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What do membranes do?
Membranes divide cytoplasm of eukaryotic cells into disticnt comartments.
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The endomembrane system includes organelles such as the?
- Endoplasmic Reticulum
- Golgi Complex
- Endosomes
- Lysosomes
- Vacuoles
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Materials are shuttled between organelles in ___ transport vesicles.
membrane-bound
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What is an acceptor compartment?
When the vesicles reach their destination, vesicles fuse with the membrane of the acceptor protein.
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What occurs in the Biosynthetic Pathway?
Synthesis, modification and transport of proteins.
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What occurs in the Secretory Pathway?
When proteins are discharged (secreted) from the cell. There are 2 types: constitutive, and regulated.
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What happens during regulated secretion?
Materials to be secreted are stored in membrane-bound secretory granules.
Example: secretion of digestive enzymes by pancreatic cells.
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One way to approach the study of cytomembranes is by Autoradiography, explain it.
Autoradiography uses readiolabeled materials that are exposed to photographic films to visualize biochemical processes.
Example: Used to determine where secretory proteins are synthesized.
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Green Flourescent Protein is another appoach to the study of cytomembranes. Explain it.
Green Flourescent Proteins are proteins that are isolated from jellyfish which emits a green flourescent light. A GFP-DNA chimera allows observation of protein synthesis in cell. Protein traffic.
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Give some insights from f Cell-Free Systems
- -do not contain whole cells
- -have provided information about the roles of proteins involved in membrane trafficking
- **Other type of info..
- -proteins that bind to the membrane to initiate vesicle formation
- -proteins responsible for cargo selection
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Why study mutants when learning about cytomembranes?
They provide insights about function of normal gene products. Isolation of proteins from yeast has led to the indentification of homologous proteins in mammals.
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Describe RNA Interference.
Cells produce small RNAs that bind to specific mRNAs and inhibit translation. Scientists can identify genes involvded in a particular process by determining which RNAs interfere with that process.
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What are the 2 components of the endoplasmic reticulum?
Rough Endoplasmic Reticulum + Smooth Endoplasmic Reticulum
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Has a network of flattened sacs (cisternae)
RER
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Is continuous with the outer membrane of the nuclear envelope.
RER
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Has ribosomes on its cytosolic surface.
RER
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This membrane type is extensively developed in some cells.
SER
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Funstion: synthesis of steroid hormones in endocrine cells.
SER
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Function: detoxification in the liver of various organic compounds.
SER
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Function: sequestration of calcium ion into cytoplasm of muscle cells.
SER
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What is the starting point of the biosynthetic pathway?
RER
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Functions: polarity of RER in some cells reflects the flow from the site of protein synthesis to the site of discharge of the protein.
RER
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Name three types of polypeptides that are synthesized on RER ribosomes of RER.
**S.I.S.**
- 1. Secreted proteins
- 2. Integral membrane proteins
- 3. Soluble proteins of organelles
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Polypeptides synthesized on "free" riobosomes include ___ of those encoded by the human genome. (its a percentage)
1/3
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(RER)
What binds to free ribosomes on cytosol?
Messenger RNA
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What the fuck can you say about membrane biosynthesis in the ER
- - membranes arise from pre-existing membranes
- - lipids are inserted into existing membranes
- - as the membrane moves one compartment to the next, its proteins and lipids are modified
- - membrane asymmetery is established initially and maintained during trafficking
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1. Where are the majority of membrane lipids synthesized?
2. What are some exceptions?
1. Most membrane lipids are synthesized in the ER
2. Sphingomyelin, glycolipids, and some unique lipids of mitochondria and chloroplasts
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Tell me 3 things about Glycosylation in RER
1. Catalyzed by glyocosyltransferases
2. Core segment of each carbohydrate chain is put together on a lipid carrier (dolichol phosphate) and then transferred to a polypeptide
3. Core carbohydrate is modified by oligosaccharyltransferase as the polypeptide is transferred into the ER lumen
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During glycosylation in the RER, a ___ goes through a system of quality control to determine its fitness for a specific compartment.
glycoprotein
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Misfolded proteins are tagged by a ___ and recognized by chaperones for refolding
terminal glucose
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Misfolded proteins are transported into the cytosol where they are destroyed in ___
proteasomes
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What does ERAD do?
Ensures the misfolded proteins do not reach the cell surface
Look at slide 29
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Tell me 3 things about the golgi complex.
- 1. Stack of flattened cisternae
- 2. Divided into several functionally distinct compartments
- 3. The cis face of the Golgi face the ER, the trans face is on the opposite side of the stack
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What does the cis golgi network (CGN) do?
Sorts proteins for the ER or the next gogi station
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What does the trans golgi network do?
Sorts proteins either to the mebrane orvarous intracellular destinations.
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Is the golgi complex uniform in composition?
No, there are differences in composition from the sis to the trans face
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Materials are carried between compartmentss using ___
coated vesicles
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What are the 2 functions of protein coats?
1. Cause membrane to curve and form a vesicle
2. Select components to be carried by vesicle
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What do COPII-coated vesicles do?
Move materials from the ER "forward" to the ERGIC and golgi complex
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What do COPI-coated vesicles do?
Move materials fromERGIC and golgi "backward" to ER, or from the trans golgi to the cis golgi cisternae
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What do Clathrin-coated vesicles do?
Move materials from the TGN to endosomes, lysosomes, and plant vacuoles.
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Adenosylation ribose factor 1 (ARF1), a G protein, is required for what?
vesicle transfer between cisternae
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Proteins are maintained in a organelle by two mechanisms, what are they?
1. Retention or resident molecules that are excluded from transport vesicles
2. Retrieval of "escaped" molecules back to the compartment where they reside
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Lysosomal enzymes are transported from the TGN in what kind of protein vesicles?
Clathrun-coated
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The discharge of a secretory vesicle or granule after fusion with plasma membrane is called ___
exocytosis
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What is triggered by an increase in Ca2+
Exocytosis
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___ contain acid hydrolases which can digest type of biological molecule
Lysosomes
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The low pH optimum of these enzymes is maintained by a proton pump (H+ - ATPase)
Lysosomes
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___ play a key role in organelle
Lysosomes
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This results from a deficiency in an enzyme responsible for degrading gangliosides, a major component of cell membranes.
Tay-Sachs
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Plant cell vacuoles ___ membrane bound, fluid filled compartments.
are
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Do plant vacuoles contain acid hydrolases?
yes
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This is the uptake of cell surface receptors and bound extracellular ligands.
Endocytosis
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This is the uptake of particulate matter
Phagocytosis
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-nonspecific uptake of extracellular fluids is endocytosis, but what kind
pinocytosis
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What is receptor mediated endocytosis
The uptake of specific extracellular ligands following their binding to receptors
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Following internalization, vesicle bound materials are transported in vesicles and tubules known as ___
endosomes
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These transport cholesterol from tissues to the liver for excretion.
High-Density Lipoproteins (HDLs)
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The uptake of large particles
phagocytosis
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Engulfment of particles by phagocytosis is driven by ___
actin containing microfilaments
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Most chloroplast proteins are imported from ___
cytosol
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