Honors Anatomy and Physiology Unit 2 Review: Chemical Basis of Life

Key Concepts and Definitions

• Matter refers to anything that occupies space and has mass
• Elements are pure substances that cannot be broken down into simpler substances by chemical means (carbon, oxygen, hydrogen)
• Atoms are the smallest unit of an element that retains its properties
  • Consist of protons, neutrons, and electrons
  • Protons have a positive charge, neutrons have no charge, and electrons have a negative charge
• Molecules are two or more atoms chemically combined (water, glucose)
• Compounds are substances made up of two or more different elements chemically combined in a fixed ratio (sodium chloride)
• Chemical bonds are attractive forces that hold atoms together in molecules or compounds
• Ionic bonds involve the transfer of electrons between atoms resulting in positively and negatively charged ions (sodium chloride)
• Covalent bonds involve the sharing of electrons between atoms (water, carbon dioxide)

Atomic Structure and Chemical Bonds

• Atomic number represents the number of protons in an atom's nucleus
• Mass number is the sum of the number of protons and neutrons in an atom
• Isotopes are atoms of the same element with different numbers of neutrons (carbon-12, carbon-13)
• Electron shells are energy levels around the nucleus where electrons orbit
  • Electrons fill shells in a specific order, with the innermost shell being filled first
  • Valence electrons are the electrons in the outermost shell and are involved in chemical bonding
• Ions are atoms or molecules that have gained or lost electrons, resulting in a net positive or negative charge (sodium ion, chloride ion)
• Electronegativity is the ability of an atom to attract electrons in a chemical bond
• Polar covalent bonds occur when electrons are shared unequally between atoms due to differences in electronegativity (water)
• Nonpolar covalent bonds occur when electrons are shared equally between atoms (oxygen gas)

Molecules Essential for Life

• Water ($H_2O$) is the most abundant molecule in living organisms and is essential for life
  • Serves as a solvent, reactant, and product in many biological processes
  • Helps regulate body temperature through evaporation and heat capacity
• Glucose ($C_6H_{12}O_6$) is a simple sugar that serves as a primary energy source for cells
  • Produced by plants through photosynthesis and broken down by cells through cellular respiration
• Amino acids are the building blocks of proteins and contain an amino group ($-NH_2$) and a carboxyl group ($-COOH$)
  • There are 20 different amino acids used to build proteins in the human body
• Nucleotides are the building blocks of nucleic acids (DNA and RNA) and consist of a nitrogenous base, a sugar, and a phosphate group
  • Adenine (A), thymine (T), guanine (G), and cytosine (C) are the nitrogenous bases found in DNA
• Lipids are a diverse group of hydrophobic molecules that include fats, oils, and steroids
  • Play important roles in energy storage, cell membrane structure, and hormone signaling

Properties of Water and Solutions

• Polarity of water molecules results from the unequal sharing of electrons between hydrogen and oxygen atoms
  • Hydrogen bonds form between water molecules due to the attraction between the positive and negative charges
• Cohesion is the attraction between water molecules, allowing for high surface tension and capillary action
• Adhesion is the attraction between water molecules and other substances (glass, cell walls)
• Water has a high specific heat capacity, meaning it requires a large amount of energy to change its temperature
  • Helps regulate body temperature and maintain stable cellular environments
• Solutions are homogeneous mixtures of two or more substances (solute and solvent)
• Solubility refers to the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature
• Concentration is the amount of solute present in a given volume of solution (molarity, molality)
• Osmosis is the movement of water across a semipermeable membrane from a region of high water concentration to a region of low water concentration
  • Plays a crucial role in maintaining cell volume and transporting substances across cell membranes

pH and Buffers in the Body

• pH is a measure of the concentration of hydrogen ions ($H^+$) in a solution
  • Ranges from 0 to 14, with 7 being neutral, below 7 acidic, and above 7 basic
• Acids are substances that donate hydrogen ions ($H^+$) to a solution (hydrochloric acid)
• Bases are substances that accept hydrogen ions ($H^+$) from a solution (sodium hydroxide)
• The pH scale is logarithmic, meaning a change of one pH unit represents a tenfold change in hydrogen ion concentration
• Buffers are solutions that resist changes in pH when small amounts of acid or base are added
  • Consist of a weak acid and its conjugate base or a weak base and its conjugate acid
• The bicarbonate buffer system is the primary buffer system in the human body
  • Maintains blood pH within a narrow range (7.35-7.45)
• Acidosis is a condition in which the blood pH falls below 7.35, while alkalosis is a condition in which the blood pH rises above 7.45
• Homeostatic mechanisms, such as respiratory and renal regulation, help maintain proper pH balance in the body

