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All the contents of the cell.
Everything but what's inside the nucleus.
Fluid suspension of the cytoplasm.
Tubules and filaments in cytoplasm
Metabolically active structure in cytoplasm, usually membrane-bound
The substance forming the contents of the nucleus; contains DNA, chromatin, nucleolus
What does the trilaminar appearance of the plasma membrane consist of?
- Outer Layer - The polar head groups from the outer leaflet of the phospholipid molecules that stain darkly on the TEM
- Middle Layer - The hydrophobic tails from both layers of the phospholipids that interdigitate in the center of the membrane and stain lightly on the TEM
- Inner Layer - The polar head groups from the inner leaflet of phospholipid molecules that stain darkly on the TEM
Name the five major functions of the plasma membrane.
- Maintain cell integrity and act as a barrier
- Permit cell-cell interactions
- Allow selective permeability
- Transport substances and molecules into and out of the cell
- Transduce extracellular (from outside of the cell) signals
What are the four ways in which proteins can associate with membranes?
- 1) Integral membrane protein - spans bilayer
- 2) Covalently linked to a fatty acid tail ie. palmitoylation
- 3) Covalently linked to a specialized P-lipid-glycophosphatidylinositol
- 4) Peripheral - associated with an integral membrane protein (non-covalent, electrostatic interactions)
Fill in the blanks.
- Sensors and effectors
- Cellular responses
Name the 8 cellular responses in cell signaling.
- Cell proliferation
- Cell differentiation
- Membrane excitability
- Learning and memory
Describe the G-Protein Coupled Receptor/cAMP cell signaling pathway.
- Ligand/signaling molecule/stimulus can be a chemical, ion, or even a photon (in eye) - induces a conformational change in GPCR
- GPCR is the receptor - G-alpha exchanges GDP for GTP
- G-protein is the transducer - G-alpha dissociates and binds to adenylate cyclase
- Adenlyate cyclase is the amplifier - when activated, cAMP is formed
- cAMP is the messenger - binds and activates the regulatory subunit of Protein Kinase A
- PKA phosphorylates protein targets and alters their activity/expression
Describe the G-Protein Coupled Receptor/IP3 cell signaling pathway.
- GPCR is the receptor
- G-protein is the transducer
- PLC (amplifier) turns the PtdIns4,5P 2 into InsP3 and diacylglycerol (messengers) - PLC is a lipid modifying enzyme which clips the head group of the InsP3 off the lipid creating a soluble InsP3 molecule
Describe the structure of the ER.
- largest organelle in the cell
- consists of sheets, tubules, and three-way junctions
- ER lumen is continuous throughout the cell
- Rough ER has associated ribosomes
- dynamic organelle - undergoes fusion and fission reactions, interacts with actin and microtubules
What are the functions of the endoplasmic reticulum?
- Rough ER functions primarily in protein synthesis/folding including glycosylation and disulfide bond formation
- Smooth ER functions in lipid synthesis and calcium storage (sarcoplasmic reticulum in muscle cells)
- Source of biogenesis of other organelles ie. peroxisomes
Describe the steps in protein synthesis/insertion on the ER.
- 'signal sequence' = N-terminal portion of growing peptide, which binds to the....
- 'signal recognition particle' in the cytoplasm, which binds to the...
- 'signal recognition particle (SRP) receptor' on the ER membrane which contributes to the formation of a channel that threads growing peptide into the ER lumen where the....
- 'signal peptidase' removes the signal sequence from the polypeptide in the ER lumen and...
- 'post-translational modifications' occur including protein folding, disulphide bond formation between strands of the protein, and glycosylation of the protein. These steps occur in the ER lumen to generate a 'completed protein' for packaging and eventual export from the ER to other cellular sites or secretion from the cell
What is ER stress?
build-up of misfolded proteins in the ER
What are the three manifestations of the Unfolded Protein Response (UPR)?
- 1) ER-associated degradation (ERAD) of the misfolded protein; specifically, it is removed from the ER and destroyed in lysosomes or the proteosome
- 2) An upregulation of the ER machinery that facilitates protein folding (induces the production of protein chaperones and lipid synthesis that associate with and help proteins fold)
- 3) 'Apoptosis'; this is the last resort whereby, if large amounts of misfolded protein cannot be destroyed or re-folded, the cell initiates a program that ultimately lead to cell death
Provide an example of the clinical relevance of the UPR.
A number of mutations in the Cystic Fibrosis Transmembrane Regulator gene, which codes for an integral transmembrane protein that is a chloride channel, cause subtle changes in the polypeptide structure that impede protein folding and initiate a UPR that significantly reduces the transport of theCFTR channel from ER to the plasma membrane and increases its destruction by ERAD. Loss of CFTR causes Cystic Fibrosis
What new pharmacologic approach is being taken to attempt to treat cystic fibrosis?
Therefore, in addition to gene therapy approaches, another therapeutic strategy being pursued is the pharmacologic suppression of the UPR to increase the delivery of the protein to the membrane of the cells affected (because some of the mild misfolding mutants are still functional as a chloride channel if they are transported to the membrane)
Describe the structure of the Golgi apparatus.
- 3-10 curved flattened cisternae (sacs) make up a stack
- multiple stacks in each cell, form a single ribbon (held together with microtubules)
- cisternae not always stacked
- numerous small vesicles
- polarized; a cis face that receives vesicles from the ER, trans face that releases mature vesicles
Name four main functions of the Golgi apparatus.
- 1) Protein and lipid glycosylation
- 2) Sphingolipid synthesis
- 3) Proteolysis of transcription factors (signaling)
- 4) Protein sorting in TGN (lysosomes, PM, secretory granules)
- different activities in different cisternae
What is the vesicular transport model?
- Cargo moves through the Golgi via small, spherical vesicles that bud off an individual cisterna and move to the next cisterna in the stack. In this model the Golgi itself would be static while the cargo is dynamically moved through it in vesicles
- Enzymes remain in compartments
- Problems - molecules larger than a vesicle
What is the cisternal maturation model?
- The cisternae themselves move through the stack carrying cargo along with them; in this model the small vesicles bud off and travel back down the stack (i.e. back towards the cis face) to recycle the Golgi enzymes so that they can work on the next wave of cargo that arrives from the ER
- Problems - Goldi enzymes not seen in Golgi vesicles; cargo moves through stack at different rates
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