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Microbiology - Exam 3 Study Guide: Short
Answer
1. Some lipid molecules have a distinctive four-ringed structure and often function as hormones. What is
the name for this group of hormones, and what are two examples of molecules in this group?: Steroids, including sterols, have this structure. Cholesterol and steroid hormones are examples.
2. What is the difference between a steroid and a sterol?: Steroids lack an -OH group that is present in sterols.
3. What is a unit membrane?: A unit membrane is the standard membrane of plasma membranes and eukaryotic organelles. Unit
membranes have a phospholipid bilayer structure.
4. What is the function of cholesterol in cell membranes?: Cholesterol makes cell mem- branes more resilient by
strengthening it.
5. How many glycosidic linkages are in the molecule below?: Two
6. What type of chemical reaction is needed to separate this molecule into three fatty acids and
glycerol?: Hydrolysis reaction
7. Indicate the a carbon on the amino acid below.: The a carbon is the carbon to which the
amino group, carboxyl group, hydrogen, and R group are joined.
8. Consider the molecule below. Of the four major types of important biological molecules, which type is
this? How can you tell? Explain why it fits into that group and then explain why it does not fit into each of the other three groups.- : This molecule is a lipid. It is nonpolar and consists of only carbon and hydrogen. It is not a monosaccharide, because it does not have -OH groups. Sugars do have -OH groups and an aldehyde or ketone (when linear).They can also form rings. It is not an amino acid, because it lacks an amino group and a carboxyl group. Finally, it is not a nucleotide, because it lacks a phosphate group, a sugar, and a nitrogenous
2 / base (let alone any nitrogen). It does not contain a sugar for the reasons already discussed.
9. Identify the functional group or groups in this molecule: CH3CH2CHO: This
molecule contains an aldehyde
10. Why is glucose usually found in nature as a ring rather than as a linear structure?: Sugars can form a
ring through the interaction of a hydroxyl group and a carbonyl group. When the ring is the right size for maintaining appropriate bond angles, then a ring is more stable than the linear molecule. Glucose has six carbons and can form either a six-membered ring or a five-membered ring.
11. Compare the structures of starch, glycogen, and cellulose. Explain why humans cannot use
cellulose as a major source of energy even though it contains glucose molecules.: Although starch, glycogen, and cellulose are all polymers of glucose, they have ditterent structures, resulting in ditterent properties. Starch consists of two types of chains, a straight chain (amylose) and a branched chain (amylopectin). Glycogen consists of one type of chain, which is more branched than amylopectin. Cellulose is not branched but has linkages between its linear chains that make it strong. Because cellulose has ditterent glycosidic linkages than those of starch and glycogen, a ditterent enzyme is needed to break it down and human do not produce this enzyme.
12. What are micelles and why is it energetically favorable for them to form?-
: Micelles are spherical structures that assemble from phospholipids with the phosphate groups toward the outside and the lipid tails toward the inside. This is energetically favorable because the lipid tails are hydrophobic and it would take more energy to keep them in contact with water than in contact with each other.
13. Is the α carbon of this molecule chiral? Explain.: Yes, the a carbon of this molecule is chiral
because it has four ditterent groups attached to it and, therefore, has two mirror image forms.
14. Provide a basic overview of the major steps of the sulfur cycle.: Hydrogen sulfide is oxidized to elemental
sulfur and then to sulfate.
15. What characteristics cause an organism to be classified as a chemo- heterotroph?:
Chemotrophs get their energy from chemical reactions.
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25. Where does the transition reaction occur in prokaryotic cells, compared with eukaryotic cells?:
Prokaryotic cells do not have mitochondria, so the transition reaction takes place in the cytoplasm. In contrast, in eukaryotic cells, the transition reaction takes place in the mitochondrial matrix.
26. In prokaryotic cells, where does the electron transport chain of aerobic respiration take place?: In
the cell membrane because these cells do not have mitochondria.
27. The figure shows a chemical reaction. Explain whether the reaction is en- dergonic or
exergonic.:
28. Based on what you know about different metabolic types of microbes, what would be the
carbon, energy, and electron requirements for a chemoorganoautotroph?: A chemoorganoautotroph would be an organism that used chemical reac- tions of organic molecules to gain energy and electrons but is also capable of fixing inorganic molecules to produce organic molecules.
29. Explain redox potential and why it is important in understanding the elec- tron transport chain.: Redox
potential describes how easily a molecule acquires electrons. A molecule with a more positive redox potential will more readily accept an electron from another molecule, being reduced in the process. In the elctron transport chain, an electron is passed from one acceptor to another, with each having a more positive redox potential than the last.
30. Which group of bacteria commonly divides using fragmentation?: Actinomycetes
31. Where are barophilic organisms found?: In environments where the pressure is unusually
high, such as deep in the ocean or far underground.
32. What happens during plasmolysis and what causes it?: The shrinkage of protoplasm away from the cell wall of a
plant or bacterium and is caused by water loss from exosmosis.
33. What is the difference between the optimum oxygen concentration and the maximum permissive
oxygen concentration?: The optimum oxygen concentration is the ideal concentration of oxygen for a particular microorganism. The maximum permissive oxygen is the highest tolerated concentration of oxygen.
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34. What is the following equation used for and what do the variables n, Nn, and N0 refer to?
Nn = N02n: N: number of generations Nn: number of cells at each generation No: start number of cells
35. Why do researchers often work with bacteria in the log phase of bacterial growth in a batch
culture, rather than in other phases?: The log phase is also the stage where bacteria are the most susceptible to the action of disinfectants and common antibiotics that attect protein, DNA, and cell-wall synthesis.
36. What are the most important signaling molecules for quorum sensing in gram-negative bacteria?
How does this compare with the signaling molecules used by gram-positive bacteria?: N-acyl derivatives of homoserine lactone (acyl HSLs)
37. What is the standard way to grow obligate anaerobes in the laboratory?: In
an anaerobic jar that includes chemical packs that remove oxygen and release carbon dioxide.
38. Why is MacConkey agar considered both a selective and a differential medi- um?: It is selective because it
only grows gram-negative bacteria and it is ditterential because it ditterentiates lactose fermenters and lactose nonfermenters based on their color.
39. Why might you need to enrich media?: To isolate bacteria that break down crude oil
40. Give an example of a halotolerant species that can cause food poisoning.: S.
aureus
41. Mixed bacterial infections can occur that include both facultative anaerobes and obligate
anaerobes. What happens when these species coexist?: The faculta- tive anaerobes use up the oxygen, creating an environment for the obligate anaerobes to flourish.
42. Staphylococci thrive on human skin. What does this tell you about their environmental
requirements?: They are facultative anaerobes. They thrive in a pH of 4-10 with an optimum of 6-7. They thrive in temperatures 30C-
