Bio Chem enzymes Step 1 contd

Question 1

This patient presents after multiple bouts of pneumonia, although he has no other medical issues and isn’t taking any medications. The gram-positive clusters seen in this patient’s sample indicate Staphylococcus aureus infection, which is a typical pathogen associated with?

Answer 1

chronic granulomatous disease (CGD). CGD is characterized by increased susceptibility to infections by catalase-positive organisms (eg, S. aureus, Escherichia coli, and Aspergillus species). CGD is the result of a deficiency in the enzyme nicotinamide adenine dinucleotide phosphate oxidase, which converts molecular oxygen (O2) to the superoxide oxygen radical (O2-). Without this step, neutrophils are unable to generate a respiratory burst, leading to increased susceptibility to infection.

Question 2

Glucose-6-phosphate dehydrogenase (G6PD) is an enzyme involved in ?

Answer 2

the glutathione antioxidant pathway in red blood cells. Patients with G6PD deficiency develop hemolytic anemia after exposure to oxidative stress.

Question 3

Myeloperoxidase (MPO) generates a cytotoxic chemical (hypochlorite) in immune cells as a mechanism of host defense. Deficiency results in?

Answer 3

increased susceptibility to infections, similar to CGD; however, patients with MPO deficiency will have a positive (normal) nitroblue tetrazolium test result.

Question 4

Superoxide dismutase is an antioxidant enzyme. Deficiency is associated with?

Answer 4

familial amyotrophic lateral sclerosis (ALS), not CGD.

Question 5

In a healthy individual, fasting eventually leads to gluconeogenesis. Synthesis of glucose from ?

What is the product of this reaction in gluconeogenesis?

Answer 5

pyruvate or lactate requires seven reactions of glycolysis that are reversible. However, there are three glycolytic reactions that are irreversible and must be circumvented by four alternative reactions that favor the synthesis of glucose.

Pyruvate carboxylase is the first irreversible enzyme to generate glucose in the process of gluconeogenesis. Pyruvate carboxylase is activated by acetyl-CoA, requires biotin and adenosine triphosphate as cofactors, and results in the conversion of pyruvate to oxaloacetate.

Question 6

Fructose-1,6-bisphosphate is the product of the enzyme fructose-1,6-bisphosphatase. Although it is an irreversible step of gluconeogenesis, this enzyme is not activated by?

Answer 6

acetyl-CoA and does not require biotin as a cofactor

Question 7

Glucose is the final product of gluconeogenesis and requires the enzyme glucose-6-phosphatase, which is not activated by ?

Answer 7

acetyl-CoA and does not require biotin as a cofactor.

Question 8

Glucose-6-phosphate is the substrate in the final reaction of gluconeogenesis and requires the enzyme glucose-6-phosphatase, which is not activated by ?

Answer 8

acetyl-CoA and does not require biotin as a cofactor.

Question 9

Phosphoenolpyruvate requires the enzyme?

Answer 9

phosphoenolpyruvate carboxykinase, which requires GTP and is activated by glucagon and inhibited by insulin.

Question 10

This patient is afebrile and presents with tachypnea and decreased oxygen saturation, suggesting a primary pulmonary problem. Diffuse wheezing should raise concern about an?

Answer 10

acute asthma exacerbation, especially in the setting of a recent mild upper respiratory tract infection. Viral upper respiratory infections, allergens, and stress are common triggers for asthma exacerbations.

Question 11

In patients with asthma, chronic inflammation of the airways leads to increased bronchiolar mucus secretion and smooth muscle contractility. This can result in?

Answer 11

obstructive lung disease and lung hyperinflation. Leukotriene (LT) C4, LTD4, and LTE4 are bronchoconstrictors. Inhibition of 5-lipoxygenase (via zileuton) to block leukotriene synthesis and inhibition of leukotriene receptors (via montelukast or zafirlukast) can alleviate asthma symptoms, although these medications are typically not first-line

Question 12

LTC4, LTD4, and LTE4 are ?

Answer 12

bronchoconstrictors that cause asthma symptoms. Antileukotrienes, such as zileuton, montelukast, and zafirlukast, are often prescribed as adjunctive treatment for asthma.

Question 13

This patient’s symptoms of malaise, headaches, fever, chills, and a nonproductive cough—in combination with fluffy bilateral infiltrates seen on a chest x-ray—are highly suggestive of ?

Answer 13

an atypical pneumonia. Mycoplasma pneumoniae is one of the most common causes of atypical pneumonia; it is most prevalent among school-aged children, military recruits, and college students.

Question 14

Macrolide antibiotics, such as azithromycin, are the first-line treatment for M. pneumoniae infection. These drugs bind to the 50S subunit of the bacterial ribosome, thus impairing ?

