Lippincott - Protein Synthesis Flashcards
direction of writing of codon
5’–>3’
number of base combinations
64
number of codons coding for amino acids
61
stop codons
UAA, UAG, UGA
start codon
AUG
protein coded for by start codon
methionine
characteristics of genetic code [4]
[1] specificity / unambiguity
[2] universality
[3] redundance / degeneracy
[4] nonoverlapping
specificity of genetic code
a particular codon codes for only one amino acid
universality of genetic code
genetic code found in all organisms
redundance / degeneracy of genetic code
a single amino acid has more than 1 coding codon
nonverlapping / commaless
code is read from a fixed starting point as a continuous sequence of bases
consequences of altering nucleotide sequence [6]
[1] silent mutation [2] missense [3] nonsense [4] triple repeat expansion [5] splice site mutation [6] frameshift
silent mutation
single nucleotide mutation does not change the amino acid sequence
missense
single nucleotide mutation changes amino acid sequence
nonsense
single nucleotide mutation produces stop codon
result of nonsense mutation
truncated protein
triple repeat expansion
amplification of a codon resulting in abnormally high amounts of a single amino acid
splice site mutations
failure to correctly splice the protein
frameshift mutation
addition or deletion causes change in reading frame and abnormal protein
how is amino acid linked to tRNA
carboxyl group of AA is in ester linkage with adenosine of CCA at 3’ end
anticodon
complement of codon in mRNA
codon
specifies amino acid needed for the sequence
responsible for attachment of AA to tRNA
aminoacyl-tRNA synthetase
mediators of circularization of mRNA preventing use of incompletely processed mRNA in translation
eIF-4 proteins, poly-A binding proteins
where do eIF-4 proteins bind?
5’ cap
prokaryotic ribosomal components
70S = 50S + 30S
eukaryotic ribosomal components
80S = 60S + 40S
[T\F] ribosomal proteins are more abundant in eukaryotic ribosomes
T
products of RER ribosomes
proteins for export
products of cytosolic ribosomes
proteins for the cell’s own use
wobble hypothesis
movement of first anticodon base allows nontraditional pairing with 3rd base of codon, allowing tRNA to recognize more than 1 codon –> more flexible
polycistronic synthesis
more than 1 coding region in mRNA
monocistronic synthesis
only 1 coding region in mRNA
type of coding in eukaryotes
monocistronic
Shine-Dalgarno sequence
[1] purine rich sequence located upstream of AUG
[2] ribosome can recognize SD sequence
[3] binding or ribosome to SD sequence puts coding regions close to AUG
direction of movement of ribosome along mRNA in translation
5’ –> 3’
sites of ribosome
A, P, E
ribosome - A site
A (aminoacyl) site; first binding site for charged tRNA - specifies the next amino acid to be added to the chain
ribosome - P site
P (peptidyl) site; second binding site for charged tRNA - carries chain of amino acids that have already been synthesized
ribosome - E site
E (exit) site; third binding site for charged tRNA - occupied by empty tRNA about to exit
elongation in transcription
addition of amino acids to carboxyl end of growing chain
elongation factors
mediate the delivery of aminoacyl-tRNA to the mRNA template in the A site
responsible for catalysis of peptide bond
peptidyltransferase
translocation
process by which the ribosome moves forward 3 nucleotides after creating a successful peptide bond
enzyme required for translocation in eukaryotes
EF-2-GTP
release factor in eukaryotes
eRF
polysomes
complex of 1 mRNA and a number of translating ribosomes
important mechanism of translation regulation in eukaryotes
phosphorylation of eIF-2
effect of eIF-2 phosphorylation
inactivation of protein, translation is not initiated
cotranslational modification of protein
modification while protein is still attached to the ribosome
posttranslational modification of protein
modification after synthesis has been completed
trimming of proteins
proteins produced as large inactive complexes; cleavage/trimming is required to activate them
examples of protein that uses trimming for regulation
inactive trypsinogen trimmed to become active trypsin
covalent modifications that may activate or inactivate proteins [4]
[1] phosphorylation
[2] glycosylation
[3] hydroxylation
[4] carboxylation
mechanisms of protein folding [2]
[1] spontaneous
[2] nonspontaneous (through chaperone)
chaperone
protein that facilitates the proper folding of other proteins
