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Membranes Chapter 5

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Page 1: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

Membranes

Chapter 5

Page 2: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Membrane Structure

The fluid mosaic model of membrane structure contends that membranes consist of:

-phospholipids arranged in a bilayer

-globular proteins inserted in the lipid bilayer

Page 3: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 4: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Membrane Structure

Cellular membranes have 4 components:

1. phospholipid bilayer

2. transmembrane proteins

3. interior protein network

4. cell surface markers

Page 5: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 6: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Membrane Structure

Membrane structure is visible using an electron microscope.

Transmission electron microscopes (TEM) can show the 2 layers of a membrane.

Freeze-fracturing techniques separate the layers and reveal membrane proteins.

Page 7: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 8: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 9: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Phospholipids

Phospholipid structure consists of

-glycerol – a 3-carbon polyalcohol acting as a backbone for the phospholipid

-2 fatty acids attached to the glycerol

-phosphate group attached to the glycerol

Page 10: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Phospholipids

The fatty acids are nonpolar chains of carbon and hydrogen.

-Their nonpolar nature makes them hydrophobic (“water-fearing”).

The phosphate group is polar and hydrophilic (“water-loving”).

Page 11: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Phospholipids

The partially hydrophilic, partially hydrophobic phospholipid spontaneously forms a bilayer:

-fatty acids are on the inside

-phosphate groups are on both surfaces of the bilayer

Page 12: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 13: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Phospholipids

Phospholipid bilayers are fluid.-hydrogen bonding of water holds the 2 layers together-individual phospholipids and unanchored proteins can move through the membrane-saturated fatty acids make the membrane less fluid than unsaturated fatty acids-warm temperatures make the membrane more fluid than cold temperatures

Page 14: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Phospholipids

Page 15: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Membrane Proteins

Membrane proteins have various functions:

1. transporters

2. enzymes

3. cell surface receptors

4. cell surface identity markers

5. cell-to-cell adhesion proteins

6. attachments to the cytoskeleton

Page 16: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 17: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Membrane Proteins

Peripheral membrane proteins

-anchored to a phospholipid in one layer of the membrane

-possess nonpolar regions that are inserted in the lipid bilayer

-are free to move throughout one layer of the bilayer

Page 18: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 19: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Membrane Proteins

Integral membrane proteins

-span the lipid bilayer (transmembrane proteins)

-nonpolar regions of the protein are embedded in the interior of the bilayer

-polar regions of the protein protrude from both sides of the bilayer

Page 20: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 21: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Membrane Proteins

Integral proteins possess at least one transmembrane domain

-region of the protein containing hydrophobic amino acids

-spans the lipid bilayer

Page 22: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 23: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Membrane Proteins

Extensive nonpolar regions within a transmembrane protein can create a pore through the membrane.

- sheets in the protein secondary structure form a cylinder called a -barrel

--barrel interior is polar and allows water and small polar molecules to pass through the membrane

Page 24: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 25: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Passive Transport

Passive transport is movement of molecules through the membrane in which

-no energy is required

-molecules move in response to a concentration gradient

Diffusion is movement of molecules from high concentration to low concentration

Page 26: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 27: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Passive Transport

Selective permeability: integral membrane proteins allow the cell to be selective about what passes through the membrane.

Channel proteins have a polar interior allowing polar molecules to pass through.

Carrier proteins bind to a specific molecule to facilitate its passage.

Page 28: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Passive Transport

Channel proteins include:

-ion channels allow the passage of ions (charged atoms or molecules) which are associated with water

-gated channels are opened or closed in response to a stimulus

-the stimulus may be chemical or electrical

Page 29: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Passive Transport

Carrier proteins bind to the molecule that they transport across the membrane.

Facilitated diffusion is movement of a molecule from high to low concentration with the help of a carrier protein.

-is specific

-is passive

-saturates when all carriers are occupied

Page 30: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Passive Transport

In an aqueous solution

-water is the solvent

-dissolved substances are the solutes

Osmosis is the movement of water from an area of high to low concentration of water

-movement of water toward an area of high solute concentration

Page 31: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 32: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Passive Transport

When 2 solutions have different osmotic concentrations

-the hypertonic solution has a higher solute concentration

-the hypotonic solution has a lower solute concentration

Osmosis moves water through aquaporins toward the hypertonic solution.

