Problem 3 - Biology Today and Tomorrow with Physiology

Question

One species' DNA differs from others in its __________ . a. sugars b. phosphates c. base sequence d. all of the above

Step-by-Step Solution

Answer

The correct answer is c. base sequence.

Step 1: Understand DNA Components

DNA is composed of nucleotides, each consisting of a sugar, a phosphate, and a nitrogenous base. The sugar and phosphate form the backbone of the DNA structure.

Step 2: Identify Variable Component

The nitrogenous bases in DNA (adenine, thymine, cytosine, and guanine) vary in sequence across species. This sequence of bases is what differs between different species.

Step 3: Evaluate Multiple Choice Answers

Compare each option to determine which reflects differences between species: (a) sugars and (b) phosphates are consistent within DNA structure, while (c) base sequence varies.

Step 4: Choose the Correct Answer

Since the base sequence is the part of DNA that varies among different species, the correct answer is c. base sequence.

Key Concepts

Nitrogenous Bases

DNA, or deoxyribonucleic acid, is made up of smaller building blocks called nucleotides. Each nucleotide consists of three main parts. One of these crucial parts is the nitrogenous base. There are four types of nitrogenous bases in DNA, each with a unique structure and function:

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

The nitrogenous bases are paired in a specific way: adenine pairs with thymine, and cytosine pairs with guanine. These pairings form the rungs of the DNA ladder structure.
The sequence of these bases encodes genetic information, as they dictate the formation of proteins and determine genetic traits.
Therefore, understanding nitrogenous bases is key to understanding how genetic information is stored and transmitted in organisms.

Nucleotide Components

A nucleotide, the basic building block of DNA, comprises three key components:

• Sugar: In DNA, this sugar is called deoxyribose. It is a pentose sugar, meaning it consists of five carbon atoms.
• Phosphate Group: This group links the sugar of one nucleotide with the sugar of another, creating the sugar-phosphate backbone of the DNA structure. This backbone provides structural support.
  
• Nitrogenous Base: As previously mentioned, each nucleotide contains a nitrogenous base. This is the variable component of DNA, allowing for genetic diversity.

The combination of these components allows for the DNA double helix structure and the replication and expression of genes.
The constant sugar-phosphate backbone ensures stability, while the variable nitrogenous bases allow for genetic variation.

Species DNA Differences

The key to the diversity of life on Earth lies in the sequence of the nitrogenous bases within DNA. While the sugar and phosphate components of nucleotides remain constant across all species, the sequence of nitrogenous bases is what varies and allows for differences between species.
Each species has a unique arrangement of adenine, thymine, cytosine, and guanine that dictates its distinct genetic traits.

• This base sequence determines the proteins that an organism can produce.
• Changes or mutations in this sequence can lead to variations within populations and form the basis of adaptation and evolution.

In summary, the unique sequences of nitrogenous bases are critical in differentiating the genetic makeup of different species, ultimately influencing their function, behavior, and appearance.