addition of the poly-A tail is coded for by the RNA
false! the poly A tail is added by a polymerase and the DNA does not contain the template for it
how does the length of the Poly-A Tail affect the mRNA
the shorter the tail, the faster the degradation and shorter the half life of the RNA
longer tails usually contribute to more stability and longer half lives
In RNA editing, the DNA template is changed to change the RNA transcribed
false, the RNA is edited after trancription and only the RNA is changed
what is RNA editing
an outside enzyme will change a nucleotide base in the RNA itself
What is the affect of RNA editing?
it changes how the RNA will be read in the ribosome and it will alter the structure of the produced polypeptide and its overall function
Does splicing occur in bacteria? By which mechansim?
rarely, usually self-splicing occurs and spliceosomes do not
Does splicing occur in eukaryotes? By which mechanism?
commonly occurs in eukaryotes primarily by spliceosomes
Does capping occur in Bacteria?
no
Does tailing occur in bacteria
yes
does RNA editing occur in bacteria
no
does RNA editing occur in eukaryotes
yes, occasionally
what does the term “polypeptide” denote
the structure
what does the term “protein” denote
the function, a protein may be made up of multiple polypeptides
what is the more accurate statement of what a structural gene codes for?
it codes for one pre-mRNA that can be spliced in to many different polypeptides
what is the genetic code
it is the code for translating groups of three nucleotides (3 codons) into different amino acids
if there are 64 combinations of the genetic code and only 20 amino aids, what accounts for the extra combinations?
codons are redundant and degenerate, meaning amino acids are coded by many amino acids
what does it mean for the genetic code to be degenerate
it means that more than one codon can specify one amino acid
is the triplet codon degenerate?
no, the codon itself can only code for one amino acid but many codons can code for the same one
which codon is non-degenerate
the methionine start codon (AUG)
what are sense codons? How many?
sense codons are codons that code for amino acids, there are 61 of them
what are non-sense codons?
nonsense codons do not code for amino acids. 3 of these code for stop codons
what does it mean for the genetic code to be nearly universal
nearly every organism follows the code, but not every one
true or false, degeneracy means that a single codon can code for more than one amino acid
false, a single codon can only code for one amino acid
degeneracy means that multiple codons can code for the same amino acid
does the first base laid down in the mRNA translate to a codon?
no, it is the 5’ UTR which is where the ribosomal binding site is
where is the ribosomal binding site?
the 5’ UTR for prokaryotes
in relation to the codon, what does a tRNA have?
it has anticodons that are antiparallel (5’-3’0 the codons
what does the start codon set?
it sets the reading frame for the ribosome which reads in non-overlapping sets of three
what does it mean for the reading frame to be non-overlapping
it means that the reading frame is only read in sets of 3
what is the idea behind the adapter hypothesis
tRNA plays a role in translating mRNA in to amino acids
what are the two roles of tRNA
it recognizes the 3 base codon and in mRNA with its anticodon sequence
it carries an amino acid that is specific for that codon
what is the general role of tRNA synthetase
it is an enzyme that ensures that the proper amino acid is bound to the tRNA
what is an uncharged tRNA vs a charged tRNA
an uncharged tRNA does not carry an amino acid yet while a charged tRNA has a specific amino acid bound to it and it carries it to the mRNA
describe the structure of tRNA
it is a single stranded RNA with double stranded regions
what is the tip of the tRNA for
it is where the amino acids are attached
what is the tail of the tRNA for
it is the anticodon region and matched with the codon in the mRNA
what is embedded within the tRNA
covalently modified bases
what are the roles of the covalently modified bases distributed throughout the tRNA
they are important for recognition by the tRNA synthetase which allows the proper amino acid to be bound
what are the roles of the covalently modified bases within the tRNA
they allow the wobble rule to occur which allows mismatches to occur in the third base of the codon
this allows the degeneracy of amino acids to occur
given the fact that the wobble rule exists, what does this mean for the amount of tRNAs we have for a specific amino acid?
we can have less tRNAs as you can have the same tRNA for degenerate codons (ex CCG and CCA would have the same tRNA)
how many types of tRNA are there? how many types of enzymes are required?
there are 20 total types of tRNAs (one type per amino acid) and 20 types of enzymes
what is an isoaccepter tRNA
there may be two tRNAs for one amino acid but they are the same type of tRNA and only require one enzyme for amino acid binding
why are tRNA synthetases responsible for the “second genetic code”
they are responsible for ensuring that the correct amino acid is added to the correct tRNA
if a mismatch occurs when a tRNA synthetase adds an amino acid, what could be the result
the polypeptide may be nonfunctional
Why is there a very low error rate with tRNA synthetases?
the modified bases in the the structure and the anticodon/codon recognition is crucial
the modified bases in a tRNA affect the following:
A.) it is important in the anticodon for the wobble position
B) it is important for the recognition of the correct tRNA into the pocket of the tRNA synthetase
C) it is important for transcription of the tRNA
A,B
C is incorrect because covalent modifications occur in post transcriptional RNA processing
what is the directionality of polypeptide synthesis? what type of bond is formed
5’-3’ attachments through peptide bonds
what is the first amino acid group called in a polypeptide
it is the N/amino terminal, it has a free amino group
what is the last amino acid called in a polypeptide
it is the C/Carboxy terminal, it has a free carboxy group
what type of synthesis is the formation of a polypeptide bond
it is a dehydration reaction
what amino acids are hydrophillic? where are they found
polar and charged, on the surface
what amino acids are hydrophobic
nonpolar, they are on the interior of the protein
what is the primary structure of a polypeptide
it is the sequence of amino acids, it can be read directly from the DNA
what is the secondary structure of a polypeptide
the polypeptide chain folds and forms alpha helixs or beta sheets
what is the tertiary structure of a polypeptide? what determines the shapr
the tertiary structure is a 3D structure that is facilitated by folding proteins
why is cysteine important in the structure of a polypeptide
it can form covalent disulfide bridges that stay bonded een under denaturing conditions
What is the quaternary structure of proteins
polypeptides may interact with other subunits to form functional proteins
Disulfide bonds that link cystseine residues across a polypeptide affects which level of folding the most?
tertiary structure
