Transcription/translation — Flashcards

Flashcard 181: A researcher is studying the expression pattern of a particular gene: - Messenger RNA (mRNA) is isolated from several tissues and subjected to gel electrophoresis and Northern blotting using a probe for exon 4 of that gene. - The resulting autoradiogram shows that the mRNA transcripts for this gene have different sizes (lengths) in different tissues. What is the most likely explanation for these findings?

Answer: Alternative RNA splicing

Extra: Alternative splicing allows a single gene to code for multiple proteins by including or excluding different exons in the final mRNA transcript. This is a common mechanism for tissue-specific gene expression (e.g., membrane-bound vs. secreted antibodies, or different isoforms of tropomyosin).

Flashcard 182: In an experiment, radiolabeled cysteine residues are attached to their appropriate tRNAs by the enzyme aminoacyl-tRNA synthetase. - The bound cysteine residues are then chemically modified to form alanine. - The end product of this reaction is a tRNA molecule that contains the cysteine anticodon but is mischarged with alanine. - What is most likely to occur to this alanine residue during polypeptide synthesis?

Answer: It will be incorporated into the polypeptide chain at a site requiring cysteine.

Extra: The ribosome recognizes the codon-anticodon interaction between the mRNA and the tRNA. It does not "proofread" the amino acid attached to the tRNA once it has been loaded. Therefore, if a tRNA is mischarged, the wrong amino acid will be incorporated based on the tRNA's anticodon.

Flashcard 183: 32 y/o man is recovering from extensive burns. -Fibroblasts near site of injury actively synthesize precursor mRNA. -The finalized mRNA then exits the nucleus and undergoes translation. -Which steps involving processing and handling of mRNA occur only within the cytoplasm of cells?

Answer: Interaction with P bodies. They play an important role in mRNA translation, regulation and mRNA degradation. They are located in cytoplasm.

Flashcard 184: Describe the key structural components of tRNA and their functions.

Answer: - 3' end: Amino acid attachment site (CCA sequence) - TψC loop: Binds to the ribosome (large subunit) - D loop: Recognized by aminoacyl-tRNA synthetase (contains dihydrouridine) - Anticodon loop: Pairs with the mRNA codon - Variable loop: Varies in size; aids in tRNA recognition and stability

Flashcard 185: A series of experiments is being conducted to determine the structure and function of different types of bacterial RNA. - A specific RNA consisting of 90 nucleotides is purified for further analysis. - It contains high amounts of chemically modified bases such as dihydrouridine, pseudouridine, & ribothymidine, & its secondary structure arises from base pairing within the chain. - What is the most likely composition of the 3' end of this molecule?

Answer: CCA because the structure is a tRNA structure due to chemically modified bases such as dihydrouridine, pseudouridine, & ribothymidine.

Flashcard 186: Which of the following mRNA processing steps occurs only within the cytoplasm? - 5' terminal guanosine triphosphate addition - Methylation of the 5' terminal guanine - Multiple adenine nucleotide attachment to the 3' end - Interaction with snRNP - Removal of intervening sequences - Interaction with P-bodies

Answer: Interaction with P-bodies

Extra: All other listed processes (capping, polyadenylation, and splicing) occur in the nucleus. P-bodies (processing bodies) are distinct foci within the cytoplasm of eukaryotic cells involved in mRNA decay, translation repression, and storage.

Flashcard 187: In an experiment studying Burkitt lymphoma, Western blot analysis shows a significant decrease in c-Myc protein levels following treatment, while c-Myc mRNA levels remain unchanged. What process was most likely directly interrupted by this treatment?

Answer: mRNA translation

Flashcard 188: 8 y/o boy present with reduced sensitivity to pain, impaired tear formation. -Disorder is caused by loss of function of the IKAP protein. -IKAP gene sequencing reveals a single nucleotide subtitution that causes a guanine residue to be replaced by adenine. -His mRNA contains both exon and introns -What is the most likely effect of this mutation?

Answer: Incorrect splicing of pre-mRNA. because splisosome usually cut at "GUAG" 5' GU & 3' AG of the introns. Ex:    5'GU-----------------------AG3'.

Flashcard 189: Aminoacyl tRNA synthetase loads amino acids (e.g., lysine) onto tRNA molecules. To which specific end and sequence of the tRNA molecule does the amino acid attach?

Answer: 3' end (CCA sequence)

Extra: The amino acid is covalently bonded to the 3' hydroxyl group of the terminal adenosine in the CCA sequence found at the 3' end of all mature tRNA molecules.

Flashcard 190: NF-kB activation pathway: Pattern-Recognition Receptors recognize PAMPs which leads to activation of _____ kinase

Answer: IKK (IκB kinase)