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Flashcards in Biochem step 1 contd Deck (30):

For monosaccharides such as glucose, galactose, and fructose to be absorbed after ingestion, they need to first pass through the apical side of the gastrointestinal (GI) epithelium. Then they pass through the basolateral side of the epithelium into the blood, as illustrated in the diagram. The apical side of the GI epithelium has numerous microvilli with dedicated transporters. Both glucose and galactose traverse the apical membrane by the action of ?

the transporter sodium-dependent glucose transporter 1 (SGLT1).
SGLT1 is a symporter, since it simultaneously transports sodium and either monosaccharide into the cell


This patient's presentation of thin, translucent skin over her abdomen with prominent varicose veins and many bruises on her shins and a family history of a similar problem suggest a diagnosis of ?

vascular Ehlers-Danlos syndrome (EDS). The image shows a berry aneurysm (red circle). Berry aneurysms are congenital and associated with several syndromes. Patients with vascular EDS are at risk for the development of berry aneurysms like the one seen in this patient. She likely experienced an acute rupture of a berry aneurysm resulting in intracranial hemorrhage and acute onset of unconsciousness and, eventually, death.
EDS is a group of disorders resulting from defects in collagen synthesis and processing. Vascular EDS (type IV) is associated with a defect in the formation of type III procollagen, a precursor of the collagen found in many tissues.


Marfan syndrome is caused by a ?

mutation of the fibrillin-1 gene on chromosome 15 and is associated with long, thin extremities; loose and occasionally hyperextensible joints; and aortic aneurysms


Patients with epidermolysis bullosa have an abnormality in ?

either keratin 14 or keratin 5, resulting in skin that readily breaks and forms blisters with minor trauma.


Osteogenesis imperfecta is caused by a ?

defect in type I procollagen and is characterized by multiple spontaneous bone fractures, retarded wound healing, and characteristically blue sclerae


A defect in type IV collagen is the underlying cause of ?

Alport syndrome. Alport syndrome is characterized by nephritis with hematuria, hearing loss, and eye disorders.


relatively young patient with severe dyslipidemia, tendon xanthoma (a nodule composed of lipid deposits) over the Achilles tendon, and a family history of early MI most likely has a form of ?

familial hypercholesterolemia. Dietary modification, drastically limiting intake of saturated and trans fats and cholesterol; weight loss; and aerobic exercise are the first-line treatment options for any patient with elevated cholesterol levels, including this one. However, these measures often have only minimal effect.

The enzyme, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, catalyzes the rate-limiting step of the de novo cholesterol synthesis pathway. Statin medications are HMG-CoA reductase inhibitors and are the first-line pharmaceutical treatment for both familial and acquired forms of hypercholesterolemia. By blocking the rate-limiting step in cholesterol synthesis, statins can increase hepatic synthesis of LDL receptors, thereby lowering serum LDL levels. One characteristic side effect of HMG-CoA reductase inhibitors is statin-induced myopathy, which causes muscle soreness and weakness, as seen in this patient. Her elevated serum creatine kinase indicates muscle injury.


This patient’s abdominal distention, hyperactive bowel sounds, and tenderness on palpation should raise the suspicion of a bowel obstruction caused by an abdominal tumor. In light of his relative youth and the frequency of cancer in his close relatives, this patient most likely has?

hereditary nonpolyposis colon cancer (HNPCC), also called Lynch syndrome. HNPCC is an autosomal dominant condition and an example of the “two-hit hypothesis”: the first mutation in the mismatch repair mechanism is inherited, and the second mutation is acquired spontaneously later in life. The process of mismatch repair is defective in patients with this condition.


Base excision repair occurs by?

removal of the base at an apurinic or apyrimidinic site. Once the nucleotide is removed, DNA polymerase fills the gap


Double-strand break repair is a complicated repair mechanism for ?

double-strand injuries secondary to radiation and free radicals.


Pyrimidine dimer repair is a mechanism that fixes ultraviolet light–induced pyrimidine dimers; deficiency of this repair mechanism is the cause of ?

xeroderma pigmentosum


APC-mediated tumor suppression is implicated in ?

familial adenomatous polyposis (FAP).


This pregnant patient presents with a very high level of β-hCG, and ultrasound findings of lucent and echogenic areas (a “snowstorm” appearance) with no fetal heartbeat detected. Based on these findings, she most likely has a ?

molar pregnancy (hydatidiform mole)
Molar pregnancy classically manifests with the triad of hyperemesis, vaginal bleeding, and hyperthyroidism. Investigators hypothesize that the symptoms of hyperthyroidism may arise because of homology between the structure of hCG and thyroid-stimulating hormone (TSH).


Three separate spontaneous abortions strongly suggests that a genetic defect is causing the fetal death. Each fetus had massive abdominal swelling and edema consistent with ?

hydrops fetalis. Defined as an abnormal accumulation of fluid in 2 or more fetal compartments resulting in general swelling of the whole body (anasarca), hydrops fetalis is incompatible with life.
Each of the parents has microcytic anemia (MCV < 80 fL). The microcytic anemia that’s associated with hydrops fetalis is α-thalassemia. There are four forms of α-thalassemia, with differing severity according to how many α-globin alleles are deleted (see table). When only one of the four alleles is deleted (thus forming only one nonfunctional α-globin chain), there is no gross clinical phenotype because three functioning alleles is sufficient to support normal hemoglobin production. However, people with such a deletion are silent carriers. This type of disease is known as α-thalassemia minima.


