Problem 4 - Astronomy: At Play in the Cosmos

Question

You find a polymer that contains the nucleobases \(A, G,\) and \(C . W h a t\) kind of molecule can it be? a. only DNA b. only RNA c. either DNA or RNA d. an amino acid e. DNA, RNA, or an amino acid

Step-by-Step Solution

Answer

c. either DNA or RNA

Step 1: Identify Nucleobases in DNA and RNA

In DNA, the nucleobases are adenine (A), guanine (G), cytosine (C), and thymine (T). In RNA, the nucleobases are adenine (A), guanine (G), cytosine (C), and uracil (U).

Step 2: Analyze the Given Nucleobases

The problem mentions the nucleobases adenine (A), guanine (G), and cytosine (C). Both DNA and RNA share these nucleobases. Therefore, having only these three nucleobases means the polymer could be either DNA or RNA.

Step 3: Evaluate Other Options

Amino acids are different from nucleic acids and they have structures that do not contain nucleobases like A, G, or C. Thus, a polymer with nucleobases is not an amino acid.

Step 4: Decision Based on Options

Given that the polymer with nucleobases A, G, C could be either DNA or RNA, but cannot be an amino acid, the correct choice considering the options is: either DNA or RNA.

Key Concepts

DNA

DNA, or deoxyribonucleic acid, is a molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses. DNA is a long polymer made from repeating units called nucleotides, each of which contains one of four types of nucleobases:

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

DNA molecules form a unique double helix structure, a twisted ladder-like shape, where the bases pair in a specific way: adenine with thymine ( (A-T) and guanine with cytosine (G-C). This pairing is crucial for DNA replication and the transmission of genetic information.
The sequence of the nucleobases in DNA encodes genetic information, which is essential for the production of proteins and regulation of cellular activities.

RNA

RNA, or ribonucleic acid, is similar to DNA but serves different functions in cells. RNA is typically single-stranded and uses ribose sugar among its backbone, unlike DNA's deoxyribose. RNA also uses four types of nucleobases, but there is a key difference:

• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Uracil (U)

Instead of thymine, RNA contains uracil, which pairs with adenine during RNA function processes. RNA plays a crucial role in various biological processes, including acting as a messenger (mRNA) that carries information from DNA to the protein synthesis sites, participating in protein synthesis (tRNA and rRNA), and regulating gene expression.
The structure and composition of RNA allow it to perform diverse tasks that are different from DNA but essential for cellular function.

Nucleobases

Nucleobases, also called nitrogenous bases, are the core components of nucleic acids like DNA and RNA. They are organic molecules that partner with sugars and phosphates to form nucleotides. There are five primary nucleobases, which categorize into two groups:

• Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U)
• Purines: Adenine (A) and Guanine (G)

These bases are fundamental for the genetic coding system, as they can create base pairs, forming the steps of the nucleic acid ladder. In DNA, with its double-stranded formation, adenine pairs with thymine, and guanine pairs with cytosine. In RNA, adenine pairs with uracil instead.
The specific sequence of nucleobases encodes genetic instructions crucial for the synthesis of proteins, which are vital for the body's structure and function.