Colicin E1 Channels in Planar Phospholipid Bilayer Membranes
Cells and Their Environment Ch. 4 Biology. Membrane Structure Phospholipid Bilayer 2 layers of...
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Transcript of Cells and Their Environment Ch. 4 Biology. Membrane Structure Phospholipid Bilayer 2 layers of...
Membrane Structure
Phospholipid Bilayer 2 layers of phospholipids Proteins
Transport Receptors
Cholesterol Maintains fluidity
Selectively Permeable
Because of polar and nonpolar regions of the phospholipid bilayer, the membrane allows certain materials in and certain materials out of the cell Small molecules Small ions Nonpolar molecules
Passive Transport
Diffusion caused by the random movement of particles across a membraneMovement due to concentration gradient Moving from a higher concentration to a lower
concentration No energy used
Movement continues until equilibrium reached Concentration is the same on both sides of the
membrane
Direction of Water Movement
Hypertonic solution Solution contains more solute than the solution
it is compared with
Hypotonic solution Solution contains less solute than the solution it
is compared with
Isotonic solution Solution contains same amount of solute as the
solution it is compared with
Facilitated Diffusion
Passive transport—no energy used
Uses transport proteins embedded in the plasma membrane (ion channels) Potassium (K+) Sodium (Na+) Calcium (Ca+) Chloride (Cl-)
Pores—always open
Gated channels—open/close in response to stimuli
Active Transport
Substances are transported across a membrane, against the concentration gradient
Use carrier proteins embedded in the membrane
Use energy (ATP)
Sodium-Potassium Pump
1. 3 Na+ ions inside the cell bind to the pump. ATP donates a phosphate to the pump
2. The pump changes shape, transporting 3 Na+ across the membrane, and are released
3. 2 K+ ions outside the cell bind to the pump and are transported across the membrane
4. The phosphate group is released and the 2 K+ are released
Vesicles Move Substances
Substances that are too large for carrier proteins (proteins and polysaccharides)
Endocytosis—movement of substances into the cell (a.k.a. phagocytosis)
Exocytosis—movement of substance out of the cell
Receptor Proteins
Protein that binds a specific signal molecule, allowing the cell to respond to the signal moleculeSome receptor proteins are attached to ion channels Changes permeability to a specific ion
Some may cause the formation of a second messenger, which acts as a signal molecule in the cytoplasmSome may act as enzymes to speed up chemical reactions by lowering the activation energy