Nucleic Acids and DNA Structure

Nucleotide: The basic building block of nucleic acids. Each nucleotide consists of three main components:
- A phosphate group
- A 5-carbon sugar (either ribose in RNA or deoxyribose in DNA)
- A nitrogenous base (which can be a purine or a pyrimidine)

Pyrimidines: Include Cytosine (C), Thymine (T, in DNA), and Uracil (U, in RNA).
Purines: Include Adenine (A) and Guanine (G).
The distinction between purines and pyrimidines is important as it affects the structure and function of nucleotides in genetic material.

Complementary Base Pairing: The specific hydrogen bonding between purines and pyrimidines. Adenine pairs with Thymine (in DNA) and Uracil (in RNA), while Guanine pairs with Cytosine (G-C bond).
This pairing is crucial to the molecular structure of DNA, contributing to the double helix shape and stability due to hydrogen bonds (A-T has 2 bonds; C-G has 3 bonds).

A nucleotide contains a nitrogenous base, which is attached to the 1' carbon of the sugar component, and this base is essential for the genetic information carried within nucleic acids.
Nitrogenous bases serve as the unique identifiers of different nucleotides, affecting the overall function and structure of DNA and RNA.

DNA's double helix structure is vital for its role as an information storage molecule. The specific sequence of bases encodes genetic information, and the complementary base pairing allows for accurate replication during cell division, ensuring that genetic information is preserved with high fidelity.

DNA vs RNA:
- DNA is double-stranded; RNA is single-stranded.
- DNA contains deoxyribose; RNA contains ribose.
- DNA has thymine (T); RNA has uracil (U) instead of thymine.

Phosphodiester Bonds: Strong covalent bonds that link nucleotides within a strand of nucleic acid, forming the sugar-phosphate backbone, crucial for the structural integrity of DNA and RNA.
Hydrogen Bonds: Weaker bonds that hold together the two strands of DNA by pairing complementary bases. Essential for the stability and separation of DNA strands during replication and transcription.

If a certain percentage of one nucleotide is known (e.g., adenine = 17%), then the percentage of the complementary nucleotide can be calculated (thymine = 17%).
The relationship is as follows: If adenine + thymine + guanine + cytosine = 100%, and since A = T and G = C, it aids in calculating unknown percentages.

A phosphodiester bond is formed during a condensation reaction where the 5' phosphate group of one nucleotide attaches to the 3' hydroxyl group of another nucleotide, releasing a molecule of water.

Increasing temperature can destabilize hydrogen bonds, potentially leading to denaturation of the DNA or RNA molecules, where strands may separate. If the temperature returns to optimal, strands can reassociate.

The structure of DNA facilitates replication, allowing for the exact copying of chromosomes due to the complementary base pairing and antiparallel nature of the strands. Enzymes can easily recognize and duplicate the sequences with minimal errors.

The two strands of DNA are oriented in opposite directions, termed antiparallel. One strand runs in a 5' to 3' direction while the complementary strand runs 3' to 5'. This arrangement is essential for DNA replication, as enzymes can only synthesize DNA in the 5' to 3' direction.

Macromolecules: Complex molecules made up of smaller units (monomers) linked through covalent bonds. In nucleic acids, these monomers are nucleotides.
Key macromolecules and their functions:
- Carbohydrates (polysaccharides): Energy storage (e.g., glycogen, starch) and structural purposes (e.g., cellulose, chitin).
- Lipids: Function as energy storage (triacylglycerols) and structural components (phospholipids, steroids).
- Proteins: Functional units (enzymes, hormones, antibodies) formed from amino acid monomers linked by peptide bonds.
- Nucleic Acids: DNA and RNA polymers composed of nucleotide monomers linked by phosphodiester bonds.

The DNA structure is defined by:
- A double helix formed by two strands running in opposite (antiparallel) directions.
- Sugar-phosphate backbone located on the outside, providing structural support.
- Nitrogenous bases positioned inwards, allowing for base pairing through hydrogen bonds.

DNA consists of two strands oriented anti-parallel with bases paired through hydrogen bonding, maintaining its helical structure. The integrity and functionality of DNA depend on the specificity of base pairing and the robustness of the phosphodiester bonds that form the backbone of the DNA molecule.