Taxonomy & Evolution (Answers)
1. K. W. Jeon observed that a previously healthy amoeba culture became sick. On examination, 150,000 bacteria were inside each sick amoeba. Many amoeba died, however, some survived and grew again as healthy cells. Examination of these survivors showed 50,000 bacteria inside each amoeba. After 5 years, Jeon transplanted the nucleus from one of these amoeba to an enucleated, uninfected amoeba. The resulting cell could not divide. When the nucleus was put into an enucleated, infect amoeba, the resulting cell did divide. Explain.

2. Mutant mitochondria can be created in the laboratory. Commonly used mutations are mit-, which is deficient in some respiratory enzymes, such as cytochrome oxides, and AmgR which is resistant to aminoglycoside antibiotics. (AmgS = sensitive to aminoglycosides.) Assume that all of the mitochondria in a yeast cell are destroyed by streptomycin treatment and two new mitochondria, a mit -, AmgS and a mit+, AmgR, are put into a yeast cell. After the yeast grows, its progeny have mitochondria that are mit+ and AmgS. Explain how these mitochondria occurred.

3. Which type of metabolism, autotrophic or heterotrophic, most likely evolved first? Provide a rationale for your choice.

4. Colorless Euglena can ingest organic molecules and grow heterotrophically. Euglena loses its chloroplasts when it is (a) grown in the dark or (b) treated with streptomycin. When return to the light, the (a) Euglena culture will produce chloroplasts but the (b) culture will never produce chloroplasts. Explain these results.

5. To date the only evidence supporting the hypothesis that eukaryotic flagella may have evolved from symbiotic bacteria is observation of the protozoan Mixotricha. This protozoan is propelled entirely by bacteria living in specialized groove on the protozoan's surface. What evidence is needed to support this hypothesis?

Cell Theory & Microscopy (Answers)
1. In 1996, scientists found what appeared to be fossils inside a meteorite from Mars that landed in Antarctica. A newspaper account described electron micrographs of sections of the meteorite: "Inside they found fossilized works 100 times smaller than the oldest fossils ever found on Earth, which also were wormlike. The fossils are arout 3.6 billion years old. The oldest fossils on Earth, microscopic worms found in Australia, are about 3.4 billion years old." What error did the reporter make when he tried to interpret the electron micrographs?

2. Assuming a typical membrane is 8 nm wide, how many membranes would have to be aligned side by side to be seen with a light microscope? With an electron microscope?

3. Use the following information to calculate the volume of each cell. Assume each cell is spherical.

	Bacterial cell	Human liver cell	Plant mesophyll cell
Diameter	2 µm	20 µm	30 µm

Calculate the number of (a) bacterial cells that will fit in a liver cell and (b) liver cells that will fit in a plant cell?

4. Your lab partner has made a methylene blue solution to stain cells. He has tried to stain bacterial, plant, and animal cells but can't get the cells colored when he asks you for help. What do you advise him?

5. Compare the contributions made by van Leeuwenhoek and Hooke.

Cell Structure (Answers)

1. If the amoeba Reticulomyxa is treated with detergent to extract its organelles, the organelles will move (20µm/sec) when ATP is added. Explain how these organelles can move.

2. Patients with Zellweger Syndrome die within a few months after birth due to the accumulation of fatty acids in cells. What organelle is missing from these patients?

3. Leukocyte adherence deficiency (LAD) is an inherited disease. People with LAD suffer from recurrent infections and fail to make pus although they have large numbers of white blood cells in their blood. Their white blood cells are lacking integrins. Explain how this deficiency leads to ineffective white blood cells.

4. The smallest eukaryotic cell is the motile alga Micromonas. What is the minimum number of organelles this alga must have?

5. Individuals with certain immune deficiencies have been shown to have neutrophils without peroxisomes. Why could this cause an immune deficiency?

Membranes (Answers)

1. You isolate three enzymes from snake venom and subject red blood cells to treatment with each enzyme. In light of what you know about the plasma membrane, explain the results

Enzyme	Hemolysis
Protease	No
Phosphatidylserine deaminase	No
Phospholipase	Yes

.

2. Escherichia coli bacteria adhere to right-side out ghosts but not to inside-out ghosts. Moreover, E. coli bacteria do not adhere to cells if mannose is in solution around the cells. Explain how these bacteria adhere to cells.

3. Patients with hereditary spherocytosis have fragile red blood cells that can't maintain their biconcave shape. What membrane component are they missing?

4. Red blood cells were placed in isotonic solutions of different substances as shown below. How do you account for the results?

