BIO 143 Lecture Notes - Lecture 5: Pinocytosis, Phagocytosis, Active Transport
8 Jun 2018
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Chapter 5: Cell Membrane Structure and Function
Cell Membrane
• isolate the contents of the cell from the inside
• regulate exchange of materials in and out of cell
• allow communication with other cells
• create attachments between cells
• regulate biochemical reactions
Fluid Mosaic Model
• membranes are fluid mosaics in which proteins move within layers of lipids
• the phospholipid bilayer is the fluid portion of the membrane
-phospholipids are the basis of membrane structure and consist of two very different parts
-plasms membranes face both exterior and interior watery environments
-hydrophobic interactions drive phospholipids into bilayers
-the phospholipid bilayer’s flexible, fluid membrane allows for cellular shape changes
-cell membranes have a varied degree of fluidity depending on their environment
cholesterol within the phospholipid bilayer also affects membrane structure and function
• a variety of proteins form a mosaic within the membrane
-proteins are embedded within, or attached to, the phospholipid bilayer
-many proteins have attached carbohydrates on their outer membrane surface
-categories of membrane proteins
The Proteins
-receptor proteins: trigger cellular responses upon binding of specific molecules, such as
hormones, sent by other cells
-recognition proteins: glycoproteins that serve as identification tags on the surface of a cell
-enzyme proteins: promote chemical reactions that synthesize or break apart biological
molecules
-attachment proteins: anchor the cell membrane to the inner cytoskeleton, to proteins outside
the cell, and to other cells
Movement of Substances Across Membrane
• Molecules in fluids move in respond to gradients
-why gradients cause molecules to move from one place to another?
• Summing up principles of diffusion
-diffusion is the net movement of molecules down concentration gradient from high to low
concentration
-great concentration = faster rate of diffusion
-higher temperature = faster rate of diffusion
-if no other processes intervene, diffusion will continue until concentration gradient is
eliminated
• Movement through membranes occurs by passive transport and energy driven
transport
-concentration gradients of ions and molecules exist across the plasma membranes of all cells
-plasma membranes are selectively permeable because they only allow only certain ions or
molecules to permeate
-simple diffusion: involves molecules diffusion directly across phospholipid bilayer down
concentration gradient
find more resources at oneclass.com
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Document Summary
Cell membrane isolate the contents of the cell from the inside regulate exchange of materials in and out of cell: allow communication with other cells, create attachments between cells regulate biochemical reactions. Fluid mosaic model: membranes are fluid mosaics in which proteins move within layers of lipids the phospholipid bilayer is the fluid portion of the membrane. Phospholipids are the basis of membrane structure and consist of two very different parts. Plasms membranes face both exterior and interior watery environments. The phospholipid bilayer"s flexible, fluid membrane allows for cellular shape changes. Cell membranes have a varied degree of fluidity depending on their environment cholesterol within the phospholipid bilayer also affects membrane structure and function: a variety of proteins form a mosaic within the membrane. Proteins are embedded within, or attached to, the phospholipid bilayer. Many proteins have attached carbohydrates on their outer membrane surface.
