exam 2 the central dogma: translation Flashcards
how does genetic information stored in chromosomes become useful
by being read and converted into proteins in the cytosol
where are mRNA molecules exported to and from
exported from nucleus to the cytosol
where do mRNA molecules get translated into proteins
cytosol, where they get translated into proteins by ribosomes
how many different combinations does the triple nucleic code allow for
4 x 4 x 4 = 64 - enough for the 20 amino acids
what is a codon
set of three nucleotides
how many codons does each amino acid usually have
more than one
what is the start codon
Met - AUG
what does degenerate mean
there are multiple codons that encode the same amino acid - no one-to-one correspondence
what is the result of the degenerate nature of the genetic code
for a given protein sequence there may be more than one RNA sequence
what happens with a degenerate code and the given RNA sequence
cannot determine 100% what the RNA sequence is from the protein sequence
why are intermediary required
amino acids cannot directly interact with mRNA
what does tRNA do
transfer RNA matches amino acids with codons
what are tRNAs
short RNAs with distinctive 3D structure
where does an amino acid get attached to a tRNA
covalently attached to 3’ end of tRNA
what is an anticodon
complementary to the appropriate amino acid’s codon
what are is the anticodon for CAG
CUG
what is the anticodon for AAA
UUU
is there an anticodon loop for every RNA
yes
what couples an amino acid to tRNA
aminoacyl-tRNA synthetase - each amino acid has a distinct one
what is an amino acid first activated by
conjunction to AMP
how is conjunction to AMP made
by taking ATP and chopping off phosphates
after being activated, what happens to amino acid
amino acid is transferred from AMP to tRNA
what does the resulting conjugate have for the amino acid transferred from AMP to tRNA
has a high-energy bond between amino acid and tRNA
what happens once the amino acid transfer to tRNA is complete
the synthetase proofreads for accuracy
what direction does protein synthesis occur in
N-terminal to C-terminal direction (amino acid is added to C-terminal end of growing chain)
where is the peptide chain attached during protein synthesis
to the last tRNA that was added
how is the peptide chain extended by one residue
new aminoacyl tRNA replaces old tRNA
what is RNA message decoded by
ribosomes
what do rRNAs make up
structural and catalytic core
what makes up the structural and catalytic core
ribozyme
what is the ribozyme
enzyme where catalytic component is RNA, not protein
what are the two units of the ribozyme
large and small
which direction does ribosome read mRNA
5’->3’, reading 3 bases (one codon) at a time
why can proteins translate while transcribing
because mRNA reads 5’->3’
how many reading frames does each mRNA have
3 - ribosomes must choose one and remain consistent or garbled translation occurs
what does AUG (Met) use
a special initiator tRNA - different than the Met tRNA used for the rest of translation
what is translation elongation facilitated by
elongation factors
what are the elongation factors in prokaryotes
Ef-Tu/Ef-G
what are the elongation factors in eukaryotes
EF1/EF2
what does GTPase activity allow for
they’re used by elongation factors to allow proofreading and to speed up ribosome translocation
what do elongation factors do
convert GTP to GDP through hydrolysis, which uses it to regulate the process and proofread
what does hydrolysis do
puts energy back in the system because forming a peptide bond is energetically expensive
what is GTP hydrolysis in cells usually for
regulating things
when does translation termination occur
when the ribosomes encounters a stop codon
what happens with translation termination
a release factor binds to the ribosomes, causing the hydrolysis of the peptidyl tRNA, releasing the completed protein
what happens to the ribosome during translation termination
it dissociates into separate small and large subunits, releasing the mRNA, release factor, and remaining tRNA
does an in-frame stop codon always lead to termination of translation
no - there are circumstances where a stop codon is translated to insert an amino acid
what does protein translation occur on
polyribosomes
how many peptide chains can a ribosome synthesize at a time
one, but a cell may need many copies of a protein for every cell of the relevant mRNA
when does a next ribosome bind to a cap
once the first ribosome has moved far enough along
what is a polyribosome
a single mRNA may have several ribosomes translating simultaneously
what interacts with each other to recognize intact mRNA
5’ cap and 3’ tail interact with each other
what types of cells do antibiotics affect
prokaryotes
what are mitochondrial ribosomes like
prokaryotic ribosomes more than eukaryotic ribosomes
what can prokaryotic ribosomes do
cross mitochondrial membrane and effect mitochondrial protein synthesis
how are RNA and protein synthesis energetically costly
adding each subunit requires the conversion of an NTP into an NMP, the equivalent of hydrolyzing 2 ATPs to ADP
what does elongation steps consume
multiple ATP/GTP molecules
what are elongation steps
movement of ribosomes and proofreading
what is the info content at the protein sequence level
info for 3D structure, cellular location, and protein functions
what is the info content at mRNA level
same info as protein in code, plus info about initiating and terminating translation and sometimes mRNA stability
what is the info content at the DNA level
same info as in mRNA, plus info about initiating/terminating transcription, splicing, and anything useful in the introns themselves
