51 you should be able to answer questions like this

51
You should be able to answer questions like this:
How many high-energy phosphate bonds are required to make a 50 amino acid polypeptide chain, in-
cluding the energy used to activate amino acids to aminoacyl-tRNAs?
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Eukaryotic Translation
There are several differences between eukaryotic and prokaryotic translation. Many of these have already
been mentioned: The ribosome is larger (80S) and has different components than the prokaryotic ribo-
some, the mRNA must be processed before it can be translated (spliced, with cap and tail added), and the
N-terminal amino acid is different (Met instead of fMet). Also remember that eukaryotic mRNA must
50
It must, if the tRNA remains H-bonded to the mRNA while moving to another spot in the ribosome.
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Because the bond between each amino acid and its tRNA is a high-energy bond whose hydrolysis drives peptide bond formation. Remem-
ber that the aminoacyl-tRNA bond was formed using the energy of two phosphate bonds from ATP.
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There are two phosphate bonds hydrolyzed per amino acid to make the aminoacyl-tRNAs, or 100 for the 50 amino acid polypeptide. Two
phosphate bonds are required for each elongation step, one for the entrance of each new aminoacyl-tRNA into the ribosomal A site and
the other for translocation. Since there are 49 elongation steps for a 50-amino acid protein, 98 high-energy bonds are hydrolyzed during
elongation. Finally, one GTP is hydrolyzed during initiation to position the first tRNA and mRNA on the ribosome, and one GTP is hy-
drolyzed in termination. Thus, a total of 200 high-energy bonds are required for the translation of a 50-amino acid protein. In other words,
it costs 4 n high-energy bonds to make a peptide chain, where n is the number of amino acids in the chain.
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MOLECULAR BIOLOGY
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not only be spliced, capped, and tailed, but it also requires transport from nucleus to cytoplasm, thus
transcription and translation cannot proceed simultaneously.
Eukaryotes do not use the Shine-Dalgarno sequence to initiate translation. There are 5' UTR sequences
in eukaryotes that function in starting translation; a common one is the Kozak sequence , which is a con-
sensus sequence typically located a few nucleotides before the start codon.
Eukaryotic translation begins with formation of the initiation complex. First, a 43S pre-initiation com-
plex forms, composed of the 40S small ribosomal submit, Met-tRNA
Met
, and several proteins called eu-
karyotic initiation factors (or eIFs). Next, this assembled complex is recruited to the 5' capped end of the
transcript, by an initiation complex of proteins (including other eIF proteins). Additional proteins are re-
cruited (such as a polyA tail binding protein) and the initiation complex starts scanning the mRNA from
the 5' end, looking for a start codon. Once the start codon has been found, the large ribosomal subunit
(60S) is recruited and translation can begin.