General Biology II Unit 1 Review: The Molecular Basis of Life

Key Concepts

• Matter consists of atoms, the fundamental unit of an element that retains its properties
• Atoms combine to form molecules through chemical bonds, including ionic, covalent, and hydrogen bonds
• Water is a polar molecule with unique properties essential for life, such as cohesion, adhesion, and high specific heat capacity
• Carbon is the basis for organic compounds due to its ability to form stable covalent bonds with other elements
• Macromolecules are large, complex molecules formed by the polymerization of smaller subunits (monomers)
  • Carbohydrates, lipids, proteins, and nucleic acids are the four main classes of biological macromolecules
• Energy is the capacity to do work or cause change and is required for all biological processes
  • ATP (adenosine triphosphate) is the primary energy currency in living systems
• Understanding the molecular basis of life has practical applications in fields such as medicine, agriculture, and biotechnology

Atoms and Molecules

• Atoms are composed of protons, neutrons, and electrons
  • Protons have a positive charge, neutrons are neutral, and electrons have a negative charge
• The number of protons in an atom determines its atomic number and element identity
• Isotopes are atoms of the same element with different numbers of neutrons
• Electrons occupy specific energy levels (shells) around the nucleus, with a maximum number of electrons per shell
  • Valence electrons in the outermost shell participate in chemical bonding
• Molecules are formed when two or more atoms bond together
  • Compounds are molecules containing atoms of different elements (water, glucose)
• Ions are atoms or molecules with a net positive or negative charge due to the gain or loss of electrons

Chemical Bonds

• Chemical bonds are attractive forces that hold atoms together in molecules or compounds
• Ionic bonds form through the transfer of electrons between atoms, creating ions with opposite charges that attract each other
  • Occurs between metals and nonmetals (sodium chloride)
• Covalent bonds form through the sharing of electrons between atoms
  • Nonpolar covalent bonds have equal sharing of electrons (oxygen gas)
  • Polar covalent bonds have unequal sharing of electrons due to differences in electronegativity (water)
• Hydrogen bonds are weak attractive forces between hydrogen atoms and electronegative atoms (oxygen, nitrogen)
  • Important in maintaining the structure of water, proteins, and DNA
• Van der Waals forces are weak intermolecular attractions between molecules
  • Contribute to the properties of gases and the folding of proteins

Water and Its Properties

• Water is a polar molecule with a bent geometry due to the unequal sharing of electrons between hydrogen and oxygen
• Hydrogen bonding between water molecules leads to cohesion (attraction between water molecules) and adhesion (attraction between water and other substances)
• Water has a high specific heat capacity, requiring a large amount of energy to change its temperature
  • Helps regulate body temperature in living organisms
• Water is an excellent solvent for polar and ionic compounds due to its polarity
  • Allows for the transport of nutrients and waste products in living systems
• The high surface tension of water results from cohesive forces, allowing some organisms to walk on water (water striders)
• Ice is less dense than liquid water due to the arrangement of hydrogen bonds, allowing aquatic life to survive in frozen water bodies

Carbon and Organic Compounds

• Carbon is the basis for organic compounds due to its ability to form four stable covalent bonds
• Carbon can form single, double, or triple bonds with other carbon atoms or elements such as hydrogen, oxygen, and nitrogen
• Hydrocarbons are organic compounds composed entirely of carbon and hydrogen (methane, propane)
• Functional groups are specific arrangements of atoms that give organic compounds their unique properties
  • Examples include hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), and phosphate (-PO4) groups
• Isomers are compounds with the same molecular formula but different structural arrangements (glucose and fructose)
• Chirality refers to the property of molecules that are non-superimposable mirror images of each other (left-handed and right-handed amino acids)

Macromolecules

• Carbohydrates are composed of carbon, hydrogen, and oxygen in a 1:2:1 ratio
  • Monosaccharides are simple sugars that serve as monomers for larger carbohydrates (glucose, fructose)
  • Disaccharides are formed by the joining of two monosaccharides (sucrose, lactose)
  • Polysaccharides are long chains of monosaccharides (starch, cellulose, glycogen)
• Lipids are hydrophobic molecules that include fats, oils, waxes, and steroids
  • Triglycerides are composed of a glycerol backbone and three fatty acid chains
  • Phospholipids have a hydrophilic head and hydrophobic tails, forming cell membranes
• Proteins are polymers of amino acids joined by peptide bonds
  • The sequence of amino acids determines a protein's primary structure and function
  • Secondary structure refers to local folding patterns (α-helices and β-sheets)
  • Tertiary structure is the overall 3D shape of a protein
  • Quaternary structure involves the interaction of multiple polypeptide chains
• Nucleic acids store and transmit genetic information
  • DNA (deoxyribonucleic acid) is a double-stranded helix composed of nucleotide monomers
  • RNA (ribonucleic acid) is single-stranded and plays a role in protein synthesis

Energy in Biological Systems

• Energy is the capacity to do work or cause change
• The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another
• The second law of thermodynamics states that entropy (disorder) increases in a closed system
• Metabolism is the sum of all chemical reactions in an organism, including energy transformations
• ATP (adenosine triphosphate) is the primary energy currency in living systems
  • Consists of an adenosine molecule, a ribose sugar, and three phosphate groups
  • Energy is released when the terminal phosphate bond is broken (hydrolysis)
• Enzymes are biological catalysts that lower the activation energy of chemical reactions
  • Specific to their substrates and can be regulated by inhibitors or activators
• Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy (glucose)
  • Occurs in chloroplasts and involves light-dependent and light-independent reactions
• Cellular respiration is the process by which cells break down glucose to release energy in the form of ATP
  • Occurs in the cytoplasm and mitochondria and includes glycolysis, the Krebs cycle, and the electron transport chain

Practical Applications

• Understanding the molecular basis of life has led to advances in medicine, such as the development of targeted therapies for cancer and genetic disorders
• Recombinant DNA technology allows for the production of human insulin in bacteria for the treatment of diabetes
• Polymerase chain reaction (PCR) is a technique used to amplify specific DNA sequences, with applications in forensics, disease diagnosis, and research
• Genetically modified organisms (GMOs) have been developed to improve crop yields, nutritional content, and resistance to pests and diseases
• Biofuels, such as ethanol and biodiesel, are produced from plant-derived carbohydrates and lipids as a renewable energy source
• Bioremediation involves the use of microorganisms to break down environmental pollutants (oil spills, heavy metals)
• Synthetic biology aims to design and construct novel biological systems or organisms with specific functions (biosensors, drug delivery systems)
• Understanding the molecular basis of evolution and adaptation informs conservation efforts and predicting responses to climate change