L6_4_14_11

L6_4_14_11 - Exam: Tuesday 4/19: coming up. 25 multiple...

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Exam: Tuesday 4/19: coming up. 25 multiple choice and 5 T/F and 2-3 essay plus extra credit You will need to bring a Parscore pink, whole page scantron sheet to exams. These are available at the bookstore. You will need to bring a #2 pencil. You need to bring a calculator. The problem sets are your study guide. The old exam shows you what kind of problems there will be. DRC reminder Guest Lecture on Thursday 4/21
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Homogenization
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Proteins are directed to their correct locations within the cell by protein trafficking Much of the lumenal space in cells are topologically equivalent and may have evolved from vesicles pinching off the plasma membrane Arrows denote outbound and inbound traffic routes
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Purification of smooth and rough microsomes
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The Signal Hypothesis - Proteins are targeted to the ER by a signal peptide that is cleaved off after translocation into the ER. Four discoveries 1) Signal peptide: 2) Protein extruded into the ER: 3) Cotranslational translocation of proteins into the ER 4) Identify the SRP
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SRP binds to the signal peptide, brings the ribosome to the ER and organizes the nascent polypeptide on the tranlocator
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7) Translocator is made up of 3 subunits. Pore is blocked when ribosome is not bound. Lateral opening is very important for transmembrane proteins (see later)
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Internal signal sequence serves as a “start-transfer” sequence and causes proteins to be inserted into the membrane in different orientations Charges on amino acids near the transmembrane segment determine the orientation of the protein. This process is poorly understood but a side with negative charges will go into the ER and a side with positive charge will be retained in the cytoplasm. - - - Negative charge is distal side of start- transfer
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For multipass transmembrane proteins with a signal peptide,the signal peptide is read and begins translocation (start) and then combinations of start transfer and stop transfer signals determine how are inserted into the lipid bilayer negative charges will go into the ER Cleavage after the first signal sequence results in the N-term in the lumen of the ER (problem in problem set
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Once a protein gets into the ER, things happen to it…. .
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3) Molecular chaperones help guide the folding of proteins. Two major families: hsp70 (BiP) and hsp60 (hsp stands for heat shock protein. Different family members work in different compartments. For example, BiP, an hsp70 family member, works in the ER. (Munro and colleagues study BiP) The hsp70 machinery can bind to nascent proteins and massage hydrophobic patches into proper conformations, using energy from hydrolysis of ATP. In contrast, hsp60 and relatives work later in the protein's life to help misfolded proteins refold.
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Hsp70 chaperone proteins use the energy from ATP hydrolysis to direct protein folding Hsp70 proteins recognize a small stretch of hydrophobic amino acids and bind to target protein, hydrolyzing ATP to ADP, undergoing a conformational change that tightens binding between the proteins. ATP binds again and hsp70 dissociates. Repeated cycles of hsp binding and unbinding are required to fold a protein.
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L6_4_14_11 - Exam: Tuesday 4/19: coming up. 25 multiple...

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