Topic Test: Small Biomolecules -
[answers given below]
Amino Acids and Nucleotides - Structural Dimorphism and Reactivity
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?
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
1. True. A peptide bond is formed between the carboxyl group of one amino
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.
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.