Week 11 PHA112 Lecture Cellular Process 2023-24 Student Handout PDF

WEEKS 11 MPharm Programme Cell Science - Cellular Process 1 & 2 Dr Praveen Bhugra PHA112 Slide 1 of 43 PHA112 Reproductive System Learning Objectives WEEKS 11 • From this lecture you should be able to: – Understand and explain in detail the different transport processes into and out of cel...

WEEKS 11 MPharm Programme Cell Science - Cellular Process 1 & 2 Dr Praveen Bhugra PHA112 Slide 1 of 43 PHA112 Reproductive System Learning Objectives WEEKS 11 • From this lecture you should be able to: – Understand and explain in detail the different transport processes into and out of cells (Passive Process; Active Process; Transport in Vesicles) – Understand and explain how substances are transported across membranes – Understand, explain and give examples of the different transport processes and how they apply to the functioning of cells and the body including nervous system and neurotransmission Slide 2 of 43 PHA112 Reproductive System WEEKS 11 Terminology: Body Fluid Pools • Intracellular (ICF) – Within cells: 2/3 of total • Extracellular (ECF): – Between cells = Interstitial – In blood vessels = Plasma – In lymphatic vessels = Lymphatic fluid ( Lymph) – Within the brain and spinal cord - cerebrospinal fluid Slide 3 of 43 PHA112 Reproductive System WEEKS 11 Terminology: Solutions • Solvent: the liquid doing the dissolving – Usually water • Solute: the dissolved material (particles or gas) • Concentration – Amount of solute in a given amount of solvent • Concentration gradient – Difference in concentration between 2 areas of solution Slide 4 of 43 PHA112 Reproductive System WEEKS 11 Molecule movement across membranes (Gradients Across the Plasma Membrane ) • Selective permeability : allows a living cell to maintain different concentrations of certain substances on either side of the plasma membrane. • Concentration gradient :difference in the concentration of a chemical from one place to another (from the inside to the outside of the plasma membrane). • Difference in electrical charges between two regions constitutes an electrical gradient. Slide 5 of 43 PHA112 Reproductive System WEEKS 11 Molecule movement across membranes (Gradients Across the Plasma Membrane) • Electrical gradient occurs across the plasma membrane, this charge difference is termed the membrane potential. • The concentration gradient and electrical gradient are important because they help move substances across the plasma membrane. • The combined influence of the concentration gradient and the electrical gradient on movement of a particular ion is referred to as its electrochemical gradient. Slide 6 of 43 PHA112 Reproductive System WEEKS 11 Molecule movement across membranes • Passive Transport ( Passive Processes) • Active Transport (Active Processes) • Endocytosis – Phagocytosis – Fluid endocytosis (pinocytosis) – Receptor – mediated endocytosis • Exocytosis Slide 7 of 43 PHA112 Reproductive System WEEKS Types of Passive Transport 11 • Simple diffusion • Facilitated diffusion • Osmosis Slide 8 of 43 PHA112 Reproductive System The Principle of Diffusion WEEKS 11 • Diffusion is a passive process in the random mixing of particles in a solution occurs because of the particles' kinetic energy. • Both the solutes, the dissolved substances, and the solvent, the liquid that does the dissolving, undergoing diffusion. Slide 9 of 43 PHA112 Reproductive System Factors Influencing Diffusion WEEKS 11 • Steepness of the concentration gradient: Difference in concentration between the two sides of the membrane, the higher the rate of diffusion • Temperature : Higher temperature, the faster the rate of diffusion • Mass of the diffusing substance: Larger the mass of the diffusing particle, the slower its diffusion rate • Surface area: Larger the membrane surface area available for diffusion, the faster the diffusion rate • Diffusion distance: Greater the distance over which diffusion must occur, the longer it takes Slide 10 of 43 PHA112 Reproductive System WEEKS Simple Diffusion 11 • No energy required • Move due to gradient – differences in concentration, pressure, charge • Move to equalize gradient – High moves toward low • Depends on Lipid solubility Slide 11 of 43 PHA112 Reproductive System WEEKS 11 Slide 12 of 43 Simple Diffusion PHA112 Reproductive System WEEKS Facilitated Diffusion 11 • Solutes too polar or highly charged to move through the lipid bilayer by simple diffusion; cross the plasma membrane by a passive process called facilitated diffusion. • Requires a carrier in membrane but not ATP • Solute goes down concentration gradient • Facilitated Diffusion through – Ion Channels – Protein transporters (also called carriers) Slide 13 of 43 PHA112 Reproductive System WEEKS Facilitated Diffusion (Ion Channel) 11 • Ion channels, integral transmembrane proteins that allow passage of small, inorganic ions that are too hydrophilic to penetrate the nonpolar interior of the lipid bilayer. • Ions such as