AP Biology Unit 1: Chemistry of Life

Comprehensive practice flashcards covering AP Biology Unit 1: Chemistry of Life, including the characteristics of life, atomic structure, chemical bonding, emergent properties of water, acid-base balance, carbon chemistry, functional groups, and the structure and function of biological macromolecules.

MR. GRECH

A biological mnemonic identifying the seven characteristics of life: metabolism, response to stimuli, growth, reproduction, evolving, cellular organization, and homeostasis.

Homeostasis

The physiological maintenance of a stable, dynamic internal state despite external fluctuations, mediated by feedback mechanisms.

Structure Determines Function Principle

The rule that the 3D molecular architecture and physical construction of a biological entity directly govern its specific activity.

Levels of Biological Organization

The structural hierarchy of life progressing from atoms and molecules up to cells, tissues, organs, organ systems, and complex multicellular organisms.

Matter and Elements

Any physical substance occupying space and having mass, occurring as pure substances that cannot be broken down chemically.

Essential Elements vs. Trace Elements

Substances required in large quantities ($C$, $H$, $O$, and $N$, comprising $96\%$ of biomass) versus those needed in minute amounts (under $0.01\%$).

Subatomic Particles

Protons ($+1$) and neutral neutrons clustered in the central nucleus, surrounded by an electron cloud of orbiting negative particles ($-1$).

Atomic Number vs. Mass Number

The specific proton count identifying a chemical element versus the total sum of protons and neutrons in its nucleus.

Isotopes

Forms of an element with identical proton counts but different neutron counts, changing physical mass without altering chemical reactivity.

Half-Life and Radiometric Dating

The fixed time for $50\%$ of a radioactive parent isotope to decay, used as a molecular clock to date fossils and geological strata.

Electron Shells and Potential Energy

Energy levels around a nucleus where electrons farther away hold greater potential energy, absorbing energy to move out and releasing energy to fall in.

Valence Electrons

Electrons in the outermost shell that participate in chemical bonding and dictate an atom's reactivity and valence capacity.

Covalent Bond

A strong, durable linkage formed when two nonmetal atoms share one or more pairs of valence electrons.

Single, Double, and Triple Covalent Bonds

Linkages sharing $2$, $4$, or $6$ valence electrons respectively, showing progressively greater bond strength and shorter bond length.

Electronegativity

The relative pulling power an atom exerts to attract shared valence electrons within a covalent chemical bond.

Nonpolar Covalent Bond

A linkage formed between atoms of similar electronegativity, producing an equal distribution of electron density and no partial charges.

Polar Covalent Bond

A bond where unequal electron sharing produces partial positive ($\delta^+$) and partial negative ($\delta^-$) charges across the atoms.

Ionic Bond

An electrostatic attraction resulting from the complete transfer of valence electrons from a metal to an electronegative nonmetal.

Cation vs. Anion

A positively charged ion formed by losing electrons versus a negatively charged ion formed by gaining electrons.

Salt (Ionic Compound)

A crystalline lattice of alternating cations and anions held by ionic bonds that readily dissociates into solvated ions in water.

Van der Waals Interactions

Weak, transient intermolecular forces caused by fluctuating electron clouds that create momentary dipoles and surface adhesion.

Chemical Equilibrium

A dynamic reaction state where forward and reverse reaction rates are identical, stabilizing reactant and product concentrations at a constant ratio.

Polar Nature of Water

An asymmetrical V-shaped geometry and large electronegativity difference creating a permanent dipole with negative oxygen and positive hydrogens.

Hydrogen Bond

A weak electrostatic attraction between an electronegative atom and a hydrogen atom already covalently linked to $O$ or $N$.

Cohesion of Water

The intermolecular property whereby water molecules stick to one another through an extensive, shifting hydrogen bond network.

Adhesion of Water

The electrostatic attraction of water molecules to foreign polar or electrically charged surfaces, such as plant xylem walls.

Surface Tension

The resistance of a liquid surface to stretching or breaking, heightened in water by cohesive lateral and downward hydrogen bonding.

Capillary Action

The spontaneous movement of liquid through narrow spaces driven by adhesion pulling upward while cohesion holds the column intact.

High Specific Heat of Water

The capacity requiring $1\,\text{cal/g/}^\circ\text{C}$ to adjust temperature, absorbing or releasing heat to break or form hydrogen bonds.

Heat of Vaporization of Water

The large quantity of thermal energy ($580\,\text{cal}$ per gram at $25\,^\circ\text{C}$) needed to break hydrogen bonds and convert liquid into vapor.

Evaporative Cooling

The cooling of a liquid surface when molecules with the highest kinetic energy escape as gas, facilitating biological thermoregulation.

