❤️AP Bio Unit 2 – Chemistry of Life

Key Concepts

• Matter consists of atoms which are the building blocks of all substances
• Atoms are composed of protons, neutrons, and electrons
  • Protons have a positive charge, neutrons have no charge, and electrons have a negative charge
• Chemical bonds form between atoms to create molecules and compounds
  • Covalent bonds involve the sharing of electrons between atoms (water, glucose)
  • Ionic bonds involve the transfer of electrons between atoms (table salt)
• Water is essential for life due to its unique properties
  • Polarity allows water to dissolve many substances (sugars, salts)
  • High specific heat capacity enables water to resist temperature changes
• pH is a measure of the concentration of hydrogen ions in a solution
  • Acids have a pH below 7, bases have a pH above 7, and neutral solutions have a pH of 7 (pure water)
• Energy is required for life processes and is obtained through chemical reactions
  • Exergonic reactions release energy (cellular respiration)
  • Endergonic reactions require energy input (photosynthesis)
• Enzymes are biological catalysts that speed up chemical reactions in living organisms
  • Enzymes lower the activation energy required for reactions to occur (lactase, amylase)

Atomic Structure and Chemical Bonds

• Atoms are the smallest unit of matter that retains the properties of an element
• The atomic number represents the number of protons in an atom's nucleus
• Isotopes are atoms of the same element with different numbers of neutrons (carbon-12, carbon-14)
• Electrons occupy energy levels or shells around the nucleus
  • The first shell can hold up to 2 electrons, the second shell can hold up to 8 electrons
• Valence electrons are the electrons in the outermost shell and determine an atom's reactivity
• Chemical bonds form when atoms share, gain, or lose electrons to achieve a stable electron configuration
• Covalent bonds form when atoms share electrons
  • Single covalent bonds involve the sharing of one pair of electrons (hydrogen gas)
  • Double and triple covalent bonds involve the sharing of two or three pairs of electrons, respectively (oxygen gas, nitrogen gas)
• Ionic bonds form when electrons are transferred from one atom to another, creating ions
  • Cations are positively charged ions that have lost electrons (sodium ion)
  • Anions are negatively charged ions that have gained electrons (chloride ion)

Molecules of Life

• Molecules are two or more atoms held together by chemical bonds
• Macromolecules are large molecules composed of smaller subunits called monomers
• Carbohydrates are macromolecules composed of monosaccharides (simple sugars)
  • Monosaccharides include glucose, fructose, and galactose
  • Disaccharides are formed when two monosaccharides are joined by a glycosidic bond (sucrose, lactose)
  • Polysaccharides are long chains of monosaccharides (starch, cellulose, glycogen)
• Lipids are a diverse group of hydrophobic molecules
  • Triglycerides are composed of a glycerol molecule and three fatty acids (oils, fats)
  • Phospholipids have a hydrophilic head and hydrophobic tails, forming cell membranes
• Proteins are macromolecules composed of amino acids
  • There are 20 different amino acids that can be combined to form proteins
  • The sequence of amino acids determines a protein's structure and function (enzymes, antibodies)
• Nucleic acids are macromolecules that store and transmit genetic information
  • DNA (deoxyribonucleic acid) is a double-stranded molecule that stores genetic information
  • RNA (ribonucleic acid) is a single-stranded molecule involved in protein synthesis

Water and Its Properties

• Water is a polar molecule with a slightly positive charge on the hydrogen atoms and a slightly negative charge on the oxygen atom
• Hydrogen bonds form between water molecules due to the attraction between the positive and negative charges
  • Hydrogen bonds give water its unique properties, such as cohesion and adhesion
• Water has a high specific heat capacity, meaning it can absorb a large amount of heat energy before its temperature increases
  • This property helps regulate temperature in living organisms and aquatic environments
• Water has a high heat of vaporization, requiring a large amount of energy to change from a liquid to a gas
  • This property helps with temperature regulation through evaporative cooling (sweating)
• Water is an excellent solvent due to its polarity
  • Hydrophilic substances readily dissolve in water (salts, sugars)
  • Hydrophobic substances do not readily dissolve in water (oils, fats)
• Cohesion is the attraction between water molecules, allowing for the formation of water droplets and surface tension
• Adhesion is the attraction between water molecules and other surfaces, allowing for capillary action in plants

