Hypoxia refers to a physiological condition in which the body lacks sufficient oxygen for normal cellular functioning. Prolonged hypoxia generally leads to an inhibition of mental capacity and a reduction in the work capacity of muscle. Severe cases of hypoxia can lead to coma or even death. Depending on the cause, hypoxia can be classified into four general types:Hypoxic hypoxia is a type of hypoxia that occurs when the partial pressure of oxygen in the blood is too low. For example, climbers at high altitude, where the air contains less oxygen, might experience hypoxic hypoxia because the partial pressure of oxygen in the air inhaled is very low, leading to insufficient partial pressure of oxygen in the blood.Anemic hypoxia describes a diminished ability of the blood to transport oxygen. Several factors can influence the oxygen-carrying capacity of the blood. Primary causes of anemic hypoxia include a lower than normal number of functional erythrocytes or an insufficient quantity of hemoglobin, the oxygen-carrying molecules of the blood. Abnormal hemoglobin can also decrease the blood's capacity to carry oxygen and lead to anemic hypoxia.Ischemic hypoxia is caused by a decreased delivery of blood to the tissues. Localized circulatory deficiencies, such as blood clots, and global circulatory deficiencies, such as heart failure, decrease the delivery of blood to the tissues, and can therefore cause ischemic hypoxia.Histotoxic hypoxia results from the inability of cells to utilize the oxygen available in the blood. Causes of histotoxic hypoxia include the poisoning of cellular enzymes involved in aerobic respiration, as well as the decreased metabolic capacity of the oxidative enzymes due to vitamin deficiency. Cyanide poisoning causes histotoxic hypoxia by blocking the action of cytochrome oxidase in the electron transport chain so that tissues cannot use oxygen even though it is available.A patent foramen ovale occurs when an infant's foramen ovale does not close completely at birth. Based on the information presented in the passage, this can lead to:
Answer(s): A
The foramen ovale is a shunt that diverts blood away from the lungs in the fetal circulatory route. The foramen ovale allows blood to enter the left atrium directly from the right atrium. If an infant's foramen ovale does not close completely at birth, deoxygenated blood will continue to flow from the right atrium directly to the left atrium without ever being oxygenated in the lungs. In the left atrium, the deoxygenated blood will mix with the oxygenated blood returning from the lungs. The overall effect will be hypoxic hypoxia as the PO2 of the blood flowing to the body is decreased.Choice B is incorrect because the defining characteristic of anemic hypoxia is the reduction of the oxygen- carrying capacity of the blood. In this case, the carrying capacity of the blood has not changed (there is no anemia or damage to hemoglobin). The problem is that much of the infant's blood never reaches the lungs to be oxygenated. The infant's blood is capable of carrying oxygen, it just does not receive enough oxygen to carry.Choice C is incorrect because the blood flow is not shunted away from the tissues which need oxygen. In ischemic hypoxia, the movement of blood is reduced, thus reducing delivery of oxygen to the tissues. In this case, the flow of blood throughout the body is not affected. It is true that the flow of blood through the heart and lungs is not normal, but the flow of blood to the tissues is normal.Choice D is incorrect because Choice A is correct.
Which of the following molecules would produce the NMR spectrum shown below?
Answer(s): D
The NMR spectra shows a distinct absorption split into 7 peaks, the classic absorption of an isopropyl group.This absorption is downfield, indicating that it is deshielded. From this information alone, we can determine that there is at least one proton with 6 equivalent neighboring protons, that is near some electronegative species.Only choice A has 6 neighboring protons that can lead to splitting into (N+1) seven peaks. The downfield shift is caused by the bromine bonded to the same carbon as the single hydrogen. Choice A is incorrect because there are no neighboring protons, and so there will be no splitting.Choice B is incorrect because there are no neighboring protons and so, splitting into seven peaklets will not occur.Choice C is incorrect because the single proton has only 3 neighboring protons and will only be split into 4 peaklets (a quadruplet). Note that the absorption for the single proton in this molecule will be shifted more downfield because there are many electronegative species around it.
Which of the following best illustrates the contracted state of the sarcomere shown below?
Answer(s): C
The sarcomere illustrated in the question stem consists of thin and thick filaments. Contraction occurs through the sliding of the thin filaments along the thick filaments, towards the center of the sarcomere. During this contraction, the length of both the thick and thin filaments remains unchanged. This sliding can be seen in the increased overlap between thick and thin filaments.Choice A is incorrect because it indicates that the thick filaments have shortened.Choice B is incorrect because it indicates that the thin filaments have shortened.Choice D is incorrect because it indicates that both the thick and thin filaments have shortened.
In the small intestine, most amino acids are transported from the lumen of the gut into the epithelial cells against their concentration gradient. This movement of amino acids is coupled to the movement of sodium ions down their concentration gradient in a form of transmembrane movement called:
Secondary active transport is defined as the transport of a material across the cell membrane against its concentration gradient without direct hydrolysis of ATP. The energy required to drive this active transport is acquired by harnessing favorable concentrations gradients, like the flow of sodium ion into a cell. Note that the sodium gradient is created by the primary active transport of sodium out of the cell by the sodium/potassium pump.Choice A is incorrect because simple diffusion is the movement of materials down a concentration gradient through the membrane without the assistance of pumps or protein channels. Small molecules () and non-polar molecules (steroids) can move into a cell by simple diffusion.Choice B is incorrect because facilitated diffusion is movement of a material along its concentration gradient through protein channels. Ions can move in and out of the cell through specific ion channels.Choice D is incorrect because primary active transport involves transport against a concentration gradient driven directly by ATP hydrolysis. The sodium/potassium pump is an ATPase (hydrolyzes ATP).
Which of the following functional groups are NOT found on the side chains of any of the naturally occurring amino acids?
Aldehydes do not occur in the 20 amino acids found in naturally occurring proteins.Choice A is incorrect because the hydroxyl group is found on serine and threonine.Choice B is incorrect because the methyl group is found on alanine and a number of other nonpolar amino acids.Choice C is incorrect because the carboxylic acid functionality is found on the side chain of aspartic acid and glutamic acid.
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