A certain chemical is found to inhibit the synthesis of all steroids. The synthesis of which of the following hormones would NOT be affected when a dose of this chemical is administered to a laboratory rat?
Answer(s): C
We're told that a certain chemical inhibits the synthesis of steroids and we're asked to decide which one of the hormones listed in the answer choices would not be affected if a dose of this chemical was administered to a laboratory rat. In other words, we need to know which of these hormones is NOT a steroid hormone. Steroids are a type of lipid with a carbon skeleton of four fused rings. Different types of steroids differ in the functional group that is attached to the carbon skeleton. Cholesterol is a very important steroid, and is in fact the precursor steroid molecule from which most other steroids, including steroid hormones, are synthesized. For example, the sex hormones testosterone, estradiol, and progesterone which are synthesized in the gonads, are steroid hormones modified from cholesterol. This means that we can rule out choice D. The adrenal cortex is another gland that secretes a family of steroid hormones called the corticosteroids. The two main types of corticosteroids are the mineralocorticoids, such as aldosterone, and the glucocorticoids, such as cortisol. This means that we can also rule out choices A and B, which leaves us with choice C, epinephrine. The adrenal medulla secretes the hormone epinephrine in response to any type of stress good or bad. Epinephrine, along with norepinephrine, are compounds called catecholamines, and are synthesized from the amino acid tyrosine by chromaffin cells in the adrenal medullA. Hence, epinephrine synthesis would NOT be affected by this chemical, which makes choice C the correct answer.
A biochemist grows two cultures of yeast one aerobically and the other anaerobically and measures the amount of ATP produced by each culture. He finds that the aerobically-grown yeast produce about 18 times as much ATP as the anaerobically-grown yeast. These observations are consistent with the fact that in the aerobically grown yeast:
Aerobic respiration cannot occur without oxygen. Why? Because oxygen is necessary for the final step of aerobic respiration, which is the electron transport chain. Here's a brief summary of glycolysis, the tricarboxylic acid cycle, also known as the Krebs cycle of the citric acid cycle, and the electron transport chain which are the three stages of aerobic respiration. Glycolysis is a series of reactions that lead to the oxidative breakdown of glucose into pyruvate. These reactions occur in the cytoplasm and result in the production of two NADH and a net gain of two ATP. Oxygen is not required for glycolysis, therefore, choice B is wrong. In the absence of oxygen that is, under anaerobic conditions the pyruvate is reduced to lactate; it undergoes this fermentation step so that NAD+ can be generated. Hence, choice D is wrong. In the presence of oxygen that is, under aerobic conditions the pyruvate is oxidized to release the considerable energy still stored in its chemical bonds. The pyruvate is transported from the cytoplasm into the mitochondrial matrix. The oxidative decarboxylation of pyruvate into Acetyl CoA is catalyzed by pyruvate dehydrogenase complex; one NADH is generated during the formation of acetyl CoA. Next, the acetyl group from the acetyl CoA combines with oxaloacetate, forming citrate. Through a complicated series of reactions, the citrate is completely oxidized, two molecules of carbon dioxide are released, and NADH, FADH2, and ATP are generated. Next, all of the molecules of NADH and FADH2 generated during glycolysis, pyruvate decarboxylation, and the TCA cycle, transfer their high potential electrons to a series of carrier molecules located in the inner mitochondrial membrane. A series of redox reactions is coupled with the phosphorylation of ADP; this is known as oxidative phosphorylation. As the electrons are transferred from carrier to carrier, free energy is released, which is then used to produce ATP. So, choice A is also wrong. The final carrier of the electron transport chain, cytochrome a3, passes its electrons to the final electron acceptor, molecular oxygen. Oxygen picks up a pair of hydrogen ions, forming water. The final ATP tally for aerobic respiration is net gain of 36 ATP. This is eighteen times as much ATP as produced during anaerobic respiration. So, choices A, B, and D are all wrong, and choice C is true and consistent with the observations made by the biochemist in the question.
