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Cell Biology Comparisons

2. The inner membranes of cyanobacteria are very similar to those of the thylakoid membrane of chloroplasts. This similarity supports the hypothesis that chloroplasts evolved from symbiotic cyanobacteria. Which other organelles may have originated in the same way? Explain, providing evidence for your choice.

4. Proviruses can be converted from the lysogenic to the lytic pathway under certain circumstances.
a. What circumstances can lead to this shift?
b. Can a virus in the lytic pathway become a provirus? Explain.

9. Some people are born with or develop a condition known as lactose intolerance that causes them to suffer intestinal discomfort when they eat lactose-containing dairy products. This occurs because the lactose that can normally be metabolized and the cleavage products that can then be passed through the intestinal lining cannot be metabolized in these individuals. Can you suggest an explanation for this?

10. Which of the following tripeptides (only one) would be most likely to be soluble in an organic (hydrophobic) solvent like benzene. Explain.
 N - phenylalanine - alanine - glycine - C
 N - leucine - alanine - lysine - C
 N - proline - phenylalanine - alanine - C
 N - arginine - lysine - proline - C
 N - glutamine - asparagine - glycine - C

11. What level of structure in DNA would be disrupted by a reagent that breaks apart hydrogen bonds? Explain.

12. Which of the four classes of amino acids has the following characteristics:
a. Side chains with the greatest hydrogen-bond-forming potential

b. The greatest potential to form ionic bonds

c. Hydrophobic interactions

13. DNA is isolated from two species. Both DNA samples are found to be of the same size (i.e. equal quantities). The samples have G+C/A+T ratios of 2.0 and 2.5.
a. Which DNA sample has a higher G+C content? Explain.

b. Which sample contains the smaller number of H bonds between strands? Explain.

16. What electron or light microscopy technique would you use to observe the following?
a. The fine detail of the outer surface of hair cells in the inner ear.

b. The interior and exterior of surfaces of the plasma membrane to support the fluid-mosaic model of membrane structure. (Hint: it is a procedure used in conjunction with Transmission Electron Microscopy.)

c. Structures in living cells.

17. Why is resolution in electron microscopes so much better than that in light microscopes? (Hint: think about wavelength size)

18. What technique would be used to determine the arrangement of atoms within a protein? (This technique has also been used to detect and locate the spatial arrangement of the atoms of DNA.)

1. Enzymes greatly decrease the activation energy. Explain two of the ways they do this and be specific in terms of chemical mechanisms.

2. You are observing an enzyme-driven reaction. To the reaction mixture, you add a chemical, X, that inhibits the reaction. You suspect that X is a competitive inhibitor. What two pieces of evidence might lead you to this conclusion?
3. You have isolated a new enzyme and have determined the velocity of reaction at three substrate concentrations. You find that the slope of the product-versus-time curve is the same for all three concentrations. What can you conclude about the conditions in the reaction mixture?
4. The ΔG of the following reaction is -2.8 kcal/mol.acetyl phosphate + ADP  acetate + ATP
Is the free energy difference per molecule of acetyl phosphate, relative to that of acetate, greater than, lesser than, or equal to that of ATP relative to its dephosphorylated counterpart?

5.
a. What is the source of pyruvic acid in the cell? Explain briefly.

b. What is the importance of ADP levels within the mitochondrion, particularly with respect to respiratory rate?

6. Determine which of the substances ubiquinone, NAD+, NADH, O2, and H2O is:
a. the strongest reducing agent ___________________

b. the strongest oxidizing agent ___________________

c. an electron carrier ___________________
7. Refer to Figure 6.7 on page 220 in the textbook. The absorption spectrum indicates the relative light absorption of various pigments in the chloroplast. Which colours of the spectrum are absorbed most strongly by (a) the chlorophylls and (b) β-carotene?
a.
b.

8. a. What do plants do to prevent water loss in a hot, dry climate?

b. How would this cause photorespiration in a C3 plant?

c. Why are C4 plants protected? i.e. why are C4 plants immune to photorespiration?

