Lec 15, 16 Transport through the cell membrane 2 - 2020 PDF

Nashwa Aly Abd El-Mottaleb Transport through The cell membrane II Code: CBF-103 By Nashwa Aly Abd El-Mottaleb Professor of Medical Physiology Faculty of Medici...

Nashwa Aly Abd El-Mottaleb Transport through The cell membrane II Code: CBF-103 By Nashwa Aly Abd El-Mottaleb Professor of Medical Physiology Faculty of Medicine Assiut University Nashwa Aly Abd El-Mottaleb 1 Transport through The cell membrane II Learning Objectives: At the end of the lecture the students should be able to:  Describe the importance of active transport as primary active transport; and secondary active transport (co-transport and counter – transport) and give examples.  Define vesicular transport and its types.  Basic principles of transport across epithelial membrane Nashwa Aly Abd El-Mottaleb 2 1  Nashwa Aly Abd El-Mottaleb II- Active Transport Characters 1. use a protein carrier. 2. Occur against the concentration gradient (uphill) 3. It requires energy in the form of ATP. Active transport is divided into two types according to the source of the energy used to cause the transport: 1. Primary active transport 2. Secondary active transport Nashwa Aly Abd El-Mottaleb 3 1- Primary active transport The the carrier derived the energy directly from ATP. Examples of primary active transport: I- Na -K pump: Characteristics - three receptor sites for binding Na+ - Two receptor sites for K+ - Binding sites for ATPase activity (pump) near the sodium. - Present in all cell membranes. II- The Ca++ pump helps in muscle contraction. III- The H+ pump form HCl in the stomach and kidney 4 Nashwa Aly Abd El-Mottaleb 2  Nashwa Aly Abd El-Mottaleb Mechanism of Na+ - K+ pump: 5 Nashwa Aly Abd El-Mottaleb 2- Secondary active transport Characters: The energy required derived indirectly from the ion gradient. Mechanism 1- Na+ co-transport: Nashwa Aly Abd El-Mottaleb 6 3  Nashwa Aly Abd El-Mottaleb 2- Na+ counter-transport: 1. Na+-Ca++ counter-transport is very important for the contraction of cardiac muscles. 2. Na+-H+ counter-transport occurs in the kidney. Nashwa Aly Abd El-Mottaleb 7 Carrier types 1-Uniporters are carriers that transport a single particle in one direction, such as the facilitated diffusion of glucose. 2- Symporters transport two particles in the same direction, such as the Na+ co- transport of glucose and amino acid. 3-Antiporters transport molecules in opposite direction, such as the Na+-Ca++ and Na+-H+ exchangers. 8 Nashwa Aly Abd El-Mottaleb 4  Nashwa Aly Abd El-Mottaleb Vesicular Transport or Bulk Transport Large particle as protein hormones and bacteria are transported by vesicular transport Endocytosis: transport into the cell. Exocytosis: transport out of the cell. Endocytosis I-Pinocytosis: The vesicles traps some of the extracellular fluid. The process is also known as “cell drinking”. II- Receptor-mediated endocytosis: 1. It is a highly selective process. 2. It is triggered by the binding of a specific molecule to a surface membrane receptor specific for that molecule. III-Phagocytosis It means engulf of large molecules such as food and bacteria into vesicles and called “cell eating”. Nashwa Aly Abd El-Mottaleb 9 by dynamin 10 Nashwa Aly Abd El-Mottaleb 5  Nashwa Aly Abd El-Mottaleb Exocytosis 1. Almost the reverse of endocytosis occurs. It is an active process (requiring energy and Ca++). - The membrane of the vesicle fuses with the plasma membrane. - Then, the area of fusion breaks down, the vesicle opens up and release its contents to extracellular space. Nashwa Aly Abd El-Mottaleb 11 Transport Across Epithelial membrane Transcellular Transport : transport through the cytoplasm of the epithelial cells. Paracellular transport means transport through the spaces between epithelial cells. It is limited by the junctional complexes that consist of three structures: 1- Tight junction (impermeable junction). 2- Gap junctions (communicating junction). 1. Desmosomes (adhering junction). 12 Nashwa Aly Abd El-Mottaleb 6  Nashwa Aly Abd El-Mottaleb 13 Nashwa Aly Abd El-Mottaleb 7