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

Verified step by step guidance

1. Step 1: Begin by drawing the chemical structure of the first dinucleotide composed of adenine (A) and guanine (G). Each nucleotide consists of three parts: a phosphate group, a deoxyribose sugar, and a nitrogenous base (A or G). Connect the phosphate group of the first nucleotide to the 5' carbon of its sugar, and link the 3' carbon of the sugar to the phosphate group of the next nucleotide, forming a phosphodiester bond between A and G.
2. Step 2: Next, draw the complementary dinucleotide composed of thymine (T) and cytosine (C) in an antiparallel orientation relative to the first strand. This means the 5' end of the T-C strand aligns opposite the 3' end of the A-G strand, so the sugar-phosphate backbone runs in the opposite direction.
3. Step 3: Position the nitrogenous bases of the two strands so that adenine (A) pairs opposite thymine (T), and guanine (G) pairs opposite cytosine (C). Remember that A-T pairs form two hydrogen bonds, while G-C pairs form three hydrogen bonds.
4. Step 4: Illustrate the hydrogen bonds between the complementary bases. For A-T, draw two dashed lines representing the two hydrogen bonds; for G-C, draw three dashed lines representing the three hydrogen bonds. These bonds stabilize the double-stranded structure.
5. Step 5: Review the entire structure to ensure correct antiparallel orientation, proper phosphodiester linkages, and accurate base pairing with hydrogen bonds. This completes the depiction of the dinucleotide duplex with complementary base pairing.

Key Concepts

Dinucleotide Structure

A dinucleotide consists of two nucleotides linked by a phosphodiester bond between the 3' hydroxyl of one sugar and the 5' phosphate of the next. Each nucleotide includes a sugar (deoxyribose in DNA), a phosphate group, and a nitrogenous base (A, T, G, or C). Understanding this structure is essential to accurately draw the backbone and base components.

Antiparallel Orientation of DNA Strands

DNA strands run in opposite directions, with one strand oriented 5' to 3' and the complementary strand 3' to 5'. This antiparallel arrangement is crucial when positioning dinucleotides opposite each other, ensuring proper alignment of bases for hydrogen bonding.

Base Pairing and Hydrogen Bonding

In DNA, adenine (A) pairs with thymine (T) via two hydrogen bonds, and guanine (G) pairs with cytosine (C) via three hydrogen bonds. These specific interactions stabilize the double helix and must be shown when drawing complementary dinucleotides in antiparallel orientation.