Chem 30B                                Name ________________________

3rd hour exam  Chpt 8 - 11                                  please print

May 21, 2003          103 points     Points are in the left margin, e.g., [6]

 

A. Fill in the blanks:  

[2] 1. Coenzymes are frequently synthesized from the Vitamins  in our diet.

[2] 2. Estrogen is a lipid hormone which belongs to which specific chemical family  ?

      Steroids

 

[2] 3. The beta pleated sheet is associated with which level of protein structure ?  2°

[2] 4. The DNA triplet corresponding to the codon  GUU is  CAA .

[2] 5. The functional group  broken down when a tripeptide is hydrolyzed is Amide or peptide

[2]  6. The synthesis of RNA from a DNA template is called transcription    

[2] 7.  A proenzyme is a(n)     inactive  form of that enzyme.

[2] 8.  When several ribosomes are attached to a single m-RNA molecule the resulting complex is called a ___polysome or polyribosome__ .

[2] 9.The most common kind of lipid in our food is triglyceride

 

[2] 10.  An enzyme with 4° structure that responds to a modulator is called allosteric

[4] 11.  In addition to phosphoglycerides, biological membranes contain

            cholesterol         and                proteins             .

[4] 12. Complete hydrolysis of a triglyceride leads to the formation of glycerol and _____fatty acids  .

 

[4] 13.  The most important  difference between a coenzyme and a prosthetic group is

 

A coenzyme is much more  tightly bound  to the protein than a coenzyme

 [6] 14. The three parts of a DNA nucleotide are:

 

a.    phosphate

b.   2-desoxyribose

c.   a heterocyclic base (A, T, G, C)

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B. 1. [6] Draw the structure of an acidic amino acid in a neutral solution, including its charges.

 

 

 

2. [8] Describe the difference between the digestion and the denaturation of a protein.  Which one involves the greater change in the proteinıs structure?

Denaturation is a proteinıs complete loss of function or activity. It is due to major changes in the 2°, 3° and 4° structure of the protein. Digestion begins with denaturation but goes much beyond that to include hydrolysis of the amino acids. When digestion is complete there is no protein left, only a mixture of  amino acids!

 

 

3. [9]   a. In the 3° structure of a protein there is only one stabilizing force that is a covalent bond.  Name it. Disulfide bond

b. Name the amino acid which leads to this bond. cysteine

c. Draw a diagram showing the chemical structure of this bond. Show the backbone as a simple line.

 

 

 

       

4. [6] Amino acids are quite soluble in water, even those with a nonpolar side chain. Explain why. What feature of amino acidıs chemical structure cause this?

Amino acids are always charged. They can be cations, anions or zwitterions. Charges (ions) are the most hydrophilic group.

 

 

5. [10] Explain in detail why and how a relatively small change in the pH of a solution can cause a major change in the activity of an enzyme.

 

 

 

 

6. [8] Some people claim that we should eat all our food raw because cooking denatures the enzymes in the food, and this decreases its nutritional value. Do you agree with this claim ?   Explain why or why not.

 

Denaturing the enzymes in our food has no effect on the foodıs nutritional value. Enzymes are proteins and a proteinıs total nutrients are its amino acids. The proteinıs structure at any level doesnıt matter. If cooking made proteins harder to digest there would be a nutrient loss. In fact, cooking usually makes proteins more available to the digestive enzymes and so increases their nutrient value.

 

The fact that vitamins may be destroyed during cooking is irrelevant to this question.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7. [9]  List and briefly describe three (3) different processes where complementary base pairing is important.

a.  DNA replication: 

 

b. Transcription of all kinds of RNA from DNA

 

c. Between m-RNA (codons)  and t-RNA (anticodons)

8. List and briefly describe three substantially different chemical structures in which hydrogen bonding  plays a significant role.  Draw simple diagrams to illustrate each example.

 

Many possible answers from biochem

 

[3]  a. Complementary base pairing  (see above)

 

 

[3]  b. Protein secondary structure: Stabilizing alpha-helix and beta pleated sheet

 

 

[3]  c. Protein tertiary  structure:

 

 

Others:

 

Boiling point of water

 

Solubility of alcohol and sugars in water.

 

 

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