Summer 2003: Lecture Exam 2

This exam consists of 50 multiple-choice questions. Each one has only one right answer. Read each question and all possible answers carefully before answering. Please mark your answers on the Scantron form provided, using only #2 lead pencil. If you erase an answer, make sure you erase it fully, or the machine may mark it incorrect. Check carefully to ensure that your answers are on the correct rows on the Scantron form.

Turn in both the Scantron form and the test paper when you are finished. Make sure your name is on both. You may write on the test paper if you wish, but anything you write on the test paper will not be graded. Good luck.

Above this line is a diagram of an amino acid called tyrosine. (The weird-looking hexagonal thing at the top part of the drawing is a kind of "shorthand" for a particular type of ring of carbon and hydrogen atoms.)

1. Which of the circled groups of atoms represent a carboxyl group?
#4.

2. The group of atoms labeled #1 represents the
R group.

3. If you had two tyrosine molecules, and you formed a peptide bond between them, the bond would form between
#4 on the first and #2 on the second.

4. In the skin of normal people, tyrosine is converted to the dark pigment melanin. When a person cannot convert tyrosine to melanin, the result is one type of albinism (lack of pigment in the skin and hair). People with this kind of albinism probably <
lack an enzyme that would convert tyrosine to melanin.

5. Albinism can hide in a family for several generations and then reappear. This makes it likely that albinism is caused by a
recessive gene.

6. Suppose two normal people marry and decide to have children, but their first child is an albino. What are the chances that their second child will be an albino as well?
25%

7. Which of the following would be an example of pleiotropy?
People with albinism often also have crossed eyes, poor vision, and weak blood vessels that tend to rupture.

8. In humans, the albinism gene is located on chromosome 11. This refers to
the 11th largest chromosome.

9. A somewhat different medical condition called ocular albinism doesn't affect the skin. People with ocular albinism don't look outwardly different from the norm. However, it reduces the amount of pigment inside the eye, which can cause vision problems. Ocular albinism is much more common in men than in women (although it is possible for a woman to have it). This suggests that it is probably
carried on the X chromosome.

10. People with one normal gene and one ocular albinism gene may have a blotched or mottled pattern of light and dark pigmented areas in the eye. This would be an example of
incomplete dominance.

11. Cells in your pancreas contain an unusually large number of ribosomes. This means that they produce
large amounts of protein.

12. If one strand of DNA reads TTCATAGGCCTAATA, how does its complementary DNA strand read?
AAGTATCCGGATTAT

13. The capsid of a virus
A, B, and C are all true -- it's made up of proteins; it is able to attach to host cells; and it contains nucleic acid.

14. Suppose you discover that a certain bacterium has DNA that is 31% adenine (A). You could use ____ to work out the rest of its composition.
Chargaff's Rules

15. In particular, if a bacterium has DNA that is 31% A, which of the following statements are true?
The DNA must also be 31% thymine (T).

16. A baby with three copies of chromosome 14 has several severe birth defects, collectively known as Patau's syndrome. Another name for Patau's syndrome would be
trisomy-14.

17. Patau's syndrome results when a sperm and an egg unite-and one of them has an extra copy of chromosome 14. This can result from the failure of paired-up chromosomes to separate in
anaphase I.

18. The type of cell division that creates eggs and sperm in the first place is
meiosis.

19. Why can't you see chromosomes in the nucleus of a cell that's not dividing?
Because they're uncoiled.

20. One difference between prokaryotes and eukaryotes is that prokaryotes have their DNA arranged in _______, whereas eukaryote DNA is arranged in ________.
loops; straight segments

21. A cell that for some reason could not make transfer RNAs would not be able to
make any proteins.

22. This is a model of a protein called the mannose-binding protein. The overall shape looks like a real mess, but the arrow points to a section of the protein that has a spiral twist. This is a(an) alpha-helix. 23. To form this kind of spiral shape, nearby amino acids have to attract each other.

