Lecture 16 Flashcards

Question

How is a protein sorted/ placed into its appropriate target organelle?

Answer 1

There is a signal sequence on the N terminal that helps the protein know which compartment to go When the ribosome translates the signal sequence ( this can be even bfr the completion of translation of proteins) the ribosome guides the protein to its destination( AGAIN this can occur while the protein is synthesized) A protein without localization signal is retained in the cytosol

Answer 2

Protein synthesis starts at the cytosol, if the mRNA doesn’t have any ER signal then the protein synthesis will remain ongoing in the cytosol But if the n terminal of the mRNA hAs a localization signal for ER then it is directed towards the ER and the rest of protein synthesis occur there. Note- polyribosome synthesis can occur at both sites

Answer 3

As soon as an ER signal is translated the SRP attaches to the mRNA and ribosome The SRP guides the ribosome to the the ER Once it reaches ER , the SRP binds to the SRP receptor on the ER membrane This binding causes the release of SRP The ribosome is then translocated from SRP receptor to a protein translocator Protein synthesis resume at original speed and the protein translocator , and positions the protein across the lipid bilayer The protein translocator binds to the signal sequence and passes the rest of the growing polypeptide into the lumen At a point SIGNAL PEPTIDASE cuts the polypeptide from the signal sequence, and the signal sequence is ejected in the bilayer and is degraded. Once the protein synthesis is completed , the TRANSLOCATED POLYPEPTIDE is released as a soluble protein into the ER lumen, and the protein translocator closes

Answer 4

Small blebs of lipid bilayer membrane surrounding an aqueous interior.

Answer 5

- soluble proteins and small molecules in the interior - integral membrane in the membrane of the vesicle —— membrane in a membrane is how membrane of other organelles grow

Answer 6

1- A single pass transmembrane protein embedded in the lipid bilayer 2- A double pass protein that has an internal ER signal sequence Start and stop determines the arrangement of a transmembrane protein in the lipid bilayer

Answer 7

There are 2 signalling sequence in the in the protein -The Start sequence at N terminal ER signal -And a hydrophobic stop transfer sequence The N sequence is attached to the protein translocator and initiates the TRANSFER . The protein translocator positions the polypeptide across the bilipid layer until the hydrophobic signal is reached The N terminal signal is cleaved by signal peptidase and the growing polypeptide is discharged into the LIPID BILAYER The N terminal signal stays in the lipid bilayer and is degraded The polypeptide continues to grow on the cytosolic side and continues to discharge into the lipid bilayer Note| the single pass transmembrane protein is retained in the lipid bilayer and doesn’t fall into the lumen , because it is supposed to be embedded in the lipid bilayer

Answer 8

The double pass transmembrane protein has an internal ER signal while the single pass had an N terminal ER sequence The same process of bringing the Ribosome to ER occurs involving a SRP , however this time it attaches to the internal hydrophobic ER signal sequence ( as there is no N terminal ER signal sequence ) The internal ER sequence acts as 1- start transfer signal and 2- anchors the final protein in the membrane The protein translocator attaches to the hydrophobic ER signal sequence and positions the rest of the polypeptide across the lipid bilayer until hydrophobic sequence is reached When a stop sequence is recognized, both sequences , the growing COOH and the N terminal sequence are released into the Lipid bilayer . No sequence is cleaved off and the entire polypeptide remains anchored to the LIPID BILAYER Note - both the internal and stop transferase signal are hydrophobic

Answer 9

Cytosol side of membrane proteins - + charged ER LUMEN OF PROTEIN- - charged This polarity is present when being synthesized The integral membrane is made of alpha helices The amino acid in the centre of protein is are hydrophobic And the charged amino acid can interact with the hydrophilic

Answer 10

They three types of protein modification are 1- disulphides bond formation 2- glycosylation 3- protein folding

Answer 11

1- disulphide bridges - stabilizes the structure of secretory proteins 2- glycosylation- short branched ovligosacharides are added from a lipid to protein by an enzyme called GLYCOSYL TRANSFERASE This helps - protection from degradation - cell cell recognition - facilitate protein folding 3- protein folding - chaperones bind and alter the folding of newly forming proteins Folding is required before proteins carry out their function

Answer 12

Golgi and ER

Answer 13

Leave the ER - can be retained within the cell or can be secreted outside OR Retain within the ER if misfolded or if used as membrane proteins

Answer 14

By ensuring - if a protein has ER retention signal ( recognized by ER membrane receptors and retained) - IF a secretory protein is folded properly - If they are misfolded CHAPERONES bind to it and retain them in ER until they are folded properly If they still dont fold properly they are destroyed

Answer 15

Correct tertiary state - native state - for functioning properly

Answer 16

Heat | Chemicals such as urea

Answer 17

When misfolded protein are retained in theER They accumulate in ER The accumulation activiate an unfolding protein - UPR UPR causes the activation of genes that increase protein folding capacity

Answer 18

1- IREI 2- PERK 3- ATF6 These 3 factors are required for activation of UPR

Lecture 16 Flashcards

(45 cards)