Chapter 3 lecture

• Macromolecules


  Molecules that make up organisms
• Macromolecules that make up organisms

  • Proteins
  • Carbohydrates
  • Nucleic acids
  • Lipids
• Function of a macromolecule

  Depends on the functional groups it contains
• Monomers


  Subunits (small molecules) that are chemically linked via condensation reactions to form polymers
• Polymers


  Large molecules made up of connecting monomers
• Macromolecules


  Polymers consisting of 1000 or more atoms
• Monomer and Polymer


  • Amino Acid
  • Protein
• Creating biological macromolecules


  1. Polymers are formed in condensation reactions

  2. Energy input required

  3. Water molecule formed as a product of condensation reactions
• Breaking down (degrading) biological macromolecules

  1. Polymers are broken down into monomers in hydrolysis reactions

  2. Energy is released

  3. Water molecule is consumed as a reactant of hydrolysis reactions
• Macromolecules may have more than one type of functional group
• Functional groups are involved in the chemistry of macromolecules
• Isomers


  • Structural isomers
  • cis-trans isomers
  • Optical isomers
• Structural isomers


  Different joining
• cis-trans isomers


  Different around double bond
• Optical isomers


  Mirror image; carbon with four different groups (asymmetric carbon)
• Proteins


  • Comprised of many amino acids (monomer)
  • Amino acids link together to form polypeptide chains
  • Each link between amino acids is a peptide bond
  • Polypeptide chains fold into specific 3-D shapes
  • Structure determines function
  • Functions include: Enzyme catalysis, Transport, ...
• General Amino Acid Structure

  • Amino acids have carboxyl and amino groups
  • Amino acids have side chains or R-groups
  • Amino acids function as both acid and base
• Cysteine is unique, the terminal —SH group of cysteine forms disulfide bridges or disulfide bonds, which are important in protein folding
• Building a Protein


  1. Amino acids form peptide bonds to build polypeptides (proteins)

  2. Peptide bonds are condensation reactions between the carboxyl end of one amino acid and the amino end of another amino acid
• Protein Structural Levels


  • Primary structure is the sequence of amino acids connected by peptide bonds
  • Secondary structure requires hydrogen bonding between amino acids making up the primary structure
  • α helix is a right-handed coil resulting from hydrogen bonding between N–H groups and C=O groups
  • β pleated sheet is two or more polypeptide chains aligned with hydrogen bonds forming between the chains
  • Tertiary structure is the folding of secondary structures into a specific 3-D shape, determined by interactions between R groups
  • Quaternary structure results from interaction of subunits of different protein molecules via hydrophobic interaction, van der Waals forces, ionic attractions, hydrogen bonds
• The folded shape of the protein is important because structure determines function
• When proteins fold (in water) the hydrophobic areas usually form the interior and hydrophilic area on the outside, reverse location for membrane proteins
• Interactions that stabilize protein structure

  • Hydrogen bond
  • Disulfide bridge
  • Polypeptide backbone
  • Ionic bond
  • Non-polar/hydrophobic
• Conditions that affect secondary and tertiary protein structure

  • Temperature
  • pH
  • Ionic Strength
  • Solubility
• Chaperones


  Proteins that help prevent newly made or denatured proteins from binding to the wrong molecules by allowing them to refold
• Protein shape can change as a result of

  • Binding interactions with other molecules (non-covalent)
  • Covalent modification
• Carbohydrates


  • Have the formula CnH2nOn
  • Sources of stored energy
  • Used to transport stored energy
  • Carbon skeletons for many other molecules
  • Form extracellular structures such as cell walls
• Types of Carbohydrates


  • Monosaccharides (single sugars)
  • Disaccharides (2 monosaccharides, covalently linked)
  • Polysaccharides (polymers of 100+ monosaccharides)
• Monosaccharides


  • All cells use glucose as an energy source
  • Exist as a straight chain or ring form, with ring form being more stable
  • Ring form exists as α- or β-glucose
  • Are comprised of 3 to 7 carbon atoms
  • Function in short-term energy storage
  • Hexoses (glucose, fructose)
  • Pentoses (ribose, deoxyribose)
• Disaccharides


  Two monosaccharides are linked together in condensation reactions to form glycosidic linkages, that can be α or β
• Polysaccharides


  • Function in long-term energy storage
  • Glycogen: animal storage form
  • Starch: plant storage form, branched
  • Cellulose: structural components, linear
• Lipids


  • Defined by their solubility rather than their chemical structure (Lipids are VERY chemically diverse)
  • Insoluble in water
  • Contain MOSTLY nonpolar covalent bonds! (C-C and C-H)
• Types & Roles of Lipids

  • Phospholipids – structural role in cell membranes
  • Steroids impact membrane fluidity
  • Carotenoids and chlorophylls capture light energy in plants
  • Fats and oils store energy
• Triglycerides: Fats & Oils


  • Function: long-term energy storage and insulation
  • Composition: 1 glycerol + 3 fatty acids (FA)
• Fatty Acid Saturation Impacts Structure

  • Saturated FAs: No C=C double bonds
  • Unsaturated FAs: One or more C=C double bonds
• Phospholipids


  • 1 FA in triglyceride is replaced with a phosphate group
  • Amphipathic: with polar & non-polar regions
  • "Head" - hydrophilic
  • "Tails" - hydrophobic
  • Form spontaneously with "heads" out and oily "tails" in, forming a phospholipid bilayer
• Carotenoids


  Light-absorbing pigments in plants
• Steroids


  • Multiple rings share carbons
  • Cholesterol is an important steroid in membranes
  • Other steroids are hormones