USMLE Biochemistry Videos & Books

2022-05-17 21:39:01 Educational objective: When mRNA is first transcribed from DNA, it is in an unprocessed form called pre-mRNA or heterogeneous nuclear mRNA (hnRNA). Several processing steps are required before finalized mRNA molecules can leave the nucleus, including 5'-capping, poly A tail addition, and intron splicing. Cytoplasmic P bodies play an important role in mRNA translation regulation and mRNA degradation. ओपन / कमेंट

2022-05-17 10:39:18 ओपन / कमेंट

2022-05-17 10:38:37 A 32-year-old man is recovering from extensive burns. Fibroblasts near the site of injury actively synthesize precursor mRNA to be used as templates for protein synthesis. After transcription, extensive
processing of the precursor RNA occurs to form the finalized mRNA sequence. The finalized mRNA then exits the nucleus and undergoes translation by ribosome complexes before being degraded. ओपन / कमेंट

2022-05-16 21:47:01 Educational objective: Southwestern blotting is used to detect DNA-binding proteins such as transcription factors, nucleases, and histones. ओपन / कमेंट

2022-05-16 07:47:01 ओपन / कमेंट

2022-05-16 07:46:01 Molecular biologists undertake a series of experiments designed lo classify proteins involved in various intracellular signaling pathways. During one of the experiments, a protein mixture obtained from a cell culture is separated by gel electrophoresis and subsequently transferred lo a filter membrane. labeled double-stranded DNA probes are then used lo detect a specific protein of interest in the sample. ओपन / कमेंट

2022-05-15 20:46:01 Educational objective: X-inactivation occurs in genetically normal females and results in conversion of the inactivated X chromosome into compact heterochromatin (Barr body). Heterochromatin is condensed chromatin composed of heavily methylated DNA in tight association with deacetylated histones. It has a low level of transcriptional activity. In contrast, euchromatin is loosely arranged and exhibits a high level of transcriptional activity. ओपन / कमेंट

2022-05-15 07:45:13 ओपन / कमेंट

2022-05-15 07:45:12 A 24-year-old woman comes to the office after discovering a new mole on her right leg. She is worried that it might be skin cancer as she has used tanning beds several times a year since age 18. Physical examination shows a 5-mm brown, oval macule on her anterior thigh with a homogeneous coloration and discrete borders. The lesion appears darker than her other moles. A biopsy of the lesion shows normalappearing nevus cells clustered in the epidermis, and she is diagnosed with a benign acquired melanocytic nevus. During histologic analysis, her epithelial cells are each found to contain a condensed body composed of heavily methylated DNA at the periphery of the nucleus. ओपन / कमेंट

2022-05-14 20:45:27 Educational objective: The poly-A tail is not transcribed from DNA; instead, it is added as a post-transcriptional modification downstream of the consensus sequence (AAUAAA) located near the 3' end of the mRNA molecule. This tail protects mRNA from degradation within the cytoplasm after it exits the nucleus. References ओपन / कमेंट