1. Storage: plant/animal starch Polysaccharides: 1. Storage: plant/animal starch ‘energy reserves’ - liver - muscles 2. Structural: cellulose chitin

Polysaccharides – It’s all in the linkage! Fig 5.7

Polysaccharides Structural polysaccharide - cellulose Hydrogen bonds between hydroxyls on C3 and C6 Food for thought…

Storage Polysaccharides - Summary Storage polysaccharide – starch (linear chains of repeating α glucose units) Plant starch Animal starch branched: (α 1-6) amylopectin or unbranched amylose always branched (α 1-6) glycogen length and location of branches is random Why store as a polymer? How are such stores tapped? Why don’t proteins branch?

Tapping Glycogen Reserves What happens to glucose now?

Proteins Amino Acid Workhorse molecules of the cell Polymers formed as a result of dehydration synthesis reactions that link together the amino acid monomers… Amino Acid Each of the amino acids has different chemical properties based on its ‘R’ group α

The Nonpolar Amino Acids + - zwitterion – can act as acid or base in the cell The Nonpolar Amino Acids

The Polar Amino Acids Polar, Uncharged Polar, Charged

Building a linear chain of amino acids Formation of a Protein Building a linear chain of amino acids Dehydration synthesis reactions link together amino acids. - Each amino acid is linked to the next by a covalent linkage called a peptide-bond - The ends of the peptide molecule are different: NH2 (end) terminal COOH (end) terminal Proteins synthesized from N C

NCC – NCC – NCC- NCC - NCC Formation of a Protein - continued Terms to note: peptide bonds side chains peptide ‘backbone’ imino groups carbonyl groups NCC – NCC – NCC- NCC - NCC

Formation of a Protein - Summary Formation of Peptide Bond Polypeptide Chain: Figure: 3.9a-c Caption: (a) When the carboxyl group on one amino acid reacts with the amino group on a second amino acid, a peptide bond forms.  (b) Amino acids can be linked into long chains by peptide bonds.  (c) The sequence of amino acids in a polypeptide chain is numbered from the N-terminus (or amino-terminus) to the C-terminus (or carboxy-terminus). Numbering System: From: Biological Science, by S. Freeman

Most Peptide Bonds in the ‘Trans’ Orientation

From: Molecular Biology of the Cell, 5th ed. Lodish et al.

The Four Different Levels Used to Describe the Structure of a Protein: Primary structure order of amino acids from the N terminus to the C terminus tremendous range in the size of proteins (toxins to titin) determines the shape/conformation of the protein Therefore, the function! Frederick Sanger first sequenced proteins in 1953 (Nobel, 1958) What determines 1º structure?

Linus Pauling Determined the structure of hemoglobin Discovered how abnormal hemoglobin causes sickle-cell disease Discovered α-helix and β-pleated sheets Won the Nobel Prize for Chemistry (1954) Won Nobel Peace Prize (1963) The only person to win two solo prizes

Secondary Structure Predictable, repeatable folding (2 types: α helix, β sheet) Forms as a result of hydrogen bonds between the imino and the carbonyl groups along the peptide backbone. Linus Pauling & Robert Corey! α helix structually the same between proteins 3.6 AA per turn Every 4th AA in close prox. Bonds are parallel to axis always intramolecular β (pleated) sheet intra or intermolecular bonds are perpendicular to the plane of the sheet parallel or antiparallel From: Biological Science, by S. Freeman

Globular and Fibrous Proteins Fibrous proteins have extensive 2º structure throughout length keratins (α-helices) Globular proteins – folded into compact rather than filamentous forms fibroin (silk protein – β sheets)

Proteins can consist of α-helices and β-pleated sheets α-helices, β-pleated sheets and regions of neither – random coils (green)

Tertiary Structure Most polypeptide chains bend and fold back upon themselves (random coils) to produce unique, complex three dimensional shapes = conformation Not repetitive (unlimited possibilities), not predictable (yet…) Lowest free energy state of the protein in its environment Involves: hydrogen bonds between polar amino acids electrostatic interactions (charged amino acids) hydrophobic interactions (nonpolar amino acids) disulfide bonds

Quaternary (4º) Structure: multimeric proteins Figure 3-6 Quaternary (4º) Structure: multimeric proteins > 1 polypeptide chain neuraminidase – homotetramer hemoglobin – heterotetramer (2α chains, 2β chains)

Quaternary (4º) Structure What kinds of chemical interactions stabilize the association of the subunits?

Protein Structure - Summary An astounding number of different proteins are possible!!! 20n where, 20 = the number of amino acids (AA) used in protein synthesis n = the length of the polypeptide chain (the total # of AA) Example: how many different proteins (i.e. sequence combinations) are possible for a polypeptide chain that contains 50 amino acids? 2050 = 2 x 1051 different sequences!!!