chapter 18

Question 1

A macromolecular complex of rRNAs and r-proteins; the site of protein synthesis.

Answer 1

ribosome

Question 2

A protein serving as a component of ribosomes.

Answer 2

ribosomal protein

Question 3

A class of RNA molecules serving as components of ribosomes.

Answer 3

ribosomal RNA (rRNA):

Question 4

A complex of an mRNA molecule and two or more ribosomes. Also called a polyribosome.

Answer 4

polysome

Question 5

A ribonucleic acid molecule with catalytic activity; an RNA enzyme.

Answer 5

ribozyme (catalytic RNA):

Question 6

The site in a ribosome where the aminoacyl-tRNA binds.

Answer 6

A site

Question 7

The site in a ribosome occupied by the peptidyl-tRNA.

Answer 7

P site

Question 8

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.

Answer 8

E site

Question 9

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.

Answer 9

tRNA charging

Question 10

A mechanism for error correction in complex biological processes that maximizes the speed of correct reactions while stalling and allowing incorrect reactions to reverse

Answer 10

kinetic proofreading

Question 11

(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.

Answer 11

initiation

Question 12

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.

Answer 12

initiation codon

Question 13

Three protein factors required to assemble the ribosomal subunits and initiator tRNA in preparation for protein synthesis in bacteria.

Answer 13

initiation factors

Question 14

A sequence in an mRNA that is required for binding bacterial ribosomes. Also called the ribosome binding site (RBS)

Answer 14

Shine-Dalgarno sequence:

Question 15

A contiguous mRNA with more than two genes that can be translated into proteins.

Answer 15

polycistronic mRNA:

Question 16

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.

Answer 16

Kozak sequence

Question 17

The charged tRNA used to initiate protein synthesis in bacteria.

Answer 17

N-formylmethionyl-tRNAfmet:

Question 18

A complex of a ribosome with an mRNA and the initiating Met-tRNAiMet or fMet-tRNAfMet, ready for the elongation steps.

Answer 18

initiation complex:

Question 19

The process by which a partially assembled eukaryotic initiation complex slides along the mRNA until it comes to a start codon.

Answer 19

scanning

Question 20

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.

Answer 20

internal ribosome entry site (IRES):

Question 21

A process of checking for appropriate codon-anticodon pairing prior to rotation of an incoming aminoacyl-tRNA into position for peptidyl transfer

Answer 21

accommodation:

Question 22

(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.

Answer 22

elongation

Question 23

(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

Answer 23

termination

Question 24

UAA, UAG, and UGA; in protein synthesis, these codons signal the termination of a polypeptide chain. Also called stop codons.

Answer 24

termination/stop codons

Question 25

(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.

Answer 25

elongation factors

Question 26

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.

Answer 26

peptidyl transferase reaction:

Question 27

(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.

Answer 27

translocation

Question 28

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

Answer 28

release factors

Question 29

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.

Answer 29

tmRNA

Question 30

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.

Answer 30

nonsense-mediated mRNA decay (NMD):

Question 31

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.

Answer 31

chaperone

Question 32

The enzymatic processing of a polypeptide chain after translation from its mRNA.

Answer 32

posttranslational modification

Question 33

An amino acid sequence, often at the amino terminus, that signals the cellular fate or destination of a newly synthesized protein.

Answer 33

signal sequence

Question 34

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.

Answer 34

signal recognition particle (SRP):

Question 35

An amino acid sequence that targets a protein for transport to the nucleus.

Answer 35

nuclear localization sequence (NLS):