To date, most of our natural antibiotics have been found to be produced by members of what genus?
A) Streptomyces
B) Bacillus
C) Penicillium
D) Paenibacillus
E) Cephalosporium
A
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Arrange the following five events in an order that explains the mass flow of materials in the phloem
1. Water diffuses into the sieve tubes. 2. Leaf cells produce sugar by photosynthesis. 3. Solutes are actively transported into sieve tubes. 4. Sugar is transported from cell to cell in the leaf. 5. Sugar moves down the stem. A) 2, 1, 4, 3, 5 B) 1, 2, 3, 4, 5 C) 2, 4, 3, 1, 5 D) 4, 2, 1, 3, 5 E) 2, 4, 1, 3, 5
Cellular respiration may occur in environments where oxygen is absent such as the subsurface layers of the microbial mats depicted in Figure 26.7
In such places, molecules other than oxygen must be used as the terminal electron acceptor used to produce energy for the cell. As stated in Chapter 6, all biochemical reactions in a cell are subject to the laws of thermodynamics. Like chemical reactions, by comparing the difference in free energy (G0 ') of the reactants and products in a biochemical reaction, you can determine how much energy is released or consumed during the course of a reaction (Figure 6.9). As discussed in Chapter 7, redox reactions are biochemical reactions that take place during cellular respiration and result in the transfer of electrons from one molecule to another. During the course of such reactions, one molecule gets oxidized, and another reduced. Redox reactions require two half reactions between pairs of compounds (called redox pairs). A list of some biologically relevant redox pairs is shown in the table to the right. The redox pairs are arranged from the strongest electron donor pairs at the top to the strongest electron acceptors at the bottom. The tendency of electrons to be passed between any two redox pairs can be measured experimentally using a voltmeter. The voltage difference, defined as the reduction potential (E0 '), has been determined for all redox pairs in the table using hydrogen as a reference standard, which has a reduction potential of zero. The greater the difference in reduction potential (E0 ') between two half reactions, the more energy that is released during a biochemical reaction. The difference in reduction potential is a direct measure of the change in free energy (G0 '). Thus, the greater the change in reduction potential between two redox pairs, the more free energy that is available for the reaction to proceed. Consider a respiring microorganism that uses pyruvate- / lactate- as an electron donor pair. If this microorganism uses oxygen as a terminal electron acceptor under aerobic growth conditions, we would calculate the change in reduction potential as follows: O2 / H2O Eo'(V) = +0.82 (acceptor pair) pyruvate- / lactate- Eo'(V) = -0.19 (donor pair) The change in reduction potential (E0 ') is calculated by subtracting the donor pair value from the acceptor pair value. E0 ' = +0.82 - (-0.19) = 1.01 V Now think about a respiring microorganism that uses the same electron donor pair, pyruvate- / lactate-, but produces energy and grows in an environment that lacks oxygen. In this case, redox reactions occur with a terminal electron acceptor pair is not oxygen but another acceptor pair shown in the table. Calculate the change in reduction potential for each option below, then circle the best acceptor pair. AsO4 3- / AsO3 3- Eo'(V) = +0.139 - (-0.19) = 0.33 NO3 - / NO2 - Eo'(V) = +0.43 - (-0.19) = 0.62 Fe3+ / Fe2+ (pH 2) Eo'(V) = +0.77 - (-0.19) = 0.96 What will be an ideal response?
P53 is a ____
a. transcription factor that turns on expression of cell division inhibiting proteins b. protein encoded by an oncogene c. protein that promotes entry into the cell cycle when DNA is undamaged d. hormone used to treat cancer e. growth promoting factor
During fetal development, when is it possible to clearly hear the fetal heartbeat when the physician applies a stethoscope to the mother's abdomen?