chapter 2

• Covalent bonds involve pairs of electrons that are shared between pairs of atoms
• Nonpolar covalent bonds involve the equal sharing of electrons
• Polar covalent bonds involve the uneven sharing of electrons due to unequal electronegative levels of the atoms involved
• electronegativity: an indication of atom's ability to attract an electron; the more electronegative an atom is, the greater ability of an atom to attract an electron.
• a hydrogen bond is a weak attractive interaction between an electronegative atom and a hydrogen atom that is covalently linked to a second electronegative atom
• water is an excellent solvent, used in many cellular reactions, and absorbs and retains heat excellently.
• The structure of water is suitable for sustaining life because:

  • of its asymmetry, with an H atom on both sides
  • highly polarized covalent O-H bonds
  • all three atoms readily form H-bonds
• Water can be used as a solvent for ions, and hydrophobic molecules including sugars, DNA, RNA, and most proteins.
• The hydrophobic effect describes the aggregation of nonpolar molecules within water to increase the system's entropy.
• There are four major categories of macromolecules, where only three out of four of them are made out of repeating units of monomers-- making them polymers.
• The four type of macromolecules include proteins, nucleic acids, polysaccharides, and lipids
• Most cell macromolecules are short-lived, except DNA, and are continually broken down and replaced.
• Types of carbohydrates include monosaccharides, disaccharides, and polysaccharides.
• Carbohydrates are the most abundant form of organic matter on earth.
• Carbohydrates are used for energy, structural components of RNA, DNA, cell walls, and glycoproteins and glycolipids.
• Ketose: sugar molecule with a carbonyl group located at an internal position, making a ketone

  
• Aldose: sugar with a carbonyl group located at the end, making an aldehyde

  
• Most sugars have the general formula of (CH2O)n
• The molecular formula of glucose is C6H12O6
• Isomers are molecules that have the same molecular formula but differ in the spatial arrangement of atoms
• Due to their hydroxyl groups, water is extremely highly water soluble
• Sugars more than 5 carbons self react to produce a ring-containing molecule.

  
• Anomeric carbon: carbon derived from the carbonyl carbon (the ketone or aldehyde function group) of the open-chain form of the carbohydrate molecule
• In solution, an anomeric carbon can open and mutarotate.
• An a stereoisomer (a-pyranose) is when the OH group of the first carbon projects below the plane of the ring. A b stereoisomer (b-pyranose) is when the OH group of the first carbon projects upward.

  
• Glycosidic bonds are covalent bonds that link together monosaccharides using their OH groups, creating a disaccharide.
• Sucrose = glucose and fructose
• Lactose = galactose and glucose

  
• Once an anomeric carbon of a monosaccharide is in a glycosidic bond, it can no longer mutarotate and the bond is in a fixed position
• An O-glycosidic bond occurs when an anomeric bond reacts with a hydroxyl
• A N-glycosidic bond is when an anomeric carbon reacts with a nitrogen.
• Glycosidic bonds can form between the anomeric carbon of a polysaccharide and a hydroxyl or a nitrogen of certain amino acids.