Question

59. If protein synthesis were attempted experimentally under in vitro conditions (in a test tube) using ribosomes from cow liver cells, tRNAs from frog eggs, mRNA from rat muscle cells, and amino acids from fruit flies, what products would result?

A. Random mixture of proteins from cow liver, frog eggs, rat muscle, and fruit flies
B. Cow liver proteins only
C. Frog egg proteins only
D. Rat muscle proteins only

Answer 1

The protein synthesis experiment with components from various organisms would yield rat muscle proteins, determined by the mRNA used. Additionally, in a test tube with synthetic RNA containing only cytosine, a polypeptide of proline would be produced, as cytosine repeats form the codon for proline.

Step-by-step explanation:

The products that would result from protein synthesis under the specified in vitro conditions would be rat muscle proteins only. This is because the sequence of amino acids in a protein is determined by the sequence of codons in the mRNA. Since the mRNA was taken from rat muscle cells, the polypeptides produced will correspond to proteins from rat muscle, despite using ribosomes from cow liver cells, tRNAs from frog eggs, and amino acids from fruit flies.

If we consider a similar experimental setup to Nirenberg and Matthaei's where synthetic RNA containing only cytosine (poly(C)) is added in a test tube containing all 20 amino acids with one type specifically labeled, we would expect to see a polypeptide chain consisting of proline. This is because the codon CCC codes for proline, and a polymer made solely of cytosine would produce a synthetic mRNA that is read as a repeat of the CCC codon.