Bio Chem enzymes, step1 Flashcards
(31 cards)
This patient’s clinical features of incoherency, flushed skin, and ataxia combined with an elevated osmolality gap suggest ?
Alcohol intoxication. His hypoglycemia (glucose level <70 mg/dL) is likely related to his alcohol use. Calculating this patient’s osmolality gap ([2 × Na+] + [BUN/2.8] + [glucose/18]) shows an increased osmolality gap. Ethanol intoxication is the most common cause of this increase. This is further substantiated by the arterial blood gas and basic metabolic panel, which show a pH <7.35, decreased CO2, decreased HCO3, and an anion gap >12 (Na – [Cl + HCO3]). Together, these indicate an anion-gap metabolic acidosis, which is characteristic of alcohol intoxication.
Ethanol is metabolized to acetaldehyde, which is then metabolized to acetate (acetaldehyde dehydrogenase). During both steps of ethanol metabolism, NADH is generated from NAD+ (see image). With an elevated NADH:NAD+ ratio in the liver, pyruvate is?
converted to lactate rather than serving as a substrate for gluconeogenesis.
Gluconeogenesis begins in the mitochondria with the formation of oxaloacetate from pyruvate. Oxaloacetate is converted to malate, which exits into the cytosol but cannot be converted back to oxaloacetate because of the lack of NAD+, thus inhibiting gluconeogenesis. Additionally, the high concentration of NADH (and lack of NAD+) prevents the oxidation of lactate back to pyruvate, resulting in lactate accumulation and lactic acidosis.
Elevated NAD+:NADH is the opposite of ?
what occurs in ethanol ingestion. This is observed in forward progression of gluconeogenesis.
Elevated NADP+:NADPH occurs in?
Elevated NADPH:NADP+ occurs in?
impaired pentose phosphate shunt pathway.
- a normally functioning pentose phosphate shunt pathway.
Elevated pyruvate:lactate occurs in ?
- Elevated lactate:pyruvate may be seen with ?
normally functioning glycolysis and the Krebs cycle.
- inherited disorders of the tricarboxylic acid cycle. In such cases, pyruvate will be converted to lactate as it cannot enter the TCA cycle.
An 8-month-old boy is brought to the emergency department because of vomiting and lethargy. His mother says the boy ate applesauce and fruit juice for lunch. Physical examination reveals slight jaundice and tachycardia, but infantile cataracts are not present. Laboratory studies show a glucose level of 60 mg/dL and slightly elevated liver enzyme levels.
Which of the following enzyme deficiencies does this boy likely have?
Aldolase B is a key enzyme involved in fructose metabolism. Hereditary deficiency of aldolase B causes fructose intolerance. When foods high in fructose and sucrose are consumed in the presence of aldolase B deficiency, there is an accumulation of fructose-1-phosphate and a decrease in available phosphate. This results in inhibition of glycogenolysis and gluconeogenesis within the liver, causing symptoms of hypoglycemia, jaundice, cirrhosis, and vomiting. Treatment involves avoidance of dietary fructose and sucrose.
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common form of ?
enzyme-deficient hemolytic anemia. It is inherited in an X-linked recessive pattern and is common in people of African and Mediterranean descent. The condition manifests by acute, self-limited episodes of intravascular hemolytic anemia due to oxidative stress triggered by infection, medications (including sulfonamides used to treat urinary tract infections and antimalarial agents), or ingestion of fava beans. G6PD is the rate-limiting enzyme in the hexose monophosphate shunt pathway that yields reduced nicotinamide adenine dinucleotide phosphate (NADPH). NADPH is necessary to keep glutathione reduced and detoxify free radicals and peroxides. A decrease in NADPH levels due to G6PD deficiency causes hemolytic anemia due to poor red blood cell defense against oxidizing agents.
Galactokinase is an enzyme involved in the digestion of?
galactose. Less common than classic galactosemia (which is caused by the absence of galactose-1-phosphate uridyltransferase), galactokinase deficiency causes galactosemia and galactosuria along with infantile cataracts.
Lactase is a brush-border enzyme involved in the breakdown of lactose into glucose and galactose. Age-dependent or hereditary deficiency of this enzyme, which is common in Asian and African-American people, causes?
lactose intolerance with symptoms of bloating, cramps, and osmotic diarrhea due to the inability to digest lactose. Treatment involves the avoidance of milk or the addition of lactase pills to the diet.
Galactose-1-phosphate uridyltransferase is an enzyme involved in the digestion of galactose. A deficiency in this enzyme results in ?
the accumulation of toxic substances (including galactitol) in many tissues, causing symptoms of infantile cataracts, hepatosplenomegaly, failure to thrive, liver cirrhosis leading to liver failure, and mental retardation. Treatment involves the exclusion of galactose and lactose (composed of glucose and galactose) from the diet.
