Which one of the following processes requires free forms of thymine containing nucleotides?
A. DNA replication
B. RNA synthesis
C. Protein synthesis
D. Starch synthesis
E. Cellulose synthesis
To determine which process requires free forms of thymine-containing nucleotides, we need to identify the process that involves the incorporation of thymine into a biological molecule.
A. DNA replication: During DNA replication, the DNA molecule is duplicated, and each strand serves as a template for the synthesis of a new complementary strand. The nucleotides required for DNA replication include adenine (A), cytosine (C), guanine (G), and thymine (T). So, thymine-containing nucleotides are required for DNA replication.
B. RNA synthesis: RNA synthesis, also known as transcription, involves the synthesis of RNA molecules using a DNA template. During transcription, the nucleotides adenine (A), cytosine (C), guanine (G), and uracil (U) are used. Uracil replaces thymine in RNA molecules. Therefore, thymine-containing nucleotides are not required for RNA synthesis.
C. Protein synthesis: Protein synthesis, also referred to as translation, is the process by which the genetic information encoded in mRNA molecules is used to synthesize proteins. Protein synthesis does not involve the incorporation of thymine-containing nucleotides. Instead, it relies on the genetic code, where specific codons of mRNA correspond to specific amino acids.
D. Starch synthesis: Starch synthesis occurs in plants and involves the formation of starch molecules, which are composed of glucose units. Thymine-containing nucleotides are not involved in starch synthesis. Starch synthesis primarily requires glucose molecules.
E. Cellulose synthesis: Cellulose synthesis occurs in plants and is responsible for the formation of cellulose, which is a structural polysaccharide found in plant cell walls. Thymine-containing nucleotides are not involved in cellulose synthesis. Cellulose synthesis primarily requires glucose molecules.
Therefore, the correct answer is A. DNA replication, as it is the only process among the options listed that requires free forms of thymine-containing nucleotides.