Hemoglobin (Hb) and myoglobin (Mb) are the O2-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the O2 carrier in blood and also plays a vital role in the transport of CO2 and H+. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held together by noncovalent attractions. The affinity of Hb for O2 varies between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up O2 more readily than large mammals because small mammals have a higher metabolic rate and require more O2 per gram of tissue.The binding of O2 to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O2 at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of O2 more energetically favorable. Conversely, the unloading of O2 at one heme facilitates the unloading of O2 at the others by a similar mechanism.Figure 1 depicts the O2-dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O2-binding sites. The fraction of O2 that is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.Figure 1Myoglobin facilitates transport in muscle and serves as a reserve store of O2. Mb is a single polypeptide chain containing a heme group, with a molecular weight of 18 kd. As can be seen in Figure 1, Mb (Curve D) has a greater affinity for than Hb.In sperm whales, the Mb content of muscle is about 0.004 moles/kg of muscle. If a sperm whale has 1000 kg of muscle, approximately how much O2 is bound to Mb, assuming that the Mb is saturated with O2?
Answer(s): A
Basically what you need to do to solve this problem is figure out how much oxygen will be bound to myoglobin, if the myoglobin in this sperm whale is completely saturated with oxygen. If you look at the answer choices, all of the values are in moles. So to equate the number of moles of oxygen that will bind to myoglobin, you need to figure out how many moles of myoglobin are present in the sperm whale's muscles. From the question stem you know that there are 0.004 moles of myoglobin per kg of muscle and the whale has 1000 kg of muscle.Multiplying these two numbers together gives you 4 moles of myoglobin. This means that the whale has 4 moles of myoglobin in its muscles. So how many moles of oxygen will there be? You need to determine how many molecules of oxygen bind to a single molecule of myoglobin. The answer is one. Why? Because myoglobin consists of a single polypeptide chain, which contains a single heme group. Thus, myoglobin binds only one molecule of oxygen. If one molecule of oxygen binds to one molecule of myoglobin, then one MOLE of oxygen will bind to one MOLE of myoglobin. And since you know that the whale has 4 moles of myoglobin in its muscle, then 4 moles of oxygen will be bound to myoglobin, when myoglobin is completely saturated with oxygen. Therefore, choice A is correct.
Just as the ingestion of nutrients is mandatory for human life, so is the excretion of metabolic waste products. One of these nutrients, protein, is used for building muscle, nucleic acids, and countless compounds integral to homeostasis. However, the catabolism of the amino acids generated from protein digestion produces ammonia, which, if not further degraded, can become toxic. Similarly, if the same salts that provide energy and chemical balance to cells are in excess, fluid retention will occur, damaging the circulatory, cardiac, and pulmonary systems.One of the most important homeostatic organs is the kidney, which closely regulates the excretion and reabsorption of many essential ions and molecules. One mechanism of renal function involves the secretion of antidiuretic hormone (ADH).Diabetes insipidus (DI), is the condition that occurs when ADH is ineffective. As a result, the kidneys are unable to concentrate urine, leading to excessive water loss. There are two types of DI central and nephrogenic. Central DI occurs when there is a deficiency in the quantity or quality of ADH produced. Nephrogenic DI occurs when the kidney tubules are unresponsive to ADH. To differentiate between these two conditions, a patient's urine osmolarity is measured both prior to therapy and after a 24-hour restriction on fluid intake. Exogenous ADH is then administered and urine osmolarity is measured again. The table below gives the results of testing on four patients. Assume that a urine osmolarity of 285 mOsm/L of H2O is normal. An elevated and potentially toxic level of ammonia in the blood (hyperammonemia) would most likely result from a defect in an enzyme involved in:
Answer(s): C
According to the passage, the catabolism of amino acids, which are the molecules that make up proteins, produces ammoniA. First of all, what does catabolism mean? You know that metabolism can be divided into catabolism and anabolism. Catabolism refers to pathways in which larger molecules are broken down into smaller parts. If you have trouble remembering the difference between catabolism and anabolism, just associate anabolism with anabolic steroids. And anabolic steroids are used by weight lifters to BUILD muscle, therefore anabolism must refer to the pathways in which smaller molecules are BUILT into larger molecules.And once you've committed that to memory, you'll always remember that catabolism must be the opposite. We know from the passage that if the ammonia that is produced as a by-product of amino acid breakdown is not further degraded, it can become toxic, depending on its concentration in the blood. To answer the question, you need to recall that the end product of amino acid degradation is urea, which means that ammonia must feed into the urea cycle. The concentration of ammonia in the blood would become elevated and potentially toxic if one of the enzymes involved in the urea cycle was defective. Thus choice C is the correct answer. Choice A, glycolysis, refers to the catabolism of glucose into pyruvate. Choice B, fatty acid catabolism, refers to the breakdown of fatty acids into acetyl CoA. Choice D, nucleic acid degradation, refers to the breakdown of DNA and RNA into nucleotides. Therefore choices A, B, and D are not involved in protein or ammino acid catabolism, and so they are all incorrect.
