Organic Chemistry in Biology

Organic vs Inorganic Compounds

Organic chemistry is the study of carbon-containing compounds, which are fundamental to living organisms. Organic compounds differ from inorganic compounds in their structure, composition, and roles in biological systems.

• Organic Compounds: Contain carbon atoms bonded to hydrogen, often with oxygen, nitrogen, phosphorus, and sulfur. Examples include carbohydrates, lipids, proteins, and nucleic acids.

• Inorganic Compounds: Typically do not contain carbon-hydrogen bonds. Examples include water, salts, acids, and bases.

• Importance: Organic compounds form the molecular basis of life, serving as building blocks for cells and tissues.

Functional Groups and Isomers

Functional Groups

Functional groups are specific clusters of atoms attached to the carbon skeleton of organic molecules, conferring unique chemical properties.

• Examples: Hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), phosphate (-PO4), methyl (-CH3).

• Role: Determine the reactivity and interactions of organic molecules.

Isomers

Isomers are molecules with the same molecular formula but different structural arrangements.

• Structural Isomers: Differ in the covalent arrangement of atoms.

• Cis-trans Isomers: Differ in spatial arrangement around a double bond.

• Enantiomers: Mirror-image isomers important in biological activity.

Monomers and Polymers

Definitions and Relationships

Large biological molecules (macromolecules) are polymers made by linking smaller units called monomers.

• Monomer: A small molecule that can join with others to form a polymer.

• Polymer: A large molecule composed of repeating monomer units.

• Examples:

  • Monosaccharide → Polysaccharide

  • Amino acid → Protein

  • Nucleotide → Nucleic acid

  • Fatty acid → Lipid (not always a true polymer)

Dehydration Reactions vs Hydrolysis Reactions

Polymer Formation and Breakdown

Biological polymers are assembled and disassembled by specific chemical reactions.

• Dehydration Reaction (Condensation): Joins two monomers by removing a water molecule. Equation:

• Hydrolysis Reaction: Breaks a polymer into monomers by adding water. Equation:

• Enzymes: Biological catalysts that facilitate these reactions.

Classes of Organic Compounds

Overview

There are four major classes of organic molecules in living organisms, each with distinct structures and functions.

• Carbohydrates: Energy source and structural material.

• Lipids: Energy storage, membrane structure, signaling.

• Proteins: Catalysis, structure, transport, defense, regulation, motion.

• Nucleic Acids: Information storage and transfer.

Level of Organization

Biological Hierarchy

Living things synthesize organic molecules that serve as building blocks for higher levels of biological organization.

• Hierarchy: Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organism

• Macromolecules: DNA, proteins, carbohydrates, and lipids are essential at the molecular and cellular levels.

• Example: DNA is found in the nucleus, proteins in the cytoplasm, and carbohydrates in cell walls.

Hydrocarbons

Structure and Properties

Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen.

• Nonpolar: Hydrophobic and insoluble in water.

• Energy Source: Found in fats and oils, store energy in C-H bonds.

• Example: Methane (CH4), ethane (C2H6).

Carbohydrates

Structure and Function

Carbohydrates are the most abundant biomolecules, composed of carbon, hydrogen, and oxygen, usually in a 1:2:1 ratio.

• Functions: Energy source, energy storage, structural components.

• Classification: Monosaccharides, disaccharides, polysaccharides.

Monosaccharides

• Definition: Simple sugars (3-7 carbons), e.g., glucose, fructose, ribose.

• Role: Glucose is the primary energy source for cells; ribose and deoxyribose are components of RNA and DNA.

Disaccharides

• Definition: Two monosaccharides joined by a glycosidic bond (dehydration reaction).

• Examples: Sucrose (table sugar), lactose (milk sugar), maltose.

• Digestion: Hydrolytic enzymes break disaccharides into monosaccharides.

Polysaccharides

• Definition: Polymers of many monosaccharides (mainly glucose).

• Functions: Short-term energy storage (starch in plants, glycogen in animals), structural support (cellulose in plants, chitin in fungi and arthropods).

• Properties: Low solubility, not sweet to taste.

Table: Classification of Carbohydrates

Lipids

Structure and Function

Lipids are hydrophobic organic molecules, including fats, oils, waxes, and steroids. They are not true polymers but are assembled from smaller components.

• Functions: Long-term energy storage, insulation, protection, membrane structure, signaling.

• Types: Triglycerides, phospholipids, waxes, steroids.

Triglycerides

• Structure: Glycerol backbone + three fatty acids.

• Fatty Acids: Can be saturated (no double bonds, solid at room temperature) or unsaturated (one or more double bonds, liquid at room temperature).

Table: Saturated vs Unsaturated Fats

Phospholipids

• Structure: Glycerol + two fatty acids + phosphate group.

• Role: Major component of cell membranes (phospholipid bilayer).

Waxes and Steroids

• Waxes: Protective coatings (e.g., plant cuticle, earwax).

• Steroids: Four fused carbon rings; include cholesterol and hormones.

Proteins

Structure and Function

Proteins are polymers of amino acids, performing diverse functions in cells.

• Functions: Structural support, catalysis (enzymes), transport, defense, regulation, motion.

• Examples: Collagen, keratin, hemoglobin, antibodies, insulin, actin, myosin.

Amino Acids

• Structure: Central carbon, amino group (-NH2), carboxyl group (-COOH), hydrogen, and unique R group.

• Properties: R group determines polarity, charge, and function.

• 20 Amino Acids: Combine in various sequences to form thousands of proteins.

Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Coiling (alpha helix) or folding (beta sheet) due to hydrogen bonding.

• Tertiary: Overall 3D shape due to interactions among R groups.

• Quaternary: Association of multiple polypeptide chains.

Protein Folding and Denaturation

• Chaperonins: Proteins that assist in proper folding of other proteins.

• Denaturation: Loss of structure and function due to changes in temperature, pH, or salt concentration.

• Example: Cooking, pickling, or straightening hair involves protein denaturation.

Nucleic Acids

DNA and RNA

Nucleic acids are polymers of nucleotides, responsible for storing and transmitting genetic information.

• Nucleotide Structure: Five-carbon sugar (ribose or deoxyribose), phosphate group, nitrogenous base.

• DNA: Double helix, deoxyribose sugar, bases A, T, G, C. Stores hereditary information.

• RNA: Single strand, ribose sugar, bases A, U, G, C. Involved in protein synthesis.

Central Dogma of Biology

• Flow of Information: DNA → RNA → Protein

• Process: DNA is transcribed to messenger RNA (mRNA), which is translated into a polypeptide at the ribosome.

ATP: Cellular Energy Currency

• Structure: Adenine, ribose, three phosphate groups.

• Role: Provides energy for cellular work.

• Equation:

Summary Table: Major Classes of Biological Molecules

Additional info: Some context and examples were inferred to clarify fragmented points and ensure completeness for exam preparation.