LO3Russell_4e_ch03 ENG(1)

Introduction to Biological Molecules

  • Biological Molecules are mainly formed of carbon compounds, critical for life on Earth.

  • Carbon Compounds: Serve as the backbone for complex structures, engaging in various chemical interactions.

Importance of Biological Molecules

  • Photosynthesis: Process by which trees and plants use sunlight energy to convert water and carbon dioxide into sugars and other compounds, forming the basis of life.

  • Dependence on Photosynthesis: The survival of plants and almost all organisms is contingent on this process.

  • Role of Carbon Compounds: Foundational structures for living organisms.

3.1 Formation and Modification of Biological Molecules

  • Carbon's Versatility: Capable of forming extensive chains and rings, leading to a vast array of organic molecules.

  • Classification of Molecules:

    • Organic Molecules: Compounds primarily based on carbon.

    • Inorganic Molecules: Compounds that do not primarily consist of carbon, often containing ions.

Organic Molecules

  • Four Major Classes of Organic Molecules:

    1. Carbohydrates

    2. Lipids

    3. Proteins

    4. Nucleic Acids

  • Covalent Bonding: Carbon atoms in organic molecules bond covalently to themselves and to other elements.

  • Hydrocarbons: Molecules that consist solely of carbon and hydrogen atoms.

Inorganic vs Organic Molecules

Property

Inorganic Molecules

Organic Molecules

Ionic Bonds

Usually contain positive/negative ions

Always involve covalent bonding

Size

Generally small

Often large, with many atoms

Presence in Nature

Often associated with non-living matter

Usually associated with living organisms

Hydrocarbons

  • Basic Structure: Carbon has four unpaired outer electrons, allowing for diverse bonding.

  • Example of Simplest Hydrocarbon: Methane (CH4CH_4).

  • Complex Hydrocarbons: Consist of two or more carbon atoms and can include various types of bonds:

    • Single bonds

    • Double bonds in linear and ring structures

    • Triple bonds between two-carbon hydrocarbons.

Functional Groups of Organic Molecules

  • Definition: Functional groups are small, reactive groups of atoms that confer specific chemical properties to larger molecules.

  • Types of Functional Groups:

    • Hydroxyl (R-OH): Found in alcohols, polar; forms hydrogen bonds.

    • Carbonyl: Two forms (aldehyde/RCHO, ketone/R-CO-R), polar; involved in carbohydrate reactions.

    • Carboxyl (R-COOH): Characterizes carboxylic acids, polar, acidic properties.

    • Amino (R-NH2): Found in amines, basic; accepts protons.

    • Phosphate (R-O-P=O): Present in nucleotides, acidic; plays roles in energy transfer.

    • Sulfhydryl (R-SH): Thiols, forms disulfide bonds important in protein structure.

Detailed Functional Group Structures

Functional Group

Structure

Significance

Hydroxyl

R−OHR-OH

Polar, forms hydrogen bonds, present in sugars.

Carbonyl

R−C(=O)R-C(=O) (aldehyde) or R−C(=O)−RR-C(=O)-R (ketone)

Major energy carriers in cells.

Carboxyl

R−COOHR-COOH

Acts as an acid by donating protons (H+).

Amino

R−NH2R-NH_2

Acts as a base; important in amino acids and proteins.

Phosphate

R−O−P(=O)OHR-O-P(=O)^{OH}

Important in energy transfer (ATP), found in nucleotides.

Sulfhydryl

R−SHR-SH

Forms disulfide bridges in proteins, affecting structure.

Isomers

  • Definition: Molecules with the same chemical formula but different structures.

  • Types of Isomers:

    1. Structural Isomers: Different connectivity of atoms (e.g., glucose vs. fructose).

    2. Stereoisomers: Same connectivity but different spatial arrangement (e.g., D and L glyceraldehyde).

  • Example of Structural Isomers: Glucose, Galactose, and Fructose all share the formula C<em>6H</em>12O6C<em>6H</em>{12}O_6 but differ structurally.

Reactions Involving Water

  • Dehydration Synthesis (Condensation Reaction): Water molecule (H2OH_2O) is removed, creating a bond between monomers.

    • Process: Monomer + Monomer → Polymer + H2OH_2O.

  • Hydrolysis: Water is added to break bonds, splitting polymers into monomers.

    • Process: Polymer + H2OH_2O → Monomer + Monomer.

Macromolecules (Biomolecules)

  • Definition: Large polymers created from monomers via covalent bonds.

  • Types of Macromolecules:

    1. Carbohydrates

    2. Lipids

    3. Proteins

    4. Nucleic Acids

  • Criteria for Macromolecule: One polymer molecule must have a mass of 1,000 daltons (Da) or more.

3.2 Carbohydrates

  • Functions of Carbohydrates:

    • Energy Source: Immediate energy for cellular functions.

    • Structural Components: Serve as building blocks (cellulose in plants).

  • Composition: Comprised of carbon (C), hydrogen (H), and oxygen (O) typically in a 1C:2H:1O ratio (CH2OCH_2O).

Monosaccharides

  • Definition: Simple sugars with a backbone of 3-7 carbon atoms.

  • Examples:

    • Glucose: critical for energy.

    • Fructose: found in fruits.

    • Ribose: part of RNA.

    • Pentoses (5 carbons) and Hexoses (6 carbons) are common.

  • Characteristics: Soluble in water, sweet tasting, can exist in linear or ring forms.

Disaccharides

  • Formation: Created from two monosaccharides via dehydration synthesis.

  • Examples:

    • Maltose: Glucose + Glucose (linkage via glycosidic bond).

    • Sucrose: Glucose + Fructose.

    • Lactose: Glucose + Galactose.

Polysaccharides

  • Definition: Large carbohydrates consisting of many monosaccharide units (more than 10 linked units).

  • Common Types:

    • Starch: Energy storage in plants (forms: amylose and amylopectin).

    • Glycogen: Energy storage in animals, stored in liver.

    • Cellulose: Major component of plant cell walls.

    • Chitin: Found in fungi cell walls and arthropod exoskeletons.

    • Peptidoglycan: Component of bacterial cell walls.

3.3 Lipids

  • Definition: Water-insoluble biomolecules mainly composed of hydrocarbons.

  • Types of Lipids:

    1. Neutral Lipids: Energy-storage molecules with no charged groups (includes oils and fats).

    2. Phospholipids: Major components of cell membranes.

    3. Steroids: Including hormones and cholesterol.

Neutral Lipids

  • Structure: Composed of fatty acids and glycerol.

  • Formation: Triglycerides form through dehydration synthesis between glycerol and three fatty acids, resulting in ester linkages.

  • Functions: Serve as energy reserves and insulation in animals.

Fatty Acids

  • Characteristics:

    • Long hydrocarbon chains with a carboxyl group.

    • Saturated Fatty Acids: Maximum hydrogen (no double bonds), typically solid.

    • Unsaturated Fatty Acids: Contain one or more double bonds, typically liquid at room temperature.

Phospholipids

  • Structure: Comprised of two fatty acid tails and a phosphate group attached to glycerol, creating a hydrophilic head and hydrophobic tail, forming the phospholipid bilayer in cell membranes.

Steroids

  • Structure: Consist of four interconnected carbon rings.

  • Examples:

    • Cholesterol: Essential for membrane structure; stabilizes cell membranes.

    • Steroid Hormones: Like testosterone and estradiol, involved in regulating biological functions.