Semester 1 BHLII Cell Membrane & Transport Across it Lec2 PDF

Level 1 Semester 1 Module (Basics of Health and Life II )  Cell membrane, Transport across it and Ion channels  INSTRUCTOR INFORMATION Name: Nihal abdelmoneim Mahmoud Department:Physiology Official e-mail:[email protected] TEL...

Level 1 Semester 1 Module (Basics of Health and Life II )  Cell membrane, Transport across it and Ion channels  INSTRUCTOR INFORMATION Name: Nihal abdelmoneim Mahmoud Department:Physiology Official e-mail:[email protected] TEL: 01001082249  ‫‪Mission and Vision of Faculty‬‬ ‫رسالة الكلية‪:‬‬ ‫تلتزم كلية الطب البشري – جامعة الدلتا للعلوم والتكنولوجيا بتقدیم برنامج تعليمي تكاملي متميز یقوم‬ ‫على المھـارة والمعرفـة ویھـدف الى تخریج أطبـاء قـادرین على الوفـاء بواجبـاتھم المھنيـة واألخالقيـة‪،‬‬ ‫والتعليم الطبي المستمر والمشاركة الفعالة في البحث العلمي وخدمة المجتمع‪.‬‬ ‫رؤیة الكلية‪:‬‬ ‫تسعى كلیة الطب البشري ‪ -‬جامعة الدلتا للعلوم والتكنولوجیا من خالل تطبیق برنامج التعلم القائم على‬ ‫اكتســاب الجدارات أن تكون في مقدمة المؤسسات الطبیة التعلیمیة المتمیزة على المستوى المحلي‬ ‫والقومى والعالمي‪.‬‬  Objectives At the end of this lecture students should: - Identify the physiological functions of the cell membrane (carbohydrate, lipid and protein). -List types of transport across the membrane. -Differentiate between simple diffusion, facilitated diffusion and osmosis. - Identify the different factors affecting the rate of diffusion - Differentiate between primary and secondary active transport. - Explain and give examples of endocytosis, phagocytosis, pinocytosis Identify the different types of transport carrier proteins. Case scenario A 13 -year-old male teenager presented to emergency department in May 2018. He complained of fainting once and had a mild cough for 3 days and low-grade fever (38.0C) prior to admission. He had history of frequent respiratory infections and no chronic diarrhea. He was a second-born to non-consanguineous healthy parents, born full term after an unremarkable pregnancy. His birth weight was 2.8 kg. No history of chronic pulmonary disease was found in his family. Case scenario On physical examination, he was undernourished with 30 kg body weight and 125 cm height. He had a BMI of 17.5, which was below the 3rd percentile for age. On auscultation, diffuse fine crackles were present throughout both lung fields. Heat and abdomen were normal. Laboratory examination showed white blood cells 13000 per microliter , reactive protein 11.33 mg/l, other tests including CBC, serum electrolytes, urine, and isolation of P. aeruginosa in sputum culture. Case scenario A Computed Tomography (CT) scan revealed right upper vesicles, bilateral bronchiectasis with obvious exudative lesions pulmonary fibrosis..Genetic testing revealed that the patient was a compound heterozygote of mutations: CFTR His symptoms improved after antibiotics and expectorant treatment. After being discharged from our hospital in May 2018. The patient was re- hospitalized nine times for pulmonary infections. He frequents respiratory infections, with isolation of P. aeruginosa and oral azithromycin prophylaxis.  The cell membrane -Very thin ,elastic ,semipermeable , dynamic -Composed of : 55%protein 42% lipids 25%phospholipids 13%cholesterol 4% other lipids 3% carbohydrates A- The cell membrane (Lipid bilayer) Phospolipid Bilayer: The phospholipid bilayer consists of two adjacent sheets of phospholipids, arranged tail to tail. -The hydrophobic tails associate with one another, forming the interior of the membrane. -The polar heads contact the fluid inside and outside of the cell.  Function of cell membrane lipids Functions: Lipids are responsible for the fluidity of the membrane. 1-Phospholipids Head(phosphate group, exterior, hydrophilic, charged) Tail(FFAs interior hydrophobic uncharged ) 2-Cholesterol Hydrophopic (embeded into phospholipid bilayer ) Give toughness to the membrane Function of cell membrane lipids The cell membrane proteins  The cell membrane proteins They are attached to or inserted within the lipid bilayer. They are two types: a- Integral proteins: that extent along the whole thickening of the cell membrane. b- Peripheral proteins: that attached to the surface of the membrane and don't penetrate it. Function of cell membrane proteins ‫هام‬ 1- These proteins link the cell membrane to the cytoskeleton in order to maintain the shape of the cell. 2- Channel: which enable the water soluble substances to pass through the membrane. These channels are highly selective. e.g. Na+ & K+ channels. 3- Carrier: The protein can change their shape to transfer Substances unable to cross the cell membrane on their own. 4- Receptors: present on the outer surface of the cell. Each receptor is specific for a certain molecule. 5- Enzymes: that controls the chemical reactions. 