Substance	Lysis	Time to lyse
Calcium chloride	No	-
Urea	Yes	1 sec
Glucose	Yes	2 hr

5. Both salt (NaCl) and sugar (sucrose) are used as food preservatives. How do they work to preserve food? Compare the osmotic pressure of 10% NaCl and 20% sucrose.

Intracellular Traffic (Answers)

1. Congenital sucrase-isomaltase deficiency (CSID) results in osmotic diarrhea because the patient cannot metabolize sucrose. CSID patients make sucrase-isomaltase and permanently store it in the ER. Provide a possible mechanism for this disease.

2. Hunter's disease and Hurler's disease are inherited conditions in which patients accumulate chondroitin in the cells. If Hunter's fibroblasts and Hurler's fibroblasts are combined in vitro they will cure each other. Explain these diseases.

3. In plant cells, secretory vesicles formed in the Golgi complex fuse with the plasma membrane and deliver cell wall materials to the exterior of the cell. During growth, enough new membrane is added to double the size of the plasma membrane every 20 minutes. How does the plant cell limit the expansion of the membrane?

4. In cells infected with Varicellavirus, the viral DNA and protein coat are synthesized in the nucleus. Pulse-chase experiments using H-3 labelled fucose have shown the viral glycoproteins are bound to the plasma membrane four hours after infection. Describe how the viral glycoprotein is made in the cell.

5. Surface proteins of cultured mouse cells were labeled with I-125 using lactoperoxidase and treated witht antibodies to the insulin receptor to locate the insulin receptor. A different cell culture was labeled and incubated at 37°C for 1 hour prior to treatment with antibodies to the insulin receptor. The experiment was repeated keeping the cells at 10°C for 1 hour. What happened to the labeled receptors at 37°C?

Chemistry Review (Answers)

1. Giraffes, termites, and koalas eat only plant matter. Since animals cannot digest cellulose, how do you suppose these animals get nutrition from the leaves and wood that they ingest?

2. Thiobacillus ferrooxidans was reponsible for destroying buildings in the Midwest by causing changes in the earth. The original rock, which contained calcium carbonate (lime) and pyrite, expanded as bacterial metabolism caused calcium sulfate (gypsum) crystals to form. How did T. ferrooxidans bring about the change from lime to gypsum?

3. When growing in an animal, Bacillus anthracis produces a capsule that is resistant to phagocytosis. The capsule is composed of D-glutamic acid. Why is this capsule resistant to digestion by the host's phagocytes?

4. The antibiotic amphotericin B causes leaks in cells by combining with sterols in the plasma membrane. Would you expect to use amphotericin B against a bacterial infection? A fungal infection? Offer a reason why amphotericin B has severe side effects on humans.

5. Sequences of amino acids in different types of human hemoglobin are shown below. Explain why some changes in amino acids alter function (i.e., hemoglobin S and Hammersmith hemoglobin) while other changes do not alter the function of the protein (human ß chain and delta chain).

Amino acid #	3	4	5	6	...9	...40	41	42	43
ß chain (normal Hb)	Leu	Thr	Pro	Glu	Ser	Gln	Arg	Phe	Glu
Hb S (sickle-cell)	Leu	Thr	Pro	Val	Ser	Gln	Arg	Phe	Glu
Hammersmith Hb (unstable)	Leu	Thr	Pro	Glu	Ser	Gln	Arg	Ser	Glu
Delta chain (normal Hb)	Leu	Thr	Pro	Glu	Thr	Gln	Arg	Phe	Glu

Energy & Enzymes (Answers)

1. Laundry detergents and drain clearners contain enzymes from Bacillus subtilis. What is the value of these enzymes in clothes washing and drain cleaning?

2. The bacterial enzyme streptokinase is used to digest fibrin (blood clots) in patients with atherosclerosis. Why doesn't injection of streptokinase cause a streptococcal infection? How do we know the streptokinase will digest fibrin and not good tissues?

3. Methyl alcohol is poisonous because the enzyme alcohol dehydrogenase converts it to formaldehyde. Why could excess ethyl alcohol prevent methyl alcohol poisoning?

4. Glyphosate is used to kill unwanted plants and it does not affect humans. It inhibits the enzyme phosphoenolpyruvate synthase. Provide an explanation for glyphosate's selectivity for plants.

5. Normal liver cells contain 2 to 8% glycogen. Liver cells from patients with von Gierke's disease contain 40% glycogen. The glycogen is degraded if it is mixed with extracts from normal liver cells but not if it is mixed with von Gierke's cells. Explain the defect in von Gierke's disease.

