Life and Its Chemistry

Fundamental Characteristics of Life

Understanding what defines life is essential in biology. Life is characterized by several fundamental properties that distinguish living organisms from non-living matter.

• Order: Living things exhibit complex organization.

• Regulation: Homeostasis maintains stable internal conditions.

• Growth and Development: Organisms grow and develop according to genetic instructions.

• Energy Processing: Living things acquire and use energy.

• Response to Environment: Organisms respond to stimuli.

• Reproduction: Life reproduces itself.

• Evolutionary Adaptation: Populations evolve over generations.

Scientific Theory and Hypothesis

Science relies on systematic investigation and explanation of natural phenomena.

• Scientific Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence and repeatedly tested.

• Hypothesis: A testable statement or prediction about a natural phenomenon.

• Spontaneous Generation: The disproven idea that life can arise from non-living matter.

• Central Dogma of Biology: Describes the flow of genetic information: DNA → RNA → Protein.

Atoms and Subatomic Particles

Atoms are the basic units of matter, composed of subatomic particles with distinct properties.

• Protons: Positively charged particles in the nucleus.

• Neutrons: Neutral particles in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus.

• Atomic Number: Number of protons in an atom; defines the element.

• Mass Number: Sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Electron Configuration: Arrangement of electrons determines chemical properties.

Elements Essential to Life

Life depends on a small subset of elements, with a few making up the majority of living matter.

• Major Elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N) make up ~96% of living matter.

• Trace Elements: Required in small amounts (e.g., iron, iodine).

Covalent Bonds and Molecules

Covalent bonds are strong chemical bonds formed by the sharing of electron pairs between atoms.

• Single Covalent Bond: Sharing one pair of electrons.

• Double Covalent Bond: Sharing two pairs of electrons.

• Triple Covalent Bond: Sharing three pairs of electrons.

• Polar Covalent Bond: Electrons are shared unequally, leading to partial charges.

• Nonpolar Covalent Bond: Electrons are shared equally.

• Valence: Number of covalent bonds an atom can form, typically determined by the number of unpaired electrons in the valence shell.

Example: Water (H2O) has polar covalent bonds; methane (CH4) has nonpolar covalent bonds.

Water

Structure and Properties of Water

Water is vital for life due to its unique chemical and physical properties.

• Polarity: Water molecules have a partial positive charge on hydrogen and a partial negative charge on oxygen.

• Hydrogen Bonds: Weak attractions between the hydrogen atom of one water molecule and the oxygen atom of another.

• Cohesion: Water molecules stick to each other.

• Adhesion: Water molecules stick to other substances.

• High Specific Heat: Water resists temperature changes.

• Solvent Properties: Water dissolves many substances due to its polarity.

Example: Water's ability to dissolve salts and sugars makes it an excellent medium for biological reactions.

Hydrogen Bonds in Water

• Each water molecule can form up to four hydrogen bonds with neighboring water molecules.

• Hydrogen bonds are responsible for water's high boiling point and surface tension.

Hydrophilic vs. Hydrophobic Substances

• Hydrophilic: Substances that interact well with water (e.g., salts, sugars).

• Hydrophobic: Substances that do not interact well with water (e.g., oils, fats).

Water as a Solvent

• Water's polarity allows it to dissolve ionic and polar substances.

• Nonpolar molecules do not dissolve well in water.

Predicting Polarity

• Organic molecules with many polar bonds (O-H, N-H) are likely to be polar.

• Nonpolar molecules have mostly C-H or C-C bonds.

Acids and Bases

Definitions and Properties

Acids and bases are important in biological systems for maintaining pH and facilitating chemical reactions.

• Acid: Substance that donates protons (H+).

• Base: Substance that accepts protons or donates hydroxide ions (OH-).

• pH Scale: Measures the concentration of H+ ions in solution.

Equation:

• Low pH (0-6): Acidic

• pH 7: Neutral

• High pH (8-14): Basic

Acid-Base Reactions

• Acids increase H+ concentration; bases decrease it.

• When acids lose a proton, they become negatively charged; when bases gain a proton, they become positively charged.

Macromolecules

Monomers and Polymers

Biological macromolecules are large molecules made by joining smaller units called monomers.

• Monomer: Small, repeating unit (e.g., glucose, amino acid, nucleotide).

• Polymer: Large molecule made of many monomers (e.g., starch, protein, DNA).

• Polymerization: Process of joining monomers to form polymers.

• Dehydration Synthesis: Reaction that links monomers by removing water.

Example: Proteins are polymers of amino acids; nucleic acids are polymers of nucleotides.

Table: Comparison of Covalent Bonds in Carbon Compounds

Additional info:

• Some context and definitions have been expanded for clarity and completeness.

• Examples and equations have been added to support understanding.