Water Chemistry & Biological Macromolecules: Key Concepts for Biology

What makes water unique among compounds on Earth?

It remains a liquid over most of Earth's surface.

Why does oxygen attract electrons more strongly than hydrogen in water?

Oxygen's nucleus has 8 protons, giving it a stronger pull on electrons than hydrogen's single proton.

Why is water a polar molecule?

Because it has unevenly distributed charges—oxygen is partially negative and hydrogen is partially positive.

What does "polar" mean?

A molecule with unevenly distributed electrical charges.

What causes hydrogen bonds to form between water molecules?

Attraction between the partially positive hydrogen of one molecule and the partially negative oxygen of another.

Are hydrogen bonds strong or weak?

They are weak attractions.

What properties of water result from hydrogen bonding?

Expansion upon freezing, high solubility, cohesion, adhesion, and capillary action.

Why is ice less dense than liquid water?

Water expands slightly upon freezing.

What is cohesion?

Attraction between molecules of the same substance.

How does cohesion relate to surface tension?

Cohesion causes water molecules to be drawn together, creating surface tension.

What is adhesion?

Attraction between molecules of different substances.

How does adhesion explain the meniscus?

Water sticks to glass due to adhesion, pulling upward along the sides.

What is capillary action?

The movement of water upward in a narrow tube against gravity, caused by adhesion and cohesion.

What are isotopes?

Atoms of the same element with the same number of protons but different numbers of neutrons.

What is an ion?

An atom or molecule that has gained or lost electrons, resulting in a net electrical charge.

What is heat capacity?

The amount of energy required to raise a substance's temperature.

Why does water have a high heat capacity?

Hydrogen bonding absorbs heat energy, preventing rapid temperature changes.

How does water's high heat capacity affect aquatic life?

It keeps oceans and lakes at stable temperatures.

What is a mixture?

A combination of substances physically mixed but not chemically combined.

What are the two types of mixtures with water?

Solutions and suspensions.

What is a solution?

A homogeneous mixture where all components are evenly distributed.

What is a solute?

The substance that is dissolved.

What is a solvent?

The substance in which the solute dissolves.

Give an example of a solution.

Salt dissolved in water (saltwater).

What is a suspension?

A mixture where materials do not dissolve but remain suspended.

Give an example of a suspension.

Blood or muddy water.

What is a heterogeneous mixture?

A mixture where components are not evenly distributed, like salad or pizza.

How do water molecules form ions?

Water can split into H⁺ and OH⁻ ions.

Is pure water neutral, acidic, or basic?

Neutral, because it has equal H⁺ and OH⁻ ions.

What determines if a solution is acidic or basic?

The concentration of H⁺ ions.

What does a low pH indicate?

An acidic solution with many H⁺ ions.

What does a high pH indicate?

A basic solution with few H⁺ ions.

What element forms the basis of organic chemistry?

Carbon.

Why is carbon unique?

It has four valence electrons and can form single, double, or triple covalent bonds.

What structures can carbon form?

Chains, rings, and branching molecules.

What are hydrocarbons?

Molecules made only of carbon and hydrogen.

What are functional groups?

Groups of atoms that give molecules specific properties.

Name three common functional groups.

Amino (-NH₂), carboxyl (-COOH), phosphate (-PO₄³⁻).

What are macromolecules?

Large molecules made of smaller units called monomers.

What is polymerization?

The process of joining monomers together to form polymers.

What is the difference between synthesis and polymerization?

Synthesis forms any compound; polymerization specifically builds polymers.

List the four major macromolecules.

Carbohydrates, lipids, proteins, and nucleic acids.

What is the monomer of carbohydrates?

Simple sugars (monosaccharides).

What is the chemical ratio for carbohydrates?

1 carbon : 2 hydrogen : 1 oxygen.

What are the functions of carbohydrates?

Store and release energy; provide structure and protection.

Give examples of carbohydrates.

Sugar, starch, cellulose.

