Biology Chapter 7 Notes

Biology Chapter 7 Notes - Chapter 7 Membrane Structure and...

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Chapter 7 – Membrane Structure and Function Overview: Life at the Edge The plasma membrane is the boundary that separates the living cell from its surroundings - The plasma membrane exhibits _____________________ , allowing some substances to cross it more easily than others Concept 7.1: Cellular membranes are fluid mosaics of lipids and proteins Phospholipids are the most abundant lipid in the plasma membrane Phospholipids are _____________________ , containing hydrophobic and hydrophilic regions The __________________ states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it Membrane Models: Scientific Inquiry Membranes have been chemically analyzed and found to be made of proteins and lipids Scientists studying the plasma membrane reasoned that it must be a __________________ Figure 7.2 In 1935, _____________________ proposed a sandwich model in which the phospholipid bilayer lies between two layers of globular proteins Later studies found problems with this model, particularly the placement of membrane proteins, which have hydrophilic and hydrophobic regions In 1972, S. J. Singer and G. Nicolson proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water Figure 7.3 Freeze-fracture studies of the plasma membrane supported the fluid mosaic model _____________________ is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer Figure 7.4 The Fluidity of Membranes Phospholipids in the plasma membrane can move within the bilayer - Most of the lipids, and some proteins, drift laterally - Rarely does a molecule flip-flop transversely across the membrane Figure 7.5 Figure 7.6 Figure 7.7 - As temperatures cool, membranes switch from a fluid state to a solid state The temperature at which a membrane solidifies depends on the types of lipids - Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids Membranes must be fluid to work properly ; they are usually about as fluid as salad oil - The steroid cholesterol has different effects on membrane fluidity at different temperatures At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids At cool temperatures, it maintains fluidity by preventing tight packing Figure 7.8
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Chapter 7 – Membrane Structure and Function Evolution of Differences in Membrane Lipid Composition Variations in lipid composition of cell membranes of many species appear to be adaptations to specific environmental conditions - Ability to change the lipid compositions in response to temperature changes has evolved in organisms that live where temperatures vary Membrane Proteins and Their Functions A membrane is a collage of different proteins, often grouped together, embedded in the fluid matrix of
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This note was uploaded on 10/04/2011 for the course BIOLOGY 1305 taught by Professor Adair during the Fall '09 term at Baylor.

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Biology Chapter 7 Notes - Chapter 7 Membrane Structure and...

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