Question

15. Translation (RNA

protein) has three main stages: initiation, elongation, and termination.

a.

Initiation

occurs when the small ___________________ subunit binds to the ____ end of

mRNA and is then joined by the large _________________ subunit (which has three sites

called the A, P, and E sites). Once the complex is formed, the _______________ begins to

read the mRNA in a ____ to ____ direction. When it reaches the first start codon (_________)

a tRNA carrying the amino acid ______________________ arrives and docks at the A site of

the large subunit.

b.

Elongation

begins when the second tRNA arrives with its amino acid. The mRNA template is

translocated so that the first amino acid is moved to the _____ site to make room on the _____

site for the second tRNA. A ____________ bond then links the two amino acids, and the first

tRNA detaches from its amino acid leaving it bound to the amino acid of the second tRNA.

Translocation occurs once more until the 1st

tRNA (now empty) moves to the ____ site where

it exits the ribosome and goes off to find/load another amino acid. This process occurs over

and over again forming many _______________ bonds as the _______________ continues to

read the mRNA and load on new amino acids.

c.

Termination

occurs when the ________________ attempts to read a _________ codon.

When this codon is reached, a special enzyme breaks the bond between the last tRNA and the

growing polypeptide chain. Both are released form the ribosome, and the two subunits

dissociate from each other.

d. (

Note:

Peptide bond formation occurs at the _______ site of the large subunit.

Answer 1

15. Translation (RNA

protein) has three main stages: initiation, elongation, and termination.

a.

Initiation

occurs when the small ribosomal  subunit binds to the 5¹ end of

mRNA and is then joined by the large ribosomal subunit (which has three sites

called the A, P, and E sites). Once the complex is formed, the ribosome begins to

read the mRNA in a 5¹ to 3¹ direction. When it reaches the first start codon (AUG)

a tRNA carrying the amino acid methionine arrives and docks at the A site of

the large subunit.

b.

Elongation

begins when the second tRNA arrives with its amino acid. The mRNA template is

translocated so that the first amino acid is moved to the P site to make room on the A

site for the second tRNA. A peptide bond then links the two amino acids, and the first

tRNA detaches from its amino acid leaving it bound to the amino acid of the second tRNA.

Translocation occurs once more until the 1st

tRNA (now empty) moves to the E site where

it exits the ribosome and goes off to find/load another amino acid. This process occurs over

and over again forming many peptide bonds as the ribosome continues to

read the mRNA and load on new amino acids.

c.

Termination

occurs when the ribosome attempts to read a stop codon.

When this codon is reached, a special enzyme breaks the bond between the last tRNA and the

growing polypeptide chain. Both are released form the ribosome, and the two subunits

dissociate from each other.

d. (

Note:

Peptide bond formation occurs at the peptidyl transferase site of the large subunit.