Na+, K+, Cl–, and Ca++ all use specific protein channels to diffuse into and out of cells • Channel is gated when part of the channel protein acts as a "plug" or "gate," changing shape in one way to open the pore and in another way to close it • Types of Gated channels : – Ligand gated – Voltage gated – Mechanically gated Slide 14 of 43 • PHA112 Reproductive System WEEKS Facilitated Diffusion (Ion Channel) 11 • Channel-mediated facilitated diffusion of potassium ions (K+) through a gated K+ channel. Slide 15 of 43 PHA112 Reproductive System WEEKS Facilitated Diffusion (Carriers ) 11 • A carrier (also called a transporter) is used to move a solute down its concentration gradient across the plasma membrane • Solute binds more often to the carrier on the side of the membrane with a higher concentration of solute • Carriers are occupied, the transport maximum is reached, the process of carrier-mediated facilitated diffusion exhibits saturation • Substances that move across the plasma membrane by carrier mediated facilitated diffusion include glucose, fructose, galactose and some vitamins Slide 16 of 43 PHA112 Reproductive System WEEKS Facilitated Diffusion (Carriers ) 11 • Glucose enters many body cells by diffusion as follows : 1. Binds to specific carrier protein - Glucose transporter on the outside of the cell surface 2. Transporter undergoes a change in shape , glucose passes the membrane 3. Transporter releases glucose on the other side of the membrane Slide 17 of 43 PHA112 Reproductive System WEEKS Osmosis 11 • Special form of diffusion • Diffusion of water through a semi-permeable membrane • Permeable to solvent • Impermeable to solute • During osmosis, water molecules pass through a plasma membrane in two ways: 1. By moving through the lipid bilayer via simple diffusion, as previously described 2. By moving through aquaporins , integral membrane proteins that function as water channels. Slide 18 of 43 PHA112 Reproductive System WEEKS Osmosis 11 Slide 19 of 43 PHA112 Reproductive System WEEKS 11 Osmolarity • The total solute concentration of a solution is known as its osmolarity. • One osmol is equal to 1 mol of solute particles. • So a 1 M solution of glucose has a concentration of 1 Osm (1 osmol per liter), whereas a 1 M solution of sodium chloride contains 2 osmol of solute per liter of solution. • A liter of solution containing 1 mol of glucose and 1 mol of sodium chloride has an osmolarity of 3 Osm. • Although osmolarity refers to the concentration of solute particles, it also determines the water concentration in the solution because the higher the osmolarity, the lower the water concentration. Slide 20 of 43 PHA112 Reproductive System Tonicity WEEKS 11 The ability of a solution to change the shape or tone of cells by altering their internal water volume is called tonicity . Figure: The effect of solutions of varying tonicities on living red blood cells Slide 21 of 43 PHA112 Reproductive System Active Transport WEEKS 11 • Uses energy to move molecules against the concentration gradient. • These transporters are often called “pumps”. • These pumps can also be saturated and use two types of energy sources: (1) The direct use of ATP in primary active transport (2) The use of an electrochemical gradient across a membrane to drive the process in secondary active transport Slide 22 of 43 PHA112 Reproductive System WEEKS Primary Active Transport 11 • The Na+/K+-ATPase primary active transporter is found in every cell and helps establish and maintain the membrane potential of the cell. • In addition to the Na+/K+-ATPase transporter, the major primary active-transport proteins found in most cells are: (1) Ca2+- ATPase (2) H+- ATPase (3) H+/K+ -ATPase Slide 23 of 43 PHA112 Reproductive System Primary Active Transport WEEKS 11 1. Cytoplasmic Na+ binds to pump protein. 6.K+ is released from the pump protein and Na+ sites are ready to bind Na+ again. The cycle repeats. Slide 24 of 43 2.Binding of Na+ promotes phosphorylation of the protein by ATP. 5.K+ binding triggers release of the phosphate. Pump protein returns to its original conformation. PHA112 Reproductive System 3.Phosphorylation causes the protein to change shape, expelling Na+ to the outside 4.Extracellular K+ binds to pump protein. WEEKS Secondary Active Transport 11 • Secondary active transport is distinguished from primary active transport by its use of an electrochemical gradient across a plasma membrane as its energy source. • Transporters that mediate secondary active transport have two binding sites, one for an ion (e.g., Na+)and another for the cotransported molecule (e.g., Glucose). • Co-transporters (symporters) move molecules in the same direction. • Counter-transporters (antiporters) move molecules in opposite directions Slide 25 of 43 PHA112 Reproductive System WEEKS 11 Slide 26 of 43 PHA112 Reproductive System WEEKS Vesicular Transport 11 • Endocytosis involves the movement of macromolecules into the cell by the pinching of the plasma membrane into membrane bound