Chapter 2: The Chemical Level of Organization

Comprehensive vocabulary flashcards covering the chemical level of organization, including atomic structure, chemical bonding, reactions, water and pH balance, and major biomolecules.

Matter

Anything that has mass and takes up space, existing in three forms: solid, liquid, and gas.

Major Elements of the Body

The four chemical elements—oxygen, carbon, hydrogen, and nitrogen—that account for over $96\%$ of total body mass.

Atomic nucleus

The central core of an atom that contains protons ($p^+$) and neutrons ($n^0$), accounting for most of the atomic mass.

Electron shells

Regions of space surrounding the atomic nucleus where negatively charged electrons ($e^-$) are found.

Atomic number

The total number of protons found in the nucleus of an atom.

Mass number

The combined total number of protons and neutrons in an atom.

Atomic mass

The average mass of all stable atoms of a given element, measured in daltons.

Isotope

Atoms of the same element that have the same number of protons but differ in their number of neutrons, resulting in a different mass but identical chemical reactivity.

Molecule

A chemical unit created when two or more atoms share electrons.

Compound

A molecule that contains two or more different chemical elements.

Valence electrons

Electrons residing in the outermost electron shell that determine the chemical reactivity of an atom.

Octet rule

The principle that atoms generally interact so that their outermost or valence electron shell is filled with $8$ electrons.

Ion

An atom that has gained or lost one or more electrons, giving it a net electrical charge.

Cation

A positively charged ion formed when an atom loses an electron (e.g., $Na^+$, $K^+$, $Ca^{2+}$).

Anion

A negatively charged ion formed when an atom gains an electron (e.g., $Cl^-$, $Br^-$).

Ionic bond

A chemical bond formed by the electrostatic attraction between oppositely charged cations and anions.

Electrolytes

Separate dissolved ions produced when ionic compounds dissociate in water.

Covalent bond

A chemical bond formed when two atoms share one, two, or three pairs of valence electrons.

Non-polar covalent bond

A covalent bond formed when two atoms attract and share electrons equally.

Polar covalent bond

A covalent bond formed when one atom attracts the shared electrons much more strongly than the other, resulting in unequal charge distribution.

Hydrogen bond

A weak electrostatic bond formed when a partial positive charge on a hydrogen atom in one molecule is attracted to a partial negative charge in another molecule.

Chemical energy

A form of potential energy stored within the chemical bonds of compounds and molecules.

Kinetic energy

The energy of motion; in reactions, released bond energy becomes the kinetic energy of moving atoms.

Exergonic reaction

A chemical reaction that results in a net release of stored chemical energy.

Endergonic reaction

A chemical reaction that requires a net input and storage of energy.

Activation energy

The minimum amount of energy colliding reactants must possess to break existing bonds and initiate a chemical reaction.

Catalyst

A substance, such as an enzyme, that accelerates a chemical reaction by lowering the required activation energy.

Synthesis reaction

A chemical reaction in which two or more atoms or molecules combine to build larger chemical products.

Anabolism

The collective term for all the synthesis reactions occurring in the human body.

Decomposition reaction

A chemical reaction in which larger molecules split apart into smaller molecules or individual atoms.

Catabolism

The collective term for all the decomposition reactions occurring in the human body.

Exchange reaction

A reaction involving both synthesis and decomposition; it represents the most common reaction type in the human body.

Inorganic compound

A structurally simple chemical substance held together by ionic or covalent bonds that usually lacks carbon atoms (e.g., $NaCl$).

Organic compound

A complex chemical compound that always contains carbon, often contains hydrogen, and relies on covalent bonds (e.g., $C_6H_{12}O_6$).

Acid

An inorganic compound that dissociates in water to release one or more hydrogen ions ($H^+$).

Base

An inorganic compound that dissociates in water to release one or more hydroxide ions ($OH^-$).

Salt

An inorganic compound that dissociates into cations and anions in water, neither of which is $H^+$ or $OH^-$.

pH scale

A logarithmic numerical scale extending from $0$ to $14$ that reflects the concentration of hydrogen ions ($H^+$) in a solution.

