Substances Transport Through Cell Membrane

Transport Transport of Substances of Substances Through Through the Cell the Cell Membrane Membrane Dr. Maha Saja

Objectives Objectives At the end of this session, the students should beable to: Describe the fluid mosaic model ofmembrane structure andfunction. Define permeability and list factors influencing permeability. Identify and describe carried-mediatedtransport processes: Primary active transport, secondary active transport, facilitatesdiffusion.

Previously.. Previously.. Fluid body compartments are divided into: Intracellular Extracellular The amount of solutes in the two compartments differ. How is this achieved and maintained? Selective permeability

What What is meant by is meant by Selective Permeability Permeability Selective The membrane allows some substances to cross it but not others. This controls the type & amount of substances entering and leaving the cell. It arises from the membrane structure.

Structure Structure of the Cell Cell Membrane Membrane of the

Structure Structure of the Membrane Membrane of the Cell Cell Cell membrane = plasma membrane. Thickness = 7.5-10 nm. Phospholipids(25%) Composed of: Lipids(42%) Proteins(55%) Carbohydrates(3%) Cholesterol(13%) Other lipids(4%) (Guyton and Hall Textbook of Physiology. 13th ed. Chapter-2)

Structure Structure of the Cell of the Cell Membrane Membrane The cell membrane =a lipidbilayer. The most abundant lipid= phospholipids. A phospholipidmolecule have twoends: Hydrophilic (phosphate end) Hydrophobic (fatty acid end) (Guyton and Hall Textbook of Physiology. 13th ed. Chapter-2)

Structure Structure of the Cell of the Cell Membrane Membrane Membrane proteins Integral Peripheral Are attached to one surface of themembrane. Span the thickness of the cellmembrane. Function as: 1. Channels (or pores). 2. Carrier proteins. 3. Receptors. Function as: Enzymes (Guyton and Hall Textbook of Physiology. 13th ed. Chapter-2)

Channel vs. Channel vs. Carrier Carrier Proteins Proteins Carrier proteins selectively bind the small molecule to be transported and thenundergo a conformational change to release the molecule on the other side of themembrane. Channel proteins form open pores through which molecules of the appropriate size (e.g., ions) cancross themembrane.

Carrier Carrier Channel Channel

Structure Structure of the Cell of the Cell Membrane Membrane Functionof CHOs: Receptors. Attachcells to each other. Immune reactions. Carbohydrates in the cell membrane are invariably attachedto: Proteins Glycoproteins Lipids Glycolipids Carbohydrate molecules protrude to the outside of the cell forming a loose carbohydrate coat = glycocalyx

The The Fluid Fluid Mosaic Model Mosaic Model of Plasma Plasma Membrane Membrane of

Movement Movement (Transport) (Transport) of Substances Substances Across Across the Membrane Membrane of Cell the Cell

Substances Substances that that can Cell Cell Membrane Membrane can Across Across the the Lipidsoluble substances Watersoluble substances Alternative route Oil and water do notmix Cross freelyby diffusion Throughmemb proteins rane

Substances Substances that that can Cell Cell Membrane Membrane can Across Across the the

Substances Substances that that can Cell Cell Membrane Membrane can Across Across the the Achieved through a trans- membrane protein carrier/transporter/channel

Transport Transport Mechanisms Mechanisms The transport of material between body or cellular compartments can be divided into: 1. Passive Transport = does not require energy. 2. Active Transport = requires energy.

Transport Transport Mechanisms Mechanisms Passive Transport Active Transport Molecules move along their energygradient. Molecules move against their energygradient. Does not require energy. Requiresenergy. Types: Primary Active Transport. Secondary ActiveTransport. Types: SimpleDiffusion. Facilitated Diffusion. Osmosis.

Passive Passive Transport Transport Mechanisms Mechanisms Passive Transport Diffusion Osmosis Movement of water from an area of low solute concentration to an area of high solute concentration. Simple Facilitated

Di Dif ffusion fusion Diffusion = the random movement of substances down an energygradient. Highconc. substances will move down their concentration gradient This gradient can be: Concentrationgr. Electrochemicalgr. Pressure gr. Lowconc.

