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Biochemistry — Step 1 practice questions
39 questions in this area, with an explanation for every answer choice.
Three samples below, free and without an account.
How this shows up on Step 1
Tested through disease rather than pathway recall. An enzyme deficiency is described by its consequences and you name the step. Metabolic pathways matter where they intersect with a recognisable clinical presentation.
Sample questions
Sample question 1
A patient with chronic hepatitis B undergoes routine surveillance imaging and lab testing. Which of the following tumor markers is most appropriately monitored for early detection of hepatocellular carcinoma in this population?
Explanations
A. PSA
PSA is used for prostate cancer, unrelated to HCC.
B. CEA
CEA is a nonspecific marker most associated with colorectal cancer monitoring, not the primary HCC surveillance marker.
C. Alpha-fetoprotein · correct
Alpha-fetoprotein is the classic tumor marker used (alongside imaging) for hepatocellular carcinoma surveillance in high-risk populations like chronic hepatitis B carriers.
D. CA-125
CA-125 is used for ovarian cancer monitoring, not HCC.
E. CA 19-9
CA 19-9 is used for pancreatic cancer, not the primary HCC surveillance marker.
Sample question 2
A researcher compares the time course of action of two hormones. Hormone A produces measurable effects within seconds, while hormone B requires several hours. Which of the following best explains this difference?
Explanations
A. Hormone A has a longer half-life than hormone B
Half-life influences duration, not the latency of onset.
B. Hormone B is degraded faster in the circulation
Degradation rate does not explain the transcriptional delay.
C. Hormone A acts on cell surface receptors triggering second messenger cascades, while hormone B is lipophilic and acts on intracellular receptors altering gene transcription · correct
Peptide and catecholamine hormones are water-soluble, circulate largely unbound with short half-lives, and bind SURFACE receptors coupled to second messengers (cAMP, IP3, tyrosine kinases) — producing rapid effects. Steroid and thyroid hormones are lipophilic, travel bound to carrier proteins with long half-lives, cross the membrane, and bind INTRACELLULAR receptors that act as transcription factors — so effects require transcription and translation and take hours.
D. Hormone A requires a carrier protein while hormone B circulates free
Carrier protein binding is a feature of the SLOW-acting steroid hormones.
E. Hormone A is lipophilic and hormone B is water-soluble
This reverses the solubility assignments.
Sample question 3
A patient with chronic kidney disease has low calcium despite adequate sun exposure and normal 25-hydroxyvitamin D. Which of the following best explains this?
Explanations
A. The failing kidney cannot perform 1-alpha-hydroxylation, so active 1,25-dihydroxyvitamin D is deficient despite adequate precursor stores · correct
Vitamin D activation requires two sequential hydroxylations: the LIVER converts cholecalciferol to 25-hydroxyvitamin D (the storage form measured clinically), and the KIDNEY performs the rate-limiting 1-alpha-hydroxylation to calcitriol, stimulated by PTH and hypophosphatemia. In chronic kidney disease the first step is intact — so 25-hydroxyvitamin D is normal — but the second fails, producing functional deficiency of the active hormone. Treatment therefore requires calcitriol or its analogs rather than ordinary vitamin D supplementation.
B. Skin synthesis of cholecalciferol is impaired
Sun exposure is stated to be adequate.
C. The liver cannot perform 25-hydroxylation
Hepatic 25-hydroxylation is preserved, as the normal level indicates.
D. The kidney performs 25-hydroxylation and the liver performs 1-alpha-hydroxylation
This reverses the organ responsibilities.
E. Dietary vitamin D absorption is blocked in kidney disease
Absorption is not the limiting step.
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