15.5 Ribosomes and Protein Synthesis

Question 1

Ribosome

Answer 1

complex macromolecule composed of structural and catalytic rRNAs, and many distinct polypeptides.
They bind messenger RNA and transfer RNA to synthesize polypeptides and proteins

Question 2

polysome

Answer 2

mRNA molecule simultaneously being translated by many ribosomes all going in the same direction

Question 3

aminoacyl tRNA synthetases

Answer 3

enzyme that “charges” tRNA molecules by catalyzing a bond between the tRNA and a corresponding amino acid

Question 4

initiation complex

Answer 4

this complex involves the small 30S ribosome,
the mRNA template, three initiation factors (IFs; IF-1, IF-2, and IF-3), and a special initiator tRNA, called tRNA

Question 5

initiator tRNA

Answer 5

in prokaryotes, called ; in eukaryotes, called tRNAi; a tRNA that interacts with a
start codon, binds directly to the ribosome P site, and links to a special methionine to begin a polypeptide chain

Question 6

start codon

Answer 6

AUG (or rarely, GUG) on an mRNA from which translation begins; always specifies methionine

Question 7

Kozak’s rules

Answer 7

determines the correct initiation AUG in a
eukaryotic mRNA; the following consensus sequence must appear around the AUG: 5’- GCC(purine)CCAUGG-3’; the bolded bases are most important

Question 8

peptidyl transferase

Answer 8

RNA-based enzyme that is integrated
into the 50S ribosomal subunit and catalyzes the formation of peptide bonds

Question 9

signal sequence

Answer 9

short sequence at the amino end of a protein that directs it to a specific cellular compartment