Just as the ingestion of nutrients is mandatory for human life, so is the excretion of metabolic waste products. One of these nutrients, protein, is used for building muscle, nucleic acids, and countless compounds integral to homeostasis. However, the catabolism of the amino acids generated from protein digestion produces ammonia, which, if not further degraded, can become toxic. Similarly, if the same salts that provide energy and chemical balance to cells are in excess, fluid retention will occur, damaging the circulatory, cardiac, and pulmonary systems.One of the most important homeostatic organs is the kidney, which closely regulates the excretion and reabsorption of many essential ions and molecules. One mechanism of renal function involves the secretion of antidiuretic hormone (ADH).Diabetes insipidus (DI), is the condition that occurs when ADH is ineffective. As a result, the kidneys are unable to concentrate urine, leading to excessive water loss. There are two types of DI central and nephrogenic. Central DI occurs when there is a deficiency in the quantity or quality of ADH produced. Nephrogenic DI occurs when the kidney tubules are unresponsive to ADH. To differentiate between these two conditions, a patient's urine osmolarity is measured both prior to therapy and after a 24-hour restriction on fluid intake. Exogenous ADH is then administered and urine osmolarity is measured again. The table below gives the results of testing on four patients. Assume that a urine osmolarity of 285 mOsm/L of H2O is normal. According to the passage, the catabolism of amino acids produces ammoniA. Therefore, after a protein rich meal, would you expect a build-up of ammonia in the lumen of the small intestine?
Answer(s): D
To answer this question, you need to recall the site of protein digestion, and the fate of the amino acids produced by this digestion. So let's review the digestive system as it relates to proteins. Food enters the stomach from the pharynx and esophagus. When protein-containing food reaches the stomach, its presence causes the release of the hormone gastrin, which stimulates the secretion of HCl, and pepsinogen, and muscular contractions of the stomach. HCl initiates the conversion of pepsinogen to its active form, pepsin.Pepsin breaks down proteins into peptides. The peptides then enter the small intestine. Three types of peptide- digesting enzymes are secreted into the small intestine; enterokinase, aminopeptidases, and dipeptidases. The combination of these three enzyme types breaks apart all peptide bonds, producing only single amino acids and dipeptides. The single amino acids and peptides are then absorbed into the epithelial cells lining the small intestine by active transport. These molecules all enter the bloodstream by way of the capillaries of the villI). Villi are the finger-like projections lining the small intestine that serve to increase the absorptive surface area of the intestine. From the bloodstream the amino acids enter individual cells. Inside these cells, the amino acids are used to either build new proteins or other biological molecules, or they are completely catabolized, in which case ammonia is produced. This ammonia then enters the urea cycle, and the urea produced in the process exits the cells and is excreted in the urine. So from this discussion of the digestion of protein, it is clear that ammonia is NOT produced inside the lumen of the small intestine. Therefore, choices A, B, and C are all wrong and choice D is the correct answer.
