Biological membranes need to have the correct fluidity to be functional. i. What

Question

Biological membranes need to have the correct fluidity to be functional. i. What are functions of biological membranes. List at least three different functions. II. What are the components of biological membranes and how are these components organized in membranes. As part of this answer be sure to identify the lipid types that are components of biological membranes. iii. Describe the factors that affect the fluidity of biological membranes in animal cells iv. What type of motion occurs in the lipid bilayers of biological membranes? Also describe the factors or proteins that assist or guide those motions For each of the following, state whether you would predict the substance to be transported across cell membranes with or without a mediator. Briefly explain your reasoning. a) steroid b) fructose c) H_2 The following are terms and processes that were identified and discussed in your reading. Choose three of the following and describe the functions of these processes. a) restriction endonucleoases; b) polymerase chain reaction; c) glucocorticoid (and example) g) translocon h) SNARE i) clathrin coated vesicle j) introns

Explanation / Answer

4)

i) Biological membranes have three important functions:

ii) Membranes consist largely of a lipid bilayer, which is a double layer of phospholipid, cholesterol, and glycolipid molecules that contains chains of fatty acids.The fatty-acid chains allow many small, fat-soluble molecules to permeate the membrane, but repel large, water-soluble molecules and electrically charged ions, such as calcium. Most plasma membranes are about 50 percent protein by weight, while the membranes of some metabolically active organelles are 75 percent protein. Attached to proteins on the outside of the plasma membrane are long carbohydrate molecules.

iii) Lipids give the biological membrane the fluid character. The mosaic nature of the membrane, its phospholipid chemistry, and the presence of cholesterol contribute to membrane fluidity.

iv) Embedded in the lipid bilayer are large proteins which transport ions and water-soluble molecules across the membrane. Some proteins in the plasma membrane form open pores, called membrane channels, which allow the free diffusion of ions into and out of the cell. Others bind to specific molecules on one side of a membrane and transport the molecules to the other side. Sometimes one protein simultaneously transports two types of molecules in opposite directions.

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