BIO 224
Exam 3
Multiple Choice (2pts)
1. The plasma membrane functions as a
a. selective barrier to the passage of molecules.
b. sensor through which the cell receives signals from the environment.
c. site for uptake of macromolecules into the cell.
d. All of the above
2. The most common molecules in cellular membranes are the
a. glycolipids.
b. phospholipids.
c. cholesterol molecules.
d. proteins.
3. Cholesterol affects the fluidity of membranes into which it inserts by
a. increasing membrane fluidity at all temperatures.
b. decreasing membrane fluidity at all temperatures.
c. decreasing membrane fluidity at high temperatures and increasing membrane fluidity at low
temperatures.
d. increasing membrane fluidity at high temperatures and decreasing membrane fluidity at low
temperatures.
4. Phospholipids in a membrane commonly
a. move laterally in the plane of the bilayer.
b. rotate within the bilayer.
c. move from one bilayer to the other.
d. Both a and b
5. The role of double bonds in the fatty acid tails of membrane phospholipids is to
a. help stabilize the membrane.
b. react with adjacent double bonds.
c. increase membrane fluidity.
d. interact with membrane proteins.
6. Lipid bilayers are permeable only to molecules that are _______ and _______.
a. large; uncharged
b. large; charged
c. small; uncharged
d. small; charged
7. Integral membrane proteins are those that are
a. directly associated with membrane lipids.
b. associated with the membrane indirectly.
c. never span the membrane bilayer.
d. None of the above
8. Transmembrane proteins can span the lipid bilayer as
a. -helices.
b. -barrels.
c. Both a and b
d. None of the above
9. Molecules that traverse a membrane against their concentration gradient do so by _______ transport.
a. active
b. passive
c. carrier-mediated
d. channel-mediated
10. Channels form pores through which molecules of appropriate size and charge can cross a
membrane, whereas carrier proteins
a. actively transport molecules.
b. selectively bind the molecule to be transported, change configuration, and release it on the other
side.
c. require ATP.
d. transport a molecule against its concentration gradient.
11. The plasma membrane barrier to passive diffusion is primarily a function of the membrane’s
a. phospholipids.
b. cholesterol.
c. proteins.
d. glycoproteins.
12. Which energy-producing process is thought to have come first during cellular evolution?
a. Photosynthesis
b. Glycolysis
c. Oxidative phosphorylation
d. All originated at the same time
13. Stanley Miller’s experiment that applied electric sparks to a reducing atmosphere of methane,
ammonia, water, and hydrogen showed that under these conditions,
a. nucleotides can form.
b. amino acids can form.
c. amino acids can polymerize into polypeptides.
d. nucleotides can polymerize into nucleic acids.
14. Eukaryotic cell nuclei contain genes that are
a. primarily of eukaryotic origin.
b. primarily of archaebacterial origin.
c. partly archaebacterial and partly eubacterial in origin.
d. derived from neither archaebacterial nor eubacterial cells.
15. Organelles such as mitochondria and chloroplasts are thought to have originated in eukaryotic cells
via a process called
a. phagocytosis.
b. endosymbiosis.
c. endocytosis.
d. autogenous formation.
16. Mitochondria and chloroplasts resemble bacteria in that they
a. have their own DNA.
b. have their own ribosomes.
c. reproduce by simple division into two.
d. All of the above
17. Most eukaryotic plasma membrane proteins are synthesized on
a. free ribosomes and inserted after translation into the plasma membrane.
b. rough ER ribosomes and carried to the plasma membrane by vesicles that pinch off from the Golgi
apparatus.
c. rough ER ribosomes and carried to the plasma membrane by vesicles that pinch off from the rough ER.
d. ribosomes associated with the plasma membrane and inserted into the membrane cotranslationally.
18. Most cellular lipids are synthesized in
a. fat droplets.
b. mitochondria.
c. the endoplasmic reticulum.
d. the Golgi apparatus.
19. Newly synthesized membrane lipids are found in both halves of membrane bilayers because they are
a. synthesized on both surfaces.
b. removed and transported to these locations by lipid transport proteins.
c. synthesized on one surface and flip spontaneously to the other surface.
d. synthesized on one surface and flipped to the other surface by proteins called flippases.
