Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chemistry 431

 Chem 431/8

 Exam I


 Fall 1994

 (100 pts)

A Key is available by clicking here

(15) 1a. Draw the structure of thefollowing peptide at pH 7 (structures of aa side- chains are on sale for 1 pt each!):


(10) b. Draw a titration curve for a peptide having the same amino acid residues as (a) above from pH 2-12 (assume that it is soluble) indicating approximate pKavalues. Label axis, buffer regions, and approximate pKa's!

(10) 2. Discuss the concept of domains in protein structure. Include in your discussion the relation between genes and domains, the potential consequences for adaptive evolution, and the effects/consequences of domain structure on protein folding and function.

(8) 3. Circle the best answerfor each of the following:

a. Glycolytic enzymes are synthesized:in the cytosol, on the endoplasmic reticulum, on the rough endoplasmic reticulum, in the golgi complex.

b. Of the following amino acids,those which are most likely to be found in a proteins interior are: (ala, ser, & cys), (gly, leu, & pro), (tyr, glu,& ala), (his, arg, & gly).

c. The most important force or bond in causing a protein to fold up into a compact form is: hydrogen bonding, disulfide bonding, hydrophobic forces, van der Waals forces.

d. The most important/characteristic "bond" type for maintaining secondary structures in protein assemblies is: hydrophobic, van der Waals, hydrogen, covalent, ion pair.

(9) 4. Briefly discuss the roles of disulfide bonds (if any) in each of the following: protein folding, protein structure, and protein function.

(14) 5. On the axis below draw typical kinetic curves for an allosteric enzyme such as we discussed in class under the following conditions: a) with no effectors present, b) in the presence of a positive effector, and c) in the presence of a negative effector. Label them!

d. Which of these curves shows the least cooperatively? Explain briefly why this should be so.

e. Challenge question: What would the effect of a competitive inhibitor on this enzyme if it were present at less than half saturating concentration? As your answer you can draw the curve for this situation on the plot above - label it!

(12) 6. List and describe as briefly as possible the six levels of protein structure we have discussed in class.

(8) 7. A typical plot for enzyme activity as a function of temperature is shown below. Describe/explain the phenomena underlying this curve.

(12) 8. Consider the process of protein folding and Briefly answer the following questions:

a. Why is it often said that proteins do not achieve the folded state with the lowest global free energy?

b. Why are alpha-helices so commonin globular proteins?

c. What advantage is there to breaking a large protein up into domains?

d. How do chaperones aid proteins in achieving their native folded structures?


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Last modified 17 August 2007