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PS4KEY - Professor Hinck Bio 110 problem set 4 1 Describe...

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Professor Hinck Bio 110, problem set 4 1) Describe the events that occur when an mRNA has a signal sequence. Start with the mRNA being translated by ribosomes in the cytosol (1) and end with the protein being bound by chaperone BiP in the endoplasmic reticulum. ANS mRNA is being translated by ribosomes in the cytosol. 1) Binding of SRP to the signal sequence causes pause in translation 2) SRP bound ribosomes attaches to SRP receptor on the surface of ER 3) SRP receptor binds the translocon and translation continues with nascent polypeptide now being fed through pore of translocon 4) When translation is complete, the signal sequence is cleaved by signal peptidase that reside in the ER membrane. 5) The translocon opens laterally and releases the signal sequence into the lipid bi layer Bip binds the polypeptide inside the ER 2) You are exploring how mRNAs are translated and translocated. I described these experiments in class where scientists performed in vitro translation of luminal ER proteins with and without microsomes harvested from rough endoplasmic reticulum. In the experiments shown in lanes 2 and 5, they added a protease, which chops up unprotected proteins. In the experiments shown in lanes 3 and 6, they lysed the microsomes and added endoH which chews up oligosaccharides. Please look at the gel below and explain exactly what you have learned from this experiment. To do this, explain each lane of the gel, that is to say explain why the protein migrated the way it did with each treatment in terms of the process of translation and translocaton into the ER. Hint: adding oligosaccharides to proteins makes them bigger and therefore decreases their mobility in the membrane.
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Professor Hinck Bio 110, problem set 4 ANS: Microsomes present added during translation 1) the protein is a certain size when the microsomes are present and no enzymes are there to change its mobility.
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