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Tutor profile: Syed S.

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Syed S.
PhD Candidate at Weill Cornell Medicine
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Questions

Subject: GRE

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Question:

The greatest prime factor of 144 is L The greatest prime factor of 96 is M. A. L > M B. L < M C. L = M D. None of the above

Inactive
Syed S.
Answer:

C. L = M First we have to find prime factors of 144 and 96: a)144 = 2*72 = 2*2*36 = 2*2*6*6 = 2*2*2*3*2*3 3 is the greatest prime factor b)96 = 3*32 = 3*8*4 = 3*4*2*2*2 =3*2*2*2*2*2 3 is also the greatest prime factor Both L and M have 3 as their greatest prime factor, hence they both are equal.

Subject: Biochemistry

TutorMe
Question:

You are trying to do mutagenesis on a linear sequence of DNA but forget to include mutagenic primers into your mix. Which of the following results are most expected to be seen on a DNA gel as a consequence?
A. Single Template Band B. Multiple Template Bands C. Single Product Band D. Multiple Product Bands E. bands resembling the DNA ladder

Inactive
Syed S.
Answer:

PCR Mutagenesis requires mutagenic primers, template DNA, polymerase, enzymatic buffers and water and sometimes secondary structure relaxing agents like DMSO. Without mutagenic primers, amplification is impossible and as a result only the original linear template band will be visible. A.

Subject: Biology

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Question:

You are running an experiment that observes lysosome membrane proteins and their regulation in trafficking pathways. Literature tells you that Lamp1 (Lysosomal-associated membrane protein) is highly expressed on the surface of lysosomes; as you read further you discover that the lumenal surface of this transmembrane protein contains up to 16-20 potential N-/O- glycosylation sites. You decide to run an SDS/PAGE gel then follow up with western blotting with a monoclonal Lamp1 antibody to identify the relative abundance of Lamp1 in your cell samples (control cells with no mutations). You previously read that the molecular weight of Lamp1 is 42kDa, but when you look at your blot you don't see a clear band at 42kDa rather a giant streak that runs from ~140kDa to ~42kDa. When you show your PI these results he confirms they are correct. Why does the western blot results show a streak and not a clear band? A. Your antibody was not specific for Lamp1 and bound to several other proteins that weighed 42kDa to ~140kDa B. Post-translational modifications of Lamp1 C. Because Lamp1 is a transmembrane protein your antibody can't access any epitope and decides to bind to a different much more accessible epitope D. Lamp1 protein is not present/expressed in your cells E. Lamp1 mRNA is modified by varying degrees of glycosylation events

Inactive
Syed S.
Answer:

B. Post translational modifications of Lamp1. The question mentions that previous literature suggests Lamp1 has multiple sites for post-translational modifications on the lumenal side. Lamp1 has so many sites for these oligosacharides because the lysosomal environment is very acidic, and as a result degradation is a common characteristic of lysosomes. Lysosomal proteins undergo lots of glycosylation to prevent their degradation, or at least express sugars that can be degraded before the protein is, to ensure the proper function of the lysosome, however the degree of glycosylation varies and as a result Lamp1 can be glycosylated up to 20 times, and as few as 0 times. A band appearing at 42kDa suggests only non-modified Lamp1 sits in the lysosome, and bands at ~140kDa suggests that all modifiable sites have modifications. Thus it is common to see streaked marks when staining for Lamp1 which would mean the Lamp1 protein is present and varyingly glycosylated.

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