Unit 5 Flashcards
Endomembrane system
Membrane limited compartments involved in processing and movement of proteins
All proteins are processed after they are translated (T or F)
True
Folding make proteins
Functional
Modifications of proteins regulates their
Activity, interactions, and stability
Cleavage of proteins can
Activate or inactivate proteins
Without modifications GFP would be primarily found in the
Cytoplasm
For GFP to be found in the ER it would have to contain
An ER targeting signal that directs it to the ER during translation
Requirements for protein import into an organelle
A specific sequence found in primary sequence, and a specific protein receptor on organelle of interest
Site of secretory protein synthesis
RER
Site of lipid and sterol synthesis
Smooth ER
What type of proteins would you expect to be sent to the ER
Soluble proteins for secretion, resident proteins of ER, membrane proteins inserted as they are synthesized
When is the signal for entry into the ER (before or after translation is complete)
Before protein is fully translated
Retention signal for ER proteins
KDEL
How do membrane bound and free ribosomes differ
Only difference is the proteins that they are making at a particular time
How do ribosomes become membrane bound
Ribosomes that are synthesizing proteins with signal sequences to be incorporated in ER membrane will be bound
Co translational modifications occurs
Occur while the protein is still being synthesized by the ribosome. Happens in rough ER and cytoplasm
Examples of proteins that undergo co translational modifications
Secrete proteins, membrane proteins, lysosomal enzymes
Post translational modifications
Occur after the protein has been fully synthesized and released from the ribosome
Examples of proteins that undergo post translational modifications
Cytoplasmic proteins, nuclear encoded proteins, mitochondrial proteins, chloroplast proteins
What two things direct ribosomes to er memebrane
ER signal sequence, signal recognition particle (srp)
Summary of co translation across er membrane
SRP will bind to exposed n terminal sequence and ribosome
Translation is paused
Protein translocation change assembles and inserts the polypeptide chain into membrane and starts to transfer across bilayer
Is the ER signal sequence hydrophobic or hydrophilic
Hydrophobic
Internal start transfer sequence characteristics
Initiates transfer of protein across er membrane
Is a membrane crossing domain
Not cleaved off
What cleaves n terminal signal sequence
Signal peptidase
What side of the plasma membrane are carbohydrates attached to
Non cytosolic side
How does a sugar move into the ER lumen
Flippase enzyme
What is glycosylation
Covalent addition of carbohydrates/ sugar chains to proteins
Purpose of glycosylation
Protein folding, stability, trafficking, and function
What amino acid is the oligosaccharide transferred to
Asn / asparagine
Missfolded proteins in the er lumen trigger production of
Chaperones
Chaperone roles
Aid in the proper folding of proteins
Prevent misfolded proteins from leaving er
Where do misfolded proteins go
Sent to Cytosol for degradation if not fixable
What tags missfolded proteins in Cytosol
Ubiquitin
4 stages of vesicle transport
Formation, transport, docking, fusion
Stages of vesicle formation
Budding, pinching off, coat is shed
The active form, GTP allows
Adaptors and coat proteins to bind
Types of coat proteins used in vesicle formation
Clathrin, COP1, COP11
What process are clathrin coated vesicles involved in
Endocytosis, traffic to lysosome, receptor recycling
Cargo moves from the ER to the golgi via what type of coated vesicles
COP11
COP1 coated vesicles travel in what direction
Golgi to er traffic
Is dynamin like proteins required for cop1 transport
No
Anterograde transport
ER to Golgi
Steps of vesicle docking
- Vesicle buds and breaks off form donor compartment (er or Golgi)
- Rab protein on vesicle enters gtp bound form
- Active rab interacts with tethering factors on target membrane
- Snare complex forms
- Membrane fusion
- Cargo delivered to target compartment
V shares are found on
Vesicle membrane
T snares are found on
Target membrane
Orientation of the membrane during docking and fusion
Remains the same (Cytosol face remains facing Cytosol)
Likely cargo In er to Golgi transport
Newly synthesized proteins
TGN to PM likely cargo
Secreted proteins and plasma membrane proteins
TGN to lysosome cargo
Lysosomal resident
The Golgi apparatus is a series of flattened stacks called
Cisternae
What part of the Golgi apparatus does new vesicles from er arrive at
Cis Golgi network
Difference between plant and mammal Golgi
Plants have more mobile Golgi that plays a large role in cell wall biosynthesis
Glycosylation continues from the er to Golgi. What happens in the Golgi
The oligosacharide is trimmed and new sugars are added one by one by transferase enzymes
Golgi vesicular transport
Cargo proteins will be moved from one cisterna to the next by transport vesicles, while resident proteins stay in their respective cisterna.
Cisterna maturation model
Vesicles carrying cargo proteins fuse to form cis cisterna and move through Golgi remaining in same cisterna. As a new cis cisterna forms the old one becomes medial
Two pathways of secretion from Golgi
Constitutive, and regulated
Is a signal required for constitutive secretory pathway
No
Main things secreted by secretory pathway
Plasma membrane proteins
Lipids
ECM proteins
What secretory pathway is known as the default
Constitutive
What secretory pathway is synonymous with this statement “vesicles only are released when a specific signal is received”
Regulated
In the regulatory pathway ____ may be be used but are not required in _____ pathway
Coat proteins, constitutive pathway
Purpose of regulatory secretive pathway
Secretion of proteins rapidly on demand
Main thing the regulatory pathway secretes
Hormone, NT, enzymes, Immune factors
What step of secretion would be disrupted under a restrictive temp / high temp
Fusion of vesicles with the target organelle
Coat protein used in retrograde transport
COP 1
What does the lysosomal targeting signal require for the secretory pathway
Signal (mannose 6 phosphate)
Receptor for mannose 6 phosphate
Summary of lysosomal secretion pathway
Addition of phosphate to mannose in cis Golgi, binding to m6p receptor, receptor dependent transport, removal of phosphate, dissociate from acidity in late endosome, receptor recycling
Why does acidic ph allow lysosomal proteins to dissociate from their cargo receptors
Change in ph reduces the receptors affinity for mp6 tag
Proteolytic cleavage
Produce smaller active proteins
Three types of endocytosis
Phagocytosis, pinocytosis, receptor mediated
Examples of phagocytes
Macrophages, neutrophilis, dendritic cells
Another word for pinocytocis
Constitutive endocytosis
Pinocytosis definition
Continuous process where cells remove excess membrane that was added by exocytosis allowing recycling of PM. Non selective process
Receptor mediated endocytosis
Receptors collect specific extra cellular compounds using clathrin for vesicle formation
Common ligands targeted in RME
Cholesterol, iron, hormones
Why is change in acidity in the endomembrane system important
Dissociation of mp6 receptor and aggregation of proteins in TGN
