Chemistry of Life: Molecules, Elements, and Isotopes

• Study of the chemistry of molecules that constitute life, including their functions and interactions
• Focuses on understanding the chemical and physical characteristics of essential biological compounds

Matter

• Anything possessing mass and volume

Elements in Living Organisms

• Composed of 92 naturally occurring elements
• 25 elements are deemed essential for life

Key Elements

• Carbon and hydrogen serve as fundamental building blocks
• Nitrogen, phosphorus, sulfur, and oxygen collaborate with carbon and hydrogen to establish molecular chemical properties

Isotopes

• Isotopes have identical proton counts but varying neutron numbers
• The number of protons determines an element's identity
• Most elements have one or more stable isotopes

Radioisotopes

• Radioisotopes are unstable element isotopes with an imbalanced neutron count
• Instability arises from spontaneous nucleus decay, emitting radiation (subatomic particles/EM waves)

Radioactive Decay

• Nuclei rearrange to attain stability through radioactive decay
• Higher instability corresponds to faster rearrangement
• Radioisotopes convert from one element to another via nucleus decay

Applications of Radioisotopes

• Radiotherapy targets and eradicates cancer cells
• Radioisotope tracing monitors the breakdown of radioactive substances injected into patients using PET scans
• Radiometric dating estimates the age of rocks and fossils by comparing isotope abundance to decay products

Half-Life

• Refers to the duration it takes for a radioactive sample to diminish to half its initial quantity

Intramolecular Forces

• Forces that maintain the bonds between atoms within a molecule

Ionic Bonds

• Forces between cations and anions
• Vulnerable to disruption in polar solvents

Covalent Bonds

• Formed through electron sharing to achieve complete valence shells

Electronegativity

• An atom's capacity to attract shared electrons
• Variations in electronegativity exist among elements

High Electronegativity

• Oxygen (O), Nitrogen (N), and Chlorine (Cl)

Low Electronegativity

• Hydrogen (H), Carbon (C), and Phosphorus (P)

Polar Covalent Bonds

• Develop from unequal electron sharing between elements of differing electronegativities
• Exhibit partially positive and negative regions
• Greater electron density regions carry partial negative charges

Nonpolar Covalent Bonds

• Occur between elements with comparable electronegativities
• Feature equal electron sharing

Intermolecular Forces

• Forces that exist between molecules
• Govern molecular interactions and substance physical properties
• Primarily attractive in nature, including hydrogen bonding and hydrophobic interactions

Hydrogen Bonding

• Occurs when hydrogen is bonded to electronegative atoms like oxygen, nitrogen, or fluorine
• Attraction between hydrogen and electronegative atoms is due to partial positive and negative regions
• Weaker than covalent/ionic bonds individually, but can be strong when many are combined

Hydrophobic Interactions

• Occur between nonpolar molecules and water
• Nonpolar molecules cluster together due to their aversion to water

Hydrophilic Interactions

• Occur between polar molecules and water, facilitated by hydrogen bond formation

Hydrophobic Effect

• The phenomenon of non-polar molecules aggregating in the presence of water

Functional Groups

• Atomic clusters attached to molecules that dictate behavior and impart specific chemical/physical properties

Hydroxyl Group Properties

• Not very reactive
• Readily engage in hydrogen bonding
• Improve molecular water solubility
• Found in carbohydrates, proteins, nucleic acids, lipids, and alcohols

Carbonyl Group Properties

• Enhance molecular water solubility
• Present in carbohydrates and nucleic acids

Carboxyl Group Properties

• Acidic due to proton donation
• Exhibit weak acidity
• Ionize via hydroxyl hydrogen release as a free proton
• Result in a negative charge (COO-)
• Found in proteins and lipids

Amino Group Properties

• Basic, capable of accepting protons
• Exhibit some water solubility depending on the length of the carbon chain
• Can ionize by accepting a hydrogen ion, becoming positively charged (NH3+)
• Commonly found in proteins and nucleic acids

Sulfhydryl Group Properties

• Less polar than hydroxyl groups and has a strong odor
• Lower boiling points and water solubility compared to alcohols of similar mass
• Two sulfhydryl groups can react to create covalent bonds (disulfide group)
• Present in proteins

Phosphate Group Properties

• Critical in biological energy storage and release via phosphate bond breakage
• Facilitate nucleotide linking
• Present in nucleic acids, ATP, DNA, and RNA

Molecular Formula

• Indicates the elements present and their quantities in a molecule

Structural Formula

• Illustrates atomic bonding patterns within molecules

Isomers

• Molecules sharing the same atomic composition but differing in connectivity, leading to distinct properties

