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Flashcards in BIO chem enzymes step1 contd Deck (30):
1

This patient presents with a painful upper extremity rash, malnutrition, diarrhea, and mental status changes. Individuals who are homeless or affected by alcohol use disorder are at risk for developing dietary vitamin deficiencies. Based on his symptoms, the most likely diagnosis is ?

niacin (vitamin B3) deficiency, also called pellagra.

2

The symptoms of pellagra are classically described as the 3 D’s: Diarrhea, Dementia, and Dermatitis. If untreated, pellagra can result in ?

the fourth D: death. Glossitis is another important symptom of niacin deficiency that is not included in the 3 D’s. Pellagra is an Italian word meaning “thickened skin,” which describes the hyperpigmentation on sun-exposed areas of the body (as seen in the image). The rash’s circumferential distribution in the C3/C4 dermatome is known as the “Casal necklace.”

3

Because niacin is derived from ?

tryptophan, a decrease in tryptophan absorption or an increase in tryptophan metabolism can produce similar symptoms. Other potential causes of niacin deficiency include malignant carcinoid syndrome (increased tryptophan metabolism) or isoniazid therapy (decreases pyridoxine [vitamin B6] required for niacin synthesis).

4

Although a deficiency of biotin (vitamin B7), pantothenic acid (vitamin B5), or zinc could lead to ?

2. Thiamine (vitamin B1) deficiency can lead to ?

dermatologic changes, none of these would explain the patient’s cognitive decline.

2. confusion and confabulation (Wernicke-Korsakoff syndrome), but it is not associated with a rash or diarrhea.

5

A deficiency of niacin (vitamin B3), tryptophan, or pyridoxine (vitamin B6) can lead to pellagra. Patients with niacin deficiency classically present with ?

the triad of diarrhea, dementia, and dermatitis.

6

A new small-molecule drug for the treatment of HIV has just been discovered. This small molecule appears to bind to a newly discovered surface G-protein–coupled receptor (GPCR), TTY2, and sets off a cascading signal that leads to apoptosis of the cell. The TTY2 receptor is expressed in cells that have been infected by HIV but is not expressed in noninfected cells. Using in vitro experiments, scientists have been able to show that binding of the TTY2 receptor will act on phospholipase C, thereby leading to an increase in intracellular calcium.

The TTY2 receptor is similar to which of the following receptors?

α1

When activated, the Gq class of GPCRs results in activation of protein kinase C and an increase in intracellular calcium. Thus, like the TTY2 receptor, the α1-adrenergic receptor is a Gq-class GPCR. Other Gq-class GPCRs include muscarinic1, muscarinic3, and histamine1.

Gq-class receptors include muscarinic1, muscarinic3, and histamine1. Gq-class receptors activate phospholipase C, causing an increase in inositol triphosphate (which leads to calcium release in the cell) and diacylglycerol, which leads to protein kinase C activation.

7

This patient’s history of poor oral intake, hemarthrosis, anemia, and signs of microhemorrhage are consistent with vitamin C deficiency, also known as scurvy, which also results in?

impaired collagen synthesis. Several vitamin deficiencies cause anemia and other hematologic disorders, but scurvy is characteristically associated with gum bleeding and swelling as well as poor wound healing. Vitamin C is vital for proline hydroxylation in collagen synthesis; therefore, deficiency of this vitamin will cause defects in structures requiring collagen.

8

Vitamin K deficiency, caused by ?

2. Vitamin A deficiency impairs?

impaired carboxylation of glutamic acid, manifests primarily as failure to clot and hemorrhage.

2. the immune response, leading to night blindness, GI and respiratory problems, and other skin disorders.

9

The electron transport chain is located on inner mitochondrial membrane and is the site of oxidative phosphorylation. The enzymes involved in this metabolic pathway are the targets of many drugs and poisons that inhibit their activities.

Which agent directly inhibits the complex that serves as the final electron acceptor in the electron transport chain?

Cyanide binds to the Fe3+ of cytochrome aa3, the fourth and final complex in the electron transport chain. This prevents the final transfer of electrons to oxygen and halts any further oxidative phosphorylation. Inhalation of high doses of cyanide leads to coma, with seizures, apnea, cardiac arrest, and death.

10

Antimycin A is an antibiotic that binds to cytochrome c reductase and prevents ?

the transfer of an electron from cytochrome b to cytochrome c in the electron transport chain.

