Question

Draw the chemical structure of a dinucleotide composed of \(A\) and G. Opposite this structure, draw the dinucleotide composed of \(\mathrm{T}\) and \(\mathrm{C}\) in an antiparallel (or upside-down) fashion. Form the possible hydrogen bonds.

Short answer

Question: Draw the chemical structure of a dinucleotide composed of Adenine (A) and Guanine (G) and another dinucleotide composed of Thymine (T) and Cytosine (C) in an antiparallel fashion. Show the hydrogen bonds that form between these two dinucleotides.

Step-by-step solution

Draw Adenine (A) and Guanine (G)

Draw Adenine (A) on the left and Guanine (G) on the right, with the sugar-phosphate backbone connecting them. The sugar molecules should be drawn with a pentagonal shape, and the phosphate groups should be indicated with the letter P inside a circle.

Draw Thymine (T) and Cytosine (C)

Now, draw Thymine (T) underneath Guanine (G) and Cytosine (C) underneath Adenine (A). Make sure to draw them in an antiparallel fashion by flipping them upside-down in relation to the first dinucleotide. Connect T and C with their sugar-phosphate backbone as well.

Form hydrogen bonds between Adenine (A) and Thymine (T)

Next, represent the hydrogen bonds between Adenine (A) and Thymine (T) by drawing two dashed lines between them. Adenine forms two hydrogen bonds with Thymine.

Form hydrogen bonds between Guanine (G) and Cytosine (C)

Lastly, form the hydrogen bonds between Guanine (G) and Cytosine (C) by drawing three dashed lines between them. Guanine forms three hydrogen bonds with Cytosine. Now you have successfully drawn the dinucleotide structure composed of A and G and the dinucleotide composed of T and C in an antiparallel fashion with the possible hydrogen bonds formed between them.

Key concepts

Nucleotides

Nucleotides are the building blocks of DNA, forming the genetic code that dictates all aspects of life. Each nucleotide is composed of three parts: a phosphate group, a five-carbon sugar molecule called deoxyribose, and a nitrogenous base.

There are four types of nitrogenous bases in DNA: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). These bases are crucial for storing genetic information.

• The phosphate and sugar form the backbone of the DNA strand through strong covalent bonds.
• The nitrogenous bases stick out from this backbone and are involved in base pairing, which is essential for DNA structure and replication.

Understanding nucleotides is key to understanding how genetic information is stored and copied from one generation to the next.

Hydrogen Bonding

Hydrogen bonding is a type of weak bond that plays an essential role in the structure of DNA. These bonds occur between nitrogenous bases across two DNA strands, holding them together.

In DNA, hydrogen bonds are crucial as they allow the two DNA strands to hold together precisely, yet they are weak enough to be separated during processes such as replication and transcription.

• Adenine forms two hydrogen bonds with Thymine.
• Guanine forms three hydrogen bonds with Cytosine.

The unique hydrogen bonding pattern ensures the stability and functionality of the DNA molecule, allowing for the accurate copying of genetic information.

Complementary Base Pairing

Complementary base pairing refers to the specific pairing of nitrogenous bases on opposite DNA strands. This specificity is crucial for the correct alignment and stability of the DNA double helix.

Each base on one strand pairs with a specific partner on the opposing strand, known as its complementary base.

• Adenine always pairs with Thymine.
• Guanine always pairs with Cytosine.

These complementary pairings are the result of the number and positioning of hydrogen bonds each base can form. This mechanism ensures that the genetic code is transcribed and replicated accurately, playing a fundamental role in heredity.

Antiparallel Orientation

The antiparallel orientation of DNA refers to the opposite directions of the two strands that make up the DNA double helix. This arrangement is key for the structural stability of the DNA molecule.

Each strand has a directionality due to the orientation of the sugar-phosphate backbone. One strand runs in a 5' to 3' direction, while the opposite strand runs in a 3' to 5' direction.

This antiparallel setup is important for several reasons:

• It enables the correct pairing and hydrogen bonding between complementary bases.
• It is essential for DNA replication, ensuring that enzymes involved in this process work correctly.

Overall, the antiparallel nature of DNA plays a critical role in its ability to store and transmit genetic information accurately across generations.