MOVEMENT OF IONS OR MOLECULES UPHILL AGAINST CONCENTRATION GRADIENT

S0metimes a large concentration of a substance is required in intracellular fluid even though ECF contains only small cocentratione.g. potassium ionsSimilarly sodium ions are in high concentration outside the cellSometimes sodium has to be transported outside the cell although its concentration is very less inside the cell

Some energy source must be there to transport excess amount of sodium to outside the cell & potassium inside the cellThis source of energy imparts energy to transporting molecule to move it against concentration gradient

TYPES:Primary active transportSecondary active transport

a)PRIMARY ACTIVE TRANSPORT:Energy derived from breakdown of ATPb)SECONDARY ACTIVE TRANSPORT:Energy derived secondarily from energy storedIn both,transport depends upon carrier proteins

PRIMARY ACTIVE TRANSPORTSODIUM POTASSIUM PUMPTransport process that pumps sodium ions outwards the cell & potassium ions inside the cellMaintains concentration difference of ions across the membraneEstablishes negative electrical voltage inside the cellBasis of nerve function transmitting nerve signals

Carrier protein is a complex of two separate globular proteinsAlpha subunit larger one beta subunit smaller oneAlpha subunit has:3 receptor sites for sodium binding2 receptor sites for potassium bindingInside portion ATPase activity

2 potassium ions bind to outside3 sodium ions bind to insideATPase activatedCleaves ATP into ADP +ENERGYLiberated energy confirmational change in carrier protein moves sodium to outside & potassium to inside

CONTROLS CELL VOLUME:Without this pump cells will swellInside cell large number of proteins & organic molecules most are negatively chargedIf no pump attract positive ions osmosis of water- cell gets swell

ELECTROGENIC NATURE:3 sodium to outside 2 potassium to insideCauses slight negativity inside the cellCreates an electrical potential

PRIMARY ACTIVE TRANSPORT OF Ca-IONS:Calcium pump to maintain concentration of calcium ionsMaintained at extremely low conc. Inside cellOne pump at cell membraneOther at membranes of intracellular orgenelles

PRIMARY ACTIVE TRANSPORT OF HYDROGEN IONS:At two placesGastric glands in stomachParietal cells hydrogen pump secretes hydrogen ions along with chloride in stomachIn distal renal tubules are intercalated cells cells have hydrogen pump secrete hydrogen ions in urine

SECONDARY ACTIVE TRANSPORTWhen sodium ions transported outside of cell by primary active transport,a large concentration gradient across cell membrane developsHigh concentration outside & low concentration inside the cellThis gradient represents a store house of energy

Diffusion energy pulls some other ions along with sodium ionsThis phenomenon is called co-transportOne form of secendory active transportOther form is counter transport

For sodium to pull other ion/substance along with it,coupling mechanism is requiredThat is achieved by a carrier proteinThat provides an attachment point for both sodium & other substance

In co-transport,sodium ions move to interior of cell & other substance attached also moves to insideIn counter transport,sodium ions move to inside of cell but other substance attached moves to outside of cellOnce both have bound ,confirmational change occurs and movement of ion/substances occur

EXAMPLESCO-TRANSPORT OF GLUCOSE & AMINO ACIDS WITH SODIUM IONS:Glucose & amino acids usually transported against large concentration gradientMechanism is co-transportTransport carrier protein has two binding sites on exterior side,one for sodium one for glucose

Property of carrier protein is that confirmational change will not occur untill both substances attechedWhen both attached ,confirmational change occurs and sodium and glucose both move insideSo sodium glucose co-transport mechanism occurs

Sodium co-transport for amino acids also occurs in same manner5 types of amino acid transport proteins to be knownCo transport of glucose & amino acids occurs specially through epithelial cells of GIT & renal tubules of kidneys to promote absorption of these substances

SODIUM COUNTER TRANSPORT OF CALCIUM & HYDROGEN IONS:Sodium-calcium counter transport occurs through all cell membranes with sodium moving to interior & calcium to outside bounded to same carrier protein

Sodium-hydrogen counter transport occurs in several tissuesProximal tubules of kidneysWhere sodium moves from lumen to inside the cell & hydrogen moves to lumen from the cell

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