Diffusion Diffusion

Types Types of of Diffusion Diffusion Diffusion Facilitated Diffusion SimpleDiffusion The transported moleculebinds to a carrier protein which then undergoes a conformational change allowing the molecule to pass through to the other side of the cellmembrane. The movement of molecules through the intermolecular spaces or membrane openings (channels) without the necessity of binding to acarrier protein on themembrane. The carrier facilitates passage of the molecule through the CM

Types Types of of Diffusion Diffusion Carrierprotein Also called Carrier-mediated diffusion . 1. Lipid-soluble substances (e.g. O2, CO2, and alcohol) Pass through the interstices of the lipid bilayer. 2. Water-soluble substances (water, ions) pass through channels that penetrate all the way through theCM. Diffusion of a substance is facilitated by the use of a specific carrierprotein. Examples (glucose, amino acids).

What What is the is the difference simple and simple and facilitated difference between facilitated diffusion? between diffusion? Simplediffusion Facilitateddiffusion The rate of diffusion increases proportionately with the concentration of the diffusing substance until it reaches a maximumVmax. At Vmax, an increase in the concentration of the diffusing substance does not increase the rate of diffusion. The rate of diffusion increases proportionately with the concentration of the diffusing substance.

The rate at which molecules can be transported by facilitated diffusion depends on the rate at which the carrier protein molecule can undergo conformational change back and forth between its bound and unbound state.

Factors Factors Affecting Affecting Net Diffusion Diffusion Net Rate Rate of of 1. Size. 2. Temperature. 3. Steepness ofthe gradient: a. Concentration difference b. Membraneelectrical difference. c. Pressure difference. 4. Charge. 5. Pressure.

Active Active Transport Transport Occurs when a cell membrane moves molecules or ions up-hill against a concentration gradient (or up-hill against an electrical or pressuregradient). Examples include: Ions like: sodium, potassium, calcium, iron, iodine, hydrogenions. Amino acids, glucose and othersugars. Requires energy and a carrierprotein.

Active Active Transport Transport According to the source of energy used to facilitate transport, it can be dividedinto; Active Transport Indirect sourceof energy PrimaryActive Transport SecondaryActive Transport Direct source ofenergy Co-transport Counter-transport

Types Types of of Active Active Transport Transport Primary Active Secondary Active The energy is derived directly from breakdown of adenosine triphosphate (ATP) or some other high-energy phosphatecompound. The energy is derived indirectly by using the concentration or electrochemical gradient generated by a primary activetransporter. Examplesinclude: Sodium-potassium ATPasepump. Calcium ATPasepump Hydrogen ATPase pump.

Primary Primary Active Active Transport Transport This pump functions by moving 3 molecules of sodium OUT and 2 molecules of potassium INTO the cell both against their concentrationgradients. The importance of thispump: Maintaining Na and K concentration differences across the cell membrane. Establishes a negative electrical voltage inside thecell. Is the basis for nerve signaltransmission.

Primary Primary Active Active Transport Transport H+ ATPasePump Presentin: Parietal cells of stomach secretion of HCl in thestomach. Intercalated cells of distal renal tubules excretion of acids fromthe body. Pumps H+ out of the cell and into thelumen.

Primary Primary Active Active Transport Transport Ca+2 ATPase Pump Presentin: Sarcoplasmic reticulum in musclecells Mitochondria Some cellmembranes. Maintains low Ca+2 concentration inside thecell.

Secondary Secondary Active (Co (Co- -transport) Active Transport Transport transport) Derives energy indirectly How?

Secondary Secondary Active (Counter (Counter- -transport) Active Transport Transport transport)

Types Types of of Secondary Secondary Active Transport Transport Active Co-Transport Counter-Transport When both substances are transported together in the same direction. When one substance is transported in the opposite direction to the othersubstance. Examples; Na+-Glucose co- transport(PCT) Na+-amino acid co- transport(PCT) Examples; Na+-H+ counter-transport (PCT) Na+-Ca+2 counter- transport(PCT)

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