Problem 1 - Biology: The Unity and Diversity of Life

Question

Which is not a nucleotide base in DNA? a. adenine b. guanine c. glutamine d. thymine e. cytosine f. All are in DNA.

Step-by-Step Solution

Answer

Glutamine is not a DNA nucleotide base.

Step 1: Recall the Structure of DNA

DNA is composed of four nucleotide bases. These bases are adenine (A), guanine (G), cytosine (C), and thymine (T). Each of these bases pairs with another to form the rungs of the DNA double helix: adenine pairs with thymine, and cytosine pairs with guanine.

Step 2: Identify the Listed Options

Review the provided options: a. adenine, b. guanine, c. glutamine, d. thymine, e. cytosine, and f. All are in DNA.

Step 3: Compare Options with DNA Bases

Compare each option listed with the known nucleotide bases in DNA. Adenine, guanine, cytosine, and thymine are indeed the bases of DNA. Glutamine is not a nucleotide base; it is an amino acid, which is a building block of proteins.

Step 4: Confirm the Answer

Since adenine, guanine, thymine, and cytosine are all the correct nucleotide bases, and glutamine is not one of them, identify glutamine as the correct answer choice. Thus, option c (glutamine) is not a nucleotide base in DNA.

Key Concepts

adenine

Adenine is one of the four main nucleotide bases found in DNA. It is abbreviated as 'A' and plays an essential role in the DNA structure. Adenine pairs specifically with thymine through hydrogen bonding. This pairing mechanism is critical for maintaining the DNA double helix structure.

• Adenine belongs to a group of molecules known as purines, which have a two-ring structure.
• In addition to its role in DNA, adenine is also a component of ATP (adenosine triphosphate), which provides energy for many processes in cells.
• It plays a key role in the storage and transmission of genetic information.

Understanding adenine's properties gives insight into how genetic information is coded and replicated during cell division.

guanine

Guanine, abbreviated as 'G', is another purine nucleotide base in DNA. This base pairs with cytosine, ensuring the stability of the DNA molecule. The bond between guanine and cytosine involves three hydrogen bonds, making it slightly stronger than adenine-thymine pairs.

• Guanine's two-ring structure, characteristic of purines, supports the formation of this stable bond.
• In nature, guanine is not limited to forming DNA but is also found in RNA, where it pairs with cytosine.
• This nucleotide was first discovered in guano (bird droppings), which is how it got its name.

The strength and stability that guanine provides are crucial for the accurate transmission of genetic information.

cytosine

Cytosine is a pyrimidine base found in DNA, symbolized by 'C'. Alongside guanine, cytosine forms one half of the guanine-cytosine base pair. This pairing involves three hydrogen bonds, making it stronger compared to adenine-thymine pairs.

• Cytosine is part of a group of nitrogenous compounds known as pyrimidines, which have a single-ring structure.
• Besides being in DNA, cytosine is also present in RNA, where it plays a role in protein synthesis.
• It can undergo a chemical reaction called deamination, which can lead to mutations if uncorrected.

Its stability and pairing properties are pivotal to maintaining genetic integrity during DNA replication and transcription.

thymine

Thymine is the nucleotide base denoted by the letter 'T', pairing exclusively with adenine in DNA. This pyrimidine nucleotide plays a critical role in encoding genetic information.

• Thymine's single-ring structure is typical of pyrimidines.
• Unlike the other three bases, thymine is found only in DNA, not in RNA, where uracil replaces it.
• Functions of thymine include aiding in DNA stability and protecting genetic information from damage.

Thymine's precise pairing with adenine is fundamental for the precise copying and transmission of genetic code during processes such as DNA replication.