Chapter 2: The Chemistry of Life – Study Notes

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Chapter 2: The Chemistry of Life

Atomic Structure and Subatomic Particles

The atom is the fundamental unit of matter, composed of a central nucleus containing protons and neutrons, surrounded by electrons in orbitals.

Protons: Positively charged particles found in the nucleus.
Neutrons: Neutral particles found in the nucleus.
Electrons: Negatively charged particles found in orbitals around the nucleus.
Atomic Number: Number of protons in an atom, determines the element.
Mass Number: Sum of protons and neutrons.

Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Chemical Bonds

Chemical bonds are forces that hold atoms together in compounds. The main types are:

Ionic Bonds: Formed when electrons are transferred from one atom to another, creating ions (e.g., NaCl).
Covalent Bonds: Formed when atoms share electrons (e.g., H2O).
Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Example: Table salt (NaCl) is held together by ionic bonds; water molecules are held together by covalent bonds and interact via hydrogen bonds.

Ions: Cations and Anions

Ions are charged atoms or molecules formed by the loss or gain of electrons.

Cation: Positively charged ion (e.g., Na+).
Anion: Negatively charged ion (e.g., Cl-).

Example: In NaCl, Na+ is a cation and Cl- is an anion.

Distribution of Sodium and Potassium

Sodium (Na+) and potassium (K+) ions are unevenly distributed across cell membranes, essential for nerve impulse transmission and muscle contraction.

Sodium: Higher concentration outside cells.
Potassium: Higher concentration inside cells.

Exergonic vs. Endergonic Reactions

Chemical reactions can either release or absorb energy.

Exergonic Reactions: Release energy (e.g., cellular respiration).
Endergonic Reactions: Absorb energy (e.g., photosynthesis).

Catabolic vs. Anabolic Reactions

Metabolism includes both breakdown and synthesis of molecules.

Catabolic Reactions: Break down molecules, releasing energy (e.g., hydrolysis).
Anabolic Reactions: Build larger molecules from smaller ones, requiring energy (e.g., protein synthesis).

Types of Chemical Reactions

Decomposition (Hydrolysis): A molecule is broken down into smaller components by adding water.
Synthesis (Dehydration Synthesis): Two molecules combine to form a larger molecule, releasing water.

Factors Affecting Reaction Rates

Temperature: Higher temperature increases reaction rate.
Concentration: Higher concentration of reactants increases rate.
Catalysts: Enzymes speed up reactions.
Particle Size: Smaller particles react faster.

Enzymes: Function and Characteristics

Enzymes are biological catalysts that speed up chemical reactions without being consumed.

Specificity: Each enzyme acts on a specific substrate.
Active Site: Region where substrate binds.
Lower Activation Energy: Enzymes reduce the energy needed for reactions.

Enzyme Catalysis

Enzymes catalyze reactions by binding substrates, forming an enzyme-substrate complex, and converting substrates into products.

Metabolic Pathways

A metabolic pathway is a series of enzyme-catalyzed reactions where the product of one reaction becomes the substrate for the next. These pathways allow for regulation and efficiency in cellular metabolism.

Properties and Distribution of Water

Water is the most abundant compound in living organisms, essential for life due to its unique properties.

Polarity: Water molecules have a partial positive and negative end.
Cohesion and Adhesion: Water molecules stick to each other and to other substances.
Solvent: Dissolves many substances, facilitating chemical reactions.

Solutions, Solvents, and Solutes

A solution is a homogeneous mixture of two or more substances.

Solvent: The substance present in the greatest amount (e.g., water).
Solute: The substance dissolved in the solvent (e.g., salt).

Solutions, Colloids, and Suspensions

These are types of mixtures based on particle size and distribution.

Type	Particle Size	Appearance	Example
Solution	Smallest	Clear	Salt water
Colloid	Intermediate	Cloudy	Milk
Suspension	Largest	Settles out	Blood

Electrolytes

Electrolytes are substances that dissociate into ions in solution, conducting electricity (e.g., NaCl in water).

Hydrophobic vs. Hydrophilic Compounds

Hydrophobic: "Water-fearing"; do not dissolve in water (e.g., lipids).
Hydrophilic: "Water-loving"; dissolve easily in water (e.g., salts, sugars).

Acids, Bases, and Salts

Acid: Releases H+ ions in solution (e.g., HCl).
Base: Releases OH- ions or accepts H+ (e.g., NaOH).
Salt: Compound formed from acid-base reaction (e.g., NaCl).

pH Scale

The pH scale measures the concentration of hydrogen ions (H+) in a solution, ranging from 0 (acidic) to 14 (basic).

pH = -log[H+]
As [H+] increases, pH decreases (more acidic).
As [OH-] increases, pH increases (more basic).

Buffers

Buffers are substances that minimize changes in pH by absorbing or releasing H+ ions. They are crucial for maintaining homeostasis in biological systems.

Biomolecules: Carbohydrates, Proteins, Lipids, Nucleic Acids

Carbohydrates: Main energy source; e.g., glucose, starch.
Proteins: Structural, enzymatic, and regulatory roles; e.g., enzymes, hemoglobin.
Lipids: Energy storage, membrane structure; e.g., triglycerides, phospholipids.
Nucleic Acids: Store and transmit genetic information; e.g., DNA, RNA.

Denaturation

Denaturation is the loss of a protein's native structure due to external stress (e.g., heat, pH), resulting in loss of function.

ATP: Energy Storage and Release

ATP (adenosine triphosphate) is the primary energy carrier in cells. It stores energy in high-energy phosphate bonds and releases it to power cellular processes.

ATP Hydrolysis: Releases energy by breaking a phosphate bond.