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. \(A-T, G-C\)

Step-by-Step Solution

Answer

Option c: A-T, G-C

Step 1: Understand Base Pairing in DNA

In DNA, the nucleotides pair in a specific way due to hydrogen bonding. There are four types of nucleotides in DNA: adenine ( A ), thymine ( T ), guanine ( G ), and cytosine ( C ). These nucleotides form pairs that hold the two strands of DNA together.

Step 2: Identify Complementary Base Pairing

Complementary base pairing rules state that adenine ( A ) pairs with thymine ( T ) and guanine ( G ) pairs with cytosine ( C ). This is also known as Chargaff's rule, named after the scientist who discovered this consistent pairing.

Step 3: Compare Options to Base Pairing Rules

Now, compare the given options to the base-pairing rules: - Option a: A-G , T-C - Option b: A-C , T-G - Option c: A-T , G-C Only Option c follows the correct base pairing of adenine with thymine and guanine with cytosine.

Step 4: Select the Correct Answer

Based on the analysis in Step 3, select the option that correctly represents the DNA base-pairing rules. Since Option c ( A-T , G-C ) correctly follows the rules, it is the correct choice.

Key Concepts

Nucleotides

DNA is a remarkable molecule made up of smaller units known as nucleotides. These nucleotides are the building blocks of DNA. Each nucleotide consists of three components: a sugar molecule (deoxyribose in DNA), a phosphate group, and a nitrogenous base.

There are four different nitrogenous bases in DNA:

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

These bases are crucial because they carry the genetic information used in the growth, development, and functioning of living organisms. They pair up in specific ways to secure the DNA strands together, creating a stable double helix structure.

The pairing between these bases is not random; it follows specific rules due to the chemical nature of the bases. Understanding these rules is key to comprehending how genetic information is stored and replicated.

Hydrogen Bonding

Hydrogen bonding plays a vital role in holding the DNA strands together. Imagine these bonds as little bridges that connect the two sides of the DNA ladder. These bridges are weak enough to allow the strands to separate when necessary, such as during replication, but strong enough to keep them together under normal conditions.

Each complementary base pair is held together by hydrogen bonds:

• Adenine (A) and Thymine (T) form two hydrogen bonds.
• Guanine (G) and Cytosine (C) form three hydrogen bonds.

This difference in bonding affects the stability of the DNA. The more hydrogen bonds between a pair, the more stable that section of the DNA is. The hydrogen bonds ensure that the base pairs fit perfectly within the DNA helix, maintaining the structure's integrity.

Chargaff's Rule

Chargaff's rule is a fundamental principle in understanding DNA base pairing. Named after the discoverer, Erwin Chargaff, this rule states that in a DNA molecule, the number of adenine (A) bases is equal to the number of thymine (T) bases, and the number of guanine (G) bases is equal to the number of cytosine (C) bases.

This observation arises from the complementary base pairing where adenine pairs with thymine, and guanine pairs with cytosine. As a result, knowing the number of one type of base in a DNA sequence allows scientists to predict the number of its complementary pair. This predictability is a cornerstone of DNA's role in heredity, ensuring that genetic information is accurately passed from one generation to the next.

Chargaff's rule not only solidified the understanding of DNA structure but also paved the way for further discoveries in genetics and molecular biology.