6- Pumps: that actively transport ions across the cell membrane, as Na+ - K+ pump. 7- Some proteins act as cell adhesion molecules to hold the cells together. Function of cell membrane carbohydrates It is present in combination with protein in the form of glycoprotein & lipids in the form of glycolipids Functions: 1- They attach cells to each other. 2- Act as receptor substances for binding hormones. 3- Some of them enter in the immune reactions and cell recognition Glycocalyx: It is glycoproteins, glycolipids and other carbohydrates attached to the cell membrane and extending from it.  Transport across the cell membrane There are three mechanisms of transport across the cell membrane: 1- Passive transport: 2- Active transport 3- Vesicular transport  Transport across the cell membrane There are three mechanisms of transport across the cell membrane: 1- Passive transport: Simple diffusion Facilitated diffusion 2- Active transport Primary active Secondary active 3- Vesicular transport Endocytosis Exocytosis Transport across the cell membrane  1-Passive transport (Diffusion) Simple diffusion. Facilitated diffusion. A-Simple diffusion: It is movement of the molecules across the cell membrane according to their concentration gradient. It doesn't need additional source of energy or carrier protein. 1-Passive transport (Diffusion) Pathways of Simple diffusion: 1- Diffusion through the lipid bilayer. (Lipid soluble substances → O2, CO2 , alcohol & nitrogen) 2- Diffusion through the protein channels. (Passage of ions extremely slow through the cell membrane) 3- Osmosis. (H2O transport) Types of protein channels: 1- Open (Leaky) channels: - They are open all the times. - e.g. Na+ & K+ leak channels which are important in resting membrane potential. 2- Gated channels: - These channels have gates which regulate the movement of ions through them. - They are classified according to the cause that open & close their gates into: a) Voltage- gated channels : e.g. Na+ & K+ voltage-gated Channels They open or close by alteration in membrane potential. They are important in action potential. b) Ligand-gated channels: e.g. acetylcholine They open or close by binding with a ligand.  3- Osmosis Definition: It is diffusion of water from lower solute concentration to higher solute concentration.  2-Facilitated diffusion It is movement of molecules across the cell membrane according to their concentration gradient - Passive & not need energy, but it needs carrier protein. - Carrier is needed to facilitate the transfer of molecules which cannot cross the cell membrane. As glucose & amino acids Mechanism: 1- The molecules attached to a binding site on the carrier protein on one side of the membrane. 2- The carrier changes its shape to be exposed to the other side of the membrane. 3- The molecules detaches from the carrier. Types of Carriers: 1- Uniports → they transport one substance only across the cell membrane. 2- Symports → transport two substances in the same direction. 3- Antiports → transport two substances in opposite direction. (they exchange one substance for another). e.g. Na+ - K+ pump is a typical antiport carrier Membrane Transport across the cell membranr  Factors Affecting the Rate of Diffusion 1- permeability of the membrane: The greater the permeability of the membrane, the more the rate of diffusion. Factors affecting the cell membrane permeability are: A) lipid solubility B) thickness of the membrane. C) number of protein channels. D) surface area of the membrane 2- temperature: The greater the temperature, the greater the thermal motion of molecules. 3- molecular weight of the difusing substances: Lighter molecules such as oxygen and carbon dioxide diffuse rapidly across the lung membrane. 4- Electrical gradient: Differences in charges between two adjacent areas produces an electrical gradient that passively induces movement of ions. 5- concentration gradient: The greater the difference in the concentration of the substance on both sides of the cell membrane , the greater the rate of its diffusion. 6- pressure difference: The greater the difference in pressure on both sides of the cell membrane, the greater the rate of diffusion of molecules from the high pressure side to the low pressure side. Summary  Active transport: It is movement of substances across the cell membrane Against the concentration gradient Carriers are involved. Needs additional source of energy Membrane Transport across the cell membrane  Types of Active transport: A- Primary active transport: Against the concentration gradient Carriers are involved. Needs additional source of energy comes directly from hydrolysis of ATP. e.g. Na+ & K+ ions.(Na+ ⁄ K+pump) Types of Carriers: Sodium-Potassium Antiport.  B- Secondary active transport When sodium ions are transported out of cells by primary active transport high sodium concentration outside the cell and low concentration inside.  