Catabolism (Answers)

1. Differentiate between starch hydrolysis and starch fermentation.

2. Streptococcus bacteria lack an electron transport chain. How does this bacterium reoxidize NADH? Where is the NADH formed?

3. Identify the metabolic pathways used by the following bacteria:

Pseudomonas	Oxidizes glucose
Lactobacillus	Ferments glucose
Alcaligenes	Neither oxidizes nor ferments glucose
Escherichia	Oxidizes and ferments glucose

4. Why can prokaryotes make 38 ATPs from 1 molecule of glucose and eukaryotes only make 34 ATPs?

5. Animals living in cold places have brown fat. Brown fat gets its color from the presence of cytochromes. In brown fat, electron transport is uncoupled from ATP synthesis.
a. What is the advantage of brown fat?
b. What is the advantage of the uncoupling?

Photosynthesis (Answers)

1. Explain why only red algae and not green or brown algae are found below about 75m in the ocean.

2. Compare and contrast oxidative phosphorylation and photophosphorylation.

3. Why can't most organisms live in 15% NaCl? How does the purple membrane of Halobacterium bacteria enable these bacteria to live in a 15%-NaCl environment?

4. Rhodopseudomonas bacteria are anaerobic photoautotrophs which use organic compounds as an electron donor. Diagram the metabolic pathways of this bacterium.

5. The absorption spectrum of Chlamydomonas is shown below. Explain the burst of oxygen in the red region?

Wavelength (nm)	500	550	600	650	700
Light absorption	+	+	-	+	+
Oxygen produced	-	-	-	+	-

Molecular Genetics (Answers)

1. The following is a code for a strand of DNA.

DNA	A	T	A	T	-	-	-	T	T	T	-	-	-	-	-	-	-	-	-
-	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19
mRNA	-	-	-	-	-	-	-	-	-	-	C	G	U	-	-	-	U	G	A
tRNA	-	-	-	-	-	-	-	-	-	-	-	-	-	U	G	G	-	-	-
Amino acid	-	-	-	-	met			-			-			-			-

(a) Fill in the blanks to complete the segment of DNA shown.
(b) Fill in the blanks to complete the sequence of amino acids coded for by this strand of DNA.
(c) Write the code for the complementary strand of DNA completed in part a.
(d) What would be the effect if C was substituted for T at base 10?
(e) What would be the effect if A was substituted for G at base 11?
(f) What would be the effect if G was substituted for T at base 14?
(g) What would be the effect if C was inserted between bases 9 and 10?
(h) How would UV radiation affect this stand of DNA?
(i) Identify a nonsense sequence in this strand of DNA?

2. Locate the promotor, the structural genes, and the termination site.

3. Replication of the E. coli chromosome takes 40-45 minutes, but the organism has a generation time of 26 minutes. How does the cell have time to make complete chromosomes for each daughter cell? For each granddaughter cell?

4. Photobacterium bacteria have a lux operon that consists of a promoter, operator, and structural genes for the enzyme liciferase. Luciferase binds with FMNH₂ and emits a photon of light to oxidize the FMNH₂. E. coli bacteria have an ara operon. When arabinose binds to the repressor, the structural genes are transcribed to degrade arabinose. Assume that you engineer Pseudomonas bacteria to contain the ara repressor gene and the lux structural genes. What happens when the recombinant Pseudomonas is exposed to (a) lux inducer, (b) arabinose, and (c) lactose.

5. Chloroquine, erythromycin, and acyclovir are used to treat microbial infections. Chloroquine acts by intercalating into DNA. Erythromycin binds in front of the A site on the 50S ribosome. Acyclovir is a guanine analog.

(a) What steps in protein synthesis are inhibited by each drug?
(b) Which drug is more effective against bacteria? Why?
(c) Which drug is more effective against viruses? Why?
(d) Which drugs will have effects on the host's cells? Why?

Biotechnology (Answers)

1. You have isolated a bacterium that produces a bacteriocin against Salmonella. The bacterium grows well in Medium 1 but doesn't produce its bacteriocin. Testing one component at a time, you determine that iron interferes with bacteriocin production. Whey you try Medium 1 without iron, the bacteria don't grow. Bacteriocin production is best in Medium 2.

