Molecular Genetics — Flashcards

Flashcard 401: Describe these 2 genetics term? -Transition -Transversion

Answer: Transition: you replaced a purine by a purine, a pyrimidine by a pyrimidine. -Transversion: you replaced a purine by a pyrimidine. A pyrimidine by a purine.

Flashcard 402: An infant appears healthy at birth but develops transfusion-dependent hemolytic anemia by age 6 months. - His erythrocytes contain insoluble aggregates of hemoglobin subunits. - The child developed normally in utero because at that time he produced high quantities of:

Answer: Gamma-globin (γ-globin)

Flashcard 403: 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 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: Match the following with their specific definition? -Unwinding of double helix -Removal of supercoils -Stabilization of unwound template strands -Synthesis of RNA primer -5' to 3 DNA synthesis & 3' to 5' exonuclease activity -Removes RNA primer -Has 5' to 3' exonuclease activity -Joining of Okazaki fragments -Similar work to DNA polymerase 3 -Connect the lagging strands together.

Answer: Unwinding of double helix: Helicase -Removal of supercoils: DNA gyrase (Topoisomerase 2) -Stabilization of unwound template strands: single stranded DNA binding protein -Synthesis of RNA primer: Primase (RNA polymerase) -5' to 3 DNA synthesis & 3' to 5' exonuclease activity: DNA polymerase 3 -Removes RNA primer: DNA polymerase 1 -Has 5' to 3' exonuclease activity: DNA polymerase 1 -Joining of Okazaki fragments: DNA ligase -Similar work to DNA polymerase 3: DNA polymerase 1, & 2 -Connect the lagging strands together: DNA ligase

Flashcard 406: True or False in relation to sickle cell anemia? a.) HbS decreases Beta -globin interaction with 2,3-diphosphoglycerate b.) HbS impairs oxygen binding to the heme moiety c.) HbS allows hydrophobic interaction among hemoglobin molecules.

Answer: a.) **False**: The mutation (Glu → Val) is on the surface of the $\beta$-globin chain and does not significantly alter the 2,3-BPG binding site. b.) **False**: HbS molecules bind oxygen normally; the pathology is the polymerization of *deoxygenated* HbS. c.) **True**: Replacing polar Glutamate with non-polar Valine creates a hydrophobic "patch" on the surface, allowing interaction with other hemoglobin molecules.

Extra: In **Sickle Cell Anemia**, a point mutation in the $\beta$-globin gene (GAG $\to$ GTG) results in the substitution of **Glutamate (polar)** with **Valine (non-polar)** at the 6th position. This hydrophobic Valine residue fits into a hydrophobic pocket on an adjacent hemoglobin molecule (specifically the $\beta$ chain of another deoxy-HbS tetramer), leading to **polymerization** and the characteristic "sickling" of the RBC.

Flashcard 407: 34 y/o woman comes for breast examination. -Screening test was performed using Polymerase chain reaction (PCR) to amplify the target of exon. -Gel electrophoresis to assess the size of the exon compared to the wild type allele.What features must be known in order to perform the amplification part of this analysis?

Answer: The nucleotide sequence of the DNA regions flanking the target exon (required for primer synthesis).

Flashcard 408: What protein is defective in Marfan syndrome?_____

Answer: Fibrillin (scaffold for elastin)

Flashcard 409: What is the mode of inheritance of porphyria cutanea tarda?_____

Answer: Autosomal dominant

Flashcard 410: What protein is associated with MHC I? _____

Answer: β2-microglobulin