Experiment 1: Effect of Temperature on Amylase Activity
The data for this activity are in Table 1.
Table 1. V of the enzyme amylase at different temperatures, [S] and pH
Environ-mental Conditions: pH = 7
[S] = 90 mM pH = 7
[S] = 60 mM pH = 7
[S]=120 mM pH = 5
[S] = 90 mM pH = 9
[S] = 90 mM
Temper-ature (ºC) V (mM/min) V (mM/min) V (mM/min) V (mM/min) V (mM/min)
15 0.00096 0.00089 0.00095 0.00124 0.00060
30 0.00158 0.00137 0.00161 0.00205 0.00097
32 0.00222 0.00200 0.00230 0.00300 0.00138
35 0.00278 0.00245 0.00288 0.00357 0.00163
37 0.00300 0.00275 0.00311 0.00395 0.00180
39 0.00293 0.00261 0.00300 0.00375 0.00177
41 0.00267 0.00256 0.00283 0.00346 0.00162
43 0.00241 0.00231 0.00245 0.00306 0.00146
45 0.00212 0.00176 0.00209 0.00272 0.00123
48 0.00171 0.00147 0.00167 0.00224 0.00100
50 0.00131 0.00120 0.00138 0.00165 0.00078
55 0.00094 0.00090 0.00104 0.00121 0.00055

9. Develop a hypothesis to predict the effect of an increase in temperature on amylase activity. Test your hypothesis using the data provided in Table 1. State your hypothesis.

10. Using the data in Table 1.
a. What is the optimal temperature for amylase activity? __________

b. Would amylase isolated from any two organisms (for example, fish amylase vs. amylase from the small intestine of humans) show the same temperature optimum? Explain your answer.

11. Explain why a temperature lower or higher than the optimum would cause decreases in amylase activity. (What is happening to the enzyme to produce these decreases in activity?)
12. If you were to carry out these temperature experiments at a higher or lower [S], what effect would [S] have on the temperature optimum for amylase? Formulate a hypothesis. Using the data from Table 1, test your hypothesis. Explain your results. (Note: Do not submit your plotted graph.)
13. If you were to carry out these temperature experiments at a higher or lower pH value, what effect would this have on the temperature optimum for amylase? Formulate a hypothesis and then, using the data in Table 1, test your hypothesis. Explain your results. (Note: Do not submit your plotted graph.)

Experiment 2: Effect of Substrate Concentration on Amylase Activity
The data for this experiment are in Table 2.
Table 2. V (mM/min) at different [S] (mM) of the enzyme amylase at 37ºC and pH = 7.0
[S] (mM) V (mM/min) [S] (mM) V (mM/min)
0.0 0 140 0.00432
2.5 0.00044 160 0.00433
5 0.00102 180 0.00432
10 0.00161 200 0.00464
20 0.00223 220 0.00447
30 0.00277 240 0.00455
40 0.00313 260 0.00454
50 0.00349 280 0.00469
60 0.00363 300 0.00472
70 0.00388 320 0.00467
80 0.00383 340 0.00471
90 0.00395 360 0.00487
100 0.00401 380 0.00477
120 0.00429 400 0.00473

14. Using the data in Table 2, examine the relationship between [S] and amylase activity. To answer the questions, plot the data: V vs [S] and 1/V vs 1/[S] (Lineweaver-Burk). (Note: Do not submit your plotted graphs.)
a. Explain the relationship and your results.
What are the Vmax and KM for amylase for this experiment?
15. Compare the values for Vmax and KM derived from each of the two plots (V vs [S] and Lineweaver-Burke).
a. Were these values similar or different? How?

b. If the values were different, explain possible reasons for these differences.

c. Which plot did you find easier to use for determining these values?

16. What do you think would happen if you carried out an experiment with concentrations of starch greater than 400 mM?

17. Briefly compare the effects of a competitive versus a non-competitive inhibitor on an amylase-catalyzed reaction i.e. how would these inhibitors respectively affect KM and Vmax?