pH and Buffers

• pH is a logarithmic scale that measures the concentration of hydrogen ions (H+) in a solution
  • The pH scale ranges from 0 to 14, with 7 being neutral
• Acids are substances that donate hydrogen ions to a solution, increasing the H+ concentration and lowering the pH
  • Examples of acids include hydrochloric acid (HCl) and acetic acid (vinegar)
• Bases are substances that accept hydrogen ions from a solution, decreasing the H+ concentration and raising the pH
  • Examples of bases include sodium hydroxide (NaOH) and ammonia (NH3)
• The concentration of H+ and OH- ions in a neutral solution is equal at 1 x 10^-7 M
• Buffers are solutions that resist changes in pH when small amounts of acids or bases are added
  • Buffers contain a weak acid and its conjugate base, or a weak base and its conjugate acid
  • The bicarbonate buffer system helps maintain blood pH around 7.4
• Living organisms require a specific pH range for optimal function of proteins and enzymes
  • Most enzymes function best at a neutral pH, while some have specific pH requirements (pepsin in the stomach)

Energy and Chemical Reactions

• Energy is the capacity to do work or cause change
• Potential energy is stored energy, while kinetic energy is the energy of motion
• Chemical reactions involve the breaking and forming of chemical bonds, resulting in the formation of new substances
• Exergonic reactions release energy and are spontaneous (cellular respiration)
  • The energy released can be used to perform work or be stored as ATP
• Endergonic reactions require an input of energy and are non-spontaneous (photosynthesis)
  • The energy input is often provided by the breakdown of ATP
• Activation energy is the minimum amount of energy required for a reaction to occur
  • Enzymes lower the activation energy by providing an alternative reaction pathway
• The laws of thermodynamics govern energy transfer in chemical reactions
  • The first law states that energy cannot be created or destroyed, only converted from one form to another
  • The second law states that entropy (disorder) tends to increase in a closed system

Enzymes and Metabolism

• Enzymes are proteins that act as biological catalysts, speeding up chemical reactions without being consumed
• Enzymes are specific to their substrates, the molecules they act upon
  • The active site of an enzyme has a complementary shape to its substrate
• Enzymes lower the activation energy of reactions by bringing substrates together and stabilizing transition states
• Factors that affect enzyme activity include temperature, pH, and substrate concentration
  • Enzymes have an optimal temperature and pH range where they function most efficiently
  • Increasing substrate concentration increases reaction rate until the enzyme becomes saturated
• Enzyme inhibitors can decrease or stop enzyme activity
  • Competitive inhibitors bind to the active site, preventing substrate binding (pesticides)
  • Non-competitive inhibitors bind to an allosteric site, changing the enzyme's shape and reducing its activity
• Metabolism is the sum of all chemical reactions in a living organism
  • Catabolism breaks down complex molecules to release energy (cellular respiration)
  • Anabolism uses energy to build complex molecules from simpler ones (protein synthesis)
• Metabolic pathways are series of enzyme-catalyzed reactions that convert a starting molecule into an end product
  • Examples include glycolysis, the citric acid cycle, and the electron transport chain

Connecting Chemistry to Biology

• The principles of chemistry underlie all biological processes
• The structure and function of biological molecules depend on their chemical properties
  • The hydrophobic and hydrophilic regions of phospholipids allow for the formation of cell membranes
  • The chemical structure of DNA allows for the storage and transmission of genetic information
• Chemical reactions in living organisms are regulated by enzymes and hormones
  • Enzymes control the rate of metabolic reactions
  • Hormones, such as insulin and glucagon, regulate blood sugar levels through chemical signaling
• The pH of different body compartments affects the function of proteins and enzymes
  • The acidic pH of the stomach allows for the activity of digestive enzymes like pepsin
  • The slightly alkaline pH of the blood allows for the efficient transport of oxygen by hemoglobin
• Energy flow in ecosystems is governed by the laws of thermodynamics
  • Producers convert light energy into chemical energy through photosynthesis
  • Consumers obtain energy by eating producers or other consumers
• The cycling of matter in ecosystems involves chemical transformations
  • The carbon cycle includes the conversion of carbon dioxide into organic compounds by producers and the release of carbon dioxide by consumers and decomposers
  • The nitrogen cycle involves the conversion of atmospheric nitrogen into usable forms by nitrogen-fixing bacteria and the return of nitrogen to the atmosphere through denitrification