Protein Synthesis Flashcards
translation
polypetide synthesis as directed by mRNA
ribosome
catalyst for translation
- made of small and large subunits (composed of proteins and rRNA) which only join for translation
- large subunit contains A, P and E sites
tRNA
small RNA molecules with intramolecular base pairing
- 2D structure has 3 loops (picture a clover sorta)
- anticodon is a three nucleotide sequence in the middle loop
- interprets the mRNA by complementary base pairing and translates in into protein
anticodon
the tree base sequence on tRNA that pairs to the codon on mRNA
amino acid
the monomeric subunit or a polypeptide
open reading frame
also called protein coding region
-everything between the start and stop codons
codon
a series of 3 adjacent nucleotides that code a specific amino acid
start codon
first codon of an open reading frame
always 5’-AUG-3’
codes for protein Met
stop codon
last codon of an open reading frame
indicates that no more amino acids should be inserted
5’ untranslated region
the region in front of (on the 5’ side) of the open reading frame, is not translated
3’ untranslated region
the region behind (on the 3’ side) of the open reading frame, is not translated
aminoacyl-tRNA synthetase
enzyme that catalyzes formation of covalent bond between tRNA and an amino acid
-recognizes one specific amino acid and all it’s associated tRNA anticodons
A site
aminoacyl-tRNA binding site
entry point for aminoacyl-tRNA into the ribosome
P site
peptidyl chain-tRNA binding site (also has an exit tunnel for the growing polypeptide)
site occupied by tRNA molecule covalently attached to the growing peptidyl chain
E site
exit site for tRNA molecule out of the ribosome
mRNA binding site
a sequence in the 5’ untranslated region of bacterial mRNA that aligns the bacterial ribosome to the correct AUG (start) codon
reading frame
refers to the three possible ways to translate a protein coding region, depending on where the ribosome starts to decode the 3-nucleotide codons
-the correct reading frame is established by aligning the ribosome to the start codon
peptidyl transferase
when the ribosome (acting as an enzyme) forms the peptide bond between the C-terminus of the growing peptide chain and the N-terminus of the new amino acid
-the peptide chain is transferred from the tRNA in the P-site to the amino acid covalently bonded to the tRNA in the A-site
polygenic
an mRNA that codes for more than one protein (occurs in prokaryotes but not eukaryotes, ex trp E,D,C,B,A genes all encoded on the same strand of E. coli mRNA)
trp operon
series of open reading frames in E. coli cells that encode the enzymes required to synthesize amino acid tryptophan
trpO
operator
- specific DNA sequence where trp repressor protein can bind if active
- regulates trp synthesis
- lies between trp promoter and trp operon
trpR
repressor protein
- changes shape in response to [trp] in cell
- when [trp] high, trp binds to the repressor, which binds to the operator and prevents RNA polymerase from binding to the promoter
- otherwise, it stays inactive and free in the cytosol
constitutive expression
gene expression that is always active because it isn’t regulated
stages of translation
initiation (assemble ribosomal subunits and mRNA, find the start codon)
elongation (adding amino acids to the growing polypeptide chain)
termination (disassemble ribosomal subunits and mRNA at stop codon)
heterochromatin
DNA packed super tightly (around histone?) such that transcription machinery cannot bind
-the gene is effectively “off”
euchromatin
more dispersed form of DNA that transcription machinery is able to bind to