Solution Preview

2. The inner membranes of cyanobacteria are very similar to those of the thylakoid membrane of chloroplasts. This similarity supports the hypothesis that chloroplasts evolved from symbiotic cyanobacteria. Which other organelles may have originated in the same way? Explain, providing evidence for your choice.
Mitochondria have many features in common with prokaryotes. As a result, they are believed to be originally derived from endosymbiotic prokaryotes. A mitochondrion contains DNA, which is organized as several copies of a single, circular chromosome. The circular structure is also found in prokaryotes, and the similarity is extended by the fact that mitochondrial DNA is organized with a variant genetic code similar to that of Proteobacteria. This suggests that their ancestor, the so-called proto-mitochondrion, was a member of the Proteobacteria.
4. Proviruses can be converted from the lysogenic to the lytic pathway under certain circumstances.
a. What circumstances can lead to this shift?
During an infection, some viruses stay inside the cells but do not make new viruses. Instead of producing virus particles, the viral gene is inserted into the host chromosome and is called a provirus. Whenever the cell divides, the provirus also divides, resulting in two infected host cells. In this cycle, called the lysogenic cycle, the viral genome replicates without destroying the host cell. In some lysogenic viruses, change in the environment can cause the provirus to begin the lytic cycle, which means the destruction of the host cell. These can include episodes of stress, or other changes to the environment.

b. Can a virus in the lytic pathway become a provirus? Explain.

No. This is because, once in the lytic cycle, the viral DNA exists as a separate molecule within the bacterial cell, and replicates separately from the host bacterial DNA. The location of viral DNA in the lysogenic phage cycle is within the host DNA, but in the lytic phage cycle, the phage is a free floating separate molecule to the host DNA. Some viruses escape the host cell without bursting the cell membrane, but rather bud off from it by taking a portion of the membrane with them. Because it is technically characteristic of the lytic cycle in previous steps, it still belongs to the lytic category, although it is sometimes called the Productive Cycle.

9. Some people are born with or develop a condition known as lactose intolerance that causes them to suffer intestinal discomfort when they eat lactose-containing dairy products. This occurs because the lactose that can normally be metabolized and the cleavage products that can then be passed through the intestinal lining cannot be metabolized in these individuals. Can you suggest an explanation for this?
This condition is caused by a lack of lactase, the enzyme required to break down lactose in the digestive system, and can result in symptoms which may include abdominal pain, diarrhea, nausea, bloating, flatulence, and acid reflux. Lactose intolerance is caused by lactase deficiency, which may be either genetic or environmentally induced. The symptoms of lactose intolerance are caused by insufficient levels of the enzyme lactase in the lining of the duodenum. Lactose, a disaccharide molecule found in milk and dairy products, cannot be directly absorbed through the wall of the small intestine into the bloodstream so, in the absence of lactase, passes intact into the colon. Bacteria in the colon are able to metabolise lactose and the resulting fermentation produces large amounts of gas that causes the various abdominal symptoms. The unabsorbed sugars and fermentation products also raises the osmotic pressure of the colon, resulting in an increased flow of water into the bowels, causing diarrhea.

10. Which of the following tripeptides (only one) would be most likely to be soluble in an organic (hydrophobic) solvent like benzene. Explain.
 N - phenylalanine - alanine - glycine - C
 N - leucine - alanine - lysine - C
 N - proline - phenylalanine - alanine - C both Phe and Ala are very hydrophobic amino acids (in particular, phenylalanine) and would be the most likely to be soluble in a hydrophobic solvent
 N - arginine - lysine - proline - C
 N - glutamine - asparagine - glycine - C

11. What level of structure in DNA would be disrupted by a reagent that breaks apart hydrogen bonds? Explain.
The secondary structure: In nucleic acids, the secondary structure is defined by the hydrogen bonding between the nitrogenous bases. Thus, a reagent that destroys hydrogen bonds would affect the secondary structure of DNA.

12. Which of the four classes of amino acids has the following characteristics:
a. Side chains with the greatest hydrogen-bond-forming potential
acidic and polar

b. The greatest potential to form ionic bonds

acidic and polar paired with a basic and polar

c. Hydrophobic interactions

non-polar and neutral

13. DNA is isolated from two species. Both DNA samples are found to be of the same size (i.e. equal quantities). The samples have G+C/A+T ratios of 2.0 and 2.5.
a. Which DNA sample has a higher G+C content? Explain.
The second sample (2.5) as it has 2.5 times the amount of G + C content to A + T content

b. Which sample contains the smaller number of H bonds between strands? Explain.

The first sample contains the smaller number of H bonds between strands. This is because A forms only a single H bond with T, whereas G will form two H bonds with C. Because the second sample has a greater amount of G + C content, it will also contain the greater number of H ...

Solution Summary

The expert compares multiple components in cellular biology.

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