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Transportation through cell membranesTransportation through cell membranes

Cell membrane structure :Cell membrane structure : Lipid bilayer ; in which protein are Lipid bilayer ; in which protein are

suspended suspended Membrane Proteins ; integral and peripheralMembrane Proteins ; integral and peripheral Cholesterol molecules Cholesterol molecules Glycoproteins “peripheral proteins + Glycoproteins “peripheral proteins +

carbohydrates”carbohydrates” Gylcolipids “peripheral proteins + lipids”Gylcolipids “peripheral proteins + lipids”

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Transport through cell Transport through cell membranesmembranes

The phospholipids bilayer is a good barrier around cells, The phospholipids bilayer is a good barrier around cells, especially to water soluble molecules. However, for the cell to especially to water soluble molecules. However, for the cell to survive some materials need to be able to enter and leave the survive some materials need to be able to enter and leave the cell.cell.

Transportation types Transportation types

1.1. DIFFUSION DIFFUSION

2.2. FACILITATED DIFFUSIONFACILITATED DIFFUSION

3.3. OSMOSISOSMOSIS

4.4. ACTIVE TRANSPORTACTIVE TRANSPORT

5.5. OTHER TYPESOTHER TYPES

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As a result of diffusion molecules reach an As a result of diffusion molecules reach an equilibrium equilibrium where where they are evenly spread out.they are evenly spread out.

DiffusionDiffusion Diffusion is the net movement of molecules (or ions) from a region of their high concentration to a region of their lower concentrationDiffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural kinetic energy.

Molecules that diffuse through cell membrane :

1. Oxygen – Non-polar so diffuses very quickly.

1. Carbon dioxide – Polar but very small so diffuses quickly.

2. Water – Polar but also very small so diffuses quickly

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Facilitated diffusionFacilitated diffusion Large polar molecules such as Large polar molecules such as

glucose glucose and and amino acidsamino acids, , cannot diffuse across the cannot diffuse across the phospholipids bilayer. Also phospholipids bilayer. Also ions such as ions such as NaNa++ or or ClCl-- cannot cannot pass.pass.

These molecules pass through These molecules pass through protein channelsprotein channels instead. instead. Diffusion through these Diffusion through these channels is called channels is called FACILITATED DIFFUSION.FACILITATED DIFFUSION.

Movement of molecules is still Movement of molecules is still PASSIVEPASSIVE just like ordinary just like ordinary diffusion, the only difference diffusion, the only difference is, the molecules go through a is, the molecules go through a protein channel instead of protein channel instead of passing between the passing between the phospholipids.phospholipids.

Protein channel Protein channel

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is a protein that allows the transport of specific substances across a cell membrane.The process by which molecules pass through a membrane via a channel protein is called carrier-mediated transport. the makeup of the amino acid chains in the protein determines the size and shape of the channel protein. This, in turn, determines what ions and micro molecules can be received by the channel protein to cross the cell membrane. Each molecule has a specific carrier protein.

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Ion channelsThey are channels from proteins which allow the passage of charged ions arranged in the form of pipes & extend through the whole length of the cell.There are 3 types :1.Un gated channels; continuously opened so the movement through it depend on the size and concentration of molecules2.Gated channels

Voltage gated channels : selective as Na+,Ca+2, and non selective Ligand gated channels :They are closed till arrive to certain particles that

make stimulation as Ca 2+ ions in myoneural junction 3.Gap junctionThey are 6 units of integral protein called cannexons (GAP junction unit)which form channel . The cannexons of 2 neighboring cells oppose each other to form a way for passage of substances.

CarriersCarriers

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1. Uniport : one molecule which is lipid or soluble .2. Symport : 2 molecules at the same direction (in intestinal mucosa) .3. Antiport : 2 molecules at different directions .N.B All of them work from outside to inside the cell or from inside to outside

the cell depending on concentration .e.g. glucose and sodium transportation.

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Na-glucose transporters :Found in intestinal mucosa & proximal tubules of the nephron in kidneys they help in reabsorption of renal glucose.Encoded by SGLT genes .

Pumps Pumps

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Def: They work against concentration rate (gradient) from low conc. To higher conc. (against diffusion law) by ATP as a source of energy .Prosperities: Transportation of ions & other molecules .Transportation by diffusion or active transportThe passage is for 1 or 2 molecules . e.g. : Na+-K+ pump in neurojunctions. “polarization & depolarization”

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Polarization & depolarization :

action potential.mp4

ReceptorsReceptors

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Def: They are polypeptide proteins or glycoprotein molecules present either intracellular or extending through the cell membrane .Types : 1.Membranous receptor . a. Extracellular domain (part) : responsible for binding . b. Trans-membranous domain . c. Intracellular domain : responsible for transmitting signal to cell .2.Intracellular receptor “cytoplasmic or nuclear “(many in mitochondrial cells ) a. Amino terminal domain : stimulates DNA to gene transcription . b. DNA binding domain : attach DNA c. Hinge region : as joint . d. Steroid binding domain.

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OsmosisOsmosis ‘‘The The diffusiondiffusion of water from an area of high concentration of of water from an area of high concentration of

water molecules (water molecules (high water potentialhigh water potential) to an area of low ) to an area of low concentration of water (concentration of water (low water potentiallow water potential) across a ) across a partially permeable membrane.’partially permeable membrane.’

Active transportActive transport‘‘The movement of The movement of large molecules large molecules “sugars, fatty acids”“sugars, fatty acids” from the from the lowlow

concentration area to the concentration area to the highhigh concentration area concentration area “energy needed” “energy needed” this energy is provided by enzymatic reactions of cell membrane’ this energy is provided by enzymatic reactions of cell membrane’

(A) (A)(B) (B)

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Endocytosis Endocytosis is the case when a molecule causes the cell membrane to bulge inward, forming a vesicle.transported binds to certain specific molecules in the membrane. Examples include the transport of insulin and cholesterol into animal cells.

Exocytosis Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane.

PhagocytosisPhagocytosis : : The transport of any solid substance from outside to inside the cell .The transport of any solid substance from outside to inside the cell .

PinocytosisPinocytosis The transport of any liquid substance from outside to inside the cell .The transport of any liquid substance from outside to inside the cell .

Receptor-mediated endocytosisReceptor-mediated endocytosis::The transport of substance from outside to inside the cell depending on integral The transport of substance from outside to inside the cell depending on integral proteins.proteins.

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Thank You Thank You

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