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Comprehensive USMLE Biochemistry Exam Bank 2024: 500+ High-Yield Questions, Detailed Answers, and Rationales for Guaranteed Success Extensive USMLE Biochemistry Exam Bank 2024: Over 500 High-Yield Questions, In-Depth Detailed Answers, and Comprehensive R
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Course
USMLE - United States Medical Licensing Ex
Institution
USMLE - United States Medical Licensing Ex
Comprehensive USMLE Biochemistry Exam Bank 2024: 500+ High-Yield Questions, Detailed Answers, and Rationales for Guaranteed Success
Extensive USMLE Biochemistry Exam Bank 2024: Over 500 High-Yield Questions, In-Depth Detailed Answers, and Comprehensive Rationales for Assured Success
Comprehensive USMLE Biochemistry Exam Bank 2024:
500+ High-Yield Questions, Detailed Answers, and
Rationales for Guaranteed Success
Extensive USMLE Biochemistry Exam Bank 2024: Over
500 High-Yield Questions, In-Depth Detailed Answers,
and Comprehensive Rationales for Assured Success
1) A newborn presents with sever acidosis, vomiting, hypotonia, and nuerologic defects. Laboratory
analysis reveals elevated levels of lactate and alanine. These observations suggest a deficiency of which
of the following enzymes?
A) Alanine aminotransferase
B) Glutamate dehydrogenase
C) Lactate dehydrogenase
D) Phenylethanolamine N-methytransferase
E) Pyruvate dehydrogenase
E) Pyruvate dehydrogenase
-
Notes:
Pyrutvate (PYR)->->-> Lactate, Acetyl CoA, Alanine by enzymes C, E, A
,2) Several members of a family have an autosomal recessive disease characterized by intellectual
deterioration, weakness, ataxia, seizures, and death at a young age. Special studies demonstrate a
deficiency of cytochrome C oxidase activity. Which of the following subcellular organelles is defective in
affected members of this family?
A) Golgi apparatus
B) Lysosomes
C) Mitochondria
D) Ribosomes
E) Smooth endoplasmic reticulum
C) Mitochondria
-
Notes:
Electron transport chain (ETC) happens in the mitochondria.
3) A 17-year-old high-school student comes to the school health clinic. She has missed her last menstrual
period and is worried about being pregnant. In the past history, it is noted that she has sickle cell trait
and mild asthma but is otherwise healthy. She has never been pregnant before and is sexually active
with one boyfriend. They use barrier contraception on an irregular basis. She reports that her boyfriend
once told her that he too had sickle cell trait. She is determined to continue with the pregnancy if her
urine pregnancy test turns out to be positive. Her main concern is whether her child will have sickle cell
anemia. At this stage, it is appropriate to counsel her that in cases where both parents have sickle cell
trait the risk of having a baby born with sickle cell anemia is which of the following?
A) 5%
B) 25%
C) 50%
D) 75%
E) 100%
B) 25%
-
,Notes:
Aa x Aa = AA + 2Aa + aa
where chance of aa is 1/4
4) A prokaryotic operon codes for two enzymes and one regulatory protein. The operon is expressed
only in the presence of a particular sugar. Initial mapping of the operon has differentiated the
nontranscribed sequences. Deletion of 10 nucleotides from one of the non transcribed sequences
results in transcription of the operon in both the presence and absence of the sugar. Which of the
following sequences was most likely affected?
A) Activator binding site
B) Activator gene
C) Operator
D) Promoter
E) Repressor gene
C) Operator
-
Notes:
Sugar independent operator command
5) Genomic DNA from a child with pyruvate kinase deficiency identifies a mutation in the 3'-splice site of
intron 3. The mRNA from the child's reticulocytes is used to produce cDNA. Primers flanking the exon
3/exon 4 border are used to amplify this region from the cDNA (RT-PCR). The products are separated by
electrophoresis and compared to the RT-PCR products from normal reticulocytes (control). The results
are shown below. Which of the following mechanisms best accounts fro the results of the splice
mutation? Control 84 bp and Patient 78 bp.
A) Exon skipping
B) Frameshift mutation
C) Missense mutation
, D) Trinucleotide expansion
E) Two-codon deletion
E) Two-codon deletion
-
Notes:
6 bp difference , 3 bp per codon
6) A 36-year-old Greek man with viral pneumonia has a self-limiting episode of hemolysis. Over the next
week, he has an increased rate of reticulocytosis. Which of the following compounds serves as a
precursor to heme in the reticulocytes?
A) alpha-Ketoglutarate
B) Fumarate
C) Isocitrate
D) Oxaloacetate
E) Succinyl-CoA
E) Succinyl-CoA
-
Notes:
Succinyl-CoA + Glycine
-ALAsynthase>
Heme Ring
7) A 22-year-old woman presents with a fusiform swelling of the Achilles tendon, which, when biopsied,
shows cholesterol-laden macrophages (foam cells) dispersed among the collagen fibers. She had been
troubled with joint pains for several years. Both her mother and father developed arthritis associated
with production of xanthomas, but their first symptoms occurred in middle age. She was referred to a
nutritionist and treated with an enzyme inhibitor. Which of the following is most likely elevated in the
blood of this woman?
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