Molecular Genetics — Flashcards

Flashcard 381: What are the following markers? -Ras -c-Jun -B1 - adrenoreceptor -S- 100 -Adenylate cyclase -C-fos

Answer: Ras: Protooncogene activates MAP kinase pathway, affect transcription, has GTPase gene product. (associated with colon, pancreatic, and lung cancer.) -c-Jun: The protein that binds to DNA in southwestern blot (double stranded DNA probe). -B1-adrenoreceptor: Gs protein couple receptor. -Adenylate cyclase: cleaves ATP to form cAMP. -S-100: calcium binding proteins. -c-Fos: Proteins that bind to DNA to form double stranded DNA probe in Southwestern blot.

Flashcard 382: 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 383: 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 384: What are the followings associated with? -Cleavage of DNA strands to remove supercoils -Excision of thymine dimers within DNA -Removal of mismatched base pairs during DNA replication -Removal of RNA primer nucleotides -Unwinding of the 2 strands of template DNA (DNA polymerase 1, DNA gyrase, UV-specific endonuclease, helicase)

Answer: Cleavage of DNA strands to remove supercoils: DNA gyrase (topoisomerase 2) -Excision of thymine dimers within DNA: UV-specific endonuclease. -Removal of mismatched base pairs during DNA replication: DNA polymerase 3 (most common), DNA pol 1, DNA pol 2. -Removal of RNA primer nucleotides: DNA polymerase 1 -Unwinding of the 2 strands of template DNA: Helicase

Flashcard 385: 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 386: 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 387: In which strands will the followings occurs? (leading or lagging strands) -Enzymatic function of DNA helicase -Interaction with single stranded DNA binding proteins -Joining of DNA fragments by ligase -Proofreading of the newly synthesized DNA -Relief of supercoils by topoisomerase

Answer: They all will occur in both leading and lagging strands except for Joining of DNA fragments by ligase which only occurs in the lagging strands.

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: A group of investigators is studying the mechanisms involved in cancer pathogenesis. -They find that interaction of a certain growth factor with its receptor leads to the following sequence of event: 1. Binding of growth factor 2. Autophosphorylation of tyrosine residues 3. Activation of phosphoinositide 3-kinase 4. Activation of protein kinase B (Akt) 5. Activation of X What is the most likely direct effect of X upon activation?

Answer: Stimulation of protein synthesis The sequence describes the **PI3K/Akt/mTOR** signaling pathway. Step 5 (X) is the activation of **mTOR**. mTOR then phosphorylates targets such as 4E-BP1 and p70S6K to increase mRNA translation. **Note:** mTOR inhibitors like **sirolimus (rapamycin)** are used to treat certain cancers and as immunosuppressants.

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.