Draw a diagram of the histidine side chain in the protonated and unprotonated states. Show the contributing resonance structures and the composite resonance structure for the protonated state.

The pka of the side chain of histidine is 6.00. What is the percent of protonated histidine at pH 6.4? 15.3% 28.5% 45.3% O 66.6%

Threonine has two chiral centers. Draw L-threonine and indicate which carbon atoms are chiral. Which carbon atom is responsible for d and L configuration?

Consider the reaction for assembly of a tetrapeptide from four amino acids: Serine + Proline + Alanine + Methionine ----> SPAM tetrapeptide Draw a free energy diagram for this reaction (you know, the one that is a line with a speed bump on it?). Remember to always label the axes on graphs, and label where the (actual) reactants and products free energies are on the curve. In addition, label activation energy and draw a dashed line showing the effect of an enzyme on the curve.

Draw the structural formula of Tyrosine. Label the carboxyl group, amino group, and R group, and explain the importance of each.

Provide the precise chemical description (anomer, isomer, and ring form) of the mono-saccharide subunits that are forming the tri-saccharide sugar molecule. Note the indicated numbering of the carbon atoms for the middle and the right subunit. Research the generic name of the tri-saccharide once you have identified the mono-saccharide subunits.  Left subunit: Middle subunit: Right subunit: Name of sugar: b) Provide the precise chemical description of the two bonds that connect the sugar subunits?

a. Suppose that you have the peptide Ala-Gly-Tyr-His-Leu and you treat it with FDNB and then 6M HCl. Draw the structures of all the products that you will have in solution (assume all reactions to go to completion).

The catalytic triad consists of Asp, His, and Ser. What would be an alternative for histidine and how would we draw the interactions in a mechanism?

A schematic diagram of the helical structure of cytochrome b562 is reproduced below. Thisprotein belongs to the family of -proteins that have a four-helix bundle. Number the helices 1 – 4according to their N  C direction. Indicate relative orientations of the macrodipoles of helices 1 – 4adjacent to the diagram of cytochrome b562. Remember that according to the definition of a dipolethat the arrow points towards the positive end.

Proline is one of the amino acids in the "special" groups of sidechains. One reason for this is the dramatic impact it can have on secondary structure.  a) draw the lewis structure for a tripeptide with the sequence Ala-Pro-Ala b) Proline residues are rarely found in alpha helices - in fact, they are often referred to as helix-disrupting amino acids. Thinking about intermolecular interactions, provide an explanation for why proline might disrupt alpha-helices. c) Proline also has a similar effect on beta-sheets, and is rarely found in the middle of beta sheets. Thinking about noncovalent interactions, provide an explanation for why proline might disrupt beta-sheets.