L7 lipids (MP1)

• The plasma membrane defines the cell, allows signal reception, and is made of lipids and proteins
• Proteins in the plasma membrane are produced in the endoplasmic reticulum, then transferred to the golgi for modification before being secreted in vesicles to the plasma membrane
• The endocytic pathway involves the cell taking components of the exterior of the cell through vesicles fused to the lysosome
• The cell's membrane-bound organelles create a crowded environment, requiring highly regulated transport
• The cytosol is a reducing environment, while the ER, golgi, and exterior are oxidizing environments
• Membranes are hydrophobic barriers, selectively permeable, and can store energy as concentration gradients
• Membranes are made of lipids and proteins, with proteins that can move laterally but never flip
• Phospholipids, present in all membranes, have a polar head with choline and other charged groups, and two fatty acid tails of varying lengths and saturation levels
• Glycolipids, found only in the plasma membrane, have two fatty acid tails with glycerol bound through acerimide and sugars instead of a phosphate group
• Cholesterol, present in all membranes but mainly in the plasma membrane, has a steriod ring making it rigid and integrates between lipids providing rigidity
• Membrane assembly involves asymmetric distribution of lipids between the outer and inner leaflets, providing different functions
• Membrane microdomains are patches with different protein contents due to longer lipid tails and increased cholesterol, regulating cell connections to the exterior
• Membranes are hydrophobic barriers made of lipids and proteins, with phospholipids present in all membranes and cholesterol mainly in the plasma membrane
• the secretory pathway is the pathway by which proteins are transported from the ER to the plasma membrane. the proteins in the plasma membrane are produced in the ER, transfered and modified to the golgi, then secreted in vesicles to the plasma membrane.
• the lumen refers to the golgi, lysosome, ER and vesicles.
• the cytosol is a reducing environment and the ER, golgi, and exterior are oxidizing environments
• disulfide bonding occurs in the exterior of the cell, no disulfide bonding in the reducing environment (cytosol)
• plasma membrane also supports the contact of the cell with its environment, allows for reorganizing other cells. transmission of signals from interior to exterior of the cell is regulated by the plasma membrane
• properties of membranes

  • membranes are hydrophobic barriers. they are flexible and have different shapes. they are slecectively permeable (small hydrophobic may be able to pass, but larger proteins cannot)
  • membranes can store energy as concentration gradients (mainly occur in mitochondria)
  • membranes are made of lipids and proteins. lipids that have a hydrophobic tail and a hydrophilic tail. not all proteins in a membrane are transmembrane proteins.
  • proteins in the membrane can move laterally or be rotation doors, but they can never flip
• all membrane lipids have a polar head and hydrophobic tail. they can move in the membrane: have lateral diffusion, can flex rotate or flip in the bilayer
• phospholipids are found in all membranes, have a polar head (with choline, other charged group, phosphate and glycerol) and 2 fatty acid tails (can be unsaturated with 1 or more double bonds or saturated with no double bonds). with a unsaturated fatty acid tail, the lipid is shorter, introducing bends in the tail reducing flexibility (stiff membrane). with a saturated fatty acid tail, the membrane becomes more fluid
• the glycerol of the head of the phospholipid has three carbons and makes an ester linkage with fatty acid tail, and the third carbon binds with the phosphate. the phosphate then binds to the polar group. depending on the polar group we have, we will name the phospholipid.
• for phospholipids: if the polar head is a choline, its called a phosphatidyl-choline (PC).

  • if the polar group is ethanolamine → phosphatidyl-ethanolamine (PE)
  • if the polar group is serine → phosphatidyl-serine
  • the difference between serine and the others is that this is the only one with a negative charge. it’s usually facing the cytosol.
  • the sphingomyelin has a choline in the polar head, but it binds differently to the fatty acids.
  • phosphatidyl-inositol has a sugar with hydroxyl groups that can be phosphorylated, this faces the cytosol
• fo glycolipids, they are only at the plasma membrane, always face the exterior of the cell, and its function is to contact the cell with its environment and with other cells. they have two fatty acid tails with a glycerol; bound differently through a ceramide (sugar molecule). they have sugars instead of phosphate groups (galactose, non-sugar, or glucose)
• cholesterol is found in all membranes (mainly in the plasma membrane), have a steroid ring making it very rigid. they have a fatty acid tail with a polar head, but are much smaller than other lipids. when cholesterol is inserted into the membrane, it reduces mobility of the surrounding phospholipids, providing rigidity to the membrane.
• outer and inner leaflets of the membranes are asymmetric providing function - meaning the lipid composition is different for each side. glycolipids, phophatidylcholines, and sphingomyelin are found in the outer leaflet. phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI) are found in inner leaflet of the plasma membrane. PS and PI transmit signal.
• plasma membrane has the highest level of cholesterol. the ER and mitochondria have higher levels of phosphatidylcholine (PC) and phosphatidylethanolamine (PE).
• membrane microdomains are patches in the membrane different from the rest of the membrane; they regulate the connection of the cell to the exterior. they are due to the lipid tails being longer (more cholesterol in that area).
• cholesterol binding straightens lipid tails, causing thicker membranes, changing the protein contents of the membrane