01:119:115 Lecture Notes - Lecture 6: Pinocytosis, Cytoskeleton, Active Transport

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Biology Lecture 6
A. Chapter 7: Membrane Structure and Function
a. The essential step of the origin of life was the evolution of biological membrane; a lipid
bilayer that separates the cell from external forces, and also functions as a way of
communication, vesicular transport, and information exchange for the cell
B. Concept 7.1: Fluid Mosaic Model
a. Fluid Mosaic model suggest that the plasma membrane is a mosaic of protein molecules
bobbing in a semi-fluid layer of phospholipids; allowing them to move laterally
b. Phospholipid molecules are arranged with cholesterol for optimum fluidity, interspersed
by integral and peripheral proteins
c. Cholesterol enables the plasma membrane in animals to stay more fluid when cell
temperature drops (and prevents fracture of the bilayer
d. Saturated vs Unsaturated hydrocarbon tails (Figure on summary slides)
e. Peripheral proteins are bound to the surface of the membrane while Integral proteins
penetrate the hydrophobic core
i. Integral proteins that span the membrane are called transmembrane proteins
ii. The hydrophobic regions of integral protein consist of one or more stretches of
nonpolar amino acids, often coiled into alpha helices
f. Six Major Functions of the Membrane Proteins
i. Transport, Enzymatic Activity, Signal Transduction, Cell-Cell recognition,
Intercellular joining, Attachment to the cytoskeleton and extracellular matrix
ii. Passive ion channels versus active carrier proteins
iii. Growth factor receptors span the membrane one or more times
iv. Carbohydrate and sugar specific lectins; viruses
g. The Role of Membrane Carbohydrates on Cell-Cell Recognition
i. Cells recognize each other by binding to the surface molecules, often containing
carbohydrates, on the extracellular surface of the membrane
1. Includes glycolipids or more commonly glycoproteins
2. Carbohydrates placed on the external side of the plasma membrane
(ECM) vary among species, individuals, and even cell types
3. Natural killer T cells have a T-cell receptor that has glycoproteins that
enables killer cell action
h. Synthesis of glycolipids and glycoproteins and orientation in the membrane;
cytoplasmic face differs from the extracellular face (arising from the vesicle, etc.)
i. Figure in text book
C. Concept 7.2: Membrane structure results in selective permeability
a. A cell must exchange materials with its surroundings, a process controlled by the plasma
b. Plasa eraes are seletively pereale, regulatig the ell’s oleular traffi
i. Hydrophobic nonpolar molecules such as gases hydrocarbons, and small steroids
diffuses through the lipid bilayer of the membrane rapidly
D. Concept 7.3: The Diffusion of solutes across a synthetic membrane
a. Passive: Down their concentration gradient
b. Osmosis is the passive diffusion of water across a selectively permeable membrane
c. Solute cannot move across the semi permeable membrane
d. Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water
e. Depends upon concentration of solute that cannot cross membrane- higher
concentration of non-penetrating solutes in surrounding solution, water will leave cell.
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