Expansion and Lower Density of Ice

when water freezes, hydrogen bonds form an open crystalline lattice, causing expansion and making ice roughly 10% less dense than liquid water

Versatility of Water as a Solvent

The ability of water to dissolve various ionic and polar solutes by using its partial charges to disrupt solute-solute interactions.

Hydration Shell

A concentric sphere of oriented water molecules that surrounds, separates, and shields individual dissolved ions or polar molecules.

Hydrophilic vs. Hydrophobic

Substances that attract water and dissolve via polar/ionic interactions versus nonpolar molecules that repel water and aggregate together.

Amphipathic Molecule

A compound possessing both a hydrophilic polar/charged domain and a hydrophobic nonpolar hydrocarbon tail, such as a phospholipid.

Dynamic Dissociation of Water

The reversible reaction generating hydronium ($\text{H}_3\text{O}^+$) and hydroxide ($\text{OH}^-$) ions at $10^{-7}\,\text{M}$ in pure water at $25\,^\circ\text{C}$.

Acid vs. Base

A solute that donates protons to increase $[\text{H}^+]$ versus a solute that reduces $[\text{H}^+]$ by accepting protons or releasing $\text{OH}^-$.

pH Scale

A logarithmic measure defined by $\text{pH} = -\log[\text{H}^+]$, where each single whole unit represents a tenfold decrease in hydrogen ion concentration.

Carbonic Acid-Bicarbonate Buffer System

The blood equilibrium ($\text{H}_2\text{CO}_3 \rightleftharpoons \text{HCO}_3^- + \text{H}^+$) that resists pH shifts in plasma by absorbing or releasing protons.

Tetravalence of Carbon

The presence of four valence electrons allowing the formation of four stable covalent bonds in a tetrahedral arrangement with $109.5^\circ$ angles.

Abiotic Synthesis and the Miller-Urey Experiment

A 1953 simulation showing that sparks acting on a reducing inorganic atmosphere can spontaneously produce organic monomers like amino acids.

Hydrocarbons

Nonpolar organic compounds consisting solely of carbon and hydrogen that are hydrophobic and store large amounts of energy.

Structural Isomers

Compounds sharing identical molecular formulas that differ in the covalent arrangement and branching patterns of their carbon skeletons.

Cis-Trans Isomers

Stereoisomers that share covalent bonds but differ in spatial orientation of groups around an inflexible, non-rotating double bond.

Enantiomers

Chiral stereoisomers that are non-superimposable mirror images around an asymmetric carbon, where usually only one form is active.

Hydroxyl Group ($-\text{OH}$)

A polar functional group characteristic of alcohols that forms hydrogen bonds and enhances the water solubility of organic molecules.

Carbonyl Group ($>\text{C}=\text{O}$)

A polar functional group with oxygen double-bonded to carbon, forming an aldehyde at the chain end or a ketone within the skeleton.

Carboxyl Group ($-\text{COOH}$)

An acidic functional group containing carbonyl and hydroxyl motifs that donates a proton to form a negatively charged carboxylate ion.

Amino Group ($-\text{NH}_2$)

A basic functional group containing nitrogen bonded to two hydrogens that accepts a proton from solution to become $-{\text{NH}}_3^+$.

Sulfhydryl Group ($-\text{SH}$)

A functional group characteristic of thiols like cysteine, capable of forming covalent disulfide bridges that stabilize protein structures.

Phosphate Group ($-\text{OPO}_3^{2-}$)

A negatively charged functional group linking nucleic acids and enabling high-energy transfers in molecules like ATP.

Methyl Group ($-\text{CH}_3$)

A nonpolar, hydrophobic hydrocarbon tag added to DNA and proteins that modulates gene expression without acid-base activity.

Adenosine Triphosphate (ATP)

An organic nucleoside linked to three phosphate groups whose exergonic hydrolysis to ADP and $\text{P}_i$ powers cellular work.

Functional Groups' Impact on Polarity

The mechanism where polar or charged chemical groups turn nonpolar hydrocarbon skeletons into hydrophilic, water-soluble biomolecules.

Macromolecules, Monomers, and Polymers

Large cellular structures assembled by linking small repeating subunit building blocks into long covalent chains.

Dehydration Synthesis (Condensation Reaction)

An enzymatic anabolic reaction assembling polymers from monomers by forming a covalent bond with the concurrent loss of water.

Hydrolysis Reaction

An enzymatic catabolic reaction splitting polymers into smaller subunits through the chemical insertion of a water molecule.

Enzymatic Catalysis in Polymerization

The biological acceleration of macromolecular condensation and breakdown reactions by protein catalysts that remain unchanged.

Monosaccharide

The simplest carbohydrate monomer, fitting the formula $(\text{CH}_2\text{O})$, with a carbonyl and multiple hydroxyl groups forming rings in water.