The patient is a young boy who presents with delayed developmental milestones, short stature, hypotonia (poor suckling as an infant), obesity, small hands and feet, and hypogonadism. These signs and symptoms are most suggestive of ?

Prader-Willi syndrome. The images below illustrate some of the typical facial features (eg, narrow forehead, downward corners of the mouth) associated with this syndrome.

Prader-Willi syndrome (deletion of q12 on paternally derived chromosome 15) is a genetic disease that manifests with hypotonia at birth and later with intellectual disability, short stature, and obesity.


The scientist in this vignette wants to measure the amount of uptake via GLUTs in different cell types. This question is using a theoretical scientific experiment to ask about the distribution and biochemical characteristics of GLUT in hepatocytes.
GLUT-2 is the isoform present in liver cells, pancreatic ß cells, renal tubular cells, and small intestinal epithelial cells. It has several important properties, including bidirectional transport and low affinity for glucose. The low affinity prevents the transporter from becoming saturated at higher glucose levels. Since Km is inversely proportional to substrate affinity, GLUT-2 has ?

a relatively high Km. GLUT-2 activity is not dependent on insulin


This patient is bleeding from an IV site and has spots of blood under his fingernails, both signs of coagulopathy in the setting of chronic antibiotic use. His lab results are consistent with deficits in both the intrinsic (aPTT) and extrinsic (PT/INR) coagulation pathways. This clinical picture is consistent with?

2. Factor II (prothrombin) deficiency results in ?

Vitamin K deficiency.

2. prolongation of the prothrombin time and partial thromboplastin time due to its role in both the extrinsic and intrinsic pathways.


This patient is complaining of cold intolerance, fatigue, and weight gain despite an attempt to lose weight. Examination reveals a simple goiter, hyporeflexia, and dry skin. These presenting symptoms are classic for ?


The likely cause of this hypothyroidism is lack of synthesis of thyroid hormone. Phenylalanine is a precursor to tyrosine, which is needed to create thyroid hormone. During thyroid hormone synthesis, iodide is first oxidized to iodine. Iodine is then added to the tyrosine residues of thyroglobulin to create monoiodotyrosine (MIT) and diiodotyrosine (DIT). MIT and DIT are then combined to create thyroxine and triiodothyronine, with thyroxine as the dominant product. Thus a deficiency in phenylalanine could cause a lack of thyroid hormone production. Phenylalanine and tyrosine are also precursors to dopa, melanin, dopamine, norepinephrine, and epinephrine.


Acute intermittent porphyria is a disorder of ?

the heme synthesis pathway that manifests with abdominal Pain, Polyneuropathy, Psychological disturbances(in this case, hallucinations), elevated Porphobilinogen in the urine causing it to take on a dark red color. It is often Precipitated by cytochrome P-450 inducers (hence the “5 P’s


Spherocytes are seen in ?

hereditary spherocytosis, an autosomal dominant disorder of the erythrocyte structural protein, spectrin. Although some patients may develop an anemia, symptoms and signs such as this patient’s abdominal pain, hyponatremia, psychosis, and porphobilinogen in the urine are not observed.


Ringed sideroblasts are a sign of ?

sideroblastic anemia, which is caused when the body fails to synthesize heme. Typically, this condition would manifest like any other anemia, with symptoms of fatigue, for example; it would not cause any of this patient’s systemic symptoms.


Increased urine uroporphyrinogen is seen in?

porphyria cutanea tarda, the most common kind of porphyria. This kind of porphyria is not associated with acute-onset severe abdominal pain, as in this patient, nor would it produce this patient’s neurologic and psychiatric symptoms.


Abnormal hemoglobin forms are suggestive of ?

sickle cell disease. Although pain is a hallmark of sickle cell crises, these episodes are not associated with hyponatremia, barbiturate use, or psychosis, which are all present in this scenario.


This patient presents with nausea, vomiting, abdominal pain, hyperventilation, and lactic acidosis with hypoglycemia. This presentation is consistent with ?

ethanol-induced hypoglycemia. Oxidation of ethanol produces the reduced form of nicotinamide adenine dinucleotide (NADH) in the liver via two key enzymes: alcohol dehydrogenase and acetaldehyde dehydrogenase.


Acute ethanol intoxication can lead to ?

hypoglycemia and gap (lactic) acidosis. This is caused by an elevated NADH:NAD+ ratio, which favors the conversion of pyruvate to lactate, and limits available pyruvate for gluconeogenesis.


Thiamine (vitamin B1) deficiency can cause?

lactic acidosis, because it is a cofactor in the pyruvate dehydrogenase complex; this causes pyruvate accumulation, which induces lactic acid production. However, thiamine deficiency would not cause the constellation of symptoms seen in this patient, including nausea, vomiting, abdominal pain, and hypokalemia.


This young woman with a recent diagnosis of breast cancer and a significant family history of breast and ovarian cancer is likely to have ?

a BRCA1 or BRCA2 mutation.These are tumor-suppressor genes whose protein products function in DNA repair. Frameshift or nonsense mutations commonly occur in BRCA1/2 and produce truncated protein products. Mutations in these genes result in a gene product that loses its function and can lead to DNA instability and subsequent gene rearrangements


Robertsonian translocations lead to ?

miscarriage, stillbirth, or chromosomal imbalances


Dominant negative effect describes ?

the mechanism for a variety of inherited diseases, such as osteogenesis imperfecta.


Gain of function mutations are seen in?

Variable expressivity is seen in?

1. HER2, MYC, and EGFR2—but not BRCA.

2. neurofibromatosis type 1.