Molecular Genetics — Flashcards

Flashcard 401: A researcher develops 2 functional mRNA sequences composed of CUC & CUU trinucleotide repeats. - He subsequently incubates them. - After a few hours, it is found that both mRNA sequences produce polypeptide chains containing leucine repeats. - This observed finding is due to what genetic principles?

Answer: Degeneracy and the Wobble hypothesis - Degeneracy: Multiple codons code for the same amino acid. - Wobble hypothesis: The 3rd position of the codon can undergo non-traditional base pairing with the anticodon, allowing a single tRNA to recognize multiple codons.

Flashcard 402: HbC disease is caused by a single amino acid substitution (Glutamate → Lysine) at position 6 of the β-globin chain. Patients homozygous for HbC (HbCC) have mild chronic hemolytic anemia. Patients with HbS (Sickle Cell Disease) generally have a more severe condition. Which property of HbS best explains why it is associated with more pronounced clinical manifestations than HbC?

Answer: HbS involves a substitution of Glutamate (polar) with **Valine (nonpolar)**, which allows for **hydrophobic interactions** and polymerization.

Extra: In HbS, the nonpolar valine residue on the surface of the β-globin chain creates a 'sticky' hydrophobic patch. In the deoxygenated state, these patches interact, causing HbS molecules to polymerize into long fibers that distort the RBC (sickling). In contrast, HbC involves a substitution with **Lysine**, which is polar/positively charged and does not promote the same hydrophobic polymerization seen in HbS.

Flashcard 403: What kind of mutation exists in the following base changes? - CUU (Leucine) → AUU (Isoleucine) - UUU (Phenylalanine) → UUC (Phenylalanine) - CAG CCC ACT → CAG TCC CAC T - CAG CAG UAA → CAG CAG CAA - UCA → UGA (Silent, Missense, Nonsense, Nonstop, Frameshift)

Answer: - **CUU (Leucine) → AUU (Isoleucine)**: Missense mutation - **UUU (Phenylalanine) → UUC (Phenylalanine)**: Silent mutation - **CAG CCC ACT → CAG TCC CAC T**: Frameshift mutation - **CAG CAG UAA → CAG CAG CAA**: Nonstop mutation (Stop codon → Amino acid) - **UCA → UGA**: Nonsense mutation (Amino acid → Stop codon)

Extra: - **Silent**: Same amino acid (often 3rd position/wobble). - **Missense**: Different amino acid. - **Nonsense**: Changes to a Stop codon (UAA, UAG, UGA). - **Nonstop**: Stop codon changes to an amino acid. - **Frameshift**: Insertion or deletion not in a multiple of 3, shifting the reading frame.

Flashcard 404: In a research study, small circular DNA molecules that resemble a bacterial chromosome are isolated from exocrine pancreatic cells. Further analysis shows that these molecules code for proteins, transfer RNA, and ribosomal RNA. From which of the following cellular structures did these DNA molecules most likely originate?

Answer: Mitochondria Mitochondria contain circular DNA chromosomes that resemble bacterial (prokaryotic) chromosomes. They are inherited maternally and encode their own proteins, transfer RNA (tRNA), and ribosomal RNA (rRNA).

Flashcard 405: 24 y/o woman is diagnosed with gestational diabetes mellitus during her 1st pregnancy. -Mother & younger sister had high blood surgars during pregnancy. -If this patient's gestational hyperglycemia is genetically predisposed, she is most likely to have decreased activity in what enzyme?

Answer: Glucokinase Glucokinase need to phosphorylate glucose to breakdown in glycolysis in order to release ATP to close down the K channel, which lead to influx of Ca that causes release of insulin. due to Maturity Onset Diabetes of the Young (MODY) (hereditary mutation of glucokinase gene) Key: Her mother & her younger sister had diabetes too during their pregnancy, very young.

Flashcard 406: What is the mode of inheritance of porphyria cutanea tarda?_____

Answer: Autosomal dominant

Flashcard 407: What is the mode of inheritance of Familial Mediterranean fever? _____

Answer: Autosomal recessive

Flashcard 408: Mutations in which tumor suppressor genes can lead to Tuberous Sclerosis?_____

Answer: TSC1 & TSC2

Flashcard 409: What is the mode of inheritance of von Hippel-Lindau disease? _____

Answer: Autosomal dominant

Flashcard 410: Which cell cycle phase is characterized by resting, non-dividing cells?_____

Answer: G0