Medium 1		Medium 2
Glucose	0.5%	Glycerol	3.5%
Citric acid	0.1%	Glucose	0.5%
20 amino acids, each	0.04%	Citric acid	0.1%
K phosphate, dibasic	0.15%	20 amino acids, each	0.04%
Mg sulfate	0.12%	K phosphate, dibasic	0.15%
Fe sulfate	0.000015%	Mg sulfate	0.12%

(a) Design a procedure to maximum the biomass and the yield of bacteriocin.
(b) What are bacteriocins?
(c) How might a bacteriocin against Salmonella be used?

2. You are attempting to insert a gene for salt water tolerance into a plant by using the Ti plasmid. In addition to the desired gene, you add a gene for tetracycline resistance (tetR) to the plasmid. What is the purpose of the tetR gene?

3. Some tomatoes have a very short shelf-life because they produce large amounts of the ripening hormone ethylene. Ethylene is a small molecule containing only two carbon atoms. It is a gas at room temperature. Explain how antisense technology has been employed to lengthen the shelf-life of these tomatoes.

4. PCR involves heating to break the hydrogen bonds in DNA, cooling to allow a primer hydrogen bond to the single strands, and incubation to allow DNA polymerase to build complementary strands of DNA. This procedure is repeated 30 times an hour to get large quantities of the desired DNA. Why did the use of DNA polymerase from the bacterium Thermus aquaticus allow researchers to add the necessary reagents to tubes in a preprogrammed heating block?

5. PCR has been used to examine oysters for the presence of Vibrio cholerae. Oysters from different areas were homogenized, and DNA was extracted from the homogenates. The DNA was digested with restriction enzyme Hinc IIA primer for the hemolysin gene of V. cholerae was used for the PCR reaction. After PCR, each sample was electrophoresed and stained with a probe for the hemolysin gene. What will the Southern blot film look like in a positive sample? A negative sample? What is the advantage of PCR over conventional biochemical tests to identify the bacteria.

Ecology (Answers)

1. A patient with a heart pacemaker received antibiotic therapy for streptococcal bacteremia. One month later, he was treated for recurrence of the bacteremia. When he returned 6 weeks later, again with bacteremia, the physical recommended replacing the pacemaker. Why did this cure his condition?

2. The vacuum-heap process is used to remove benzene and other hydrocarbons from soil contaminated by gasoline and oil. The pipes are used to add nitrates, phosphates, oxygen, or water. Why are each of these added? Why is it not always necessary to add bacteria?

3. Explain the effect of dumping untreated sewage into a pond on the eutrophication of the pond. The effect of sewage with secondary treatment? Contrast your previous answers with the effect of each type of sewage on a fast-moving river.

4. Fill in the following table:

Process	Chemical Reactions	Microorganisms
Ammonification
Nitrification
Denitrification
Nitrogen fixation

5. In the sulfur cycle, microbes degrade organic sulfur compounds, such as _____ to release hydrogen sulfide, which can oxidized by Thiobacillus to _____. This ion can be assimilated into amino acid by ____- or reduced by Desulfovibrio to ____. Hydrogen sulfide is used by photoautotrophic bacteria as an electron donor to synthesize _____. The sulfur-containing by-product of this metabolism is _____.

Cell Growth & Recognition (Answers)

1. The following cell cultures were exposed to tritium-labeled thymidine and examined by autoradiography for labeled nuclei. What can you conclude from these data?

	Labeled nuclei after exposure to thymidine, hr
	11	12	13	14	15	16	17	18
Human diploid fibroblasts	-	-	-	-	+	+	+	+
HeLa	-	-	-	-	-	-	-	+
CHO	+	+	+	+	+	+	+	+

2. Sexual dimorphism, that is, differences between males and females of a species, is often created by cell death. The songs of male and female zebra finches are different. The song is controlled by a site in the brain called the RA nucleus. Estrogen treatment during development causes a male song in female birds. Explain the role of cell death in song production.

3. Homeotic genes have been extensively studied in Drosophila embryos. The embryo is 14 parasegments long, with parasegment 1 in the head region. The products of Antp are normally present in parasegments 4 and 4 and the products of Ubx are found in paragements 5-6. If Ubx is deleted, products of Antp are found in parasegments 5-6. If gene abd is deleted, Antp and Ubx products are found through parasegment 12. Since these genes are present in every cell in the fly's body, propose a mechanism for controlling their expression.

4. The synthetic auxins, 2,4-dichlorophenoxyacetic acid (2,4-D), is widely used as a herbicide. Explain how a plant growth hormone can kill plants.

5. Cholera toxin causes G protein to bind to adenylate cyclase. How does this result in the watery diarrhea of cholera?

Cancer (Answers)

1. Explain how radiation can be used to cure cancer as well as cause cancer.

2. Women with the normal BRCA 1 gene do not inherit familial breast cancer, while women who inherit a mutated form of BRCA 1 are predisposed to develop breast cancer. Propose a mechanism of action for this gene.

