Comprehensive Biology: Molecular Structures, Bonds, and Cell Functions

Compound

Atoms joined together by bonds.

Protons

The number of these particles determines atomic identity.

Electrons

Their arrangement determines bonding ability.

Properties

Characteristics of matter that depend on atomic composition and bonding.

Essential Elements

About 20-25% of naturally occurring ones are required for life.

CHON

Carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter.

Oxygen

This element is the most abundant in the human body.

Half-life

Time it takes for 50% of a radioactive sample to decay.

Radiometric Dating

Method that uses half-lives to estimate the age of material.

Shell Energy

When electrons drop levels, light energy is sometimes released.

Covalent Bond

Type of bond where two atoms share valence electrons.

Nonpolar Bond

Sharing of electrons occurs evenly between atoms.

Molecule

Two or more atoms held together by covalent bonds.

Single Bond

One pair of valence electrons is shared.

Double Bond

Two pairs of valence electrons are shared.

Electronegativity

Attraction of an atom for electrons in a bond.

Fluorine

Element with the strongest attraction for electrons.

Francium

Element with the weakest attraction for electrons.

Electron Pull

The higher the attraction, the more electrons are drawn in.

Hydrogen Bond

Attraction formed when hydrogen bonds with another element.

Cohesion

Water molecules bond to each other.

Adhesion

Water molecules bond to other substances.

Ionic Bond

Electrons are transferred to achieve stability.

Chemical Bonds

Can be weak or strong depending on type.

Trace Elements

Substances needed for life in very small amounts.

Isotopes

Radioactive forms used as tracers in metabolism.

Energy

Capacity to cause change.

Van der Waals

Weak attraction between oppositely charged regions of molecules.

Reactant

Substance present at the start of a chemical reaction.

Product

Material produced after a chemical reaction.

Reversible Reaction

Process shown by opposite arrows that can move in both directions.

Polarity

Unequal sharing of electrons makes water molecules have charged regions.

Ice Density

Solid water is less dense than liquid, allowing it to float.

Properties of Water

Key features include cohesion, temperature moderation, expansion upon freezing, and solvent abilities.

Surface Tension

Strong attraction at the surface caused by cohesive forces.

Xylem

Plant tissue that transports water upward.

Transpiration

Process where plants release water into the atmosphere.

Calorie

Amount of heat needed to raise 1g of water by 1°C.

Specific Heat

Water requires a large amount of energy to change temperature.

Bond Breaking

Energy is absorbed when hydrogen connections are disrupted.

Bond Forming

Energy is released when hydrogen connections are created.

Evaporative Cooling

As liquid leaves, the surface that remains becomes cooler.

Solvent

Water surrounds ions or molecules, allowing them to dissolve.

Hydrophilic

Substances that mix well with water.

Hydrophobic

Substances that avoid mixing with water.

Molecular Mass

Total of all atomic masses in a molecule.

Hydrogen Ion

Presence of this particle makes a solution acidic.

Hydroxide Ion

Presence of this particle makes a solution basic.

Reactivity

Both acidic and basic ions interact easily in chemical reactions.

Cell pH

Most living cells maintain a level near neutral.

Buffers

Substances that stabilize by releasing or absorbing H+ or OH-.

Ocean Acidification

Absorption of CO₂ lowers seawater pH.

Carbon Basis

The element forms the backbone of most biological molecules.

Four Bonds

This element always makes four covalent connections.

Ring Structures

Some molecules of this element can close into circular shapes.

Miller Experiment

Early Earth conditions produced amino acids from abiotic molecules.

Carbon Versatility

The diversity of life stems from the many ways this element bonds.

Valence Electrons

Four outer electrons allow complex bonding.

Bond Partners

Common elements that pair include hydrogen, oxygen, nitrogen, and itself.

Isomers

Same molecular formula but different structures cause different functions.

Structural Isomers

Variations arise from different atomic arrangements.

Cis-Trans Isomers

Variations depend on whether groups are on the same or opposite sides.

Enantiomers

Mirror-image molecules that may act differently in biology.

Ibuprofen

Only the S-form of this molecule is biologically effective.

Albuterol

Only the R-form of this molecule works effectively in medicine.

Functional Groups

Specific atom clusters that affect molecular properties and reactions.

Hydroxyl

Functional group found in alcohols.

Carbonyl

Carbon double-bonded to oxygen, found in ketones and aldehydes.

Ketone

Carbonyl group positioned internally in a molecule.

Aldehyde

Carbonyl group positioned externally in a molecule.

Amino

Group that is part of proteins and amino acids.

Sulfhydryl

Group containing sulfur and hydrogen.

Methyl

Group that can regulate genes by turning them off.

Carbohydrates

Sugars and starches built from carbon, hydrogen, and oxygen.

Proteins

Macromolecules made from amino acids.

Nucleic Acids

DNA and RNA, carrying genetic information.

Lipids

Fats and oils important for energy storage and membranes.

ATP

Molecule that stores and releases energy for cells.

ADP

Form created when one phosphate group is removed.

AMP

Form created when two phosphate groups are removed.

Phosphate Break

Energy is released when bonds between phosphate groups are broken.

Hidden Hydrogens

When carbon lacks bonds, assume hydrogen atoms fill them.

Alcohol Dehydrogenase

Enzyme that helps break down alcohol in the body.

Monosaccharide

Single sugar molecule serving as a basic energy source.

Polysaccharide

Long chains of sugar molecules linked together.

Glycosidic Linkage

Bond formed between two monosaccharides.

Storage Polysaccharides

Sugars stored in molecules such as starch and glycogen.

Structural Polysaccharides

Sugars arranged for support, like cellulose and chitin.

Starch

Plant polysaccharide that stores energy.

Glycogen

Animal polysaccharide used for energy storage.

Cellulose

Plant structural polysaccharide forming cell walls.

Chitin

Polysaccharide found in arthropod exoskeletons and fungi.

Fats

Molecules constructed of glycerol and fatty acids.

Triacylglycerol

Three fatty acids attached to one glycerol.

Dehydration Synthesis

Formation of triacylglycerol releases three water molecules.

Saturated Fat

Type of fat with only single carbon bonds, solid at room temperature.

Unsaturated Fat

Type of fat with double bonds, liquid at room temperature.

Phospholipid

Molecule with hydrophilic heads and hydrophobic tails forming membranes.

Steroids

Lipids with a carbon skeleton of four fused rings.

Cholesterol

Steroid important for cell membranes and hormone synthesis.