Chapter 5: Microbial Metabolism
Below you will find answers to the "Review" study questions found at the end of chapter 5 in Microbiology: An Introduction, 7th edition.
1.Metabolism is the sum of all chemical reactions that occur within a living organism.
2.Catabolic reactions break down organic compounds and release energy, while anabolic reactions use the products of catabolism and energy to build cell material.
3.
a. active site (top of enzyme image)
b. same as above
c. other site, not active site (lower right)
d. non-competitive inhibitor
4.
a.When the enzyme and substrate combine, the substrate molecule will be transformed.
b.When the competitive inhibitor binds to the enzyme, the enzyme will not be able to bind with the substrate.
c.When the noncompetitive inhibitor binds to the enzyme, the active site of the enzyme will be changed so the enzyme cannot bind with the substrate.
d.The noncompetitive inhibitor.
5.(a) is the Calvin-Benson cycle, (b) is glycolysis, and (c) is the Krebs cycle.
6.Glycerol is catabolized by pathway (b) as dihydroxyacetone phosphate. Fatty acids by pathway (c) as acetyl groups.
7.In pathway (c) at a-ketoglutaric acid.
8.Glyceraldehyde-3-phosphate from the Calvin-Benson cycle enters glycolysis. Pyruvic acid from glycolysis is decarboxylated to produce acetyl for the Krebs cycle.
9.In (a), between glucose and glyceraldehyde-3-phosphate.
10.The conversion of pyruvic acid to acetyl, isocitric acid to a-ketoglutaric acid, and a-ketoglutaric acid to succinyl~CoA.
11.By pathway (c) as acetyl groups.
12.
| Uses | Produces | |
| Calvin-Benson cycle | 6 NADPH | |
| Glycolysis | 2 NADH | |
| Pyruvic acid à acetyl | 1 NADH | |
| Isocitric acid à a-ketoglutaric acid | 1 NADH | |
| a-ketoglutaric acid à Succinyl~CoA | 1 NADH | |
| Succinic acid à Fumaric acid | 1 FADH2 | |
| Malic acid à Oxaloacetic acid | 1 NADH |
13.Dihydroxyacetone phosphate; acetyl; oxaloacetic acid; a-ketoglutaric acid.
14.The optimum temperature for an enzyme is one that favors movement of molecules so the enzyme can "find" its substrate. Lower temperatures will decrease the rate of collisions and the rate of reactions. Increased temperatures will denature the enzyme.
15.Ethyl alcohol, lactic acid, butyl alcohol, acetone, and glycerol are some of the possible products. Refer to Table 5.4 and Figure 5.18b.
16.
| Organism | Carbon Source | Energy Source |
| Photoautotroph | CO2 | Light |
| Photoheterotroph | Organic molecules | Light |
| Chemolithoautotroph | CO2 | Inorganic chemicals |
| Chemoorganoheterotroph | Organic molecules | Organic chemicals |
17.
| ATP generated by | Reaction |
| Photophosphorylation | An electron,
liberated from chlorophyll by light, is passed down an electron transport chain. |
| Oxidative phosphorylation | Cytochrome c passes two electrons to cytochrome a. |
| Substrate-level phosphorylation | Picture unavailable |
18.
a.Oxidation-reduction: A coupled reaction in which one substance is oxidized and one is reduced.
b.The final electron acceptor in aerobic respiration is molecular oxygen; in anaerobic respiration, it is another inorganic molecule.
c.In cyclic photophosphorylation, electrons are returned to chlorophyll. In noncyclic photophosphorylation, chlorophyll receives electrons from hydrogen atoms.
19.The pentose phosphate pathway produces pentoses for the synthesis of nucleic acids, precursors for the synthesis of glucose by photosynthesizing organisms, precursors in the synthesis of certain amino acids, and NADPH.
20.Oxidation
21.Reactions requiring ATP are coupled with reactions that produce ATP.
22.
The reaction rate will increase until the enzymes are saturated.
Below you will find answers to the "Multiple-Choice" study questions found at the end of chapter 5 in Microbiology: An Introduction, 7th edition.
1.a
2.d
3.b
4.c
5.c
6.b
7.b
8.a
9.c
10.b
Chapter 6: Microbial Growth
Below you will find answers to the "Review" study questions found at the end of chapter 6 in Microbiology: An Introduction, 7th edition.
1. In binary fission, the cell elongates and the chromosome replicates. Next, the nuclear material is evenly divided. The plasma membrane invaginates toward the center of the cell. The cell wall thickens and grows inward between the membrane invaginations; two new cells result.
2.Refer to Figure 6.14. The period of no cell division is called lag phase. During lag phase, the bacteria are synthesizing enzymes that are necessary for growth. In lag phase, the cells are dividing at the maximum rate under the conditions provided. The number of cells dividing equals the number of cells dying in stationary phase. When the number of deaths exceeds the number of divisions, death phase is observed.
3.Carbon (C) is required for synthesis of molecules that make up a living cell. Carbon-containing compounds also are required as an energy source for heterotrophs.
4.Most bacteria grow best between pH 6.5 and 7.5.
5.The addition of salt or sugar to foods increases the osmotic pressure for microorganisms on the food. The resulting hypertonic environment causes plasmolysis of the microbial cells.
