Problem 2 - Biology Concepts and Applications

Question

What are the base-pairing rules for DNA? a. \(A-G, T-C\) b. \(A-C, T-G\) c. \(A-T, G-C\) d. A-A, G-G, C-C, T-T

Step-by-Step Solution

Answer

Option c (A-T, G-C) is the correct base-pairing rule for DNA.

Step 1: Understanding DNA Base-Pairing

DNA is composed of four nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C). These bases pair together in specific ways to form the rungs of the DNA double helix. This base-pairing is crucial for DNA replication and function.

Step 2: Identifying Correct Pairings

The base-pairing rule states that adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C). This ensures the DNA structure is stable and that the information can be accurately copied.

Step 3: Evaluating Multiple Choice Options

Given the pairings from the rule (A-T and G-C), compare these to the options provided: - Option a: A-G, T-C (This is incorrect, bases are not paired as given.) - Option b: A-C, T-G (This is incorrect, bases are not paired as given.) - Option c: A-T, G-C (This matches the correct base-pairing rules.) - Option d: A-A, G-G, C-C, T-T (These are incorrect, as they suggest non-standard and unrecognized pairings.)

Step 4: Selecting the Correct Answer

Since Option c (A-T, G-C) aligns perfectly with the established base-pairing rules for DNA, select this as the correct answer.

Key Concepts

Nitrogenous Bases

DNA, or deoxyribonucleic acid, is made up of smaller units known as nitrogenous bases. These are the building blocks of DNA's structure, and there are four different types.

• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)

These bases connect in pairs, forming the rungs of the DNA ladder. Each nitrogenous base can only pair with one other specific base to create stable structures. This pairing is fundamental for the way DNA works.
For proper cell function and genetic inheritance, the base pairing needs to be precise. Adenine pairs with thymine and guanine pairs with cytosine. Memorizing these pairs helps in understanding DNA replication and genetic coding.

DNA Double Helix

Often visualized as a twisted ladder, the DNA double helix is a result of the specific pairing of its nitrogenous bases.
The structure of the double helix is both intricate and elegant. The two strands of DNA run in opposite directions or "antiparallel" and are held together by the hydrogen bonds between the nitrogenous base pairs.

• The sugar-phosphate backbone forms the sides of the ladder.
• The paired bases form the rungs.

This arrangement allows the DNA to be tightly packed into chromosomes and efficiently relay genetic information. Without the correct base-pairing, the structural integrity and function of the double helix would be disrupted, possibly resulting in genetic mutations.

DNA Replication

Before a cell divides, it must replicate its DNA so each new cell has the same genetic information. This is a complex, yet highly coordinated process.

• The first step in replication is the unwinding of the DNA double helix.
• Then, the hydrogen bonds between the bases break, separating the two strands.
• Next, each strand serves as a template for a new strand.

The correct nitrogenous bases are brought in and paired with the exposed bases on each strand, creating two identical DNA molecules. Adenine finds its partner thymine, and guanine pairs with cytosine. This ensures the new DNA strands are exact copies of the original, maintaining genetic consistency across generations.