Composition and Function of the Plasma Membrane PDF

Illustration by Smart-Servier Medical Art Composition and Function of the Plasma Membrane SBI4U  Illustration by Smart-Servier Medical Art Phospholipids Why are phospholipids important for cell membranes?  01 Model...

Illustration by Smart-Servier Medical Art Composition and Function of the Plasma Membrane SBI4U  Illustration by Smart-Servier Medical Art Phospholipids Why are phospholipids important for cell membranes?  01 Model Fluid Mosaic Illustration by Smart-Servier Medical Art  Illustration by Smart-Servier Medical Art Fluid Mosaic Model The idea that a biological membrane consists of a fluid phospholipid bilayer, in which proteins are embedded and float freely Illustration by Smart-Servier Medical Art  Fluid Mosaic Model Mosaic, comes from the fact that there are many Fluid, comes from the fact that the different proteins found in the cell membrane. phospholipids in cell membranes are constantly Some are used for transport, some are enzymes moving. They may vibrate, flex back and forth, used for biochemical reactions. spin around their long axis, move sideways, and exchange places within the same half of Due to their size, proteins in the cell membrane the bilayer. move a lot more slower than the phospholipids. Some proteins anchor cytoskeleton filaments, 10 nm thick. A sheet of paper The bilayer is ____ meaning that these proteins do not move. 100000 nm thick. 10 is ________ Glycolipid: any membrane lipid that is bound to a carbohydrate Glycoprotein: a membrane component that contains a sugar, or carbohydrate, bound to an amino acid  Fluid Mosaic Model Is it symmetrical? Asymmetrical! This highlights the different roles of each membrane half. Glycolipids and carbohydrates attach to proteins on the outer side, while cytoskeleton components bind to proteins on the inner side. Hormones and growth factors bind to external receptor proteins, triggering internal reactions that signal the cell. For instance, serotonin, a hormone and neurotransmitter, facilitates nerve cell communication. Without enough serotonin between nerve cells, or the serotonin not binding properly, people may experience depression.  02 Phospholipids Illustration by Smart-Servier Medical Art  Fluidity Two factors influence the fluidity of the phospholipid bilayer. Composition Temperature Composition: Saturated vs unsaturated fatty acids The fluidity of the membrane is directly related to the degree of which it is unsaturated Temperature: Colder -> less fluid (& vice versa) Sterols: Has OH group attached to steroid (Ex. cholesterol) “Membrane stabilizers”. At high temperatures, sterols restrain the movement of phospholipids. At low temperatures, sterols occupy empty space, preventing the formation of a non-fluid gel.  Proteins 03 Membrane Illustration by Smart-Servier Medical Art  Four Types of Membrane Proteins Transport Enzymatic Many substances cannot diffuse through Some membrane proteins, such as membranes. Some cross via hydrophilic those associated with respiration protein channels, while others are and photosynthesis, are enzymes. transported by shape-shifting membrane proteins. Attachment/ Signal Recognition Membrane proteins can bind to specific Proteins exposed to both internal and external chemicals, like hormones, triggering membrane surfaces serve as attachment points changes on the inner membrane surface and for cytoskeleton elements, cell-cell recognition initiating a cascade of events inside the cell. components, and the extracellular matrix. For example, surface proteins can detect disease-causing microbes, triggering an immune response.  Membrane Proteins Integral membrane protein: a protein that is embedded in the lipid bilayer Peripheral membrane protein: a protein on the surface of the membrane Transmembrane protein: a protein with a segment of non-polar amino acids that are hydrophobic and stay within the membrane, as well as polar hydrophilic regions that are exposed to the environment. They span the entire membrane bilayer. Pg.86 Practice: Questions on Illustration by Smart-Servier Medical Art