11

2,4-Dinitrophenol is a chemical used to make dyes, as well as a cellular metabolic poison. It uncouples ?

oxidative phosphorylation by carrying protons across the mitochondrial membrane. The energy produced by the transport of electrons is released as heat rather than being used to synthesize ATP. In high doses, the drug aspirin (and other salicylates) uncouples oxidative phosphorylation, which explains why a fever can accompany toxic overdoses of these drugs.

12

Oligomycin is an antibiotic that binds to ATP synthase and blocks?

the reentry of protons into the mitochondrial matrix. Because the pH and electrical gradients cannot be dissipated, further electron transport stops because of the difficulty of pumping any more protons against the steep gradients. Since electron transport and oxidative phosphorylation are tightly coupled, any inhibition of one leads to inhibition of the other.

13

Rotenone inhibits?

the transfer of electrons to ubiquinone in the electron transport chain. It is commonly used in insecticides and pesticides.

14

This man presents with worsening weakness and fatigue, as well as bruising, swollen gums, and possible poor immune function. In the context of probable malnutrition, he most likely has scurvy. In addition to the patient's homeless state and his description of erratic eating, the odor of alcohol on his breath suggests a possible history of alcoholism and associated poor overall nutrition. Alcoholism and poor nutrition can result in?

vitamin C (ascorbic acid) deficiency. As a result, proline and lysine are not hydroxylated in the endoplasmic reticulum during the formation of collagen. This leads to manifestations including ecchymoses, petechiae, bleeding gums, and the characteristic corkscrew hairs.

15

Collagen formation does not involve any of the following: glycosylation of proline and lysine in the endoplasmic reticulum, hydroxylation of proline and isoleucine in ?

the Golgi apparatus, or glycosylation of proline with either isoleucine or lysine in the Golgi apparatus. Only asparagine, serine, threonine and rarely post-translationally hydroxylated amino acids can undergo glycosylation.

16

A 3-year-old boy is taken to his pediatrician because of a 3-day history of a productive cough and fever. This visit is the third time in the past 9 months that he has been seen by a doctor. His mother vaguely recalls his brother having similar problems when he was a child. As part of his work-up, the patient has a nitroblue tetrazolium dye reduction test, which is negative.

Which of the following is expected in this patient?

Recurrent infections, with susceptibility to bacterial and fungal organisms

Chronic granulomatous disease is an X-linked disorder caused by a defect in phagocytosis by neutrophils, owing to a lack of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. This enzyme is responsible for the respiratory burst that produces superoxide (O2-) from molecular oxygen (O2), using NADPH as an electron donor. The negative NBT test (indicating a failure of the reaction to turn blue) reflects that there is abnormal NADPH oxidase activity, indicating chronic granulomatous disease. Patients with this disease have a marked susceptibility to opportunistic infections with bacteria, especially Staphylococcus aureus, Escherichia coli, and fungi such as Aspergillus.

17

A 40-year-old woman presents to a community clinic because she is concerned that she may have contracted HIV from unprotected sex with a former lover. Physical exam reveals cervical lymphadenopathy. Blood is drawn and sent for HIV testing.

The woman's blood is subjected to a screening process. Which of the following mechanisms underlies the test that is used to screen for HIV?

Antigen-antibody reaction and activity-based dye detecting host antibodies by using viral components.

Enzyme-linked immunosorbent assays (ELISAs) test for antibodies using known antigens, or vice versa. In the case of HIV, it is used to determine if a person's immune system has antibodies to HIV proteins, and hence has encountered that particular antigen. Similarly to Western blot, it also requires epitope (the binding site on the antigen) to variable-chain (the specificity subunit of the antibody) interactions. Clinically, the ELISA method is highly sensitive (>99%) for detecting HIV infection after the development of antibodies.

18

This patient’s symptoms of acute epigastric pain radiating to the back that is worse after meals, tender and distended abdomen with guarding, fever, and elevated serum lipase levels suggest the diagnosis of acute pancreatitis. Along with the discovery of milky-white plasma, this young man most likely has ?

type I dyslipidemia, or familial hyperchylomicronemia.


Familial hyperchylomicronemia is caused by a deficiency of lipoprotein lipase, an enzyme found in capillary walls of adipose and muscle tissue.

