Question

Which of the following statements about the process of DNA replication is correct? a. New DNA molecules are composed of two completely new strands. b. New DNA molecules are composed of one strand from the old molecule and one new strand. c. New DNA molecules are composed of strands that are a mixture of sections from the old molecule and sections that are new. d. None of the above statements is correct.

Short answer

The correct answer is b. New DNA molecules are composed of one strand from the old molecule and one new strand.

Step-by-step solution

Understanding DNA replication

DNA replication is the process of producing two identical replicas from one original DNA molecule. This is accomplished by separation of the original DNA strand into two parts, and then each of these serves as a template for the synthesis of a complementary strand.

Analyzing the given statements

Let's analyze each option: \n a. This statement is incorrect. Not both of the strands in the new DNA molecule are completely new. Each new DNA molecule has one strand from the original molecule. \n b. This statement is correct. One strand of the new DNA molecule comes from the original one and the other one is newly synthesized. This is why DNA replication is called semi-conservative. \n c. This statement is incorrect. Not sections, but entire strands from the original DNA molecule are kept in the new ones. \n d. As statement b. is correct, this option cannot be correct.

Key concepts

Semi-Conservative Replication

The term "semi-conservative replication" describes the way DNA replicates. Each new DNA molecule contains one original strand and one new strand. This method preserves half of the parental DNA in each of the daughter DNA molecules. As a result, when cells divide, the genetic material is accurately replicated, ensuring consistency across generations.
This is crucial because it helps in maintaining the integrity of the genetic code. If replication errors occur, they could potentially lead to mutations. Most of the time, our cellular machinery can correct these mistakes. The semi-conservative nature of DNA replication was first proven by the famous Meselson and Stahl experiment. They showed that after replication, each DNA molecule consists of one old and one new strand. Thus, the semi-conservative method is a perfect balance between accuracy and efficiency.

DNA Strands

DNA strands are the main components of DNA molecules, and they carry genetic information. Each DNA molecule consists of two strands that run in opposite directions, forming a double helix. These strands are composed of nucleotides, which include a sugar, a phosphate group, and a nitrogenous base.
In the double helix, the strands are held together by hydrogen bonds between complementary bases. Adenine pairs with thymine, and cytosine pairs with guanine, keeping the two strands bound in a stable structure. During replication, these strands are separated to allow the formation of new complementary strands.

• The original or "parental" strand serves as a template.
• The new strand is formed complementary to the template.
• This ensures that the genetic information is accurately copied to the next generation of cells.

Understanding the structure and function of DNA strands is essential for grasping how genetic material is transferred from one generation to the next.

DNA Synthesis

DNA synthesis is the process through which new DNA strands are formed. This occurs during replication, where an existing DNA molecule is copied. The process begins with the unwinding of the double helix, followed by the separation of the strands. Each separated strand serves as a template for synthesizing the new complementary strand.

• Enzymes called DNA polymerases are crucial in this process. They add nucleotides to the growing strand, complementary to the template strand.
• Primase enzyme lays down a primer, which is the starting point for DNA synthesis.
• Each new nucleotide is added in accordance to the exposed template strand, ensuring base pairing is correct.

DNA synthesis is essential for cell division, allowing cells to pass genetic information during growth, development, and repair. While the process is highly accurate, errors can sometimes occur, leading to mutations. How well DNA synthesis is conducted can have direct implications on genetic stability and overall organism health.