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Chapter Five: The Plasma (Cell) Membrane
Functions: •helps give the cell mechanical strength & shape
•regulates the passage of material in/out of cell
•important in cell signaling, contains receptors that allow molecules to locate, bind to and effect cells.
The cell membrane is a fluid, dynamic (changing & moving) structure. It is not static
Four Components of the Plasma Membrane: (see figure 5.1 page 92)
1. Phospholipid bilayer (see figure 5.2 page 93) -fluid structure -describe the structure/nature of the phospholipid (head and tail)
-how are the phospholipids arranged in the cell membrane?
-what substances can pass through the phospholipid bilayer and why?
Also what substances cannot pass and why not?
2. Cholesterol - List the 2 functions of cholesterol: 3. Proteins: embedded in the lipid layer - two types: integral and peripheral: how are they different? - Describe the following protein functions: (Figure 5.3 page 94) a. structural support
b. recognition:
c. communication: how does a receptor protein work?
d. transport: channels can be passive (leaky or always open) or active
4. Glycocalyx •composed of glycoproteins (proteins with sugars attached) •form a "sugar coating" on our cells. •functions:
The Fluid-Mosaic Membrane Model Proteins can move sideways within the phospholipid layer
How Molecules Cross the Membrane •kinetic energy allows molecules to move and bounce off of each other. •increase temperature = increased energy
- anything that increases kinetic energy increases diffusion rate Which would have faster rate of diffusion small or large molecules?
- plasma membrane is semipermeable which means its selective about what it lets in and out
Two methods of moving substances
- active: requires ATP and a carrier proteins
- passive: does not require ATP
Passive methods: diffusion, facilitated diffusion, osmosis
Diffusion: See web animation 5.1 on Krogh website •net movement of a substance from a region of higher concentration to a region of concentration.
•utilizes a concentration gradient
•physical process can be observed w/ any type of molecule (example: put sugar in coffee and the sugar diffuses into entire solution)
- limited by sized of molecule and if its lipid soluble. -anything small enough or lipid soluble will diffuse across a cell membrane (along its concentration gradient)
•examples of substances that utilize diffusion?
Osmosis: •the diffusion of •the volume of H2O molecules is inversely related to its solute concentration. (a beaker with more solutes has less water – it is more concentrated than one with fewer solutes, which is more dilute and has more water)
Active Processes: active transport, endocytosis, exocytosis Require ATP
Active Transport: •moves molecules against their concentration gradient
•requires both carrier proteins &
•proteins involved in active transport called Pumps
Exocytosis “exo” to leave
•required for
Endocytosis : “endo” within
Three types: Describe and provide examples for each:
a. pinocytosis- “cell drinking”
b. receptor mediated endocytosis -substance must first bind to receptor to enter cell
- if not enough receptors molecule cannot enter cell
-example LDL “bad cholesterol” – if can’t get into cell, remains in blood and damages blood vessels, leads to clots
c. phagocytosis – “cell eating” Define this process:
Macrophages are cells that specialize in phagocytosis
