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____/12 Points
Building Compounds Lab – Penicillin
Penicillin was discovered by bacteriologist Alexander Fleming working at St. Mary's Hospital in
London in 1928. He observed that a plate culture of Staphylococcus bacteria had been
contaminated by a blue-green mold and that colonies of bacteria adjacent to the mold were being
dissolved. Curious, Alexander Fleming grew the mold in a pure culture and found that it produced a
substance that killed a number of disease-causing bacteria. Naming the substance penicillin, Dr.
Fleming in 1929 published the results of his investigations, noting that his discovery might have
therapeutic value if it could be produced in quantity. It was not until World War II that sufficient
quantities of penicillin were produced. This drug has since saved countless lives worldwide and is
regarded as one of the greatest achievements in medical history. The structure of penicillin is
shown below. Note the implied carbon at the points where the bonds (lines) intersect.
1.
Construct the beta-lactam ring with your modeling kit (2 points). Teacher initials __________
Is this an easy structure to build? Explain briefly.
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2.
According to VSEPR theory, what should the bond angle between the nitrogen and carbon at 1
be? How does this bond angle compare to the actual bond angle you find (2 points)?
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3.
The center of the penicillin molecule contains a beta-lactam ring. How does the structure of
this ring relate to its function? Refer to questions #1 and #2 for clues. Then use the textbook
and the internet to research the answer to the questions as a group. Cite the source used in
MLA format. Be sure to include and underline the following words in your description: cell
wall, penicillin, bond angles, enzyme, beta-lactam ring, bacteria, electron domains (8 points).
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Source:
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Answer Key
Question 1:
Teacher initials (1 point)
Yes, the structure is difficult to build because of the high degree of ring strain in the structure. (1 point)
Question2:
According to VSEPR theory the carbon has three electron domains. Therefore, the bond angle on the carbon
should be 120°. This is much greater than the actual bond angle which is closer to 90 degrees.
Question 3: - Answer
The beta-lactam ring structure is important to penicillin’s function. The ring contains bond angles that are
much smaller than what would be predicted in VSEPR theory. For example the carbon at position 1 would
be expected to form bond angles of 120° due to the three electron domains around it. However, the bond
angle is much smaller. As a result, the ring is under tremendous strain. This makes the ring unstable. The
ring will attach to an enzyme, DD-transpeptidase, blocking the formation of peptidoglycan cross-links in the
bacterial cell wall. The loss of the function for the enzyme weakens the cell wall, eventually leading to cell
death.