chapter 18 Flashcards
A macromolecular complex of rRNAs and r-proteins; the site of protein synthesis.
ribosome
A protein serving as a component of ribosomes.
ribosomal protein
A class of RNA molecules serving as components of ribosomes.
ribosomal RNA (rRNA):
A complex of an mRNA molecule and two or more ribosomes. Also called a polyribosome.
polysome
A ribonucleic acid molecule with catalytic activity; an RNA enzyme.
ribozyme (catalytic RNA):
The site in a ribosome where the aminoacyl-tRNA binds.
A site
The site in a ribosome occupied by the peptidyl-tRNA.
P site
The site in a ribosome occupied by the tRNA molecule released after the growing polypeptide chain is transferred to the aminoacyl-tRNA. Also called the exit site.
E site
The second step in the attachment of an amino acid to a tRNA, in which the aminoacyl-tRNA synthetase transfers the bound aminoacyl-AMP to the 2′-OH or 3′-OH of the 3′-terminal adenosine residue of the tRNA.
tRNA charging
A mechanism for error correction in complex biological processes that maximizes the speed of correct reactions while stalling and allowing incorrect reactions to reverse
kinetic proofreading
(2) The first of three stages in the synthesis of RNA, in which the RNA polymerase binds to the promoter sequence on the DNA.
(3) The first of three stages in the synthesis of a protein, in which the ribosome binds to the mRNA and initiator aminoacyl-tRNA.
initiation
AUG (sometimes GUG or, even more rarely, UUG in bacteria and archaea); codes for the first amino acid in a polypeptide sequence: N-formylmethionine in bacteria; methionine in archaea and eukaryotes. Also called a start codon.
initiation codon
Three protein factors required to assemble the ribosomal subunits and initiator tRNA in preparation for protein synthesis in bacteria.
initiation factors
A sequence in an mRNA that is required for binding bacterial ribosomes. Also called the ribosome binding site (RBS)
Shine-Dalgarno sequence:
A contiguous mRNA with more than two genes that can be translated into proteins.
polycistronic mRNA:
A sequence around the start codon in eukaryotic mRNA that enhances its translation. The Kozak sequence has a purine nucleotide three residues before, and a G residue immediately after, the start codon.
Kozak sequence
The charged tRNA used to initiate protein synthesis in bacteria.
N-formylmethionyl-tRNAfmet:
A complex of a ribosome with an mRNA and the initiating Met-tRNAiMet or fMet-tRNAfMet, ready for the elongation steps.
initiation complex:
The process by which a partially assembled eukaryotic initiation complex slides along the mRNA until it comes to a start codon.
scanning
A site on the 5′ side of the start codon in some viral and eukaryotic mRNAs where a eukaryotic ribosome can bind in the absence of a 5′ cap.
internal ribosome entry site (IRES):
A process of checking for appropriate codon-anticodon pairing prior to rotation of an incoming aminoacyl-tRNA into position for peptidyl transfer
accommodation:
(1) The second of three stages of RNA synthesis, in which ribonucleotides are added to the 3′ end of the growing RNA molecule.
(2) The second of three stages of protein synthesis, in which amino acids are added to the C-terminal end of the growing peptide chain.
elongation
(1) The third of three stages of RNA synthesis, in which the RNA polymerase and the RNA product are released from the DNA template.
(2) The third of three stages of protein synthesis, in which the ribosome and the peptide product are released from the mRNA template
termination
UAA, UAG, and UGA; in protein synthesis, these codons signal the termination of a polypeptide chain. Also called stop codons.
termination/stop codons
(1) Proteins required in the elongation phase of eukaryotic transcription.
(2) Proteins required in the elongation phase of protein synthesis. See also eEF1α, eEF1βγ, eEF2, EF-G, EF-Ts, and EF-Tu.
elongation factors
The reaction that synthesizes the peptide bonds of proteins—nucleophilic attack of the α-amino group of the ribosomal A-site aminoacyl-tRNA on the carbonyl carbon of the ester bond linking the fMet (or the growing peptide chain) to the P-site tRNA. The reaction is catalyzed by a ribozyme, part of the rRNA of the large ribosomal subunit.
peptidyl transferase reaction:
(1) Enzyme-catalyzed movement across a membrane.
(2) Movement along a double-stranded nucleic acid without strand separation. (3) Movement of a ribosome by one codon along the mRNA.
translocation
Protein factors required for the release of a completed polypeptide chain from a ribosome. Also called termination factors. See also RF-1, RF-2, and RF-3
release factors
A bacterial RNA that has the properties of a tRNA at its 5′ end and the properties of an mRNA, including a stop codon, at its 3′ end. When aminoacylated, the 5′ end can bind in the A site of a ribosome stalled on a truncated mRNA, and the 3′ end can serve as a template for continued translation through a termination codon that recruits the termination factors required for proper termination and ribosome recycling. Also called transfer-messenger RNA.
tmRNA
A pathway for degradation of mRNA molecules with a premature stop codon, triggered by the presence of an exon junction complex on a transcript that has been translated.
nonsense-mediated mRNA decay (NMD):
Any protein that interacts with partially folded or improperly folded polypeptides, facilitating the correct folding pathway or providing a microenvironment where proper folding can occur.
chaperone
The enzymatic processing of a polypeptide chain after translation from its mRNA.
posttranslational modification
An amino acid sequence, often at the amino terminus, that signals the cellular fate or destination of a newly synthesized protein.
signal sequence
A protein-RNA complex that recognizes and binds the signal sequence in a nascent polypeptide and delivers the ribosome to a peptide translocation complex in the endoplasmic reticulum.
signal recognition particle (SRP):
An amino acid sequence that targets a protein for transport to the nucleus.
nuclear localization sequence (NLS):