Phenylalanine hydroxylase is an enzyme that converts phenylalanine into tyrosine. A deficiency in this enzyme causes the?
genetic condition of phenylketonuria (PKU), in which phenylalanine accumulates and tyrosine becomes an essential amino acid. Symptoms include intellectual disability and developmental retardation, fair skin, eczema, and a musty body odor. In healthcare settings in the United States, screening for PKU occurs at birth, and treatment involves avoidance of dietary phenylalanine and increased dietary intake of tyrosine.
Hexokinase catalyzes the first step of glycolysis, the phosphorylation of glucose in the 6-carbon position. In the liver, a unique hexokinase known as glucokinase catalyzes this step. A researcher wishes to determine whether other tissues, in addition to the liver, express glucokinase.
Which of the following techniques would be most useful in determining if glucokinase exists in a tissue?
A Western blot can be used to detect the presence of a specific protein in a sample of tissue.
A Western blot involves the use of gel electrophoresis to separate the proteins in a sample of interest. An antibody against the target protein is then added, and this primary antibody is then detected with a labeled secondary antibody. This technique will determine if the target protein is expressed in the sample. In this case, the Western blot can therefore be used to detect glucokinase in these tissues by using an antibody against it.
A Northern blot analysis detects ?
RNA using a DNA probe to bind to the sample RNA (DNA-RNA hybridization). In this example, a Northern blot would allow the researcher to detect the presence of RNA for glucokinase but not the actual protein itself. Since other factors, such as RNA processing, may affect whether or not a mRNA is actually translated, it is not the best test to detect glucokinase
A Southern blot detects?
DNA and will not give the researcher any information about gene expression. All tissues have similar DNA sequences and a Southern blot would not be able to detect any significant changes between tissues
A polymerase chain reaction can help us amplify a ?
2.A Northwestern blot can help the researcher detect ?
DNA sequence but not detect a specific protein.
- RNA binding proteins. Glucokinase does not bind to RNA; therefore, this test would not be useful in detecting its expression.
Essential amino acids and fats must be obtained through?
the diet because they cannot be synthesized in the human body. Essential amino acids can be remembered by using the mnemonic PVT TIM HALL: Phenylalanine, Valine, Threonine; Tryptophan, Isoleucine, Methionine; Histidine, Arginine, Leucine, and Lysine. The essential fatty acids are linoleic and linolenic acid.
Tyrosine is a nonessential amino acid, which is synthesized from phenylalanine by the enzyme phenylalanine hydroxylase. It does not need to be obtained directly from the ?
diet. The exception is for individuals who lack phenylalanine hydroxylase and thus cannot synthesize tyrosine; these patients with phenylketonuria do require tyrosine in the diet, but this is a rare exception.
Valine is an essential glucogenic amino acid, which cannot be synthesized by a ?
healthy adult. Glucogenic amino acids can be converted into glucose through gluconeogenesis. Ketogenic amino acids can only be converted to ketone bodies (not glucose) through ketogenesis. Both of these processes occur in the liver.
Leucine is an essential ketogenic amino acid, which cannot be ?
synthesized endogenously. Consequently, individuals must obtain leucine through the diet.
Folic acid is produced by symbiotic bacteria from the precursor ?
p-aminobenzoic acid. This production is inhibited by sulfa antibiotics. Folic acid is also obtained from green leafy vegetables and cereal.
The presence of greater than or equal to 6 café-au-lait spots of at least 5 mm in diameter in pre-pubertal children is most consistent with ?
neurofibromatosis type 1 (NF-1 or von Recklinghausen disease). NF-1 is an autosomal dominant neurocutaneous disorder caused by a mutation in the NF1 tumor suppressor gene, located on chromosome 17. Café-au-lait spots are hyperpigmented macules with either smooth or irregular borders that appear on the trunk soon after birth. Other symptoms typically seen in NF-1 patients include: Lisch nodules: pigmented, asymptomatic hamartoas of the iris; presence of axillary or inguinal freckles; numerous neurofibromas; optic nerve gliomas; skeletal abnormalities (ie, scoliosis, vertebral defects, long bone dysplasia); other associated tumors (ie, meningiomas, astrocytomas, gliomas, and pheochromocytomas).
Bilateral vestibular schwannomas are found in ?
neurofibromatosis type 2
- Hypopigmentation of the hair is associated with?
- Brushfield spots are present in ?
- Cutaneous angiofibromas (adenoma sebaceum) are characteristic of?
Chédiak-Higashi syndrome.
- Down syndrome
- tuberous sclerosis.
This patient has photosensitive dermatitis (rough red rash on sun-exposed areas), diarrhea, and central nervous system disturbances (gait abnormality, tremors, and poor academic performance) pointing to a diagnosis of ?
pellagra. Pellagra, caused by niacin deficiency, can be a result of insufficient dietary intake or a hereditary metabolic disease that leads to reduced renal tubular reabsorption of tryptophan (Hartnup disease). The classic triad of pellagra is diarrhea, dermatitis, and dementia (the 3 D’s of B3).
