Question

In a strand of normal DNA, the base ________ is always found paired with the base adenine, whereas _________ is always found paired with cytosine.

Short answer

In a strand of normal DNA, the base thymine (T) is always found paired with the base adenine (A), whereas guanine (G) is always found paired with cytosine (C).

Step-by-step solution

Step 1. Understand the base pairing rules in DNA

In a normal DNA strand, there are four types of bases: adenine (A), cytosine (C), guanine (G), and thymine (T). The structure and stability of DNA are maintained by the interactions between these bases. The base pairing rules state that adenine always pairs with thymine, and cytosine always pairs with guanine, forming A-T and C-G pairs.

Step 2. Identify the base that pairs with adenine

According to the base pairing rules, adenine (A) always pairs with thymine (T). Therefore, the base that is always found paired with adenine is thymine.

Step 3. Identify the base that pairs with cytosine

According to the base pairing rules, cytosine (C) always pairs with guanine (G). Therefore, the base that is always found paired with cytosine is guanine. In conclusion, in a strand of normal DNA, the base thymine (T) is always found paired with the base adenine (A), whereas guanine (G) is always found paired with cytosine (C).

Key concepts

The Mystery of Adenine-Thymine Pairing

In the intricate world of DNA, bases pair together to form the double-helix structure. One of the most important partnerships within this structure is the adenine-thymine pairing. Adenine (A), known for its tendency to form two hydrogen bonds, is always paired with thymine (T). This infallible rule is crucial for DNA stability and replication.

When adenine forms a bond with thymine, the structure is stable but not identical to other pairs, allowing the DNA to twist and form its unique spiral shape. These two bases fit together almost like perfect puzzle pieces, where adenine's two-binding sites align well with thymine's complementary binding sites.

- Adenine and thymine are able to create two hydrogen bonds.
- Their pairing is relatively less strong than cytosine-guanine due to fewer hydrogen bonds.
- Adenine's shape is complementary to thymine, allowing precise bonding.

This pairing is the primary code for storing genetic information and is crucial for life as we know it.

Unveiling Cytosine-Guanine Pairing

Cytosine-guanine pairing is another critical base pairing in DNA. Cytosine (C) is always paired with guanine (G) within the DNA strand. Unlike the adenine-thymine pair, cytosine and guanine form three hydrogen bonds, which makes their bond more robust, and to some extent, this contributes to the overall DNA stability.

The extra hydrogen bond in the cytosine-guanine pair leads to a stronger attraction that makes these sections of DNA more stable and harder to break apart during processes like DNA replication.

- Cytosine and guanine form three hydrogen bonds.
- This pairing is stronger than adenine-thymine pair due to additional bonding.
- Guanine's three-binding sites perfectly match with cytosine's complementary sites.

This strength might play a role in the regulatory functions of DNA, where hotter parts of the DNA (richer in C-G pairs) might affect gene expression differently.

Understanding Nucleotides: The Building Blocks of DNA

Nucleotides are the fundamental units of DNA, storing the genetic blueprints of life. Each nucleotide is made up of three components: a sugar molecule, a phosphate group, and a nitrogenous base. These nitrogenous bases are the keys to DNA's unique properties and are classified into four types: adenine (A), thymine (T), cytosine (C), and guanine (G).

DNA is structured in such a way that nucleotides form long chains, intertwined in a ladder-like structure. The sugar and phosphate form the "rails" of the ladder, while the nitrogenous bases form the "rungs," pairing according to specific rules.

- Nucleotides connect to form the backbone of the DNA ladder.
- Their order determines genetic instructions.
- Nucleotides bond through specific pairings: A with T, and C with G.

The arrangement of these nucleotides dictates everything from eye color to metabolism, indicating just how critical these small molecules are to organisms. They truly form the language of life, communicating in codes transcribed and translated to produce proteins, the workhorses of cells.