Dr Asma Jabeen Assistant professor

 Define active transport and describe its general mechanism.  Identify the types of active transport(primary and secondary) and contrast the differences in between.  Give examples for the substances using active transport as a method of transport  Compare and contrast passive diffusion, facilitated diffusion and active transport  Brief the mechanism of vesicular transport(exocytosis & endocytosis)

Active transport When a cell membrane moves molecules or ions “uphill” against a concentration gradient (or uphill against an electrical or pressure gradient), the process is called Active transport. Types:  Primary active transport  Secondary active transport

Substances that use active transport mechanism  Sodium ions  Potassium ions  Calcium ions  Iron ions  Hydrogen ions  Chloride ions  Iodide ions  Urate ions  Several sugars and amino acids

Role of Carrier proteins  In active transport, the transport depends on carrier Proteins that penetrate through the cell membrane  The carrier protein is capable of imparting energy to the transported substance to move it against the electrochemical gradient

Primary active transport The energy for the process is derived directly from the breakdown of adenosine triphosphate (ATP) or of some other high energy phosphate compound. Examples:  Na K pump  Primary active transport of Calcium  Primary active transport of Hydrogen ions

Sodium Potassium Pump

Carrier protein with 2 globular subunits: Alpha and beta  Alpha subunit (100,000 mol. Wt.) (larger) 1.Has 3 receptor sites for Na on inside 2.Has 2 receptor sites for K on outside 3.Inside portion has ATPase activity  Beta subunit ( 55,000 mol. Wt.) (smaller) Anchors the protein complex in the lipid membrane. Na-K pump…..General Characteristics

How the Na K pump works?  Binding of three sodium inside and two potassium outside activates ATPase function, cleaves ATP, splitting it to ADP and liberates high energy phosphate bond of energy.  The liberated energy then cause a chemical and conformational change in protein carrier molecule, extruding the three sodium out and two potassium to inside.

Reverse function of Na K Pump If the electrochemical gradients for Na and K are experimentally increased enough,,so that the energy stored in Their gradients is greater than chemical energy of ATP hydrolysis, ions will move down their conc gradient and ATP will be formed from ADP and phosphate.

Significance of sodium potassium pump  For some cells such as electrically active nerve cells, 60 to 70% of the cell’s energy requirement may be devoted to pumping sodium out of cell and K into the cell  This pump performs a continual surveillance role in maintaining normal cell volume

 By the movement of sodium and potassium ions, a net of one positive charge is moved from the Interior of the cell to the exterior for each pump cycle creating negativity on the inside. It is said to be Electrogenic because it creates an electrical potential across the cell membrane Significance of sodium potassium pump

Primary active transport of Calcium ions Calcium ions are normally maintained at extremely low Concentration in the cytosol of virtually all cells in the Body…about 10,000 times less than that in ECF. This is achieved by two primary pumps:  One is in cell membrane, pumps calcium to outside  Other one pumps calcium into one of the vesicular organelles such as SR of muscle, mitochondria of all cells  The carrier protein acts as an ATPase enzyme

Primary active transport of Hydrogen ions: At two places in the body, primary active transport Of hydrogen ions is important: 1.In the gastric glands of the stomach 2.In the late distal tubules and cortical collecting ducts of the kidneys

Energetics of Primary active transport The energy required is proportional to the logarithm of The degree that the substance is concentrated: Energy(in calories per osmole) = 1400 log C1/C2 The energy required to concentrate a substance 100 folds is twice as compared to concentrating a substance 10 times

Secondary Active Transport The concentration gradient developed due to diffusion of sodium is a storehouse of energy..This diffusion energy of sodium can pull other substances along with sodium through the cell membrane. Types of Active transport:  Co transport  Counter transport

Co- Transport  The carrier serves as an attachment point for both the Sodium ions and the substance to be transported.  Once attached, the energy gradient for sodium causes both the sodium ions and other substance be transported together to interior of cell  e.g. Co transport of glucose and amino acids along with sodium

Co- Transport

Counter transport The type of active transport in which the sodium ions move in one direction and other ions in the opposite direction  Sodium - hydrogen counter transport  Sodium – calcium counter transport

Counter Transport

Passive diffusion, facilitated diffusion & Active transport

Occurs down a concn. gradient No mediator or involves a “channel” or “carrier” No additional energy Occurs against a concn. gradient Involves a “carrier” Requires ENERGY

Vesicular Transport

Ingestion by the cell -Endocytosis Very large particles enter the cell by a specialized function Of the cell membrane called endocytosis.  Pinocytosis  Phagocytosis  Pinocytosis means ingestion of minute particles that form vesicles of extracellular fluid and particulate constituents inside the cell cytoplasm  Phagosytosis means ingestion of large particles, such as bacteria, whole cells or portions of degenerating tissue

Molecules attach to cell-surface receptors concentrated in clathrin- coated pits Receptor binding induces invagination Also ATP-dependent and involves recruitment of actin and myosin Receptor-mingestediated endocytosis: Figure 2-11 Ingestion by the cell -Endocytosis

Digestion of Substances in Pinocytotic or Phagocytic Vesicles Figure 2-12 Endocytosis

 Define active transport and describe its general mechanism.  Identify the types of active transport(primary and secondary) and contrast the differences in between.  Give examples for the substances using active transport as a method of transport  Compare and contrast passive diffusion, facilitated diffusion and active transport  Brief the mechanism of vesicular transport(exocytosis & Endocytosis)

Thank You