What is a disaccharide?

Two monosaccharides joined together, e.g., glucose + fructose = sucrose.

What is a polysaccharide?

Many sugars joined together, e.g., starch, cellulose, glycogen.

What is the monomer of lipids?

Fatty acids.

What are lipids made of?

Carbon, hydrogen, and oxygen; sometimes phosphorus or nitrogen.

Are lipids soluble in water?

No, they are hydrophobic and nonpolar.

What determines if a lipid is saturated or unsaturated?

The presence of double carbon bonds.

What is a polyunsaturated lipid?

A lipid with multiple double bonds.

What are lipids used for?

Energy storage, membranes, waterproofing, hormones.

Are lipids polymers?

No, they are made of different components (glycerol + fatty acids).

What is a triglyceride?

A lipid formed from glycerol and three fatty acids.

What is a phospholipid?

A lipid with a phosphate head and two fatty acid tails; major component of cell membranes.

What is cholesterol?

A waxy, fatlike substance used to build cell membranes and hormones.

What is the monomer of proteins?

Amino acids.

How many amino acids exist?

More than 20.

What elements do proteins contain?

C, H, O, N, and sometimes S.

What is a peptide bond?

A covalent bond joining amino acids.

What is a polypeptide?

A chain of amino acids.

What is a protein?

One or more polypeptides folded into a functional molecule.

What are some functions of proteins?

Enzymes, hormones, antibodies, and structural support.

What determines a protein's shape?

The sequence and interactions of amino acids.

List the four levels of protein structure.

Primary, secondary, tertiary, quaternary.

What happens in the primary structure?

Amino acids link in a specific sequence with peptide bonds.

What happens in the secondary structure?

Hydrogen bonds create coils (alpha helices) and folds (beta sheets).

What happens in the tertiary structure?

3D folding from hydrogen, ionic, and van der Waals interactions.

What is the quaternary structure?

Two or more polypeptides combine into a larger functional protein.

What is the monomer of nucleic acids?

Nucleotides.

What are the three parts of a nucleotide?

5-carbon sugar, phosphate group, and nitrogenous base.

What elements make up nucleic acids?

C, H, O, N, and P.

What does ATP do?

Captures and transfers chemical energy.

What are the two types of nucleic acids?

DNA and RNA.

What sugar does DNA contain?

Deoxyribose.

What sugar does RNA contain?

Ribose.

What are DNA's nitrogen bases?

A, T, C, G.

What are RNA's nitrogen bases?

A, U, G, C.

What is the structure of DNA?

Double-stranded, antiparallel, and twisted into a double helix.

What bonds connect DNA base pairs?

Hydrogen bonds.

Which bases pair in DNA?

A-T (2 bonds) and C-G (3 bonds).

What is hydrolysis?

The process of breaking polymers into monomers using water.

What is a chemical reaction?

A process that changes one set of compounds into another.

What are reactants and products?

Reactants enter a reaction; products are formed.

What happens to energy in chemical reactions?

It is released or absorbed when bonds are formed or broken.

What is an exothermic reaction?

A reaction that releases energy.

What is an endothermic reaction?

A reaction that absorbs energy.

What is a catalyst?

A substance that speeds up a chemical reaction by lowering activation energy.

What is an enzyme?

A biological catalyst made by living cells.

Are enzymes specific?

Yes, each enzyme catalyzes only one type of reaction.

What are substrates?

The reactants that bind to an enzyme's active site.

How do enzymes speed up reactions?

They bring reactants together and lower the activation energy.

What can affect enzyme activity?

Temperature and pH changes.

What happens if an enzyme is denatured?

Its active site changes shape and can no longer function.

What are anabolic enzymes?

Enzymes that build complex molecules from smaller ones.

What are catabolic enzymes?

Enzymes that break complex molecules into simpler ones.

What does lactase do?

Breaks down lactose.

What does sucrase do?

Breaks down sucrose.