VO 3 cell biology

• Proteins have specific signal sequences or patches that guide them to the correct organelle.
• Proteins that function in the cytosol do not contain sorting signals and remain there after synthesis.
• The endomembrane system regulates protein traffic and performs metabolic functions in the cell.
• Sorting signals are recognized by sorting receptors, which deliver the protein to the appropriate target organelle.
• Transport vesicles become loaded with molecules from one compartment and discharge their cargo into another compartment by fusing with its membrane.
• Some proteins remain in the cytosol as permanent residents.
• Protein translocation involves the direct transport of specific proteins across a membrane.
• The TOM, TIM, SAM, and OXA complexes are involved in protein translocation across mitochondrial membranes.
• Proteins can move between compartments through gated transport, transmembrane transport, or vesicular transport.
• Gated transport involves movement between the cytosol and the nucleus through nuclear pore complexes.
• Transporters bind the specific solute to be transported and undergo conformational changes to transfer the solute across the membrane.
• Passive transport occurs spontaneously down a concentration gradient through the lipid bilayer, channels, or passive transporters.
• Active transport requires an input of metabolic energy and is mediated by transporters that pump solutes against their concentration or electrochemical gradient.
• Channels interact with the solute more weakly and form continuous pores that allow specific solutes to pass through them.
• Transport through channels occurs at a faster rate than transport mediated by transporters.
• Aquaporin water channels have two short α helices that span halfway through the lipid bilayer and allow water molecules to cross the membrane.
• Visualising cells: The resolution of a light microscope is limited by the wavelength of visible light, ranging from about 0.4 μm to 0.7 μm.
• In animal cells, there are variations in the subunit composition of translocator complexes to adapt to the needs of specialized cell types
• Phosphoglycerides have a three-carbon glycerol backbone.
• Protein translocation involves the use of transmembrane protein translocators to transport specific proteins across a membrane
• The TIM23 complex is bound to a multimeric protein complex containing mitochondrial hsp70, which acts as an import ATPase
• The TIM22 and TIM23 complexes have structurally related protein components and likely have a common evolutionary origin
• Vesicular transport involves the transfer of soluble components and membrane proteins from one compartment to another
• Proteins can move between compartments through vesicle budding and fusion during vesicular transport
• The TOM, TIM, SAM, and OXA complexes are multimeric membrane protein assemblies that catalyze protein translocation across mitochondrial membranes
• The third carbon atom of the glycerol is attached to a phosphate group, which is linked to one of several types of head group.
• Hydrophilic molecules dissolve in water because they contain charged groups or uncharged polar groups that can form either favorable electrostatic interactions or hydrogen bonds with water molecules.
• Cholesterol, a sterol, is an important component of eukaryotic plasma membranes.
• Phosphoglycerides, sphingolipids, and sterols are the major lipids in cell membranes.
• Cholesterol molecules regulate the fluidity of the membrane.
• Phosphoglycerides are derived from glycerol, while sphingolipids are derived from sphingosine.
• Two long-chain fatty acids are linked through ester bonds to adjacent carbon atoms of the glycerol.
• Adipocytes, or fat cells, contain a giant lipid droplet that fills up most of their cytoplasm.
• Cholesterol decreases the permeability of the lipid bilayer to small water-soluble molecules by decreasing the mobility of the first few CH2 groups of the phospholipid chains.
• Membrane structure: The plasma membrane encloses the cell, defines its boundaries, and maintains the essential differences between the cytosol and the world outside.
• Cholesterol modulates the properties of lipid bilayers by inserting into the bilayer and interacting with the hydrocarbon chains closest to the polar head groups.
• Cholesterol tightens the packing of lipids in a bilayer, but does not make membranes less fluid.
• Neutral lipids are deposited between the two monolayers of the endoplasmic reticulum membrane in the formation of lipid droplets.
• Lipid droplets are structures where cells store excess lipids, which can be retrieved for membrane synthesis or as a food source.
• The fluidity of a lipid bilayer depends on its composition and temperature.