B- Secondary active transport This gradient represents a storehouse of energy because the excess sodium outside the cell membrane is always attempting to diffuse to the interior. Under appropriate conditions, this diffusion energy of sodium can pull other substances along with the sodium through the cell membrane. Secondary active transport  Sub types of 2ndry active transport a) Co-transport: Na+ and substance transported move in the same direction. Examples: Glucose, galactose and amino acids co-transport with Na+ ions. (In GIT mucosa and renal tubule) Co-transport: b) Counter transport: Na+ and transported substance move in opposite directions. Examples: Na+/H+ exchange (H+ out and Na+ into cells). Na+/ Ca²ᶧ exchange (Ca²ᶧ out and Na+ into cells). b) Counter transport:  Vesicular transport Large particles can enter or leave the cell by this type of transport. Types: A- Endocytosis: - It is a process by which large particles can enter the cell. - It needs energy supplied by ATP. Endocytosis has two forms: 1- Pinocytosis (cell drinking): Definition: It means ingestion of small vesicles containing extracellular fluid and large molecules such as protein molecules. 2- Phagocytosis ( cell eating): Definition: It is a process by which large particles such as bacteria or dead tissue are engulfed by the cell. Mechanism: 1- the protein is attached to the cell membrane. 2- the membrane invaginates inward. 3- the edges of the membrane is closed over the attached protein or extracellular fluid. 4- the invaginated part breaks away from the surface of the cell forming a vesicle inside the cell. Phagocytosis occurs in the same way as pinocytosis except that it involve large particles B- Exocytosis (cell vomiting): - It is a process by which secretory products of the cell such as hormones can leave the cell. - It needs energy supplied by ATP. Mechanism: 1- the secretory vesicles moves to the cell membrane. 2- the membrane of the secretory vesicle fuses to the cell membrane. 3- the area of fusion break down. 4- leave the contents of the vesicles outside the cell and the cell membrane intact. Case Discussion/reflection A case of Cystic Fibrosis(CF) The symptoms of CF result from a malfunctioning membrane ion channel called the cystic fibrosis transmembrane conductance regulator(CFTR). The CFTR protein is an integral membrane protein that transports Cl– ions out of the cell. In a person who has CF, the gene for the CFTR is mutated, thus, the cell manufactures a defective channel protein that typically is not incorporated into the membrane, but is instead degraded by the cell Questions When two molecules are transported at a time in the same direction it is called as: A) Primary active transport B) Secondary active transport C) Co-transport D) Diffusion E)Osmosis Questions Which of the following methods of transport does not require energy or carrier protein? A. secondary active transport B. facilitated diffusion C. simple diffusion D. primary active transport E.Co-transport Questions Which of these statements about the fecilitated diffusion of glucose is true? A) The movement is from the region of lower to the region of higher concentration B) Carrier proteins are required C)Required energy obtained from ATP directly D) It is an example of Counter transport E)Occurs through protein channels Questions Which of the following statements is true about active transport: A) It occurs against both concentration and electrical gradient B) It doesnt require energy C) It doesnt require carrier protein D) Na+ ⁄ K+pump is an example for secondry active tranport E)Na+ ⁄ Glucose transport is an example for primary active tranport Questions Which of the following is charectristic for simple diffusion: A) It is an active process B) Occurs against both concentration and electrical gradient C) It requires protein channel for diffusion of ions D) Its rate is increased with increased molecular weight E)Its rate is decreased with increased surface area Questions Which of the following describes simple diffusion: A) It require energy derived from ATP B) It needs carrier proteins C) Ions diffuse though the lipid bilayer membrane directly D) Co2 and O2 diffuse through protein channel only E)Osomsis is a form of simple diffusion Questions Which of the following describes method of transport through which large particles can enter or leave the cell? A) Primary active transport B) Secondary active transport C) Vesicular transport D) Diffusion E)Osmosis Questions Which of the following factors increase the rate of diffusion across the cell membrane ? A) increase membrane thickness B) decrease surface area of the membrane C) increase molecular weight of the transported substance D) increase lipid solubility of the substance E) decrease temperature  SAQ Define Diffusion ?List 4 factors affecting rate of diffusion ? List 4 functions of membrane protein ? Define active transport ?list 2 types of active transport? List 2 subtypes of secondary active transport? Enumerate 3 types of carrier protein? References: 1.Textbook a) Textbook of Medical Physiology (Guyton & Hall) b) Fundamentals of Human Physiology (Lauralee Sherwood) 2. Internet