Title: Cell Membrane and Transport
1Chapter 3 6
- Cell Membrane and Transport
2Chapter 3 Outline
- Plasma Membrane
- Extracellular Environment
- Movement Across Plasma Membrane
- Osmosis
- Membrane Transport Systems
3Cell
- Basic unit of structure function in body
- Highly organized molecular factory
- Has 3 main components plasma membrane, cytoplasm
organelles
Fig 3.1
4Plasma Membrane
- Surrounds gives cell form selectively
permeable - Formed by a double layer of phospholipids
- restricts passage of polar compounds
Fig 3.2
5Plasma Membrane continued
- Proteins customize membranes
- Provide structural support
- Serve as transporters, enzymes, receptors
identity markers
Fig 3.2
6Plasma Membrane continued
- Carbohydrates in form of glycoproteins
glycolipids are part of outer surface - Impart negative charge to surface
Fig 3.2
7Bulk Transport
- Move large molecules particles across plasma
membrane - Some cells use phagocytosis to take in
particulate matter - E.g. white blood cells macrophages
Fig 3.3
8Bulk Transport
- Some cells use endocytosis to take in large
compounds - Membrane invaginates to take in a vesicle of
extracellular substance - Pinocytosis is non-specific intake
9Bulk Transport
- Receptor-mediated endocytosis uses receptors to
take in specific compounds - Including some viruses
1. plasma membrane pit forming
3.vesicle forming
2.membranepouching inward
4. vesicle inside cell
Fig 3.4
10Bulk Transport
- Cells use exocytosis to export products into the
extracellular fluid - Via secretory vesicles
11Surface Specializations
- Some epithelial cells have cilia projecting from
surface - Hair-like structures that beat in unison
- E.g. cilia lining respiratory reproductive
tracts
Fig 3.5
12Surface Specializations
- Some epithelial cells have microvilli on surface
to increase surface area for absorption (Fig 3.6) - Fingerlike structures to expand surface area
13Extracellular Environment
- Includes all constituents of body outside cells
- 67 of total body H20 is inside cells
(intracellular compartment) - 33 is outside cells (extracellular
compartment-ECF) - 20 of ECF is blood plasma
- 80 of ECF is interstitial fluid contained in
gel-like matrix
14Transport Across Plasma Membrane
- Plasma membrane is selectively permeable
- Many important molecules have transporters
channels - Carrier-mediated transport specific protein
transporters - Non-carrier mediated transport occurs by
diffusion
15Transport Across Plasma Membrane continued
- Passive transport moves compounds DOWN
concentration gradient - requires no energy
- Active transport moves compounds UP a
concentration gradient - requires energy transporters
16Diffusion
- Random motion of molecules
- Net movement is from region of high to low
concentration
17Diffusion
- Non-polar compounds readily diffuse thru cell
membrane - Also some small molecules (C02 H20)
- Diffusion of H20 osmosis
18Diffusion continued
- Cell membrane is impermeable to charged most
polar compounds - Must have an ion channel or transporter to move
across membrane
19Fig. 6.4
20Diffusion continued
- Rate of diffusion depends on
- Magnitude of its concentration gradient
- Permeability of membrane to it
- Temperature
- Surface area of membrane
21Osmosis
- Net diffusion of H20 across a selectively
permeable membrane - H20 diffuses down its concentration gradient
- H20 is less concentrated where there are more
solutes - Solutes have to be osmotically active
- i.e. cannot freely move across membrane
22Osmosis continued
- H20 diffuses down its concentration gradient
until it reaches equilibrium. - Some cells have water channels (aquaporins) to
facilitate osmosis
23Osmotic Pressure
- Force that would have to be exerted to stop
osmosis - Indicates how strongly H20 wants to diffuse
- Is proportional to solute concentration
24Molarity Molality
- 1 molar solution (1.0M) 1mole of solute
dissolved in 1L of solution - Doesn't specify exact amount of H20
- 1 molal solution (1.0m) 1 mole of solute
dissolved in 1 kg H20 - Osmolality (Osm) is total molality of a solution
- E.g. 1.0m of NaCl yields a 2 Osm solution
- Because NaCl dissociates into Na Cl-
25Fig. 6.8a
26Fig. 6.8b
27Molarity Molality
- Osmolality (Osm) is total molality of a solution
- E.g. 1.0m of NaCl yields a 2 Osm solution
- Because NaCl dissociates into Na Cl-
28Tonicity
- Effect of a solution on osmotic movement of H20
- Isotonic same osmotic pressure
- Hypertonic higher osmotic pressure are
osmotically active - Hypotonic lower osmotic pressure
- Isosmotic solutions same osmolality as plasma
- Hypo-osmotic solutions lower osmotic pressure
than plasma - hyperosmotic higher pressure than plasma
29Effects of tonicity on RBCs
Fig 6.11
crenated
6-19
30Regulation of Blood Osmolality
- Blood osmolality maintained in narrow range
around 300m Osm - If dehydrated, osmoreceptors in hypothalamus
stimulate - ADH release
- Which causes kidney to conserve H20
- thirst
31Carrier-Mediated Transport
- Molecules too large polar need protein carriers
- Protein carriers exhibit
- Specificity for single molecule
- Competition among substrates for transport
- Saturation all carriers are occupied
- Tm (transport maximum)
32Facilitated Diffusion
- Is passive transport down concentration gradient
by carrier proteins
33Active Transport
- Transport of molecules against a concentration
gradient - ATP required
Fig 6.16
34Na/K Pump
- Uses ATP to move 3 Na out 2 K in
- Against their gradients
35Secondary Active Transport
- Uses energy from downhill transport of Na to
drive uphill movement of another molecule - Also called coupled transport
- ATP required to maintain Na gradient
36Transport Across Epithelial Membranes
- Absorption is transport of digestion products
across intestinal epithelium into blood - Reabsorption transports compounds out of urinary
filtrate back into blood
37Transport Across Epithelial Membranes continued
- Transcellular transport moves material from 1
side to other of epithelial cells - Paracellular transport moves material through
tiny spaces between epithelial cells
38Fig. 6.20a