Unit 0: The Chemical Context of Life

Flashcards testing core concepts of chemical bonds, water properties, pH, functional groups, and biological macromolecules based on AP Biology Topic 1 notes.

What four elements make up $96\%$ of living matter?

Carbon, Hydrogen, Oxygen, and Nitrogen make up $96\%$ of living matter.

How do protons, electrons, and neutrons differ in charge and location within an atom?

Protons are positively charged ($+$) and located in the nucleus; electrons are negatively charged ($-$) and located in electron shells around the nucleus; neutrons have no charge and are located in the nucleus.

What are isotopes, and how do carbon-12 and carbon-14 illustrate this concept?

Isotopes are forms of an element with differing numbers of neutrons. Carbon-12 and carbon-14 both have 6 protons, but carbon-12 has 6 neutrons while carbon-14 has 8 neutrons.

What is the difference between nonpolar covalent bonds and polar covalent bonds?

Nonpolar covalent bonds occur when valence electrons are shared equally between atoms. Polar covalent bonds occur when one atom is more electronegative, resulting in unequal sharing of electrons.

How do ionic bonds form between atoms?

Ionic bonds form when two atoms attract valence electrons so unequally that the more electronegative atom steals an electron from the less electronegative atom, forming oppositely charged ions that attract each other.

What are hydrogen bonds and where do they play a critical role in biological macromolecules?

Hydrogen bonds are weak bonds formed between a partial positively charged hydrogen atom of one molecule and a strongly electronegative oxygen or nitrogen atom of another. They play a major role in the three-dimensional shape of proteins and nucleic acids.

How do cohesion and adhesion differ regarding water molecules?

Cohesion is the linking of like water molecules to each other (e.g., surface tension). Adhesion is the clinging of water molecules to a different substance (e.g., water clinging to xylem tube walls).

How does water's high specific heat contribute to life on Earth?

Specific heat is the amount of heat required to raise or lower the temperature of a substance by $1^\circ\text{C}$. Water's high specific heat resists rapid temperature changes, keeping ocean temperatures relatively stable to support aquatic life.

Why does ice float, and why is this property essential for aquatic ecosystems?

Water is less dense as a solid than as a liquid, causing ice to float. Floating ice insulates bodies of water underneath and prevents them from freezing solid, allowing aquatic life to survive.

How do acidic and basic solutions differ in terms of pH and ion concentration?

Acidic solutions have an excess of $\text{H}^+$ ions and a pH below $7.0$. Basic solutions have an excess of $\text{OH}^-$ ions and a pH above $7.0$.

What is the function of buffers in biological systems, and what is a primary example in blood plasma?

Buffers minimize changes in pH by accepting $\text{H}^+$ ions when in excess and donating $\text{H}^+$ ions when depleted. Carbonic acid ($\text{H}_2\text{CO}_3$) is a key buffer in blood plasma and the ocean.

What chemical properties of carbon allow it to form diverse biological molecules?

Carbon has 4 valence electrons, can form up to 4 covalent bonds (single, double, or triple), and can build large structures shaped as chains, rings, or branches.

What are isomers?

Isomers are molecules that share the same molecular formula but differ in the spatial arrangement of their atoms, resulting in different biological properties.

How do dehydration synthesis reactions and hydrolysis reactions differ?

Dehydration synthesis joins monomers into polymers by removing a water molecule. Hydrolysis breaks polymers down into monomers by adding a water molecule.

How do the linkages in starch and cellulose differ, and how does this affect human digestion?

Starch contains $1\text{-}4\ \alpha$ linkages while cellulose contains $1\text{-}4\ \beta$ linkages. Humans possess enzymes to digest the $1\text{-}4\ \alpha$ linkages of starch, but cannot digest the $1\text{-}4\ \beta$ linkages of cellulose.

What is the structural difference between saturated and unsaturated fatty acids?

Saturated fatty acids have no carbon-carbon double bonds and pack solidly at room temperature. Unsaturated fatty acids contain one or more double bonds ($\text{C=C}$), creating kinks that keep them liquid at room temperature.

How are phospholipids arranged in a cell membrane?

Phospholipids form a bilayer with their hydrophilic (polar) phosphate heads facing outward toward the aqueous environment/cytosol and their hydrophobic fatty acid tails sandwiched in the interior.

What are the four structural levels of proteins?

Primary (unique amino acid sequence), Secondary ($\alpha$ helix or $\beta$ pleated sheet via backbone hydrogen bonding), Tertiary (3D globular shape from R group interactions), and Quaternary (association of two or more polypeptide chains).

What happens when a protein undergoes denaturation?

Denaturation occurs when a protein loses its specific shape and biological function due to environmental factors such as excess heat or changes in pH.

What three components make up a nucleotide monomer?

A nucleotide consists of a nitrogenous base, a pentose (5-carbon) sugar, and a phosphate group.

What structural differences distinguish DNA from RNA?

DNA is double-stranded, contains deoxyribose sugar, and uses thymine. RNA is single-stranded, contains ribose sugar, and uses uracil instead of thymine.