DNA Structure and Nucleotides

DNA (Deoxyribonucleic Acid)

• Nucleotides are the fundamental building blocks, consisting of deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), or guanine (G).
• DNA has a double helix structure, featuring two strands of nucleotides running in opposite directions, coiling around each other.
• Base pairing rules dictate that adenine pairs with thymine, and cytosine pairs with guanine, stabilized by hydrogen bonds.

Basic Functions of DNA

• Information Storage: DNA houses genetic information that governs the characteristics and functions of organisms.
• Transcription and Translation: Genetic instructions in DNA are transcribed into RNA and translated into proteins, which manage cellular activities.
• Replication: DNA is capable of self-replication, essential for cell division and growth.
• Inheritance: Genetic material is passed down from generation to generation, determining traits inherited by offspring.

RNA (Ribonucleic Acid)

• Nucleotides comprise ribose sugar, a phosphate group, and one of four bases: adenine (A), uracil (U, replacing thymine in DNA), cytosine (C), or guanine (G).
• RNA is usually single-stranded but can fold into secondary structures.
• In RNA, adenine pairs with uracil, while cytosine pairs with guanine.

Proteins

• Proteins are composed of amino acids which have an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom (-H), and a side chain (R group) that varies among different amino acids.
• Peptide Bonds: Amino acids join via peptide bonds to form polypeptide chains.

Levels of Protein Structure

• Primary Structure: The linear sequence of amino acids in a polypeptide chain.
• Secondary Structure: Local folding into alpha-helices and beta-sheets, maintained by hydrogen bonds between amino acids.
• Tertiary Structure: The 3D configuration of a single polypeptide determined by interactions among R groups.
• Quaternary Structure: The arrangement of multiple polypeptide chains (subunits) into a functional protein, involving interactions among side chains, hydrogen bonds, and disulfide bonds.