Small organic molecules are the building blocks of biological

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					       Small organic molecules are the building blocks
               of biological macromolecules…
        Building blocks              Larger units

                  Sugars                               Polysaccharides


             Fatty acids                            Fats/lipids/Membranes

            Amino acids                                   Proteins


            Nucleotides                                 Nucleic acids


Adapted from ECB figure 2-15 (Garland Publishing)
Most lipids are in membranes   Plasma membrane




                   Various organelle membranes
Fatty Acids
(Amphipathic)     Hydrophilic
                Carboxylic acid
                  head group




        Hydrophobic
        hydrocarbon
            tail
Fatty acids are distinguished by chain length and double bonds




Stearic acid
  18 carbons
  Saturated = no double bonds      Oleic Acid
   (common in fats)                     18 carbons
                                        Unsaturated 1 double bond,
                                        (common in oils)
 Most lipids in cells are formed by covalent bonds
         between fatty acids and glycerol
ECB Fig. 11-10

                    Triacyl Glycerol = 3 fatty
                    acids bonded to glycerol
                    Ester bond - carboxylic acid and
                    alcohol

                    (animal fat, plant oils)
                    Energy storage




                    Very Hydrophobic
     Phospholipid - 3 parts
 Major component of membranes

Polar Head Group = phosphate + polar moiety (Variable)




         glycerol


Hydrophobic tails =
fatty acid side
chains
  Bilayer
Phospholipid
                                 Phospholipid




                         Hydrophilic
 Hydrophobic tail region   region
Lipid bilayer forms sphere in aqueous solution




                         Forms barrier defining
                         inside and outside spaces
          Cell Membrane-more complex
Contains a variety of lipids, proteins, and carbohydrates

Outer leaflet
                                      Lipids

                                        Lipid bilayer
                                        5 nm

                                            Multiple types of lipids
Inner                                       are found in membranes
leaflet
                             Protein
   Cytosol (inside)
                            ECB Fig. 11-4
      Three Types of Membrane Lipid Molecules
  Phospholipids   all amphipathic    Glycolipids
                                                  (sugar lipid)
                               Sterols
                     serine   (cholesterol)




          ECB 11-7




                                              galactocerebroside
phosphatidylserine
     Lecture 4
Membranes
   Fatty Acids
   Phospholipids
   Lipid bilayer
   Other membrane lipids
   Membrane properties


Proteins
   Amino Acids
   Peptide bond
   Protein Structure
Influence of FA saturation on lipid bilayer order
      ordered                   less ordered




  Saturated straight            Unsaturated
  hydrocarbon chains        hydrocarbon chains
   (no double bonds)        (with double bonds)

  Less ordered state increases membrane fluidity
         Membrane Fluidity (viscosity)
      Describes the physical state of the membrane



                Pure lipid bilayer - two states


        Liquid state                             Gel state
Hydrophobic tails free to move        Movement is greatly restricted
                                            (crystalline gel)

 Liquid at temperatures     Transition            Crystalline gel at
Above the transition temp. temperature         temperatures below the
                                                   transition temp

     Living cells require a fluid membrane, but not too fluid:
     Membrane fluidity is regulated by the cell

                    11.2-membrane_fluidity.mov
Membrane fluidity is governed by FA length and
                  saturation
1. Fatty acid length - shorter the FA, the lower the
   transition temperature (melting point), favors liquid state

2. Fatty acid saturation - the more saturated, the
   higher the transition temperature, favors gel state

         Melting points of 18-carbon Fatty Acids
           Fatty Acid       Double bonds   Melting point (˚C)
          Stearic acid           0              70
          Oleic acid             1               13
          a-Linoleic acid        2               -9
          Linolenic acid         3              -17

3. Presence of cholesterol - broadens the temperature
    over which transition occurs.
                   Polar head      Cholesterol
                     group
  Rigid                           stiffens lipid
 Planar
Steroid                              bilayers
  ring
                       Nonpolar
                        hydro-
                        carbon
                          tail              Polar head
                                              group

     ECB 11-16                            Stiffened
                                           region
  Mainly in animal cells,
  Not in plants                               Fluid
                                             region
Lipid composition varies in inner and outer leaflet




                                      Glycolipids in outer
                                      leaflet



                                       Phospholipids
1. Spin (fast)


2. Lateral
 movement
 (less fast)


3. Flip-flop
Almost never
Lipid Bilayer   Small hydrophobic
                   Molecules
Permeability    O2, CO2, N2, benzene


                Small Uncharged
                 polar molecules
                H2O, glycerol, ethanol


