what is the surface area to volume ratio of a sphere with...
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Warm Up
What is the Surface Area to
Volume Ratio of a sphere with a
radius of 5mm? Of 10 mm? What
sphere can eliminate wastes and
move materials quicker?
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Cell Membrane and FunctionChapter 7
• Big Idea #2: Biological systems use energy to
grow, reproduce, and maintain dynamic
homeostasis.
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Essential Knowledge• 2B1:Cell membranes are selectively
permeable due to their structure
• 2B2: Growth and dynamic homeostasis are
maintained by the constant movement of
molecules across membranes
• 2B3: Eukaryotic cells maintain internal
membranes that partition the cell into
specialized regions
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• Separates internal and external env.
• Is selectively permeable: some
substances can cross
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Semi-Permeability
Due to structure
Has phosholipids, proteins, cholesterol,
glycoproteins, and glycolipids
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Fig. 7-2
Hydrophilichead
WATER
Hydrophobictail
WATER
Made of a double
phospholipid layer that is
amphipathic (hydrophobic
and hydrophilic areas)
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Fig. 7-3
Phospholipid
bilayer
Hydrophobic regionsof protein
Hydrophilicregions of protein
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• Can be hydrophilic w/ charged and polar side
groups.
• Can be hydrophobic w/ nonpolar side groups
Embedded Proteins
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Fig. 7-8
N-terminus
C-terminus
Helix
CYTOPLASMICSIDE
EXTRACELLULARSIDE
Hydrophobic area ex: coiled,
nonpolar alpha helices
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Cholesterol• Steroid found in b/t
phospholipids.
• In high temps
less fluid
membrane.
• In low temps
Stops solidification
of membrane
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Fig. 7-5a
(a) Movement of phospholipids
Lateral movement
(107 times per second)
Flip-flop
( once per month)
Membrane is fluid Moves
When Cold, Moves Less!!
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Cell to Cell Recognition
• Cells “talk” w/ membrane carbs may be
covalently bonded to lipids (glycolipids) or to
proteins (glycoproteins)
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Permeability of Lipid Bilayer
• Pass: Small, uncharged molecules and
small nonpolar molecules (N2)
• Others need help with channels or pumps
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Aquaporins
Channel protein that allows water to
move across
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Binds to molecules and changes shape
to shuttle them across
membrane…extremely specific
Transport Proteins
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Cell Walls
Provides a structural boundary
Cell Wall
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• Bacteria Cell Wall: Made of
peptidoglycan
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• Plant Cell Wall: Made of Cellulose
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• Fungi Cell Wall: Made of Chitin
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• Movement of molecules in and out of
cell w/out using energy.
• AKA Diffusion
Passive Transport
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• High to low
concentrations!
• Import
resources/
export of wastes
Concentration Gradient
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Osmosis• Passive transport: movement of H2O
across membrane.
• High to Low!
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Lower
concentrationof solute (sugar)
Fig. 7-12
H2O
Higher
concentrationof sugar
Selectivelypermeable
membrane
Same concentration
of sugar
Osmosis
Osmosis
Video Clip!
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Tonicity• Ability of a solution to cause a cell to gain or
lose water osmoregulation
• Isotonic solution: Solute concentration is the
same as that inside the cell; no net water
movement across the plasma membrane
• Hypertonic solution: Solute concentration is
greater out of cell; cell loses water
• Hypotonic solution: Solute concentration is
high inside cell; cell gains water
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Fig. 7-13
Hypotonic solution
(a) Animal
cell
(b) Plant
cell
H2O
Lysed
H2O
Turgid (normal)
H2O
H2O
H2O
H2O
Normal
Isotonic solution
Flaccid
H2O
H2O
Shriveled
Plasmolyzed
Hypertonic solution
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Facilitated Diffusion• Channel protein
carries molecules
across (high to low
conc.)
• Polar molecules
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Fig. 7-15
EXTRACELLULAR FLUID
Channel protein
(a) A channel protein
Solute CYTOPLASM
Solute Carrier protein
(b) A carrier protein
Fa
cil
ita
te
d D
iff
us
ion
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Active Transport
• Energy-requiring:
move across cell
membrane from
low to high conc.
• Uses ATP
• Embedded
proteins
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• Allows cells to maintain concentration gradients
that differ from their surrounding
Ex: Sodium-Potassium Pump
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Fig. 7-17Passive transport
Diffusion Facilitated diffusion
Active transport
ATP
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Exocytosis
• Internal vesicles fuse w/ plasma mebrane to
secrete large macromolecules out of cell.
• Requires ATP!
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• Cell takes in macromolecules by forming
new vesicles derived from plasma
membrane.
Endocytosis
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Eukaryotes Compartmentalize…
• Minimizes competing interactions and increases
surface area.
• Keep reactions and enzymes localized
• Bacteria and Archaea (ancient) can’t do this