Page 33: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 34: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Passive Transport

Organisms can maintain osmotic balance in different ways.1. Some cells use extrusion in which water is ejected through contractile vacuoles.2. Isosmotic regulation involves keeping cells isotonic with their environment.3. Plant cells use turgor pressure to push the cell membrane against the cell wall and keep the cell rigid.

Page 35: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Active Transport

Active transport

-requires energy – ATP is used directly or indirectly to fuel active transport

-moves substances from low to high concentration

-requires the use of carrier proteins

Page 36: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Active Transport

Carrier proteins used in active transport include:

-uniporters – move one molecule at a time

-symporters – move two molecules in the same direction

-antiporters – move two molecules in opposite directions

Page 37: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Active Transport

Sodium-potassium (Na+-K+) pump-an active transport mechanism-uses an antiporter to move 3 Na+ out of the cell and 2 K+ into the cell-ATP energy is used to change the conformation of the carrier protein-the affinity of the carrier protein for either Na+ or K+ changes so the ions can be carried across the membrane

Page 38: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 39: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Active Transport

Coupled transport

-uses the energy released when a molecule moves by diffusion to supply energy to active transport of a different molecule

-a symporter is used

-glucose-Na+ symporter captures the energy from Na+ diffusion to move glucose against a concentration gradient

Page 40: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 41: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Bulk Transport

Bulk transport of substances is accomplished by

1. endocytosis – movement of substances into the cell

2. exocytosis – movement of materials out of the cell

Page 42: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Bulk Transport

Endocytosis occurs when the plasma membrane envelops food particles and liquids.1. phagocytosis – the cell takes in particulate matter2. pinocytosis – the cell takes in only fluid3. receptor-mediated endocytosis – specific molecules are taken in after they bind to a receptor

Page 43: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 44: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 45: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 46: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Bulk Transport

Exocytosis occurs when material is discharged from the cell.

-vesicles in the cytoplasm fuse with the cell membrane and release their contents to the exterior of the cell

-used in plants to export cell wall material

-used in animals to secrete hormones, neurotransmitters, digestive enzymes

Page 47: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

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Page 48: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

Cell Surfaces in Animals •Junctions Between Cells are points of contact between cells that allow them to behave in a coordinated manner.

•Anchoring junctions mechanically attach adjacent cells.•In adhesion junctions, internal cytoplasmic plaques, firmly attached to cytoskeleton within each cell are joined by intercellular filaments; they hold cells together where tissues stretch (e.g., in heart, stomach, bladder).•In desmosomes, a single point of attachment between adjacent cells connects the cytoskeletons of adjacent cells.•In tight junctions, plasma membrane proteins attach in zipper-like fastenings; they hold cells together so tightly that the tissues are barriers (e.g., epithelial lining of stomach, kidney tubules, blood-brain barrier). •A gap junction allows cells to communicate; formed when two identical plasma membrane channels join.

•They provide strength to the cells involved and allow the movement of small molecules and ions from the cytoplasm of one cell to the cytoplasm of the other cell.•Gap junctions permit flow of ions for heart muscle and smooth muscle cells to contract.

Modification of Cell Surfaces

Page 49: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

Cell-Surface Modifications:Junctions

Page 50: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

•The extracellular matrix is a meshwork of polysaccharides and proteins produced by animal cells.

•Collagen gives the matrix strength and elastin gives it resilience.•Fibronectins and laminins bind to membrane receptors and permit communication between matrix and cytoplasm; these proteins also form “highways” that direct the migration of cells during development.•Proteoglycans are glycoproteins that provide a packing gel that joins the various proteins in matrix and most likely regulate signaling proteins that bind to receptors in the plasma protein.

Extracellular Matrix

Page 51: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

•Plant cells are surrounded by a porous cell wall; it varies in thickness, depending on the function of the cell.•Plant cells have a primary cell wall composed of cellulose polymers united into threadlike microfibrils that form fibrils.•Cellulose fibrils form a framework whose spaces are filled by non-cellulose molecules.•Pectins allow the cell wall to stretch and are abundant in the middle lamella that holds cells together.•Non-cellulose polysaccharides harden the wall of mature cells. •Lignin adds strength and is a common ingredient of secondary cell walls in woody plants.•Plasmodesmata are narrow membrane-lined channels that pass through cell walls of neighboring cells and connect their cytoplasms, allowing direct exchange of molecules and ions between neighboring plant cells.

Plant Cell Walls

Page 52: Membranes Chapter 5. 2 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in

Cell-Surface Modifications:Plasmodesmata