Aldose vs. Ketose Sugars

Carbohydrate classification depending on whether the carbonyl group is located at the terminal carbon or within the internal carbon chain.

Disaccharide

A double sugar formed when two monosaccharides join through a dehydration reaction, such as maltose, sucrose, or lactose.

Glycosidic Linkage

A covalent ether bond formed between two monosaccharides during an enzymatic condensation reaction.

Starch (Amylose and Amylopectin)

A plant storage polysaccharide of $\alpha\text{-glucose}$ monomers arranged in helical chains with $1\text{-}4$ and $1\text{-}6$ branch points.

Glycogen

A highly branched glucose storage polysaccharide deposited in animal liver and muscle tissues for rapid glucose release.

Cellulose and Chitin

Structural polysaccharides: unbranched $\beta\text{-glucose}$ in plant cell walls, and nitrogenous units in arthropod exoskeletons and fungi.

Lipids Overview

A varied group of non-polymeric, hydrophobic biomolecules built predominantly from hydrocarbons, including fats, phospholipids, and steroids.

Triacylglycerol (Fat)

A storage lipid formed by linking three fatty acid hydrocarbon chains to a three-carbon glycerol molecule via ester bonds.

Saturated Fatty Acids

Fatty acid chains lacking carbon-carbon double bonds, maximizing hydrogen atoms and packing closely to stay solid at room temperature.

Unsaturated Fatty Acids

Fatty acid chains containing one or more cis double bonds that form kinks, preventing tight packing and keeping the lipid liquid.

Trans Fats

Synthetically hydrogenated lipids with trans double bonds that allow linear packing, extending shelf life while increasing heart disease risk.

Phospholipid Architecture

An amphipathic membrane lipid containing a polar phosphate head and two nonpolar fatty acid tails joined to glycerol.

Steroids and Cholesterol

Lipids composed of a carbon skeleton with four fused rings, functioning as membrane fluidity buffers and hormone precursors.

Amino Acid Structure

A protein monomer comprising an asymmetric alpha carbon bonded to an amino group, carboxyl group, hydrogen, and a variable R group.

Amino Acid Side Chain Classification (R Groups)

The grouping of protein monomers into nonpolar, polar uncharged, acidic (negative), and basic (positive) classes based on side-chain traits.

Peptide Bond Formation

The covalent link created when dehydration synthesis connects the carboxyl carbon of one amino acid to the amino nitrogen of another.

Polypeptide Directionality

The structural polarity of an amino acid chain, oriented from an initial free N-terminus to a terminating free C-terminus.

Primary Structure of Proteins

The linear sequence of amino acids linked by peptide bonds, directly encoded by an organism's genetic material.

Secondary Structure of Proteins

Localized folding patterns ($\alpha\text{-helices}$ and $\beta\text{-pleated sheets}$) stabilized by hydrogen bonds between backbone atoms.

Tertiary Structure of Proteins

The overall 3D folding of a single polypeptide chain determined by interactions among variable R groups, including disulfide bridges.

Quaternary Structure of Proteins

The multi-subunit functional protein complex formed by the association of two or more folded polypeptide chains.

Protein Denaturation and Renaturation

The loss of native 3D conformation and function caused by extreme pH, temperature, or salt, which may sometimes be reversed.

Sickle-Cell Disease Molecular Basis

A genetic condition where substituting hydrophobic valine for hydrophilic glutamic acid in $\beta\text{-globin}$ deforms red blood cells.

Nucleotide Monomer

The subunit of nucleic acids, consisting of a five-carbon pentose sugar, a nitrogenous base, and one to three phosphate groups.

Pyrimidines vs. Purines

Single six-membered nitrogenous base rings (cytosine, thymine, uracil) versus fused six- and five-membered double rings (adenine, guanine).

Phosphodiester Linkages and Backbone Directionality

Covalent bonds linking a $3'\text{-OH}$ group to a $5'\text{-phosphate}$ group, forming a directional sugar-phosphate backbone running $5' \rightarrow 3'$.

Antiparallel Double Helix of DNA

The duplex structure of DNA where complementary strands wind around a helical axis in opposite directions ($5' \rightarrow 3'$ and $3' \rightarrow 5'$).

Complementary Base Pairing

Specific hydrogen bonding matching adenine to thymine (two bonds) and guanine to cytosine (three bonds) across nucleic acid strands.

Structural Differences Between DNA and RNA

Deoxyribose, thymine, and double strands in DNA versus ribose ($2'\text{-OH}$), uracil, and versatile single strands in RNA.

Molecular Genealogy and Evolutionary Analysis

The comparison of DNA and protein sequence alignments across taxa to measure evolutionary divergence and determine common ancestry.