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Old 09-29-2012
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DNA Mechanism CFTR gene

A caucasian couple comes to you with complains that their five month old child "always seems to be sick and isn't growing as well as the first son". They give a recurrent history of respiratory infections, and what the mother suspects are delayed milestones. Her skin tastes salty on some occasions. On examination, the child seems pale and irritable, albeit physically normal, and is on on below normal percentile for weight. On discovering a positive family history in this consanguineous couple, you order levels of Serum immunoreactive trypsin. What is the molecular pathology for this disease?

A) Deletion of a gene coding for Phenylalanine at position 508 in chromosome 7, leading to absence of production of a cell membrane protein.
B) Frame-shift mutation in the gene coding for Phenylalanine at position 508 in chromosome 7, resulting in absence of transcription of a cytoskeletal protein.
C) Deletion of a gene coding for Phenylalanine at position 508 in chromosome 7, leading to production of an abnormal cell membrane protein.
D) Mutation in gene coding for Phenylalanine at position 508 in chromosome 7, leading to abnormally shaped protein placed in cell membrane.
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Deletion of a gene coding for Phenylalanine at position 508 in chromosome 7, leading to production of an abnormal cell membrane protein.
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yes, will go with D
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Old 09-29-2012
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i will go for C
miss folded protein is degraded before it is translocated to cell membrane
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Quote:
Originally Posted by venky2600 View Post
yes, will go with D
you wanted to say : " yes, will go with C? "

cause the gene product is degraded by ubiquitine proteasome pathway even before it reaches cell membrane.
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Default The correct answer is C.

This question is meant to test an important mechanism in the pathology leading to Cystic Fibrosis. The gene that encodes the CFTR protein is found on the human chromosome 7, on the long arm at position q31.2. The most common mutation, ΔF508 results from a deletion (Δ) of three nucleotides which results in a loss of the amino acid phenylalanine (F) at the 508th position on the protein. As a result the protein does get produced, but gets folded abnormally after production, and hence gets 'tagged' for destruction with ubiquitin. Proteasome, a barrel shaped protein complex, subsequently degrades this tagged protein. The absence of this chloride channel in the membrane, hence, is attributed to the channel's destruction before reaching the cell surface, and not from an underlying defect in its production.
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Quote:
Originally Posted by beka-CTS View Post
you wanted to say : " yes, will go with C? "

cause the gene product is degraded by ubiquitine proteasome pathway even before it reaches cell membrane.
thanks for reminding.
oh god...this happened to me lot many times.......
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