Membrane Transport How stuff gets in or out

Membrane Transport Objectives:  Relate membrane structures to transport processes

Membrane Transport Objectives:  Relate membrane structures to transport processes  Compare and contrast types of transport processes

Membrane Transport The cell membrane’s most important function is to select what goes in and out of the cell.

Membrane Transport The cell membrane’s most important function is to select what goes in and out of the cell. This property is known as selective permeability.

Membrane Transport Two processes allow materials to move in and out of the cell: 1) passive transport

Membrane Transport Two processes allow materials to move in and out of the cell: 1) passive transport 2) active transport

Passive Transport Passive transport requires No Energy (ATP).

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Passive Transport There are three types:  Simple diffusion

Passive Transport There are three types:  Simple diffusion  Facilitated diffusion

Passive Transport There are three types:  Simple diffusion  Facilitated diffusion &  Osmosis

Passive Transport Simple Diffusion Substances move from a high concentration to a low concentration. This influenced by:  Temperature

Passive Transport Simple Diffusion Substances move from a high concentration to a low concentration. This influenced by:  Temperature  Concentration

Passive Transport Simple Diffusion Substances move from a high concentration to a low concentration. This influenced by:  Temperature  Concentration  Distance

Passive Transport Simple Diffusion In the cell, only nonpolar and lipid soluble substances diffuse directly through the bilayer.

Copyright © 2010 Pearson Education, Inc.. Extracellular fluid Lipid- soluble solutes Cytoplasm

Passive Transport Simple Diffusion Common substances that diffuse in this manner include Oxygen and Carbon Dioxide

Passive Transport Facilitated Diffusion Molecules which can not pass through the lipid bilayer because of size or polarity pass through using protein carriers or channels.

Passive Transport Carriers are integral proteins and are typically designed for a specific type of molecule, for example, glucose.

Passive Transport Carriers are integral proteins and are typically designed for a specific type of molecule, for example, glucose. What is meant by an integral protein?

Passive Transport What is meant by an integral protein? This is a protein that transverses the entire membrane.

Passive Transport Carriers are integral proteins and are typically designed for a specific type of molecule, for example, glucose. Rate is only limited by the number of carriers on the membrane.

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Passive Transport Channels are integral proteins that allow smaller molecules (ions and water) to pass through.

Passive Transport Channels are integral proteins that allow smaller molecules (ions and water) to pass through. They can be specific for certain types of ions (Na + or K + )

Passive Transport Channels are integral proteins that allow smaller molecules (ions and water) to pass through. They can be specific for certain types of ions (Na + or K + ) Some are always open while others are gated and open only when stimulated.

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Passive Transport

Osmosis is the diffusion of water across a semi permeable membrane.

Passive Transport Osmosis is the diffusion of water across a semi permeable membrane. Water moves depending on its concentration through channels lined with proteins called aquaporins.

Passive Transport Osmosis is the diffusion of water across a semi permeable membrane. Water moves depending on its concentration through channels lined with proteins called aquaporins. It can also pass through the lipid bilayer!

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Passive Transport The rate of osmosis is dependent on the concentration of impermeable molecules and permeable molecules.

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Passive Transport In biological systems, the ability of a solution to change the shape of a cell by osmosis is called tonicity.

Passive Transport Isotonic solutions do not change the shape of the cells. In the hospital these are iv solutions of 0.9% NaCl or 5% dextrose (D5W).

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Passive Transport Hypertonic solutions do change the shape of the cells because the concentration of impermeable solutes is greater than the cell. In the hospital these are used in cases of cerebral edema. Pulls water out of the cell.

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Passive Transport Hypotonic solutions do change the shape of the cells because the concentration of impermeable solutes is less than the cell. In the hospital these are used in cases of dehydration

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Active Transport Active transport requires Energy (ATP).

Active Transport Active transport requires Energy (ATP). Substances move from a LOW to a HIGH concentration.

Active Transport

Active transport requires membrane proteins that are specific for a particular substance. There are two types:  Primary Active Transport

Active Transport Active transport requires membrane proteins that are specific for a particular substance. There are two types:  Primary Active Transport&  Secondary Active Transport

Active Transport Primary Active Transport uses ATP directly to move a solute across the plasma membrane, against the gradient.

