Molecular Genetics — Flashcards

Flashcard 381: Describe the characteristics or mutations associated with the following Hemoglobins: - Hemoglobin C - Hemoglobin F - Hemoglobin H - Hemoglobin S

Answer: - **HbC**: Glutamate → **Lysine** mutation at position 6 of the β-globin chain. - **HbF**: Fetal hemoglobin (α2γ2); has higher O2 affinity than HbA. - **HbH**: β4 tetramers; occurs in **3-gene deletion** α-thalassemia. - **HbS**: Glutamate → **Valine** mutation at position 6 of the β-globin chain.

Extra: Note: **Hb Barts** (γ4) occurs in **4-gene deletion** α-thalassemia (Hydrops fetalis). Both HbH and Hb Barts have very high oxygen affinity and are poor at oxygen delivery. Mnemonic for β6 mutations: - Hb**S**: **V**aline (**S**ickle) - Hb**C**: **L**ysine (Ly-**C**-ine)

Flashcard 382: In an experiment, a protein mixture obtained from a cell culture is separated by gel electrophoresis and subsequently transferred to a filter membrane. -Labeled: Double-stranded DNA probes are used to detect a specific protein of interest in the sample. -What protein is most likely to be detected by this method? a.) Ras b.) C-Jun c.) B1- adrenoreceptor d.) S-100 e.) Adenylate cyclase

Answer: C-jun Other possible answers: c-Fos, or c-Jun & c-Fos because Double stranded DNA probes were use, which means they are using Southwestern blotting technique, (DNA - binding protein).

Flashcard 383: A 2 y/o boy comes with easy bruising. -Parent stated he develops marked bruising & open wounds following minor trauma. -Skin is difficult to suture due to its extreme fragility. -Physical exam: Hyperextensible skin, multiple ecchymoses over the forearms. - Skin biopsy: defect in extracellular processing of collagen. -Which steps of collagen synthesis is most likely impaired in this patient?

Answer: N-terminal propeptide removal or N & C terminal propeptide removal. due to defect in procollagen peptidases (defect in collagen 3 & 5) that lead to Ehlers-Danlos syndrome. (hyperextensible skin, joint laxity, tissue fragility)

Flashcard 384: 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 385: What exonuclease activities are present in DNA polymerase I and DNA polymerase III?

Answer: DNA Polymerase I: Both 5'→3' and 3'→5' exonuclease activities DNA Polymerase III: 3'→5' exonuclease activity only

Flashcard 386: In an experiment, individual bacterial colonies lack a specific enzyme involved in DNA replication. - This enzyme is responsible for removing short fragments of RNA that are base-paired to the DNA template. - Which enzyme is most likely deficient in this strain of E. coli?

Answer: DNA polymerase I It removes RNA primers (5' to 3' exonuclease activity) and replaces them with DNA nucleotides. **Note:** Do not confuse with **Primase**, which synthesizes the RNA primers.

Flashcard 387: 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 388: Identify the location or function of the following molecular markers: - CCA sequence - Poly-A tail - 7-methylguanosine cap - TATA box

Answer: - **CCA sequence**: Located at the 3' end of **tRNA**; the site where amino acids bind ("**C**an **C**arry **A**mino acids"). - **Poly-A tail**: Added to the 3' end of **mRNA** after transcription (post-transcriptional modification). - **7-methylguanosine cap**: Located at the 5' end of **mRNA** (post-transcriptional modification). - **TATA box**: An upstream eukaryotic **DNA promoter** sequence that binds TATA-binding protein (TBP) to initiate transcription.

Flashcard 389: What are the following processes or structures associated with? - Protein degradation - mRNA splicing

Answer: 1. Protein degradation: **Proteasomes** (ubiquitin-mediated degradation) 2. mRNA splicing: **Spliceosomes** (snRNPs)

Extra: Proteasomes degrade nuclear and cytoplasmic proteins tagged with ubiquitin. Spliceosomes consist of snRNPs and other proteins that remove introns from pre-mRNA. Clinical correlate: Anti-Smith antibodies (highly specific for SLE) are directed against snRNPs. Anti-U1 RNP antibodies are associated with Mixed Connective Tissue Disease (MCTD).

Flashcard 390: 65 y/o woman with chronic obstructive pulmonary disease & type 2 DM. -She's hospitalized with septicemia. -Cultures shows rapidly dividing gram-negative bacteria. -Replication of theses microbial cells requires synthesis of two daughter strands of DNA using the parents strands as templates. -Which processes will differ the most between the 2 dauther strands formed at each replication fork?

Answer: Joining of DNA fragments by ligase which is specific for lagging strands.