24. This protein's tertiary structure could be described as
the overall folding scheme of the entire molecule.

25. What did Watson and Crick do?
Work out the double helix structure of DNA.

26. Corn snakes (Elaphe guttata) are elegant creatures that are completely harmless to humans. Typical corn snakes have an attractive pattern of black spots on an orange background. However, some corn snakes have no black anywhere on their bodies, and look orange all over. Suppose you crossed an orange-and-black spotted snake with a solid orange snake and found that all the babies had orange and black spots. This would mean that the black-spotted allele was ___ to the non-black allele.
dominant

27. Now suppose that you took one of the black-spotted babies from the question above, let it grow up, and crossbred it with a solid orange snake. You could refer to the babies that you got from this cross as the
F₂ generation.

28. What proportions of colors would you expect to find in the offspring of this second cross?
Half should have orange and black spots, and half would be solid orange.

29. There are also corn snakes that never have any orange color on their bodies. These snakes may or may not have black spots, but the background color is nearly white, not orange. The orange allele is dominant to the white allele. Which of the following could be the genotype of a snake that was white with black spots?
BBoo

30. Truly albino corn snakes have neither orange nor black coloration. Suppose you crossbred two corn snakes that both had the genotypes BbOo. What proportion of the babies would be true albinos?
1/16.

31. Frederick Griffiths
discovered the "transforming principle."

32. In a eukaryote, where does transcription take place?
In the nucleus.

33. Plants normally use an enzyme called EPSP synthase in making certain amino acids from a substrate. The herbicide Roundup^TM chemically looks like this substrate, and it can keep a plant from making amino acids because it can enter and block the active site on the enzyme. This is an example of
competitive inhibition.

34. A chemical reaction that releases energy, such as the explosion of gunpowder, still needs a bit of energy input-for instance, from a spark, a percussion cap, or a lit match-to get it started. This is called the
activation energy.

35. Anything that reduces the amount of energy that needs to be added to get a chemical reaction started is a (an)
catalyst.

36. This group of atoms is called methyl methacrylate. If you link many of these molecules together in a chain, you get the plastic Plexiglas or Lucite (same thing, different brand names). This makes methyl methacrylate a/an: monomer.

This was just reported in the May 2003 issue of the magazine Scientific American: The biotechnology company VaxGen has just announced the results of its clinical trial of an HIV vaccine. If this vaccine works, injecting it into people will protect them from getting infected with HIV (human immunodeficiency virus), the cause of AIDS.

37. HIV is a retrovirus, which specifically means that it can
reverse transcribe its RNA to make a DNA molecule.

38. HIV is an exception to the Central Dogma of Molecular Biology, which may be summarized as:
DNA --> transcription --> RNA --> translation --> protein

39. When HIV reproduces, it frequently develops errors in its genetic material. Such "copying errors" are known as
mutations.

40. The scientist who provided a crucial piece of data to Watson and Crick, and whom some feel never got the credit she really deserved, was
Rosalind Franklin.

41. It is possible for two parents to have children with all four blood types (quite legitimately-no sneakin' around or anything). For this to happen, what must the parents' genotypes be?
AO and AO.

42. If a piece of DNA breaks its hydrogen bonds, the DNA
unzips into two strands.

43. A typical cell in a camel's body contains seventy chromosomes. Suppose a camel cell undergoes meiosis. After meiosis, the original cell has produced __ cells with __ chromosomes each.
four; thirty-five

44. This is a diagram of a chromosome in the stage of mitosis called prophase. Which part is the centromere? #3. 45. Which part is one chromatid? #1 + #4.

46. When a protein is actually made, what molecules bring the amino acids to the ribosome?
Transfer RNAs.

47. A polymer of amino acids is held together by
Sean Connery, George Lazenby, Roger Moore, Timothy Dalton, and Pierce Brosnan.
Actually, I'm kidding. It's held together by peptide bonds.

48. This is a plant cell in the stage of mitosis called prophase. What will happen in the stage of mitosis immediately after this one? The chromosomes will line up in the center.

49. What's the RNA codon for the amino acid tryptophan?
UGG
That's the only option that's a codon (i.e. made of three bases) and that includes U (uracil).

50. What is the national anthem of the United States of America?
"The Star-Spangled Banner"