Nucleic Acids

Overview of Nucleic Acids

Nucleic acids are essential macromolecules that store and transmit genetic information in living organisms. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

• DNA: Stores genetic information, found in chromosomes, and transmits genetic info to offspring.

• RNA: Involved in protein synthesis and gene regulation.

Polymer: Nucleic acids are polymers made of nucleotide monomers.

Nucleotides: Building Blocks of Nucleic Acids

Nucleotides are the monomers of nucleic acids, each consisting of three components:

• Phosphate group

• Pentose sugar (deoxyribose in DNA, ribose in RNA)

• Nitrogenous base (Adenine, Thymine, Cytosine, Guanine in DNA; Uracil replaces Thymine in RNA)

Example: ATP (Adenosine Triphosphate) is a nucleotide with three phosphate groups, serving as the cell's main energy currency.

Components of Nucleotides

Energy in Nucleotides

The energy stored in nucleotides like ATP is found in the phosphate bonds. Hydrolysis of these bonds releases energy:

• ATP (most energy)

• ADP (adenosine diphosphate)

• AMP (adenosine monophosphate, least energy)

Nucleic Acid Polymers and DNA Structure

Nucleic acids are formed by covalent bonds between the sugar and phosphate groups of nucleotides, creating a sugar-phosphate backbone. DNA is typically double-stranded and forms a double helix.

• Double helix: Two strands run antiparallel and are held together by hydrogen bonds between complementary bases.

• Base pairing: Adenine pairs with Thymine (A-T), Cytosine pairs with Guanine (C-G).

Properties of DNA Double Helix

• Strands are antiparallel (run in opposite directions).

• Strands are not complementary in direction.

• Base stacking interactions stabilize the helix.

• Hydrogen bonds hold the two strands together.

Types of RNA

There are three main types of RNA, each with distinct functions:

• mRNA (messenger RNA): Carries genetic information from DNA to ribosomes for protein synthesis.

• tRNA (transfer RNA): Brings amino acids to the ribosome during translation.

• rRNA (ribosomal RNA): Forms the core of ribosome structure and catalyzes protein synthesis.

Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information:

• DNA (information storage) → RNA (information transfer) → Protein (functional molecules)

Key processes:

• Transcription: DNA is copied into RNA.

• Translation: RNA is used to synthesize proteins.

• Replication: DNA is copied to produce identical DNA molecules.

Proteins

Gene Expression: DNA to Protein

Gene expression is the process by which information from a gene is used to synthesize a functional gene product, typically a protein. This involves transcription (DNA to RNA) and translation (RNA to protein).

Protein Functions

Proteins perform a wide variety of functions in cells:

• Enzymes: Catalyze biochemical reactions (e.g., digestive enzymes).

• Transport proteins: Move substances across membranes (e.g., hemoglobin).

• Storage proteins: Store amino acids or other substances (e.g., ferritin).

• Defensive proteins: Protect against disease (e.g., antibodies).

• Structural proteins: Provide support (e.g., collagen).

• Contractile and motor proteins: Enable movement (e.g., actin, myosin).

• Regulatory proteins: Control gene expression and cell processes.

Amino Acids and Polypeptides

Proteins are polymers built from amino acid monomers. There are 20 different amino acids, each with a unique side chain (R group) that determines its properties.

• Polypeptide: A chain of amino acids linked by peptide bonds.

• Essential amino acids: Amino acids that cannot be synthesized by the body and must be obtained from the diet.

Classification of Amino Acids

Peptide Bonds

Amino acids are joined by peptide bonds, which are covalent bonds formed between the carboxyl group of one amino acid and the amino group of another.

Levels of Protein Structure

Proteins have four levels of structure, each contributing to their function:

• Primary structure: Sequence of amino acids in a polypeptide chain, held together by covalent peptide bonds.

• Secondary structure: Local folding into alpha helices and beta sheets, stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape formed by interactions between R groups, including hydrophobic interactions, ionic bonds, and disulfide bridges.

• Quaternary structure: Association of multiple polypeptide chains to form a functional protein complex (e.g., hemoglobin).

Protein Denaturation

Proteins can lose their structure and function through denaturation, caused by changes in pH, temperature, or exposure to chemicals. Denatured proteins are often inactive.

Summary Table: Levels of Protein Structure

Key Vocabulary

• Genome

• Nucleic acid

• Deoxyribose

• Ribose

• Polypeptide

• Peptide bond

• Transcription

• Translation

• Replication

• Denatured/Renatured

Important Equations

• ATP hydrolysis:

• Peptide bond formation:

Example: Complementary Base Pairing

• Adenine (A) pairs with Thymine (T) in DNA.

• Cytosine (C) pairs with Guanine (G) in DNA.

• In RNA, Uracil (U) replaces Thymine.

Gene Expression: Two Stages

• Transcription: DNA → RNA

• Translation: RNA → Protein

Additional info: Some explanations and definitions have been expanded for clarity and completeness, including the classification of amino acids and the summary tables.