Active Transport Primary Active Transport uses ATP directly to move a solute across the plasma membrane, against the gradient. The best example is the sodium-potassium pump.

Active Transport

Secondary Active Transport uses a single ATP to indirectly move more than one substance across the cell membrane.

Active Transport Secondary Active Transport uses a single ATP to indirectly move more than one substance across the cell membrane. The ATP creates a gradient for one substance and as it flows back with the gradient it carries another substance with it.

Active Transport There are two types of secondary active transport:  Symport which moves two transported substances in the same direction

Active Transport There are two types of secondary active transport:  Symport which moves two transported substances in the same direction &  Antiport which moves them in opposite directions.

Active Transport

Example, Na + is pumped out of the cell by primary active transport.

Active Transport Example, Na + is pumped out of the cell by primary active transport. It then flows passively back into the cell and uses that energy to move other substances through.

Copyright © 2010 Pearson Education, Inc.. 12 The ATP-driven Na + -K + pump stores energy by creating a steep concentration gradient for Na+ entry into the cell. As Na + diffuses back across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradient into the cell. (ECF = extracellular fluid) Na + -glucose symport transporter loading glucose from ECF Na + -glucose symport transporter releasing glucose into the cytoplasm Glucose Na + -K + pump Cytoplasm Extracellular fluid

Active Transport Vesicular Transport is another type of active transport where large macromolecules and fluid are transported.

Active Transport Vesicular Transport is another type of active transport where large macromolecules and fluid are transported. There are two types:  Exocytosis

Active Transport Vesicular Transport is another type of active transport where large macromolecules and fluid are transported. There are two types:  Exocytosis

Active Transport Vesicular Transport is another type of active transport where large macromolecules and fluid are transported. There are two types:  Exocytosis &  Endocytosis

Active Transport Endocytosis is the process where materials are taken into the cell using a membranes with a protein coated vesicle.

Active Transport Endocytosis Endocytosis

Copyright © 2010 Pearson Education, Inc. Coated pit ingests substance. Protein- coated vesicle detaches. Coat proteins detach and are recycled to plasma membrane. Uncoated vesicle fuses with a sorting vesicle called an endosome. Transport vesicle containing membrane components moves to the plasma membrane for recycling. Fused vesicle may (a) fuse with lysosome for digestion of its contents, or (b) deliver its contents to the plasma membrane on the opposite side of the cell (transcytosis). Protein coat (typically clathrin) Extracellular fluid Plasma membrane Endosome Lysosome Transport vesicle (b) (a) Uncoated endocytic vesicle Cytoplasm

Active Transport Exocytosis is the process where materials are removed from the cell using a membranes with a protein coated vesicle.

Active Transport Exocytosis Exocytosis

Copyright © 2010 Pearson Education, Inc. 1 The membrane- bound vesicle migrates to the plasma membrane. 2 There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins). (a)The process of exocytosis Extracellular fluid Plasma membrane SNARE (t-SNARE) Secretory vesicle Vesicle SNARE (v-SNARE) Molecule to be secreted Cytoplasm Fused v- and t-SNAREs 3 The vesicle and plasma membrane fuse and a pore opens up. 4 Vesicle contents are released to the cell exterior. Fusion pore formed

Resting Membrane Potential The transport processes discussed are responsible for the generation of a membrane potential or voltage.

Resting Membrane Potential The transport processes discussed are responsible for the generation of a membrane potential or voltage. The result is that at rest, cells exhibit a resting membrane potential between -50 to -100 millivolts.

Resting Membrane Potential This is achieved by a process of active transport and movement of ions to either the exterior or interior of the cell.

Resting Membrane Potential Inside the cell, potassium ions are in large concentration while outside sodium ions are in large concentration. Inside the cell are large negatively charged proteins.

Resting Membrane Potential

Due to the preferential “leaking” of potassium ions to the outside, there is a net NEGATIVE voltage relative to the outside.

Resting Membrane Potential

– Stimulation of the membrane results in a sudden change in polarity called an action potential. This can lead to: Muscle Contraction Gland Secretion Nerve Impulse