Organic Compounds and Macromolecules

• Organic compounds are carbon-based molecules that are essential for life
• Carbohydrates are composed of carbon, hydrogen, and oxygen atoms in a 1:2:1 ratio (glucose, starch)
  • Serve as energy sources and structural components in living organisms
• Proteins are polymers of amino acids joined by peptide bonds
  • Play diverse roles in the body, including catalyzing reactions, providing structure, and transporting molecules
• Lipids are a diverse group of hydrophobic molecules that include fats, oils, and steroids
  • Function in energy storage, cell membrane structure, and hormone signaling
• Nucleic acids (DNA and RNA) are polymers of nucleotides that store and transmit genetic information
  • DNA is a double-stranded helix, while RNA is single-stranded
• Macromolecules are large, complex molecules formed by the polymerization of smaller subunits (monomers)
  • Examples include polysaccharides, proteins, and nucleic acids
• Dehydration synthesis is the formation of a covalent bond between monomers with the release of a water molecule
• Hydrolysis is the breakdown of a covalent bond between monomers with the addition of a water molecule

Chemical Reactions in Living Systems

• Metabolism refers to the sum of all chemical reactions that occur within a living organism
• Anabolism is the synthesis of complex molecules from simpler molecules, requiring energy input (protein synthesis)
• Catabolism is the breakdown of complex molecules into simpler molecules, releasing energy (cellular respiration)
• Enzymes are biological catalysts that speed up chemical reactions without being consumed in the process
  • Lower the activation energy required for a reaction to occur
  • Are highly specific to their substrates and are sensitive to changes in temperature and pH
• Substrate is the molecule or molecules upon which an enzyme acts
• Active site is the region of an enzyme where the substrate binds and the reaction occurs
• Cofactors are non-protein molecules that assist enzymes in their catalytic function (metal ions, vitamins)
• Cellular respiration is the process by which cells break down glucose to release energy in the form of ATP
  • Occurs in three stages: glycolysis, the Krebs cycle, and the electron transport chain
• Photosynthesis is the process by which plants and other autotrophs convert light energy into chemical energy (glucose)
  • Occurs in two stages: the light-dependent reactions and the Calvin cycle

Practical Applications and Lab Techniques

• Spectrophotometry is a technique used to measure the absorption of light by a solution
  • Can be used to determine the concentration of a substance in a solution (protein, DNA)
• Chromatography is a technique used to separate mixtures of substances based on their physical and chemical properties
  • Examples include paper chromatography, thin-layer chromatography, and gas chromatography
• Electrophoresis is a technique used to separate charged molecules (proteins, DNA) based on their size and charge
  • Commonly used in DNA fingerprinting and protein analysis
• Centrifugation is a technique used to separate substances based on their density by applying centrifugal force
  • Used in the isolation of cell organelles and the purification of proteins and nucleic acids
• Microscopy is the use of microscopes to observe small structures and organisms
  • Light microscopy uses visible light and can achieve magnifications up to 1000x
  • Electron microscopy uses a beam of electrons and can achieve much higher magnifications (up to 1,000,000x)
• Polymerase chain reaction (PCR) is a technique used to amplify specific DNA sequences
  • Involves the use of primers, DNA polymerase, and thermal cycling to produce millions of copies of a target DNA sequence
• Recombinant DNA technology involves the manipulation and insertion of DNA from one organism into another
  • Used in the production of genetically modified organisms and in gene therapy
• Biochemical assays are used to measure the presence, activity, or concentration of specific molecules or enzymes
  • Examples include the Bradford assay for protein concentration and the ELISA for antibody detection