Topic Test: Small Biomolecules -                                      [answers given below]
      Amino Acids and Nucleotides - Structural Dimorphism and
Reactivity

True/False
1.  The peptide bond, is a covalent bond, formed between the carboxyl group of
            one amino acid and the amino group of a second amino acid?
2.  The covalent bond between 2 or nucleotides forming a nucleic acid is a phosphodiester bond?
3.  Nucleotides are both informational and energy containing biomolecules? 

Multiple Choice
4.  The monomer molecule used by cells to make proteins, is (are)?
      a) monosaccharide sugars     b) fatty acids     c) amino acids     d) glycerol      e) nucleotides

5.  The monomer composed of a nitrogenous base, a 5 carbon sugar, and a phosphate is?
       a) an amino acid    b)  a nucleotide     c)  a lipid     d) a protein     e) a polysaccharide

6. Which of the amino acids side chains would contribute to a protein portion or regions that had hydrophobic (fatty) properties?
  a) -H          b) - CH 2-SH           c) -CH 2-COOH       d) -CH 2-OH       e) -CH 2-CH3

 

Short Answer/Problem Solving

7. What happens to the R groups of each amino acid when a peptide bond is formed
               between two amino acids?
8.  Why do you think it is that most proteins, which occur in the cyotsol of cells,
               are negatively charged?

9.  If one were to link 100 amino acids together by peptide bonds through
                condensation reaction, how many peptide bonds would be formed?

 

 

 

 

 

 

 

 

 

 

 

Topic Test :  Answers

True/False

1.  True.    A peptide bond is formed between the carboxyl group of one amino acid
                    and the amino group of a second amino acid by the elimination of water
                    in a condensation reaction.

2.  True.    A phosphodiester bond is formed between the phosphate of one nucleotide
                        (on the number 5 carbon of its sugar) and the hydroxyl on the number 3
                         carbon of another nucleotide, through the elimination of water in
                         a condensation reaction.
3.  True.     The nucleotides, ATP and GTP, are key energy providing molecules for
                        many coupled reactions in cells. In addition, the nucleotides in unique
  
                     sequences make up the codon of the genetic code. 

Multiple Choice
4.  c.    The monomers used by cells to make proteins are the 20 common amino acids.
5.  b.    A nucleotide is the monomer composed of a nitrogenous base, a 5 carbon sugar, and a phosphate.
6.  e.    -CH 2-CH 3 is a non-polar aliphatic side group which possesses hydrophobic
                (fatty) properties, and in consort with like groups can create a fatty pocket
  
             with the structure of a protein.

 

Short Answer/Problem Solving
7.   When peptide bonds are formed between amino acids, the R groups of each amino acid alternate on opposite side of the linear chain of amino acids formed.  This opposite side alternating orientation of the R groups helps reduce steric and electrostatic repulsion of R groups between themselves, thereby stabilizing the molecule's structure.

8.  Proteins, which are dissolved in the aqueous phase of the cell, the cyotsol, are negatively charged, because, at the pH of the cytosol most of the carboxyl groups present on the R groups will lose their proton (-COOH to -COO -) to aqueous solution, leaving a preponderance of the carboxyl groups ionized.  Since most protein are negatively charges, it also suggests that there must be a greater proportion of acidic amino acids, than basic amino acids in the average protein.

9.  Linking 100 amino acids together would produce 99 peptide bonds.  One end of  the protein would have an open amino group and the other end other protein would have an open carboxyl group; an N-terminal and a C-terminal.

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