Biology
Membrane Lecture Notes
Learning Targets 5, 6
LT5a-c Structure of membranes correlates with functions
 Boundary that controls traffic into and out of the cell
 Main component: phospholipids fig. 4.5a o polar (hydrophilic) phosphate “head” o nonpolar (hydrophobic) fatty acid “tails”
 phospholipid bilayer self-assembles in water o heads face out o tails face in toward each other away from water
 Permeability: o Pass easily: O
2
and CO
2
both nonpolar like membrane interior o Water passes thru aquaporins (protein passageway) o Channels: for charged, hydrophilic, or large particles
MEMBRANE STRUCTURE AND FUNCTION
LT5 Fluid Mosaic model of the plasma membrane
“Fluid” The molecules can migrate through the layer that they are in but they will very seldom flip-flop.
“Mosaic” The pattern or collection of molecules (phospholipids and proteins) that makes up the plasma membrane.
LT5a,b Describe the diverse functions of membrane
proteins
50 different types of proteins found in RBC’s.
Six Functions:
1.
Support: (see graphic) a.
integrins give the membrane a stronger framework. b.
Span the membrane and attach to the cytoskeleton on the inside and the extracellular matrix (ECM) on the outside
2.
cell-cell recognition: (see graphic) a.
glycoproteins (sugar-protein) b.
glycolipids (sugar-phospholipid) c.
“glyco” or sugar acts as ID tags i.
embryo sorts cells into tissues and organs ii.
immune system to recognize and reject foreign cells like bacteria
3.
intercellular junctions:
4.
enzymes (see below)
5.
signal transduction (see below)
6.
transport (see below)
LT5c
Selective Permeability: Membranes allow some substances to cross more easily than others.
LT6a-c Define diffusion and describe the process of passive transport.
Diffusion: Particles spread out evenly in an available space, from high concentration to low due to thermal motion (heat). NEVER requires energy.
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Passive Transport: The diffusion of a molecule across a membrane from high to low concentration or down its concentration gradient.
Small, nonpolar molecules like O
2
and CO
2
diffuse easily.
Small, polar water diffuses easily.
Large, polar molecules and ions can diffuse across using a transport protein
(facilitated diffusion).
Passive
H  L
No energy
Examples:
Diffusion
 osmosis
Facilitated Diffusion
 Glucose
Active
L  H
Uses Energy endocytosis exocytosis
Na + /K + pump
LT6b Explain how osmosis can be defined as the diffusion of water across a membrane.
 Osmosis is a special case of diffusion, it is specifically for water.
 It is defined as water moving across a membrane from H  L concentration.
 Predicting how water will move across a membrane will be your main challenge in this chapter.
LT6c Distinguish between hypertonic, hypotonic, and isotonic solutions.
Hyper = “over” like “hyperactive”
Hypo = “under” like “hypodermic needle”
Iso = “same” like “isosceles triangle”
Tonic = solute
These terms are relative. We will always be comparing one side of a membrane to the other side. (outside a cell vs. inside the cell.)
LT6c Explain how animal and plants cells change when placed into hypertonic
STEPS in determining the direction of osmosis
Latin Solute
English Solute
English Water
Place your L, then H  L
Decide if water is entering or leaving the cell
(Draw a PICTURE!)
Determine the results
Determine what will happen hypertonic
“over” salty
“under” watery
H  L use next figure or hypotonic solutions.
Complete your “Osmosis Worksheet” to practice.
LT6b - Compare the processes of facilitated diffusion and active transport.
Facilitated Diffusion:
 uses a protein embedded in the membrane to facilitate, or help, a substance diffuse across the membrane.
 Example: Glucose has its own protein in the cell membrane for this purpose.
 It is diffusion, so the sugar moves from H  L concentration of sugar.
LT7a,b Active Transport:
 USES ENERGY
 L  H Moves molecules against their concentration gradient.
 Examples: o endocytosis o exocytosis o Na + /K + pump
1.
Structure, movement, communication among cells
 cytoskeleton
 microtubule polymerization/depolymerization
 Motor Proteins hauling a vesicle along cytoskeleton
 Fantastic Vesicle Traffic
 A Day in the Life of a Motor Protein
 plasma membrane: leaflets are different in structure
 Harvard, Inner Life of the Cell: Plasma membrane leaflets, rafts, microtubules etc.
 cilia, flagella
 Bacterial Flagellum: advanced structure
 cell wall
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