USMLE Biochemistry Videos & Books

2022-08-25 21:45:33 Educational objective: The human leukocyte antigen (HLA) genes encode major histocompatibility complex (MHC) molecules that are key to activation of the immune system in response to foreign (non-self) antigens. All the HLA genes are clustered together, meaning that there is a low rate of crossover and that offspring essentially inherit 2 HLA haplotypes, one from each parent. Therefore, the probability that a sibling would be an identical HLA match is 1/4. ओपन / कमेंट

2022-08-25 08:44:02 ओपन / कमेंट

2022-08-25 08:44:01 A 50-year-old previously healthy man is evaluated for progressive fatigue, weakness, and recurrent gingival bleeding. Laboratory studies reveal normocytic normochromic anemia, thrombocytopenia, and leukocytosis with circulating myeloblasts. Bone marrow biopsy establishes a diagnosis of acute myeloid leukemia. Induction chemotherapy followed by a11ogeneic hematopoietic cell transplantation (HCT) is planned. Molecular typing of human leukocyte antigen (HLA) -A, -B, -C, -DP, -DO, and -DR is performed. The patient's biological sister, with whom he shares both parents, is eligible for stem cell donation and undergoes HLA typing. ओपन / कमेंट

2022-08-24 21:44:01 Educational objective: Many frequently encountered diseases (eg, hypertension, spinal bifida) display multifactorial inheritance, which involves the complex interaction of numerous genetic and environmental factors to determine phenotypic expression. Although the exact inheritance risk cannot be determined, the closer a relative is to the affected person, the more likely the relative is to develop the trait. ओपन / कमेंट

2022-06-22 09:36:02 ओपन / कमेंट

2022-06-22 09:36:01 A 43-year-old man is evaluated for progressive neuropsychiatric symptoms. A year ago, he began feeling depressed and having hallucinations. Five months later, he developed intermittent paresthesias and progressively worsening choreiform movements, myoclonus, and ataxia. These symptoms have not improved despite multiple hospitalizations; an extensive workup has been unrevealing. The patient is a slaughterhouse worker with extensive exposure to bovine offal. As part of the evaluation for prion disease, a tissue sample digested with protease is processed via gel electrophoresis and transferred to filter paper. Antibodies to a specific prion protein are added to the filter. Next, a marked protein that combines with the antibody-protein complex is used to determine whether the test is positive. ओपन / कमेंट

2022-06-21 20:35:34 Educational objective: A frameshift mutation occurs with the deletion/addition of a number of bases not divisible by 3 in the coding region of a gene. Frameshift mutations alter the reading frame of the genetic code, dramatically changing the protein structure and often resulting in the formation of a premature stop codon. ओपन / कमेंट

2022-06-21 08:35:21 ओपन / कमेंट

2022-06-21 08:34:01 A 34-year-old woman comes lo the office due to dysuria. The patient has a history of recurrent urinary tract infections. A urine sample is collected and sent for culture. Gram-negative bacteria isolated from the urine are found to form pink colonies on lactose-containing MacConkey agar. Several days later, bacterial isolates from a second urine sample are found to form white colonies when plated on the same type of medium. Genetic analysis shows that the more recent isolates have a single nucleotide deletion within the lac operon DNA sequence. ओपन / कमेंट

2022-06-20 20:34:01 Educational objective: Nondisjunction is the failure of chromosome pairs to separate properly during cell division. This could be due to a failure of homologous chromosomes to separate in meiosis I or a failure of sister chromatids to separate during meiosis II or mitosis. ओपन / कमेंट