Answer:
OPTION b. "<em>The 3D shape of a protein is determined largely by the ribosome forming the protein" </em>
is NOT an accurate description of protein synthesis and folding.
Explanation:
<em>a. Many copies of a protein can be synthesized simultaneously from the same mRNA</em>. TRUE. As a ribosome moves along the mRNA chain synthesizing a new protein, another ribosome might follow it, synthesizing another protein from the same mRNA chain. And so on. So, at the same time, many ribosomes might be attached to the mRNA, synthesizing many copies of the protein, but at different development levels. The mRNA chain together with many ribosomes is called a <em>polyribosome</em>.
b. <em>The 3D shape of a protein is determined largely by the ribosome forming the protein</em>. FALSE. What determined the 3D structure of the protein is the amino acid sequence of that particular polypeptide. Each amino-acid has different properties (hydrophobic, hydrophilic, positively charged, negatively charged) and they interact with each other by different bonds that depend on those poperties. So the amino acids composing the proteins and their interaction, is what models the structure of the protein.
c. <em>The entire chain of amino acid exits the ribosome before it begins folding into its 3D shape</em>. TRUE. When the ribosome reaches the end codon, the elongation process has finished, and the new protein leaves the ribosome and is translocated to the RER lumen where it is going to get folded.
d. <em>The first encoded amino acid in every protein is methionine. </em>TRUE. Almost always, the first amino acid located by the tRNA is the methionine, codified by the initiation codon AUG. This amino acid is frequently eliminated at the end of the process.
