Lecture 3 Outline (Ch. 7)

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Lecture 3 Outline (Ch. 7)

• I. Membrane Structure
• II. Membrane Proteins
• III. Permeability
• Transport Across Membranes
• A. Passive
• B. Facilitated
• C. Active
• D. Bulk
• V. Lecture Concepts

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Membrane structure
1915, knew membrane made of lipids and proteins
Reasoned that membrane bilayer
Where to place proteins?
Lipid layer 1
Proteins
Lipid layer 2
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Membrane structure
Experiment to determine membrane fluidity
marked membrane proteins mixed in hybrid cell
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Membrane structure
Membrane fluidity
phospholipid f.a. tails saturation affects
fluidity
cholesterol buffers temperature changes
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Membrane structure
fluid mosaic model 1970s
fluid phospholipids move around
mosaic proteins embedded in membrane
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Membrane structure
freeze fracture
proteins intact, one layer or other
two layers look different
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Membrane structure
cell membrane amphipathic
- hydrophilic hydrophobic
hydrophilic
hydrophobic
hydrophilic
membrane proteins inserted, also amphipathic
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Membrane Proteins
Membrane proteins
Integral inserted in membrane
- transmembrane span mem.
Peripheral next to membrane
- inside or outside
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Membrane Proteins
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Selectively Permeable Membranes
Cell membranes only allow some molecules across
w/out help
Small, non-polar molecules OK ex. hydrocarbons,
O2, CO2
No charged, polar, or large molecules ex.
sugars, ions, water
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Transport Across Membranes

• Types of transport
• Passive transport
• Facilitated diffusion
• Active transport
• Bulk transport

Energy Required? Directionality?
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Passive Transport - Simple Diffusion
NO ENERGY required
- non-polar molecules (hydrocarbons, O2, CO2)
DOWN concentration gradient
molecules equally distribute across available
area
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Passive Transport - Osmosis
osmosis movement of water across cell membrane
water moves via special channels
moves into/out of cell until solute
concentration is balanced
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Passive Transport - Osmosis
tonicity solutes in solution in relation to
cell
- hypotonic fewer solutes in solution
- isotonic equal solutes in solution
- hypertonic more solutes in solution
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Passive Transport - Osmosis
Paramecium example
regulate water balance
pond water hypotonic
water into contractile vacuole
water expelled
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Facilitated Diffusion
NO ENERGY required
- Large, charged, polar (sugar, ions, water)
DOWN concentration gradient
Use transport proteins - channel or carrier
proteins
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Active Transport
ENERGY IS required
- Usually ions or large molecules (Na, K,
glucose)
UP/AGAINST concentration gradient
transport carrier proteins
a. ion pumps
b. co-transporters
Ex. Na-K ion pump
- Na ions inside to out
- K ions outside to in
- net high Na outside, high K inside cell
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Active Transport
ATP used pump H ions out
Ex. proton (H) pump
against concentration and charge gradients
gradients used by cell for energy potential
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Bulk Transport
ENERGY IS required
Several or large molecules
Molecules moved IN - endocytosis
phagocytosis food in
pinocytosis water in
receptor-mediated endocytosis proteins bind
molecules, vesicles inside
Molecules moved OUT - exocytosis
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Self-Check
Type of transport Energy required? Movement direction? Examples
Simple diffusion no Down conc. gradient O2, CO2, non-polar molecules
Osmosis
Facilitated diffusion
Active transport
Bulk transport
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Lecture 3 concepts

• Describe the fluid mosaic model including
  meaning and experimental evidence
• List and describe types of membrane proteins
• Define amphipathic explain application to cell
  membranes
• Discuss what is meant by a selectively permeable
  membrane and how this applies to cell membranes
• Name types of transport across cell membranes and
  describe each one
• Given a tonicity of solution, determine direction
  of water movement and hypothesize result on a
  cell
• Write out a list of new terminology and provide
  descriptions