Problem 19 - Anatomy and Physiology of Animals

Question

Which of the following is part of the elongation step of DNA synthesis? a. pulling apart the two DNA strands b. attaching complementary nucleotides to the template strand C. untwisting the DNA helix d. none of the above

Step-by-Step Solution

Answer

Option b is correct: attaching complementary nucleotides to the template strand.

Step 1: Understand the Stages of DNA Synthesis

DNA synthesis occurs in several stages: initiation, elongation, and termination. In the initiation phase, various proteins prepare the DNA for copying, including untwisting and separating the DNA strands for accessibility.

Step 2: Clarify the Elongation Process

The elongation step in DNA synthesis involves the addition of nucleotides to the growing DNA strand complementary to the template strand. DNA polymerase is the enzyme responsible for catalyzing the addition of nucleotides.

Step 3: Analyze the Options

Option a (pulling apart the two DNA strands) and option c (untwisting the DNA helix) are part of the initiation phase, not elongation. Option b (attaching complementary nucleotides to the template strand) is the correct process occurring during elongation.

Key Concepts

Elongation Step

The elongation step is a crucial part of DNA synthesis where the actual construction of the DNA strand takes place. During this stage, DNA polymerase, which is an essential enzyme in replication, extends the newly forming DNA strand by adding nucleotides. These nucleotides are attached in a sequence complementary to the template strand, ensuring an accurate copy of the DNA is created.

• This process ensures the fidelity of the DNA replication.
• Elongation allows the genetic information to be passed down accurately during cell division.

Understanding elongation is key to grasping how cells replicate their genetic information before cell division occurs.

Initiation Phase

The initiation phase of DNA synthesis is the first step where the DNA molecule is prepared for replication. It's like setting up the stage before the show begins. During this phase, several proteins and enzymes work together to make the DNA strand accessible.

• This includes untwisting the DNA helix, making it easier to separate the double strands.
• The two strands are pulled apart by another set of proteins, creating a replication fork.

Once the DNA is unwound and separated, it is ready for the elongation step where new strands are synthesized.

DNA Polymerase

DNA polymerase is a pivotal enzyme in the process of DNA replication. Its main task is to drive the elongation step by adding nucleotides to the growing DNA strand.

• DNA polymerase ensures that nucleotides are added in the correct sequence, following the template strand.
• It also checks and corrects errors, playing a role in maintaining genetic integrity.

Without DNA polymerase, the entire process of DNA synthesis would not be possible, showing just how crucial this enzyme is in biology.

Nucleotide Addition

Nucleotide addition is a key part of the elongation process. This is where individual nucleotides are bonded together to form a new DNA strand.

• Nucleotides are added one by one to the growing DNA chain.
• Each new nucleotide is complementary to its corresponding base on the template strand.

The sequence of nucleotide addition ensures that the new DNA molecule is a perfect copy of the original, reflecting one of the core principles of genetics: the transmission of genetic information from one generation to the next.