Buffer

A chemical compound that stabilizes pH by converting strong acids and bases into weak ones by donating or removing protons ($H^+$).

Carbonic acid/bicarbonate buffer system

A vital physiological buffer mechanism ($H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$) that shifts to donate or absorb $H^+$ to prevent large changes in fluid pH.

Dehydration synthesis

A chemical reaction that joins two smaller molecules (monomers) into a larger product while generating a water molecule ($H_2O$).

Hydrolysis

A decomposition reaction that breaks chemical bonds in polymers through the addition of a water molecule ($H_2O$).

Carbohydrate

An organic molecule composed of carbon, hydrogen, and oxygen that primarily serves as a cellular fuel source for generating ATP.

Monosaccharide

A single-sugar monomer that serves as the basic building unit of carbohydrates (e.g., glucose, fructose).

Disaccharide

A sugar molecule formed by combining two monosaccharides via dehydration synthesis (e.g., lactose, sucrose).

Polysaccharide

A large carbohydrate polymer composed of many monosaccharide units linked together through dehydration synthesis reactions.

Glycogen

A highly branched polysaccharide that functions as the principal storage form of glucose in the human body.

Lipid

A diverse class of hydrophobic, non-polar organic molecules consisting mainly of carbon and hydrogen atoms with few oxygen atoms.

Fatty acid

The simplest lipid type, consisting of a non-polar hydrocarbon chain attached to a carboxylic acid group.

Saturated fatty acid

A fatty acid whose hydrocarbon chain contains only single carbon-carbon bonds and is fully saturated with hydrogen atoms.

Unsaturated fatty acid

A fatty acid whose hydrocarbon chain contains one or more carbon-carbon double bonds.

Triglyceride

A lipid composed of three fatty acid molecules attached to a single glycerol molecule; serves as a concentrated form of stored chemical energy.

Phospholipid

A diglyceride containing a polar head group and two non-polar fatty acid tails that forms the structural bilayer of cell membranes.

Steroid

A lipid composed of four interconnected carbon rings, synthesized from cholesterol and functioning in membrane structure, signaling, or digestion.

Protein

A complex macromolecule constructed from amino acid polymers that performs structural, regulatory, contractile, immunological, transport, and catalytic functions.

Amino acid

The monomer of proteins, containing an amino group, a carboxylic acid group, and a variable side chain ($R$ group).

Peptide bond

The covalent bond that links the amino group of one amino acid to the carboxyl group of another via dehydration synthesis.

Primary structure of a protein

The unique linear sequence of amino acids linked together by peptide bonds in a polypeptide chain.

Secondary structure of a protein

The localized twisting and folding of the polypeptide backbone into alpha helices or beta pleated sheets, stabilized by hydrogen bonds.

Tertiary structure of a protein

The overall three-dimensional shape of a polypeptide chain, maintained by disulfide bridges, hydrogen bonds, ionic bonds, and hydrophobic interactions between $R$ groups.

Quaternary structure of a protein

The structural arrangement that arises when two or more individual polypeptide chains interact to form a functional complex.

Enzyme

A protein catalyst that increases the rate of specific biochemical reactions without being consumed or permanently altered.

Active site

The specific region on an enzyme where substrate molecules bind to form an enzyme-substrate complex.

Nucleotide

The monomeric subunit of nucleic acids, consisting of a nitrogenous base, a five-carbon sugar, and a phosphate group ($PO_4^{3-}$).

Deoxyribonucleic acid (DNA)

A double-stranded helical nucleic acid polymer that stores genetic instructions organized into segments called genes.

Ribonucleic acid (RNA)

A nucleic acid polymer involved in gene expression and protein synthesis that translates genetic coding from DNA.

Adenosine triphosphate (ATP)

The principal cellular energy currency, consisting of adenine, ribose, and three phosphate groups, which stores and transfers energy between reactions.