Growth hormone decreases the sensitivity of cellular receptors to insulin. Therefore, a patient with acromegaly, which is caused by the oversecretion of growth hormone, would be expected to have:
Answer(s): B
According to the question stem, acromegaly is a condition that results from an oversecretion of growth hormone. In addition, you're told that growth hormone decreases the sensitivity of insulin receptors. Therefore, to answer this question you've got to determine the physiological effects of an insensitivity to insulin. You should know that insulin is secreted by the pancreas in response to high blood glucose concentration, and that it lowers blood glucose by stimulating the conversion of glucose into its storage form, glycogen. This means that the cell surface receptors of acromegaly patients do not bind insulin as much as normal cells. Therefore, the effects of insulin will be diminished in an acromegaly patient. What does this mean? If insulin cannot exert its effects on the cells, then excess glucose will not be converted into glycogen. Hence, the patient will have excess glucose in other words, a high blood glucose concentration. Therefore, choice B must be the correct answer and choice A must be the wrong answer. Choice C is wrong because a high blood glucose concentration leads to the excretion of glucose, along with the loss of water in the urine, meaning that patients with acromegaly will have an increased, NOT a decreased, urine volume. Choice D is wrong because cardiac output is defined as the volume of blood pumped by the heart per unit time, which is not even directly related to the sensitivity of insulin receptors.
Which of the following products may be formed in the reaction below?
Answer(s): D
This question asks you to predict the reaction products from the acid hydrolysis of an ester. When esters are hydrolyzed, they yield carboxylic acids and alcohols. From the hydrolysis of this ester, you would expect 2- butenoic acid and isobutanol. Choice D is isobutanol and is the correct answer. The other choices do not reflect possible products from this reaction. Choice A is an unsaturated aldehyde and choice C is an alkane; neither type of compound can be obtained by hydrolyzing an ester. Initially, choice B may look like the carboxylic acid that is obtained from hydrolysis of the ester, but in fact, the double bond is absent, so this answer choice is also incorrect.
A student was given a sample of an unknown liquid and asked to determine as much as possible about its structure. He was told that the compound contained only carbon, hydrogen, and oxygen, and had only one type of functional group. The student found its boiling point to be 206° C. Using mass spectroscopy, he determined its molecular weight to be 138 g/mol. Finally, he took the infrared spectrum of the compound, which is shown below.From this spectrum, the student quickly reached a conclusion about the functional group. He then turned his attention to the fingerprint region of the compound, which generally has a complicated pattern of peaks that are determined by the structure of the hydrocarbon portion of a molecule. The student decided that the large peak at 750 cm-1 must indicate that this was a disubstituted aromatic compound.The overlapping set of peaks near 3000 cm-1 includes one peak at 2850 cm-1. What type of functional group could this indicate?
Answer(s): A
The peak at 2850 cm-1 is characteristic of the C-H stretch of an alkyl group; in the case, it is attributed to the methyl group of the alkoxide. That's not a terribly exciting functional group, so you might not have known this right off the top of your head, but you could get it by a process of elimination. Choice B, a phenol group, would produce a broad peak somewhere between 3600 and 3200 cm-1, which represents the oxygen-hydrogen bond that is characteristic of all hydroxyl groups and is pretty unmistakable. Since this peak is not present in this spectrum, choice B must be incorrect. Choice C, a carboxyl group, would also produce a broad peak due to its hydroxyl group; this can be anywhere from 300 to 2400 cm-1, and tends to be even broader than a regular hydroxyl peak. The other peaks near the methoxy group peak are much too sharp to belong to a carbonyl group; they actually represent the carbon-hydrogen bonds of the aromatic ring. Whenever you look at the IR spectrum of an organic compound, remember that there will always be some kind of peak or peaks between 2800 and 3300 cm-1 that's simply due to the carbon backbone alkane, alkene, alkyne, aromatic, or mixtures of all of these. Anyway, getting back to the question, a carboxyl group would also produce another peak associated with the carbon-oxygen double bond, around 1700 cm-1, and that's also lacking in this spectrum, so choice C is definitely wrong. Finally, choice D, an aldehyde group, would have the same peak at about 1700; it would also produce two characteristic peaks in the range of 2720 and 2820 cm-1, called Fermi doublets.Neither of these are present, so D is also wrong.
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