Structural Isomers

• Variations in bonding arrangements

Stereoisomers

• Variations in the spatial arrangement of groups

Positional Isomerism

• Distinguished by the placement of a functional group

Chain Isomerism

• Characterized by variations in the carbon backbone

Functional Isomerism

• Defined by differences in functional groups

Geometric Isomerism

• Same functional groups but different arrangements around a double bond
• Cis: groups are on the same side
• Trans: groups are on opposite sides

Enantiomers

• Display identical molecular formulas and connectivity but are non-superimposable mirror images of each other
• Commonly occur with asymmetrical carbons that bind to 4 distinct groups

Carbohydrates

• Composed of C, H, and O in the ratio of CnH2nOn
• Possess numerous hydroxyl and carbonyl groups, making them polar and water-soluble
• Serve as immediate energy sources and long-term energy storage
• Sugars and starches offer cells accessible energy

Monosaccharides

• Contain 3-7 carbon atoms
• An abundance of hydroxyl (OH) groups
• Water-soluble
• Examples include glucose, fructose, and galactose

Glucose Stereoisomers

• Hydroxyl (OH) group orientation on carbon 1 determines alpha or beta glucose
• Both forms are present when dissolved in water
• Alpha: OH on bottom
• Beta: OH on top

Disaccharides

• Formed when two monosaccharides are joined by a glycosidic linkage
• 1-4 linkages form chains
• 1-6 linkages form branches

Sugar Equations

• Glucose + Fructose = Sucrose
• Glucose + Glucose = Maltose
• Glucose + Galactose = Lactose

Amylose and Amylopectin

• Amylose is unbranched, comprising 20% of starch
• Amylopectin is branched, making up 80% of starch

Starch vs Glycogen

• Energy storage units, but glycogen's highly branched structure enables quicker energy breakdown due to increased surface area

Cellulose

• A Major plant cell wall component
• Contains beta-glycosidic bonds between glucose monomers, indigestible by humans
• Lacking the necessary enzyme to recognize these linkages, it provides no nutrient value but aids digestion
• High-fiber foods are rich in cellulose

Alpha vs Beta Glycosidic Linkage

• Alpha = OH groups of joining monomers have the same orientation
• Beta = OH groups of joining monomers have opposite orientation - one beta monomer must flip to align OH groups closer

Lipids

• Consist of C, H, and O, with a higher proportion of C and H and less O
• Serve as major energy storage molecules in animals due to energy-rich C-H bonds
• Yield twice the energy per gram compared to carbohydrates but are less accessible to cells due to hydrocarbon chains
• Hydrophobic but soluble in oils and nonpolar solvents
• Examples include oils, fats, waxes, phospholipids, and steroids

Lipid Functions

• Long-term energy storage
• Insulation
• Steroid hormone production
• Protection
• Major cell membrane component as phospholipids
• Provide water-repellent layers on fruits, leaves, fur, feathers

Triglycerides

• Formed from one glycerol molecule and three fatty acids
• Glycerol contains three carbons, each with an OH group
• Fatty acids are long hydrocarbons terminated by a carboxyl group
• Ester bond formation occurs between the hydroxyl group of glycerol and the carboxyl hydrogen of fatty acids, creating a triglyceride

Fatty Acid Types

• Saturated: contain only single bonds
• Monounsaturated: contain at least one double bond
• Polyunsaturated: contain two or more double bonds
• Trans: contain a trans double bond

Hydrogenation

• The process of adding hydrogen to convert liquid oil into solid fat
• Converts cis fats into trans fats

Phospholipids vs Triglycerides

• Phospholipids only have two fatty acids, whereas triglycerides have three
• The third fatty acid is replaced by phosphate and choline

Phospholipid Bilayer

• A cell membrane component
• Hydrophilic heads face the aqueous environment of the extracellular fluid and cytoplasm
• Hydrophobic tails form the interior

Steroids

• Lipids composed of four carbon-based rings
• The arrangement of carbon rings and the presence of functional groups determine the steroid type
• Examples: cholesterol, testosterone, estrogen, steroid ointments, and anabolic steroids

Waxes

• Solid at room temperature
• Plants produce them to coat leaf and fruit surfaces, preventing water loss and repelling insects
• Animals secrete it to provide water repellency on skin, fur, feathers, and insect exoskeletons

Explore the molecular chemistry of life, detailing the functions and interactions of essential biological compounds. Covers elements in living organisms, with a focus on key elements like carbon, hydrogen, and nitrogen. Discusses isotopes and radioisotopes, highlighting their significance in understanding matter.