Cells have a mechanism for tagging and destroying proteins containing a C-termin

Question

Cells have a mechanism for tagging and destroying proteins containing a C-terminal poly(Lys) sequence. What is the source of these proteins and why is destroying them helpful for the cell? 1. Cystic fibrosis is caused by a mutation in the 250,000-bp CFTR gene. The mature CFTR mRNA is only 6129 nucleotides. 2. Why is the mature mRNA so much shorter than the gene from which it was transcribed What is the minimum number of nucleotides required to encode the 1480- residue CFTR protein? a. b. 3. The CFTR gene (remember this from a previous clinical connection?) contains the sequence a. b. ATCATCTTTGGTGTT.., which codes for residues 506-510 of the protein. Identify the residues in this segment of the protein. In the most common mutated form of the gene, this same segment of DNA has the sequence ATCATTGGTGTT What type of mutation has occurred and how does it affect the sequence of the encoded protein? c. 4. A portion of DNA from a phage genome is shown. How many reading frames are possible? Specify the amino acid sequences for all the possible reading frames. a. b. Which frames represent open reading frames? 5-CGATGAGCCTTTCAGCACCGCTTAGTGAGGTTGCGCGCCACG-3' 3-GCTACTCGGAAAGTCGTGGCGAATCACTCCAACGCGCGGTGC-5' Explain why a redundant genetic code helps protect an organism from the effects of mutations 5. Name the amino acids that are attached to the 3' end of the E. coli tRNA molecules with the anticodon sequences a. GUG, b. GUU, or c. CGU 6.

Explanation / Answer

1) Co-translational protein quality control has its origins in mRNA surveillance pathways for the degradation of aberrant transcripts . quality control in the cell maintained by the ubiquitine ligases to degrade or destroy the proteines. Polylysine at the C-terminal is the indication to unfolded or protein not used for further functions.

ribosome-associated quality control is one of the pathway involved in quality controll where stalling poly(A) sequences at the C-terminal needed to initiate RQC in instances of inappropriate poly-adenylation at cryptic sites within an opewhich n reading frame. Early studies in yeast suggested that stalling was due to the translation of poly-basic residues (AAA codes for lysine).

2 i) due to alternating splicing mature mRNA becomes short and some of the coding exons removed during exon suffling.

2 ii) because the exons spiced during spicing process that needed to synthesized functional protein needed to form normal CFTR.

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