LEC: UNIT 10

Question 1

The synthesis of polypeptides using the genetic code from RNA

Answer 1

Translation

Question 2

T/F: DNA serves as the template during translation

Answer 2

F

Question 3

specifies how an mRNA sequence is translated to a polypeptide

Answer 3

genetic code

Question 4

Enumerate the features of the genetic code

Answer 4

 Triplet (codons)
 Nonoverlapping
 Commaless
 Degenerate
 Universal (nearly)

Question 5

How many codons are in the genetic code?

Answer 5

64 codons (61 for amino acids, 3 as stop codons)

Question 6

The _____ moves along the mRNA three bases at a time rather than one or two at a time

Answer 6

ribosome

Question 7

Enumerate the requirements for translation

Answer 7

• RNAs (mRNA, tRNA, rRNA)
• Ribosome
• Protein factors (IFs, EFs, RFs)
• Activated substances

Question 8

This serves as adaptor molecule, that provides physical and informational link between mRNA and the polypeptide being synthesized

Answer 8

tRNA

Question 9

Enumerate the structure of tRNA

Answer 9

o Acceptor arm
o D arm
o Anticodon loop
o V loop
o TψC arm

Question 10

_____ pairing is a non-standard base pairing between the base at 5’ end of anticodon and the base at 3’ end of codon.

Answer 10

Wobble base

Question 11

Identify the phase of translation: starts at the N-terminal end, and grows from N-terminus to C-terminus

Answer 11

Initiation

Question 12

Requirements for initiation

Answer 12

o fmet-tRNA
o initiation codon (AUG) of mRNA
o 30S ribosomal subunit
o 50S ribosomal subunit
o initiation factors IF-1, IF-2, & IF-3
o GTP, Mg2+

Question 13

3’-UAC-5’ triplet on tRNAfmet recognizes the AUG triplet (the start codon) when it occurs at the beginning of the mRNA sequence that directs polypeptide synthesis

Answer 13

Shine-dalgarno sequence

Question 14

Start codon is preceded by a _____ purine-rich leader segment, 5’-GGAGGU-3’, which usually lies about 10 nucleotides upstream of the AUG start signal and acts as a ribosomal binding site

Answer 14

Shine-Dalgarno

Question 15

Enumerate the three steps of elongation phase

Answer 15

o aa-tRNA binding
o Peptide bond formation
o Translocation

Question 16

Enumerate the requirements of the termination phase

Answer 16

o RF-1 (Release factor-1) which binds to 5′-UAA-3′ and 5′-UAG-3’ or
o RF-2 (Release factor-2) which binds to 5′-UAA-3′ and 5′-UGA-3′
o RF-3 (with bound GTP)which does not bind to any termination codon, but facilitates the binding of RF-1 and RF-2

Question 17

T/F: in the termination phase, only 3/4 of the comples dissociates

Answer 17

F. The entire complex dissociates

Question 18

Identify the event: newly synthesized polypeptides are frequently modified before they reach their final form where they exhibit biological activity

Answer 18

Posttranslational processing and modifications

Question 19

During the posttranslational processing and modifications, N-formylmethionine in _____ (prokaryote or eukaryote) is cleaved

Answer 19

prokaryotes

Question 20

Enumerate the binding sites for tRNA on the 50s subunit during the elongation phase

Answer 20

P (peptidyl) site, A (aminoacyl) site, E (exit) site