Lecture 7-Protein Transport Flashcards
What is the difference between the smooth and rough endoplasmic reticulum?
Smooth ER- lacks ribosomes
Rough ER- has ribosomes
Where are calcium ions strored?
Smooth ER
What organelle is abundant in cells that secrete hormones like the liver?
Smooth ER
What is the endoplasmic reticulum mainly responsible for?
Proteostasis
What two things does proteostasis ensure?
- Amount of proteins will be regulated
- Quality of proteins will be regulated
What is the first step of cotranslational translocation?
SR-SRP complex bring hydrophobic polypeptide to ER
What is the second step of cotranslational translocation?
SR-SRP complex leaves. Hydrophobic polypeptide is looped into the translocon/binds to recognition site
What is the third step of cotranslational translocation?
Hydrophobic loop pushes open the plug
What is the fourth step of cotranslational translocation?
Signal peptide leaves translocon by lateral gate and the signal peptidase degrades it
What is the final step of cotranslational translocation?
Polypeptide is released in ER lumen at the end of translation
What are the three regions in the translocation process?
Cytosol–>ER Membrane–>ER lumen
What two items are required in order to initiate the translocation of the first transmembrane?
Signal recognition particle (SRP) and its receptor (SR)
What is the threading of the subsequent transmembrane domains managed by? (2 concepts)
- The ribosome-translocation assembly
- The hydrophobicity of the translated domain
What do the ‘N’ terminus and ‘C’ terminus represent?
N terminus- first amino group has free amino group
C terminus- last amino group has free carboxyl group
Properly folded/modified proteins are packaged into ______ to be shipped to the ____ ______ and other locations in the cell
Vesicles
Golgi Apparatus
What do chaperone proteins do?
Assist in the folding of proteins/identify improperly folded proteins that need to undergo degradation
What is the function of the ER-associated degradation (ERAD) pathway?
Degrades troubled proteins by ubiquitin-proteasome system (UPS)
What are the four main steps of the ERAD pathway?
- Cell recognizes protein as misfolded
- Protein is ubiquitinated
- Protein is retrotranslocateted from ER cytosol to cytoplasm (kicked out)
- Protein is degraded by proteosome
Which response is activated if the ERAD pathway cannot handle the misfolded proteins?
The Unfolded Protein Response (UPR)
What two ways does the UPR assist in misfolded proteins?
- Inhibits protein translation (stop making more proteins)
- Increase chaperon protein levels entering the ER
What is the last resort if the ERAD pathway and UPR homeostasis cannot be restores/ER stress continues
Autophagy (cell suicide)
What is the role of the Golgi apparatus?
Major sorting and dispatch station for the products of the ER
like the mail room
What face do vesicles enter and exit in the golgi?
Enter- cis face (faces ER)
Exits- trans face (faces cell membrane)
What are three protein destinations from the golgi?
- Lysosomes (degradative proteins)
- Plasma membrane (channels)
- Extracellular fluid (hormones)
What is a vesicle?
-Enclosed lipid bilayer (liposome)
-Contains cytoplasm and carries materials
What is endocytosis and what are the three types?
Endocytosis brings substances into the cell (entering cytoplasm)
Three types: phagocytosis, pinocytosis, and receptor-mediated endocytosis
What is exocytosis?
Exocytosis moves substances out of the cell or into a membrane (exiting cytoplasm)
What is the role of phagocytosis?
Means “to eat”
-Engulfs large particles
-Example: macrophages
What is the role of pinocytosis?
Means “to drink”
-Little sips of extracellular fluid and small particles
What are three types of coated vesicles used in receptor mediated endocytosis?
COP2, COP1, and Clathrin
COP2 goes from ____ to ____
ER to Golgi
COP1 goes from ____ to ____
Golgi to ER membrane
Clathrin goes from _____ to _____
Plasma membrane to plasma membrane
Explain the process of clathrin in receptor mediated endocytosis
- Cage is made of triskelion proteins
- Triskelions bind together to give structure to vesicle
- Dynamin separates vesicle from membrane
- Coat is shed when vesicles dock at target membrane
Cage, bind, separate, shed
What are the 5 steps for exocytosis-SNARE complex?
- v-SNAREs in the vesicle bind to t-SNAREs in the target membrane
- Water is squeezed from between the two membranes
- Stalk formation
- Hemi-fusion
- Fusion/release substance into extracellular membrane
Bind, water, stalk, small fusion, big fusion
What are four SNARE proteins?
VAMP
Syntaxin
SNAP-25
Synaptotagmin
What does calcium bind to in order to activate the SNARE Complex?
Synaptotagmin
What three SNARE proteins wind together as alpha helices?
VAMP, Syntaxin, and SNAP-25
When is cargo released in SNARE complex?
Vesicle is brought close enough to the target membrane and fuses
What part of the cytoskeleton only supports cell structure?
Intermediate filaments
What part(s) of the cytoskeleton supports cell structure AND transport?
Microtubules and Actin
What part of the cytoskeleton is responsible for short transport?
Actin
What part of the cytoskeleton is responsible for long transport?
Microtubules
What is a dimer? What is the structure/function of a dimer?
Two intermediate filament monomers join to form a dimer
Has rope like consistency (flexible but strong!)
What is the orientation of microtubules?
Hint: where do the plus/minus ends face
Plus end- towards membrane
Minus end- towards nucleus
What does actin polymerize into?
Double strand filament
What are three functions of F-actin?
- Short distance transport
- Muscle contraction
- Cell division
What are three types of motor proteins?
Kinesin
Dynein
Myosin
What are motor proteins? What is their function?
-ATPases
-Bind and cleave ATP to ADP
-Energy released powers movement alone cytoskeleton
Is Kinesin a microtubule or actin?
Microtubule
Long transport
Explain the kinesin mechanism
- ATP binding purple foot swings blue foot forward
- Blue foot releases ADP when attaching to beta subunit
- Purple foot breaks ATP down to ADP+Pi and foot releases
- Purple foot swings forward when ATP enters blue foot
Is Dynein a microtubule or actin?
Microtubule
Long transport
Which end does Kinesin move to?
Which end does Dynein move to?
Kinesin- plus end
Dynein- minus end
Is myosin a microtubule or actin?
Actin
Which end does Myosin V move to?
Which end does Myosin VI move to?
Myosin V- plus end (towards membrane)
Myosin VI- minus end (towards nucleus)
The presence of a signal peptide in a protein sequence indicates that it will LEAST likely be processed in the
Rough ER
Golgi apparatus
Cytoplasm
None of the above
Cytoplasm
What is the last resort for ER stress due to unfolded proteins?
ERAD
UPR
Proteosome
Autophagy
Autophagy
Which of the following proteins are MOST directly affected by changes in Ca2+ concentration?
VAMP/synaptobrevin
Syntaxin
Synaptotagmin
SNAP-25
Synaptotagmin
Mutations in which of the following will affect vesicle transport from the Golgi apparatus to the ER?
VAMP
Clathrin
COP I
COP II
COP I