vesicles • Exocytosis involve the movement of macromolecules out of the cell by the fusion of membrane bound vesicles to the plasma membrane Slide 27 of 43 PHA112 Reproductive System WEEKS 11 Vesicular Transport - Endocytosis • Packaging of extracellular materials in vesicles at the cell surface • Involves relatively large volumes of extracellular material • Requires energy in the form of ATP. • Three major types 1.Receptor-mediated endocytosis 2.Pinocytosis 3.Phagocytosis Slide 28 of 43 MPharm PHA112 Reproductive System WEEKS 11 Receptor Mediated Endocytosis • A highly selective process • A vesicle forms after a receptor protein in the plasma membrane recognizes and binds to a particular particle in the extracellular fluid. • Examples: cells take up cholesterol-containing low-density lipoproteins (LDLs), transferrin (an iron-transporting protein in the blood), some vitamins, antibodies, and certain hormones • Involves formation of vesicles at surface of membrane • Clathrin-coated vesicle in cytoplasm Slide 29 of 43 MPharm PHA112 Reproductive System WEEKS 11 Receptor mediated endocytosis 1. 2. 3. 4. 5. Binding Vesicle formation Un-coating Fusion with endosome Recycling of receptors to plasma membrane 6. Degradation in lysosomes Slide 30 of 43 MPharm PHA112 Reproductive System WEEKS Pinocytosis 11 • Plasma membrane forms an invagination, sinks inward, pinches off and forms a vesicle • Materials dissolve in water to be brought into cell • Called “cell drinking” • The most common form of endocytosis in most cells, especially absorptive cells in the intestines and kidneys • Most proteins and other large molecules are taken up this way Slide 31 of 43 MPharm PHA112 Reproductive System WEEKS Phagocytosis 11 • Used to engulf large, solid particles such as food, bacteria, etc. into vesicles • Cell eating • A few body cells, termed phagocytes, are able to carry out phagocytosis • Vital defence mechanism that helps protect the body from disease. Slide 32 of 43 MPharm PHA112 Reproductive System WEEKS Exocytosis 11 • Movement of molecules out of the cell via vesicles. • Exocytosis performs several functions for cells: 1. Provides a way to replace portions of the plasma membrane that endocytosis has removed 2. Adds new membrane components to the membrane 3. Provides a route by which membraneimpermeable molecules (such as protein hormones) the cell synthesizes can be secreted into the extracellular fluid Slide 33 of 43 MPharm PHA112 Reproductive System Exocytosis (Process) WEEKS 11 1. The membrane-bound vesicle migrates to the plasma membrane 4. Vesicle contents are released to the cell exterior Slide 34 of 43 MPharm PHA112 2. There, proteins at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins). 3. The vesicle and plasma membrane fuse and a pore opens up. Reproductive System WEEKS 11 Exocytosis Exocytic vesicle immediately after fusion with plasma membrane. Slide 35 of 43 MPharm PHA112 Reproductive System WEEKS Exocytosis 11 • Cytoplasmic vesicle merges with the plasma membrane and releases its contents • Requires energy (ATP) and Ca2+ ions • Example: – Golgi body vesicles merge with the plasma membrane and release their contents – Nerve cells release neurotransmitters e.g. acetylcholine (ACh), noradrenaline (NA) etc. are stored in vesicles – Hormones are released e.g. insulin from storage vesicles in β-cells of pancreas Slide 36 of 43 MPharm PHA112 Reproductive System WEEKS 11 Exocytosis and Nervous System Function • A nerve cell communicates to another cell by releasing chemicals via exocytosis at the synaptic terminal Slide 37 of 43 MPharm PHA112 Reproductive System WEEKS 11 Exocytosis and Nervous System Function Slide 38 of 43 MPharm PHA112 Reproductive System WEEKS 11 Exocytosis in Presynaptic Neuron Slide 39 of 43 MPharm PHA112 Reproductive System WEEKS 11 Process of neurotransmission Slide 40 of 43 MPharm PHA112 Reproductive System WEEKS Transcytosis 11 • Used to successively to move a substance into, across, and out of a cell. • Active process • Vesicles undergo endocytosis on one side of a cell, move across the cell, and then undergo exocytosis on the opposite side. • Occurs most often across the endothelial cells that line blood vessels and when a woman is pregnant, some of her antibodies cross the placenta into the foetal circulation via transcytosis vesicle merges with the plasma membrane and releases its contents Slide 41 of 43 MPharm PHA112 Reproductive System WEEKS 11 Summary of Transport Processes Slide 42 of 43 MPharm PHA112 Reproductive System WEEKS 11 Further Reading Refer to the Following Textbooks • Ross and Wilson Anatomy and Physiology in Health and illness 13th Edition • Gerard J. Tortora and Byran H. Derrickson Principles of Anatomy and Physiology 13th Edition • Frederic H. Martini Fundamentals of Anatomy & Physiology 7th Edition • Lauralee Sherwood Human Physiology from cells to systems 7th Edition • Walter F. Boron and Emile L. Boulpaep Medical Physiology 3th Edition Slide 43 of 43 PHA112 Reproductive System