19

LDL cholesterol receptor dysfunction is characteristic of familial hyperbetalipoproteinemia, also known as type II hyperlipidemia. Mutations in apolipoprotein E (ApoE) can lead to?

familial dysbetalipoproteinemia, or type III dyslipidemia. These types of dyslipidemia are not associated with the bout of acute pancreatitis and milky supernatant seen in this patient, but would be distinguished by their xanthomas and atherosclerosis

20

Inability to effectively clear VLDL particles describes the pathogenesis of both familial hypertriglyceridemia (type IV dyslipidemia) and familial mixed hypertriglyceridemia (type V dyslipidemia). While both of these are associated with the patient’s presentation of?

acute pancreatitis, they are also associated with significant comorbidities including obesity, diabetes, and hyperuricemia not seen in this previously healthy patient. An increase in Apo CII is not associated with any of the familial dyslipidemias; however, a decrease in Apo CII can be a rare cause of hyperchylomicronemia.

21

This teenager has multiple angiokeratomas (the small, reddish-black papules on his abdomen and scrotum), acroparesthesia (intermittent peripheral paresthesias), and heat intolerance. These findings in a young patient are classic indicators for ?

Fabry disease.
Fabry disease is an X-linked recessive lysosomal storage disease. It is caused by a deficiency of the enzyme α-galactosidase A, resulting in the accumulation of ceramide trihexoside.

22

If you selected lactosyl cerebroside, you are thinking Fabry disease; however, lactosyl cerebroside is ?

the end product of the conversion of ceramide trihexoside via α-galactosidase A. Therefore, it is deficient in patients with Fabry disease.

23

Krabbe disease, due to?
2. Gaucher disease, due to?
3. Niemann-Pick disease, due to?

accumulation of galactocerebroside
2. accumulation of glucocerebroside
3. accumulation of sphingomyelin

24

This patient inquires about limiting carbohydrates in her diet to maintain a desired weight. Carbohydrates are metabolized by glycolysis. Glycolysis is the biochemical pathway (shown in the diagram) that involves the oxidation of glucose to pyruvate, which then goes on to enter the Krebs cycle. The rate-limiting step of glycolysis is the conversion of ?

fructose-6-phosphate to fructose-1,6-bisphosphate by the enzyme phosphofructokinase. Citrate is an intermediate produced in the Krebs cycle that has a role in the regulation of glycolysis by inhibiting the action of phosphofructokinase.

25

Acetyl-coenzyme A has an important role in the synthesis and oxidation of ?
2. Alanine is an amino acid that serves as carrier of ?

fatty acids, as well as in the initiation of the Krebs cycle.

2. amino groups from muscle to liver.

26

Reduced nicotinamide adenine dinucleotide is produced in the Krebs cycle and acts as?

2. Glucose-6-phosphate is produced in the first step of glycolysis from glucose, and although this enzyme is related to carbohydrate metabolism, it is not responsible for regulating?

an electron carrier to the electron transport chain to produce ATP via oxidative phosphorylation.

2. the rate-limiting step.

27

This patient with coarse facial features (prominent forehead, enlarged tongue), hyperactive and aggressive behavior, and numerous pearly skin lesions most likely has ?

Hunter syndrome. This syndrome is an X-linked disorder caused by a deficiency of the lysosomal enzyme iduronate sulfatase. In patients with Hunter syndrome, pearly, papular skin eruptions are usually first seen around the scapulae but then spread to involve the trunk and upper thighs. These skin eruptions are pathognomonic. Other signs and symptoms of Hunter syndrome may include a deep, hoarse voice; skeletal irregularities; a distended abdomen; and diarrhea.

28

A deficiency in a-L-iduronidase causes ?

Hurler syndrome. Among other signs and symptoms, patients with Hurler syndrome have characteristic corneal clouding, which is absent in patients with Hunter syndrome.

29

ß-Glucosidase deficiency and sphingomyelinase deficiency are responsible for?

Gaucher disease and Niemann-Pick disease, respectively. Gaucher disease and Niemann-Pick disease are sphingolipidosis diseases that are not associated with coarse facies, and both present with hepatomegaly and neurologic defects.

30

A deficiency in a-galactosidase A is seen in?

Fabry disease. Patients with Fabry disease exhibit peripheral neuropathy, angiokeratomas, and hypohidrosis.
Hexosaminidase A deficiency is responsible for Tay-Sachs disease. Patients with Tay-Sachs disease have progressive neurodegenerative delay and the classic “cherry-red” spot on the macula.