91Ó°ÊÓ

Describe the structure and complementary base pairing of DNA. a. DNA is made up of two strands that are twisted around each other to form a helix. Adenine pairs up with thymine and cytosine pairs with guanine. The two strands are anti-parallel in nature; that is, the 3’ end of one strand faces the 5’ end of other strand. Sugar, phosphate and nitrogenous bases contribute to the DNA structure. b. DNA is made up of two strands that are twisted around each other to form a helix. Adenine pairs up with cytosine and thymine pairs with guanine. The two strands are anti-parallel in nature; that is, the 3’ end of one strand faces the 5’ end of other strand. Sugar, phosphate and nitrogenous bases contribute to the DNA structure. c. DNA is made up of two strands that are twisted around each other to form a helix. Adenine pairs up with thymine and cytosine pairs with guanine. The two strands are parallel in nature; that is, the 3’ end of one strand faces the 3’ end of other strand. Sugar, phosphate and nitrogenous bases contribute to the DNA structure. d. DNA is made up of two strands that are twisted around each other to form a helix. Adenine pairs up with thymine and cytosine pairs with guanine. The two strands are anti-parallel in nature; that is, the 3’ end of one strand faces the 5’ end of other strand. Only sugar contributes to the DNA structure.

Step by step solution

01

Understanding the Problem

The problem asks for the description of DNA structure and complementary base pairing. Four statements are provided, and the correct one needs to be identified based on the given information about DNA.

02

Analyze DNA Structure

DNA is made up of two strands that form a double helix. Each strand consists of a sugar-phosphate backbone with nitrogenous bases extending from it. The nitrogenous bases pair specifically: Adenine (A) pairs with Thymine (T) and Cytosine (C) pairs with Guanine (G).

03

Evaluate Strand Orientation

The strands of DNA are anti-parallel, meaning the 3’ end of one strand aligns with the 5’ end of the other strand. This alignment is crucial for the function of DNA. Evaluate each option based on this criterion.

04

Check Component Contribution

DNA structure is made up of three main components: sugar (deoxyribose), phosphate groups, and nitrogenous bases (Adenine, Thymine, Cytosine, and Guanine). All three components contribute to the structure, not just sugar.

05

Identify the Correct Option

Based on the structure, complementary base pairing, anti-parallel orientation, and all contributing components, the correct answer is option (a): DNA is made up of two strands that are twisted around each other to form a helix. Adenine pairs up with thymine and cytosine pairs with guanine. The two strands are anti-parallel in nature; that is, the 3’ end of one strand faces the 5’ end of other strand. Sugar, phosphate, and nitrogenous bases contribute to the DNA structure.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

double helix

DNA is renowned for its iconic structure known as the double helix. Imagine a twisted ladder. This ladder is composed of two strands that spiral around each other. Each strand forms part of the helical structure. The twisting of these two strands is what gives the DNA its helical shape. These two strands are often visualized as the sides of the ladder, while the rungs are made up of the paired nitrogenous bases. This helical structure is foundational to DNA's function, aiding in the storage and transfer of genetic information.

complementary base pairing

A critical aspect of DNA's double helix structure is the way its bases pair up. This is known as complementary base pairing. There are four types of nitrogenous bases in DNA: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). They follow specific pairing rules:
- Adenine pairs with Thymine
- Cytosine pairs with Guanine
Because these pairs always match together (A-T and C-G), they are described as complementary. This specificity is crucial for DNA replication and function. When the DNA replicates, the base pairs ensure the new strands are exact copies of the original.

anti-parallel strands

Apart from being double helical and having complementary bases, DNA strands are also anti-parallel. This means that the directions of the two strands run opposite to each other. In the language of DNA, the 3’ end of one strand aligns with the 5’ end of the other. The 3’ and 5’ denote the carbon positions in the DNA's sugar molecule, deoxyribose. This orientation is vital for the replication and function of DNA.
The antiparallel nature of DNA ensures that enzymes can read the strands efficiently during processes like replication and transcription, making it indispensable for cellular function.

nucleotide components

The building blocks of DNA are called nucleotides. Each nucleotide has three components:
- A sugar molecule (deoxyribose)
- A phosphate group
- A nitrogenous base (Adenine, Thymine, Cytosine, or Guanine)
The sugar and phosphate form the DNA strand's backbone. This backbone is like a string holding the bases together, while the nitrogenous bases extend from the backbone and pair up to form the rungs of the DNA ladder, engaging in complementary base pairing. Without these components, the structure and function of DNA would fall apart, underscoring their importance.