6.
a.Catalyzes the breakdown of H2O2 to O2 and H2O.
b.H2O2; peroxide ion is O22-.
c.Catalyzes the breakdown of H2O2; NADH + H+ + H2O2 ---> NAD+ + 2H2O
d.O2-•; this diatom has one unpaired electron.
e.Converts superoxide to O2 and H2O2; 2O2-• + 2H+ ---> O2 + H2O2 The enzymes are important in protecting the cell from the strong oxidizing agents, peroxide and superoxide, that form during respiration.
7.Both environments prevent molecular oxygen from reaching the bacterial cells. In reducing media, thioglycolate combines with dissolved oxygen, thereby removing it from the medium. In an anaerobic incubator, air is replaced with an atmosphere of CO2 (and N2). Clostridium is an obligate anaerobe that lacks superoxide dismutase and catalase. Consequently, the accumulation of superoxides and peroxides will kill the cell in an aerobic environment.
8.Direct methods are those in which the microorganisms are seen and counted. Direct methods are direct count, standard plate count, filtration, and most probable number.
9.The growth rate of bacteria slows down with decreasing temperatures. Mesophilic bacteria will grow slowly at refrigeration temperatures and will remain dormant in a freezer. Bacteria will not spoil food quickly in a refrigerator.
10.
| Number of cells | X |
2n generations | = |
Total number of cells |
| 6 | X |
27 | = |
768 |
11.Petroleum can meet the carbon and energy requirements for an oil-degrading bacterium; however, nitrogen and phosphate are usually not available in large quantities. Nitrogen and phosphate are essential for making proteins, phospholipids, nucleic acids, and ATP.
12.A chemically defined medium is one in which the exact chemical composition is known. A complex medium is one in which the exact chemical composition is not known.
13.
Below you will find answers to the "Multiple-Choice" study questions found at the end of chapter 6 in Microbiology: An Introduction, 7th edition.
1.c
2.a
3.c
4.a
5.c
6.d
7.e
8.a
9.b
10.b
Chapter 7: The Control of Microbial Growth
Below you will find answers to the "Review" study questions found at the end of chapter 7 in Microbiology: An Introduction, 7th edition.
1.
a.Lysis.
b.Altered permeability and leakage of cell contents.
c.Destruction of enzymes and structural proteins such as those in the plasma membrane.
d.Interference with protein synthesis and cell division.
2.Autoclave. Due to the high specific heat of water, moist heat is readily transferred to cells.
3.Most organisms that cause disease or rapid spoilage of food are destroyed by pasteurization.
4.Variables that affect determination of the thermal death point are:
a.The innate heat resistance of the strain of bacteria.
b.The past history of the culture, whether it was freeze-dried, wetted, etc.
c.The clumping of the cells during the test.
d.The amount of water present.
e.The organic matter present.
f.Media and incubation temperature used to determine viability of the culture after heating.
5.
a.Ionizing radiation can break DNA directly. However, due to the high water content of cells, the formation of free radicals (H• and OH•) that break DNA strands is likely to occur.
b.Ultraviolet radiation damages DNA by the formation of thymine dimers.
6.Microorganisms tend to die at a constant rate over a period of time. The constant rate is indicated by the straight line after exposure to the bactericidal compound.
7.
| Sterilization Method | Temp. | Time | Type | Preferred Use | Mechanism of Action |
| Autoclaving | 121ºC | 15 min | Moist | Media, equipment | Protein denaturation |
| Hot air | 170ºC | 2 hr | Dry | Glassware | Oxidation |
| Pasteurization | 72ºC | 15 sec | Moist | Milk, alcoholic drinks | Protein denaturation |
8.All three processes kill microorganisms; however, as moisture and/or temperatures are increased, less time is required to achieve the same result.
9.Salts and sugars create a hypertonic environment. Salts and sugars (as preservatives) do not directly affect cell structures or metabolism; instead, they alter the osmotic pressure. Jams and jellies are preserved with sugar; meats are usually preserved with salt. Molds are more capable of growth in high osmotic pressure than bacteria.
10.
1.Acts rapidly.
2.Attacks all, or a wide range of, microbes.
3.Is able to penetrate.
4.Readily mixes with water.
5.Is not hampered by organic matter.
6.Stable.
7.Does not stain or corrode.
8.Nontoxic.
9.Pleasant odor.
10.Economical.
11.Safe to transport.
11.
| Method of Action | Standard Use |
| a. Disrupts plasma membrane | Skin surfaces |
| b. Inhibits protein function | Antiseptic |
| c. Oxidation | Disinfect water |
| d. Denatures proteins, destroys lipid | Skin surfaces |
| e. Oligodynamic | AgNO3 to prevent gonococcal eye infections |
| f. Inactivation of proteins | Chemical sterilizer |
| g. Denatures proteins | Chemical sterilizer |
| h. Oxidation | Antiseptic |
12.Disinfectant B is preferable because it can be diluted more and still be effective.
13.Quaternary ammonium compounds are most effective against gram-positive bacteria. Gram-negative bacteria that were stuck in cracks or around the drain of the tub would not have been washed away when the tub was cleaned. These gram-negative bacteria could survive the washing procedure. Some pseudomonads can grow on quats that have accumulated.
Below you will find answers to the "Multiple-Choice" study questions found at the end of
Chapter 7 in Microbiology: An Introduction, 7th edition.
1.d
2.b
3.d
4.d
5.b
6.b
7.b
8.a
9.a
10.b
Note: The answers to the Critical Thinking and Clinical Applications questions are posted on the board outside the lab and at the back of the lab.