Just as the ingestion of nutrients is mandatory for human life, so is the excretion of metabolic waste products. One of these nutrients, protein, is used for building muscle, nucleic acids, and countless compounds integral to homeostasis. However, the catabolism of the amino acids generated from protein digestion produces ammonia, which, if not further degraded, can become toxic. Similarly, if the same salts that provide energy and chemical balance to cells are in excess, fluid retention will occur, damaging the circulatory, cardiac, and pulmonary systems.One of the most important homeostatic organs is the kidney, which closely regulates the excretion and reabsorption of many essential ions and molecules. One mechanism of renal function involves the secretion of antidiuretic hormone (ADH). Diabetes insipidus (DI), is the condition that occurs when ADH is ineffective. As a result, the kidneys are unable to concentrate urine, leading to excessive water loss. There are two types of DI central and nephrogenic. Central DI occurs when there is a deficiency in the quantity or quality of ADH produced. Nephrogenic DI occurs when the kidney tubules are unresponsive to ADH. To differentiate between these two conditions, a patient's urine osmolarity is measured both prior to therapy and after a 24-hour restriction on fluid intake. Exogenous ADH is then administered and urine osmolarity is measured again. The table below gives the results of testing on four patients. Assume that a urine osmolarity of 285 mOsm/L of H2O is normal.Which of the following substances would NOT be found in appreciable quantity in the urine of a healthy individual?
Albumin is a protein produced by the liver. It is very important in maintaining the plasma osmolarity of the blood.The glomerulus, which is the network of blood vessels enveloped by the part of the nephron known as Bowman's capsule, has small holes in its endothelial lining called fenestrations. When proteins travel through the glomerulus, they are prevented from entering the nephron due to the size of the fenestrations and the negative electrical charge of glycosylated proteins lining the fenestrations. Therefore, albumin is not normally found in urine because it is prevented from entering the nephron, and so choice A is the right answer. The presence of protein in a urine sample is typically a sign of renal disease. Each of the other choices are normally found in appreciable quantity in the urine. Urea, choice C, is the primary excretory byproduct of the urea cycle.Sodium and potassium homeostasis are kept in balance by the regulation of their excretion in urine.
Just as the ingestion of nutrients is mandatory for human life, so is the excretion of metabolic waste products. One of these nutrients, protein, is used for building muscle, nucleic acids, and countless compounds integral to homeostasis. However, the catabolism of the amino acids generated from protein digestion produces ammonia, which, if not further degraded, can become toxic. Similarly, if the same salts that provide energy and chemical balance to cells are in excess, fluid retention will occur, damaging the circulatory, cardiac, and pulmonary systems.One of the most important homeostatic organs is the kidney, which closely regulates the excretion and reabsorption of many essential ions and molecules. One mechanism of renal function involves the secretion of antidiuretic hormone (ADH). Diabetes insipidus (DI), is the condition that occurs when ADH is ineffective. As a result, the kidneys are unable to concentrate urine, leading to excessive water loss. There are two types of DI central and nephrogenic. Central DI occurs when there is a deficiency in the quantity or quality of ADH produced. Nephrogenic DI occurs when the kidney tubules are unresponsive to ADH. To differentiate between these two conditions, a patient's urine osmolarity is measured both prior to therapy and after a 24-hour restriction on fluid intake. Exogenous ADH is then administered and urine osmolarity is measured again. The table below gives the results of testing on four patients. Assume that a urine osmolarity of 285 mOsm/L of H2O is normal.Which of the following would you most likely expect to find in a patient with diabetes insipidus?
As explained in the passage, diabetes insipidus is a condition in which ADH is ineffective, and as a result, the kidneys reabsorb less water and are unable to concentrate urine. What is the result of this? Very dilute urine.So, urine output is increased in a patient with diabetes insipidus, which means that choice D is correct. Since water reabsorption is decreased, this means that plasma osmolarity will be increased, and so choice A is wrong. Choice C is wrong because the presence of glucose in the urine is one of the symptoms and tell-tale signs of diabetes mellitus. Diabetes mellitus is the result of an insulin deficiency; without insulin, glucose is not converted into glycogen, and as a result, some of it gets excreted in the urine because the kidneys are overwhelmed by the excess glucose in the bloodstream. Choice B is wrong because an increased urine osmolarity would mean that there was a greater concentration of dissolved solutes per liter of urine, which is not the case if there is an excess of water being excreted. It should be noted that a diabetes insipidus patient with an intact thirst mechanism and access to water will NOT become dehydrated. They will drink enough water to replace what is lost in the urine.
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