20. Vesicles initially enter the Golgi apparatus by fusing with
a. the cis (convex) face. They exit from the trans (concave) face.
b. the trans (concave) face. They exit from the cis (convex) face.
c. both faces. They exit from the sides of cisternae.
d. None of the above
21. Which of the following classes of lipids is synthesized in the Golgi apparatus?
a. Phospholipids
b. Glycolipids
c. Cholesterol
d. Ceramide
22. Mitochondrial and chloroplast proteins are synthesized on
a. ER ribosomes.
b. free cytosolic ribosomes.
c. organellar ribosomes.
d. Both b and c
23. Which of the following contain their own genomes?
a. Mitochondria, but not chloroplasts and peroxisomes
b. Chloroplasts, but not mitochondria and peroxisomes
c. Mitochondria and chloroplasts, but not peroxisomes
d. Mitochondria, chloroplasts, and peroxisomes
24. Mitochondrial DNA is inherited by means of
a. Mendelian genetics.
b. random assortment.
c. paternal transmission.
d. maternal transmission.
25. Thylakoids are often arranged in stacks called
a. dictyosomes.
b. quanta.
c. grana.
d. plastids.
26. The principal difference between eukaryotic and prokaryotic cells is that eukaryotic cells have
a. larger ribosomes than prokaryotic cells.
b. cell walls, while prokaryotic cells do not.
c. DNA replication and transcription in the same compartment, while prokaryotic cells do not.
d. a nucleus, while prokaryotic cells do not.
27. The major pathway for molecules to pass into and out of the nucleus is through
a. gap junctions between the nuclear envelope membranes.
b. porin channels in the nuclear envelope membranes.
c. nuclear pore complexes.
d. diffusion through the membrane bilayers of the nuclear envelope.
28. The nuclear envelope is continuous with the
a. mitochondrial outer membrane.
b. rough endoplasmic reticulum.
c. Golgi apparatus.
d. plasma membrane.
29. Deduction of the structure of DNA was based on X-ray crystallographic studies done by
a. Beadle and Tatum.
b. Meselson and Stahl.
c. Wilkins and Franklin.
d. Watson and Crick.
30. An experiment in which cells were grown in media containing 15N in place of 14N and then their DNA
separated by equilibrium centrifugation demonstrated that
a. DNA is replicated by DNA polymerase.
b. DNA replication is conservative.
c. DNA replication is semiconservative.
d. A forms double helices by means of hydrogen bonding between base pairs.
31. The genomes of salamanders contain ten times more DNA than the genomes of humans because
salamanders
a. have ten times more genes than humans have.
b. need more DNA so they can regenerate new limbs.
c. have more noncoding DNA than humans have.
d. are more complex than humans.
32. The human genome is estimated to contain about _______ genes.
a. 10,000–15,000
b. 20,000–25,000
c. 100,000–150,000
d. 200,000–250,000
33. Pseudogenes are
a. genes that code for an RNA but do not code for a protein.
b. nonfunctional gene copies.
c. inactive genes.
d. repetitive DNA sequences.
34. The DNA of eukaryotic cells is wrapped around histones to form structures called
a. nucleoli.
b. nuclear matrices.
c. nucleosomes.
d. centromeres.
35. Which of the following statements about introns is true?
a. They are part of a gene, but they are absent from the corresponding mRNA.
b. They are sequences within genes that are not transcribed.
c. They make up only a small fraction of the DNA of a mammalian gene.
d. Prokaryotes do not have introns in their genes.
36. DNA polymerases can synthesize DNA
a. de novo, by catalyzing the polymerization of free dNTPs.
b. by adding dNTPs to complementary dNTPs on a single-stranded DNA.
c. by adding dNTPs to a hydroxyl group on the end of a growing polynucleotide chain hydrogen-bonded
to a strand of RNA.
d. by adding dNTPs to a hydroxyl group on the end of a growing polynucleotide chain hydrogen-bonded
to a strand of DNA.
37. Short segments of newly synthesized DNA on the lagging strand of DNA are called
a. Okazaki fragments.
b. replicons.
c. origins of replication.
d. lagging fragments.
38. Origins of replication are the
a. sites where DNA transcription starts.
b. binding sites for the protein complex that initiates DNA synthesis.
c. loops with two replication forks seen in replicating DNA.
d. forks where DNA replication is occurring.
39. Pyrimidine dimers
a. block DNA replication and transcription.
b. can be repaired by photoreactivation.
c. can be repaired by nucleotide-excision repair.
d. All of the above
40. Recombination of DNA strands is important because it can
a. rearrange DNA sequences to change gene expression during development.
b. repair damaged sequences.
c. increase genetic diversity in the next generation.
d. All of the above
Short Answer/Essay (5 pts)
41. Explain how gene amplification can contribute to tumor development.
42. What are two important functions of centromeres?
43. Addition or deletion of one or two nucleotides in the coding part of a gene produces a nonfunctional
protein, whereas addition or deletion of three nucleotides often results in a protein with nearly normal
function. Explain.
44. Why is RNA thought to have arisen on Earth prior to proteins and DNA?
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