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Chemistry 130
Practice Final Exam
May 1, 2003
Dr. Nash
50 Points Possible
NAME:__________________
1. Draw any of the -amino acids, any amino acid you like. (-amino acids are the ones
that are used to make proteins Draw it both as a zwitterion and in its neutral form. What
is a zwitterion and why do they form?
2. Draw any other -amino acid. Indicate with a (*) the chiral carbon, if any. Draw it as
both a zwitterion and in its neutral form.
3. Draw a dipeptide by linking the amino acids you chose from (1) and (2) above using a
peptide bond. Draw the mechanism for the formation of this peptide bond. Circle the it.
4. Draw the mechanism for the hydrolysis of the peptide bond of the dipeptide you drew
in (3). (i.e., the reverse process from problem 3, unlinking the two amino acids by
splitting the peptide bond using water)
5. Draw a saturated fatty acid
6. Draw an unsaturated fatty acid
7. Draw a triglyceride fat.
8. Draw the mechanism for the hydrolysis of the triglyceride fat from (12) to form
glycerol and a fatty acid. (i.e. the reverse of the esterification process that make the
triglyceride fat in the first place).
9. How is the fat you drew in (12) modified to form a phospholipid (Draw it).
10. How is it that phospholipids are perfect to form cell membranes. What is it about
these molecules that make them so good at distinguishing the inside and outside of a
micelle (like a cell) from the membrane itself. (USE THE WORDS BILAYER, SELFASSEMBLY, HYDROPHOBICITY, AND HYDROPHILICITY)
11. Draw a structure for each of the following named molecules
a) Butane
b) Pentene
c) Hexanal
d) Propyne
e) Octanol
f) Heptanone
g) Methyl Butyl ether
f) Ethanoic acid
g) Ethyl ethanoate
12. There twenty naturally occuring -amino acids.
a) Using the symbol R to represent a general sidechain, draw the structure of an
-amino acid.
b) amino acids can sometimes exist as ‘zwitterions’. What does this mean and
why?
c) if R represents a H atom, the amino acid is called glycine (gly),. Draw the
molecule and tell me if glyciene an enantiomer. If it does, mark with an asterisk
(*) the chiral carbon and draw the enantiomer.
d) if R represents a methyl group (-CH3), then the amino acid is called alanine
(ala). Draw the molecule and tell me if alanine has an enantiomer. If it does,
mark with an asterisk the chiral carbon atom and draw the enantiomer.
e) Recall that proteins are long chains of amino acids held together by peptide
bonds. Draw the polypeptide (short chain of amino acids) comprised by two
alanine molecules and one glycine molecule in the order (ala)-(gly)-(ala). Draw a
box around the peptide bonds in the molecule and mark with an asterisk any chiral
carbons atoms.
f) Digestion of proteins involves the ‘hydrolysis’ of a peptide bond to break the
bond connecting two amino acids. Draw a mechanism for this process for the
dipeptide (gly)-(ala). (A mechanism is a structural drawing showing which bonds
are broken, which are made, and where the electrons are going)
13. Draw a fatty acid, any fatty acid
14. Triglyceride fats can be made (and indeed, your body does this) by reacting fatty
acids with glycerol in a ester hydrolysis reaction similar to the ones you studied in lab.
Draw a mechaism for this type of reaction to form a triglyceride fat.
15. Soaps are made from triglyceride fats, how is this done and why is it that soaps are
good at removing ‘greasy crap’ from your hands.
16. Fats are in a class of substances known as lipids. A triglyceride fat can be ‘modified’
by replacing one of the fatty acid ester groups with a phosphate ion (PO43-). These socalled phospholipid form the substance of cell. How do they do this and why are they
perfectly suited to do it.
17. Cyanic acid, HCNO, is a weak acid having a Ka of 3.5 x 10-4
(a) 0.015 moles of HCNO is dissolved in enough water to make 0.5L of solution, what is
the pH of this resuling solution?
(b) What is the pOH of this solution from (a)
(c) 0.015 moles of HCNO and 0.025 moles of NaCNO ( this sodium salt containing the
cyanate ion CNO- is soluable) are dissolved in enough water to make 1.0 L of solution.
What is the pH of this solution?
(d) Is the solution from (c) a buffer? Why or why not?
(d) 0.010 moles of HCl are dissolved in 1L of water, what is the pH of this solution.
(e) 0.010 moles of HCl are dissolved in 1L of the solution from (c) What is the pH of the
solution?
(f) 0.010 moles of NaOH are dissolved in 1L of water, what is the pH of this solution?
(g) 0.010 moles of NaOH are dissolved in 1L of a solution prepared like that from (c),
what is the pH of this solution.
(h) So, is the solution from (c) a buffer or not? Why or why not
(i) can you think of why a buffer might be useful in biological systems?