Nucleic Acids and Genomes: Structure, Function, and Biological Themes

Nucleic Acids and Genomes

Introduction to Nucleic Acids

Nucleic acids are essential macromolecules that store and transmit genetic information in all living organisms. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Their structure and function are central to understanding genetics and molecular biology.

• Nucleic acids are polymers made of nucleotide monomers.

• DNA stores hereditary information; RNA helps express this information.

• Other major macromolecules include proteins, carbohydrates, and lipids.

Discovery of DNA Structure

The structure of DNA was elucidated through a series of experiments and evidence, leading to the double helix model.

• Key evidence: Chargaff's rules (A=T, G=C), X-ray diffraction images (Rosalind Franklin), and Watson & Crick's model building.

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

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

Structure of Nucleic Acids

Nucleic acids are composed of nucleotides, each consisting of a nitrogenous base, a pentose sugar, and a phosphate group.

• Nucleotide: Nitrogenous base + sugar + phosphate group.

• Sugars: Ribose in RNA, deoxyribose in DNA.

• Nitrogenous bases: Purines (Adenine, Guanine), Pyrimidines (Cytosine, Thymine in DNA, Uracil in RNA).

• Phosphodiester bonds: Link nucleotides in a chain, forming the sugar-phosphate backbone.

Equation for Phosphodiester Bond Formation:

$\text{Nucleotide}_1 + \text{Nucleotide}_2 \xrightarrow{\text{Dehydration Synthesis}} \text{Dinucleotide} + H_2O$

Polynucleotide Structure and Directionality

Nucleic acid chains have directionality, with a 5' end (phosphate group) and a 3' end (hydroxyl group).

• Antiparallel strands: In DNA, two strands run in opposite directions (5' to 3' and 3' to 5').

• Hydrogen bonds: Hold complementary bases together.

• Van der Waals interactions: Stabilize the stacked base pairs.

DNA vs. RNA

DNA and RNA differ in structure, function, and location within the cell.

• DNA: Double-stranded, contains deoxyribose, uses thymine.

• RNA: Single-stranded, contains ribose, uses uracil.

• Types of RNA: Messenger RNA (mRNA), Transfer RNA (tRNA), Ribosomal RNA (rRNA).

Functions of Nucleic Acids

Nucleic acids play key roles in genetic information storage, transmission, and expression.

• DNA: Stores genetic information in the nucleus (eukaryotes) or cytoplasm (prokaryotes).

• mRNA: Carries genetic code from DNA to ribosomes for protein synthesis.

• tRNA: Delivers amino acids during translation.

• rRNA: Forms the core of ribosomes.

Genome Structure: Prokaryotes vs. Eukaryotes

The organization of genetic material differs between prokaryotic and eukaryotic cells.

Feature	Prokaryotes	Eukaryotes
Chromosome shape	Circular	Linear
Number of chromosomes	Single	Multiple
Location	Cytoplasm (nucleoid)	Nucleus
Non-coding DNA	Minimal	Extensive
Histones	Absent	Present

Macromolecules and Biological Themes

Macromolecules are large molecules made of smaller subunits. They play diverse roles in cellular structure and function.

• Carbohydrates: Energy source and structural support.

• Proteins: Catalysis, structure, transport, signaling.

• Lipids: Membrane structure, energy storage.

• Nucleic acids: Genetic information storage and transfer.

Emergent properties: New characteristics arise at higher levels of biological organization.

Anabolic and Catabolic Reactions

Cells build and break down macromolecules through anabolic and catabolic reactions.

• Anabolic reactions: Build complex molecules from simpler ones; require energy (e.g., DNA synthesis).

• Catabolic reactions: Break down complex molecules into simpler ones; release energy (e.g., hydrolysis).

Equation for Dehydration Synthesis:

$\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{Dehydration Synthesis}} \text{Polymer} + H_2O$

Equation for Hydrolysis:

$\text{Polymer} + H_2O \xrightarrow{\text{Hydrolysis}} \text{Monomer}_1 + \text{Monomer}_2$

Genomics and Proteomics

Modern biology explores entire genomes and proteomes to understand complex traits and diseases.

• Genomics: Study of all genes in an organism, their interactions, and environmental influences.

• Proteomics: Study of all proteins, their structure, function, and modifications.

Genomics enables analysis of multifactorial diseases and uses advanced technology for broad insights.

Summary Table: Key Macromolecules

Macromolecule	Monomer	Bond Type	Main Function
Carbohydrate	Monosaccharide	Glycosidic bond	Energy, structure
Protein	Amino acid	Peptide bond	Catalysis, structure
Lipid	Fatty acid, glycerol	Ester bond	Membranes, energy storage
Nucleic acid	Nucleotide	Phosphodiester bond	Genetic information

Additional info:

• Some context and explanations were inferred from fragmented notes and standard biology curriculum.

• Images referenced (DNA double helix) support the topic of nucleic acids and genomes.