3. EB virus is known to cause Burkitt's lymphoma in regions in Africa with malaria. In the U.S., EB viral infectious mononucleosis is common and Burkitt's lymphoma occurs in AIDS patients. Explain the occurrence of Burkitt's lymphoma.

4. Most ras protooncogene mRNA contains an extra exon that includes a number of UAA codons. Cancer cells produce ras mRNA missing this exon. Why doesn't the longer mRNA cause cancer? Where does the mistake most likely occur in the abnormal ras product?

5. The fos and jun genes make transcription factors but only in the presence of PDGF. Fos and Jun proteins are present in large amounts in cancer cells but their genes are not considered oncogenes. What gene might be the actual oncogene? PDGF is not found in the cytoplasm or nucleus of target cells. Suggest a mechanism by which PDGF can stimulate Fox and Jun production. Why are both Fos and Jun needed?

Cell Communication (Answers)

1. In 1986, Rita Lei-Montalcini received a Nobel Prize for her discovery. She observed that when mouse sarcoma (cancer) cells are grown in chick embryo cells, the chick cells develop nerve cells. what did Montalcini discover?

2. The most common hereditary hemophilia is von Willebrand disease (vWD). Patients with vWD form abnormal platelet plugs which result in prolonged bleeding time. Platelets from a patient with vWD do not adhere to vWD endothelial cells. The vWD plates will adhere to normal endothelial cells but not to normal embryonic cells. Explain the defect in vWD.

3. Organophosphate insecticides are competitive inhibitors of acetylcholinesterase. What is the effect of organophosphates on an animal? Which of the following drugs could be used to counteract organophosphate poisoning?

Drug	Method of Action
Atropine	Blocks muscarinic acetylcholine receptors
Curare	Competitive inhibition of acetylcholine receptors
Physostigmine	Competitive inhibition of acetylcholinesterase

4. The toxins of poison arrow frogs are losted below. Complete the table to show the symptoms of poisoning.

Toxin	Molecular action	Effect on neuron
Batrachotoxin	Prevents Na gate closure
Pumilotoxin B	Prevents reuptake of Ca
Histrionicotoxin	Prevents K efflux

5. Changing the [Na+] outside the cell doesn't change the resting membrane potential. Why not?

Viruses (Answers)

1. You are growing Bacillus subtilis in nine 16,000-liter bioreactors to produce enzymes for industrial use. The Bacillus culture had been growing for two days when the cells in one of the fermenters disappeared. Explain what happened in this fermenter.

2. In some viruses, capsomeres function as enzymes as well as structural supports. Of what advantage is this to the virus?

3. Why was the discovery of simian AIDS and felina AIDS important?

4. Prophages and proviruses have been described as being similar to bacterial plasmids. What similar properties do they exhibit? How are they different?

5. Thirty-two people in the same town reported to their physicians with fever (40°C), jaundice, and tender abdomen. All 32 had eaten an ice-slush beverage purchased from a local convenience store. Liver function tests were abnormal. Over the next several months, the symptoms subsided and liver function returned to normal. What is the disease? This disease could be caused by a member of the Picornavirida, Hepadnaviridae, or Flaviviridae. Differentiate among these families by method of transmission, morphology, nucleic acid, and type of replication.

Immunity (Answers)

1. In thrombocytopenic purpura, a drug such as aspirin coats platelets and the platelets are destroyed by complement. Provide a mechanism for this disease.

2. Bone marrow transplants can reject the host in graft-versus-host disease. Explain how this occurs. Why are bone marrow transplants done?

3. After working in a mushroom farm for several months, a worker develops these symptoms: hives, edema, and swollen lymph nodes.

(a) What do these symptoms indicate?

(b) What mediators cause these symptoms?

(c) How may sensitivity to a particular antigen be determined?

(d) Other employees do not appear to have immunological reactions. What could explain this?

(Hint: The allergen is conidiospores from contaminating molds, not the mushroom crop.)

4. Physicians administering live, attenuated mumps and measles vaccines prepared in chick embryos are instructed to have epinephrine available. Because epinephrine will not treat these viral infections, what is purpose of keeping this drug on hand?

5. A patient with dysgammaglobulinemia suffers from recurrent mucus-membrane infections because they are lacking one type of antibody. Which type? Propose a mechanism whereby suppressor T cells are responsible for this disease?