Lecture 4-7-16 Jyoti
Lecture 4-7-16 Jyoti BIO 2600
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This 3 page Class Notes was uploaded by Markiesha Notetaker on Friday April 8, 2016. The Class Notes belongs to BIO 2600 at Wayne State University taught by Dr. Jyoti Nautiyal in Winter 2016. Since its upload, it has received 33 views. For similar materials see Intr To Cell Biology in Biology at Wayne State University.
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Date Created: 04/08/16
Lecture 4-7-16 Review of Chapter 15 Eukaryotic system and how proteins are sorted and sent to specific destinations. They are identified by a stretch of amino acids in the genome (DNA) and that is what tells where they will go in the cell. Some will be identified by sequence at N-terminus and some will be at C-terminus. Specific for ER proteins To be imported- at the N-terminus Retention- KDEL No retention signal- protein will be secreted from ER ** Review experiment from slide. Features of sequence tag Signal sequence is necessary (needed to reach destination) Signal sequence is sufficient ( Modes of transport Nuclear pore – protein can be folded Translocation (across membrane)- protein has to be linear Vesicular transport When the protein is needed it will be imported, when it is not needed it will be sent out. This is regulated by correct folding of the protein. When it is folded with the sequence exposed, it will be imported. When it has done its job inside of the cell, the folding is different and it is then sent out of the cell. (Slide 14) **** When membrane transport is happening, it is happening simultaneously as the protein is being transcribed. Translocator protein is important in order to pass the protein through the membrane. Serves as a gate to get the protein in because the inside of the membrane is hydrophobic and will not allow for the protein to pass. New information Transmembrane proteins When adding phospholipids, you also have to add membrane proteins. Transmembrane domain acts as a stop-transfer sequence that is hydrophobic. As the protein is being pushed into the cell by the protein translocator, it will stop pushing through once the stop-transfer sequence is inserted into the membrane. The rest of the protein will stay on the outside of the cell. ER Lumen is equivelant to outside surface. Protein goes from cytosol to inside of ER. ER is represented as “outside”. In this way, the N-terminus will continue to be on the “outside” surface of the membrane and will serve as the receptor region. Multiple transmembrane protein You can have multiple stop and start sequences. N and C-terminus will remain on the cytosolic side. 1. Entire protein in lumen a. Proteins goes through membrane b. Signal sequence is at N-terminus and gets cleaved off 2. Single transmembrane protein a. N-terminus has signal sequence b. Sequence get cleaved off 3. Multipass membrane protein a. Internal start sequence is located in the beginning but not N-terminus b. Signal does not get cleaved off, its stays in the membrane Vesicular transport Membrane bound packages Soluble proteins are usually sent through this mechanisms Slide 22 Golgi apparatus folds are called cisternae From ER to Golgi Cis face Golgi to rest of cell Trans face Protein in ER goes to Golgi via the cis face. Modifications in the Golgi. Protein leaves via the trans face. 1. Leaves the cell via exocytosis. 2. Sent to endosome to eventually go to lysosome Plasma membrane expands (increases) during exocytosis. (Increases length of plasma membrane) Plasma membrane decreases during endocytosis. (Reduce length of plasma membrane) These two processes keep the plasma membrane balanced. Donor compartment- formation of vescicle (budding) Goes to target compartment and fuses with it. When naked transport vesicle is released, motor and transport proteins are needed to move the vesicle around. *** Know slide 26 Docking involves t-snare and v-snare Lipids are able to fuse by lipids moving around laterally. Clicker question Right answer: Disulfide bonds do not form spontaneously within the ER. Disulfide bonds do stabilizes the structure of proteins, they do occur by the oxidation of pairs of cysteine side chains, and the do not form under reducing environments. Only when a protein is folded properly, will it be able to leave the ER. This system is very strict. Example) Cystic fibrosis The disease makes it so that the protein does not fold correctly and therefore it cannot leave the ER. This causes a lot of issues within the body. N-linked gylcoslyation When sugar is attached to protein in the ER Once attached, it is sent to golgi apparatus. Golgi modifies it more, adding more sugars, take off some sugars Protein is finalized Constitution Secretion Default pathway Does not need a signal to secrete Regulated Secretion Has to wait on a stimulus before secretion of the materials Pinocytosis- most common way of endocytosis
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