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Altius FL #4 Questions
#1 Posted : Monday, July 12, 2021 3:17:07 AM
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Question 6: What exactly is an allosteric modulator? Is it separate from uncompetitive/non-competitive inhibitors? Also, can co-enzyme not covalently form prosthetic groups? According to the classroom companion, this seems to be the case?

Can you please explain the difference between translation in the cytosol vs ER? Does translation happen on smooth ER?

Question 40: How can we infer that option C is the correct answer? Especially because the passage does not discuss age and brain cancer directly?

Question 46: How can we assume steroids are part of the membrane? I know that cholesterol plays a role in the fluidity of the membrane, but steroids are derived from cholesterol so how do we know it is included?

Question 55: Can you please explain how DSB repair works? I don't think we talked about this in class
#2 Posted : Tuesday, July 20, 2021 9:36:35 PM
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In pharmacology and biochemistry, allosteric modulators are a group of substances that bind to a receptor to change that receptor's response to a stimulus. Some of them, like benzodiazepines, are drugs. noncompetitive inhibitors bind to a site other than the active site and render the enzyme ineffective, whereas competitive inhibitors will block the active site. Allosteric inhibition generally acts by switching the enzyme between two alternative states, an active form, and an inactive form. Allosteric effectors are molecules that bind to an enzyme at a site other than the enzyme’s active site and regulate its function. Because allosteric effectors either upregulate or downregulate enzyme function, the zinc mentioned in the stem cannot be an allosteric regulator. According to the stem, the enzyme cannot function normally without the zinc, whereas enzymes can and do function without allosteric modulators, they just function differently under that regulation (e.g., increased or decreased reaction rate, binding affinity, etc.)

Coenzymes are organic molecules that are required by an enzyme to function, but are not usually covalently bound. They are differentiated from prosthetic groups because they are loosely bound to the enzyme, whereas prosthetic groups are tightly bound (usually, but not universally, via a covalent bond). While coenzymes are always organic non-protein molecules, prosthetic groups can be either organic or inorganic. Because zinc is covalently bound to the enzyme, it is not “loosely” bound and therefore cannot be classified as a coenzyme.

In prokaryotes (bacteria and archaea), translation occurs in the cytosol, where the large and small subunits of the ribosome bind to the mRNA. In eukaryotes, translation occurs in the cytoplasm or across the membrane of the endoplasmic reticulum in a process called co-translational translocation.

You can always assume there will be cholesterol (a steroid) in the cell membrane as it is key in regulating fluidity.

DSBs can be repaired using several different mechanisms. Both ends can be simply rejoined with little or no further processing (nonhomologous end joining, or NHEJ) or can be repaired using homologous sequences (red DNA; homologous recombination) after 5'-3' degradation has occurred (resection). The 3'-OH group exposed after resection can be used to prime DNA synthesis using a homologous region as a template after DNA strand invasion. The newly synthesized DNA (light blue) can then be joined with the 5' end of the resected strand, forming a double Holliday junction (double-strand break repair; DSBR), or can be displaced and reannealed (synthesis-dependent strand annealing; SDSA); or DNA synthesis can continue to the end of the chromosome (break-induced replication; BIR). If two homologous regions flank the DSB, they can anneal after being exposed by DNA resection (single-strand annealing; SSA), which causes the deletion of the intervening region. An additional mechanism that shares components with both SSA and NHEJ and that uses short homology stretches (usually 2-3 bp) flanking the DSB can also be used (microhomology-mediated end joining; MMEJ).
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