                Large, uncharged
                 Polar molecules
                Amino acids, glucose,
                    nucleotides


                      IONS
                 H+, Na+, HCO3-,
                 K+, Ca2+, Cl-, Mg2+
                                         ECB Fig.12-2
             Cell membrane




   ECB Fig. 11-4


Have discussed lipid bilayer, cholesterol, glycolipid
            Now move on to proteins
     Small organic molecules are the building blocks
             of biological macromolecules…
      Building blocks              Larger units

              Sugars                                   Polysaccharides


          Fatty acids                               Fats/lipids/Membranes

          Amino acids                                     Proteins


          Nucleotides                                   Nucleic acids


Adapted from ECB figure 2-15 (Garland Publishing)
 Proteins serve many functions in cells

Transport proteins - move molecules across membranes
Enzymes
Structural proteins
Motor proteins
Signaling proteins
Gene regulatory proteins
Etc.
Amino Acids - the building blocks of proteins

                       20 different amino acids

                       All amino acids have
                       the same backbone,
                       but the “R” group
                       varies.




  See ECB Fig. 2-21
                     Amino Acid Groups
        Based on chemical characteristics of R groups
                      Polar Amino Acids

1. Polar and negative charge (aspartic acid and glutamic acid)


   2. Polar and positive charge (arginine, lysine, histidine)


   3. Polar and uncharged (asparagine, glutamine, serine,
                    threonine, tyrosine)


  4. Nonpolar (alanine, glycine, valine, leucine, isoleucine,
  proline, phenylalanine, methionine, tryptophan, cysteine)
                          Polar Charged Amino Acids (5)
  Negative charge




  Aspartic           Glutamic
Acid (Asp, D)       Acid (Glu, E)

                Positive charge




                       Lysine       Arginine    Histidine
                      (Lys, K)      (Arg, R)    (His, H)
   Polar
Uncharged
Amino Acids
    (5)
                Serine         Threonine
               (Ser, S)         (Thr, T)




   Glutamine      Asparagine     Tyrosine
    (Gln, Q)       (Asn, N)      (Tyr, Y)
                                   Non-polar
                                  amino acids
                                    (10 total)

Alanine     Valine     Leucine
(Ala, A)   (Val, V)    (Leu, L)




   Isoleucine Methionine Phenylalanine Tryptophan
    (Ile, I)   (Met, M)    (Phe, F)     (Trp, W)
           Non-polar amino acids
                 (cont’d)
Glycine
(Gly, G)




                   Proline
Cysteine           (Pro, P)
(Cys, C)
Polymerization of Amino Acids to Proteins


                         +
                             H2O       Condensation rx
          Peptide bond


  Amino                                    Carboxyl
  end                                      end


                    Dipeptide
                                See also ECB figure 5-1
   Lecture 4
Membranes
   Fatty Acids
   Phospholipids
   Lipid bilayer
   Other membrane lipids
   Membrane properties


Proteins
   Amino Acids
   Peptide bond
   Protein Structure
  4 Levels of Protein Structure
1˚ structure: the linear sequence of amino acids
   N-terminal to C-terminal

2˚ structure: stretches of the polypeptide chain
   that fold into a-helix or b-sheet (H-bonding)


3˚ structure: 3-dimensional conformation of a
   polypeptide chain


4˚ structure: multiple polypeptide chains interacting
   to form a complex
                 1˚ structure = sequence of amino acids




(ECB Fig. 4-2)
Higher levels of organization are determined by protein folding




                  Tertiary                  quaternary
                 structure                   structure
Secondary
structure
Improper protein folding is associated with disease

   Prion diseases - scrapie (sheep), mad cow (bovine), chronic wasting
   disease (deer, elk), Creutzfeldt-Jacob disease (CJD, humans)




  Alzheimers and Huntingtons diseases - aggregated proteins in brain
    Secondary Structure

a-helix and b-pleated sheet
ahelix

          H bond
                   C
                   O

                   H
                   N




      H bond                R groups are on outside of helix
      between peptide
      bonds, 4 a.a. apart
H bond
         b pleated sheet
  Tertiary Structure
3-D conformation of a single polypeptide chain
Driven by many types of bonds (H-bonds, hydrophobic
interactions, van der Waals, etc.)

Disulfide bond formation (between cysteine residues)
Folding into tertiary structure forms domains in
                   polypeptide


                        Two different domains


        Single domain


                                                Polypeptide made
                                                up of several
                                                domains
                Quaternary structure
  Multiple polypeptides interact via noncovalent and covalent
  (disulfide) bonds
                                                 Disulfide bridge

                    tetramer
dimer