Answer 14

the elongation of peptide chains and ultimately causing a premature termination of translation.

Question 15

Penicillin works by blocking the ?

Answer 15

transpeptidase cross-linkage in bacterial cell walls and is effective in the treatment of Streptococcal pneumonia, the number one cause of community-acquired lobar pneumonia. Although this patient presents with symptoms of a lower respiratory tract infection, his cough is nonproductive, and a chest x-ray does not show a lobar consolidation.

Question 16

Rifamycins, such as rifampin and rifabutin, are antibiotics that inhibit ?

Answer 16

DNA-dependent RNA polymerase and are given prophylactically to individuals in close contact with a patient who has meningococcal meningitis. This patient’s medical history is not significant for such exposure.

Question 17

Isoniazid inhibits ?

Answer 17

mycolic acid synthesis and is used in the treatment of tuberculosis, which manifests with hemoptysis and appears as apical lung involvement on a chest x-ray. This patient’s presentation is not consistent with tuberculosis.

Question 18

Metronidazole works by ?

Answer 18

forming free radical toxic metabolites that damage bacterial cell DNA and is used in the treatment of infections caused by Giardia, Entamoeba, Trichomonas, Gardnerella vaginalis, anaerobes (eg, Clostridium difficile), and Helicobacter pylori. These microorganisms are not associated with respiratory symptoms.

Question 19

This patient is experiencing hallucinations, delusions, and dilated pupils, but very few observable behavioral changes or changes in his vital signs. These symptoms are consistent with ?

Answer 19

lysergic acid diethylamide (LSD) abuse. LSD is a hallucinogenic drug that can cause marked anxiety or depression, nausea, weakness, and paresthesias. No antidote is currently available for the treatment of LSD toxicity.

Question 20

Alcohol intoxication is characterized by ?

Answer 20

a general disinhibition, slurred speech, and ataxia. It does not usually cause patients to hallucinate or become delusional. Alcohol withdrawal, however, can lead to delirium tremens, and benzodiazepines, such as lorazepam, can be used to prevent delirium tremens and other signs of alcohol withdrawal.

Question 21

Heroin intoxication can manifest with?

Answer 21

pinpoint pupils, decreased levels of consciousness, low heart and respiratory rates, and sometimes cyanosis. This patient has dilated pupils and does not have respiratory depression, making opioid intoxication unlikely. Treat heroin overdose with the opioid antagonist naloxone.

Question 22

Marijuana can cause many of the symptoms this patient is experiencing. However, marijuana intoxication typically manifests with ?

Answer 22

other symptoms, including increased appetite, dry mouth, and conjunctival injection, which are not seen in this patient. Additionally, hallucinations usually arise only after very high doses of marijuana. Current recommendations suggest supportive therapy for patients presenting with marijuana intoxication (eg, placing the patient in a dark room, assurance, decreased stimulation). Occasionally, benzodiazepines can be beneficial in the reduction of symptoms, but generally are not used.

Question 23

Phencyclidine (PCP) intoxication causes ?

Answer 23

altered mental status, hallucinations, hypertension, tachycardia, and nystagmus. There are no vital sign abnormalities in this patient, making PCP intoxication unlikely.

Question 24

This patient shows signs of progressive hearing loss, coarse facial features, hepatomegaly, developmental delay, and laboratory finding of iduronate sulfatase deficiency, all of which suggest? Hunter syndrome.

Answer 24

Hunter syndrome. Hunter syndrome is an X-linked recessive disorder characterized by intellectual disability, hearing loss, coarse facies, and hepatosplenomegaly. There is no corneal clouding (as opposed to in Hurler syndrome). It is caused by a deficiency in iduronate sulfatase, leading to accumulation of the mucopolysaccharides dermatan and heparan sulfate in affected tissues.

Question 25

Niemann-Pick disease type A/B is due to a deficiency of?

Answer 25

sphingomyelinase; if untreated clinical features include a progressive neurodegenerative course consisting of hepatosplenomegaly, foam cells, and cherry-red spots on the macula.

Question 26

Gaucher disease is due to a deficiency in?

Answer 26

ß-glucosidase; clinical features include hepatosplenomegaly, osteoporosis, and bone crises.

Question 27

Krabbe disease is ?

Answer 27

due to a deficiency in galactocerebrosidase and consists of progressive peripheral neuropathy, destruction of oligodendrocytes, developmental regression, optic atrophy, and globoid cells.

Question 28

Tay-Sachs disease is due to ?

Answer 28

a deficiency in hexosaminidase-A, and patients have progressive developmental regression, seizures, and onion-skin lysosomes.