Organic Compounds

Definition and Properties

Organic compounds are fundamental to life and are defined as molecules containing carbon atoms. Carbon's unique chemical properties make it a versatile element, capable of forming a wide variety of structures.

• Organic compounds: Carbon-based molecules found in living organisms.

• Carbon atoms can form four covalent bonds, allowing for diverse molecular shapes and sizes.

• Examples include carbohydrates, lipids, proteins, and nucleic acids.

Variations in Carbon Skeletons

Structural Diversity

The backbone of organic molecules, known as the carbon skeleton, can vary greatly, contributing to the diversity of organic compounds.

• Carbon skeletons can differ in length.

• They may be unbranched (linear) or branched.

• Double bonds may be present, affecting the molecule's shape and reactivity.

• Carbon skeletons can be arranged in rings, as seen in aromatic compounds.

Models of Organic Compounds

Representations

Organic molecules can be represented in several ways to illustrate their structure and function.

• Structural formula: Shows the arrangement of atoms.

• Ball-and-stick model: Highlights the spatial relationships between atoms.

• Space-filling model: Demonstrates the actual volume occupied by the molecule.

• Examples: Octane (component of gasoline) and dietary fats.

Carbon Chemistry

Functional Groups and Reactivity

The chemical properties of organic compounds depend on their carbon skeleton and the atoms attached to it, known as functional groups.

• Functional groups: Specific groups of atoms directly involved in chemical reactions.

• Common functional groups include hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), and phosphate (-PO4).

• Functional groups determine the chemical behavior of organic molecules.

Classes of Biological Molecules

Major Types

Biological molecules are classified into four major groups, three of which are considered macromolecules due to their large size.

• Carbohydrates: Sugars and polymers of sugars.

• Lipids (fats): Hydrophobic molecules, not true polymers.

• Proteins: Polymers of amino acids.

• Nucleic acids: DNA and RNA, polymers of nucleotides.

• Macromolecules: Very large molecules formed by joining smaller units (monomers).

Synthesis and Breakdown of Polymers

Polymerization and Hydrolysis

Macromolecules are formed and broken down by specific chemical reactions.

• Dehydration reaction: Links two monomers together by removing a molecule of water.

• Hydrolysis: Breaks down polymers by adding water, splitting the bonds between monomers.

Equation for Dehydration Reaction:

Equation for Hydrolysis:

Lipids

Structure and Properties

Lipids are a diverse group of hydrophobic molecules, primarily composed of carbon chains or rings. Unlike other macromolecules, lipids do not form polymers from monomers.

• Hydrophobic: Lipids do not mix with water.

• Examples include fats, oils, and steroids.

Triglycerides

A typical fat molecule, or triglyceride, consists of a glycerol backbone joined to three fatty acid chains.

• Formed by dehydration reactions between glycerol and fatty acids.

• Functions: Energy storage, cushioning, and insulation.

Saturated vs. Unsaturated Fats

The presence or absence of double bonds in fatty acid chains determines whether a fat is saturated or unsaturated.

• Saturated fats: No double bonds; solid at room temperature.

• Unsaturated fats: One or more double bonds; liquid at room temperature.

Steroids

Steroids are lipids characterized by a carbon skeleton with four fused rings.

• Cholesterol: Key component of cell membranes.

• Other examples: Testosterone, estrogen.

Carbohydrates

Structure and Function

Carbohydrates are sugars and polymers of sugars, serving as a primary energy source and structural component in cells.

• Monosaccharides: Simple sugars (e.g., glucose, fructose); monomers of carbohydrates.

• Disaccharides: Formed by joining two monosaccharides via dehydration reaction (e.g., lactose).

• Polysaccharides: Long chains of monosaccharides; complex carbohydrates (e.g., starch, glycogen, cellulose).

Monosaccharides

Monosaccharides are the simplest carbohydrates and cannot be broken down into smaller sugars.

• General formula: (e.g., glucose: )

• Isomers: Molecules with the same formula but different arrangements (e.g., glucose and fructose).

Polysaccharides Comparison Table

Polysaccharides serve different functions in organisms.

Proteins

Structure and Function

Proteins are polymers made from 20 different amino acid monomers. They perform a wide variety of functions in cells.

• Functions: Catalysis (enzymes), transport, structural support, signaling, movement.

• Protein shape determines its function.

Amino Acids

Amino acids have a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group).

• Hydrophobic side chains: Nonpolar, avoid water (e.g., leucine).

• Hydrophilic side chains: Polar, interact with water (e.g., serine).

General structure of an amino acid:

Protein Structure

Proteins are formed by linking amino acids through peptide bonds (dehydration reactions), creating polypeptide chains. The sequence of amino acids determines the protein's three-dimensional structure and function.

• Primary structure: Sequence of amino acids.

• Secondary structure: Local folding (alpha helices, beta sheets).

• Tertiary structure: Overall 3D shape.

• Quaternary structure: Association of multiple polypeptides (if applicable).

Nucleic Acids

Structure and Function

Nucleic acids store genetic information and provide instructions for building proteins. The two main types are DNA and RNA.

• DNA (deoxyribonucleic acid): Stores genetic information.

• RNA (ribonucleic acid): Involved in protein synthesis.

Nucleotide Structure

Nucleic acids are polymers made from nucleotide monomers. Each nucleotide consists of:

• A five-carbon sugar (deoxyribose in DNA, ribose in RNA)

• A phosphate group

• A nitrogen-containing base

DNA and RNA Bases

DNA nucleotides contain one of four nitrogenous bases:

• Adenine (A)

• Guanine (G)

• Thymine (T)

• Cytosine (C)

RNA contains uracil (U) instead of thymine.

Base Pairing Rules

Specific base pairing ensures accurate genetic information transfer:

• A pairs with T (in DNA)

• G pairs with C

• In RNA, A pairs with U

Structure of DNA and RNA

• DNA: Double helix formed by two polynucleotide strands.

• RNA: Single-stranded molecule.

Summary Table: DNA vs. RNA

Example: DNA stores hereditary information, while RNA helps translate that information into proteins.