Lec3 Membrane Structure & Function 2 PDF

Cell Structure and Function II Prepared by: Dr. Omar Abdullah Bamaga Associate. Prof. of medical parasitology 1  What is the cytoskeleton Definition: a microscopic network of protein filaments and tubules in the cytoplasm Consist from 3 type...

Cell Structure and Function II Prepared by: Dr. Omar Abdullah Bamaga Associate. Prof. of medical parasitology 1  What is the cytoskeleton Definition: a microscopic network of protein filaments and tubules in the cytoplasm Consist from 3 types of filaments (elongated chain of protein): (a) Microfilaments (b) Microtubules (c) Intermediate filaments 2 2  Cytoskeleton 3 Functions of the cytoskeleton: 1) Supports the cell 2) Gives a cell its shape 3) Facilitates movement.  Has roles in molecule transport and cell division 3 3  a) Microfilaments  Called Actin filaments because they are mostly composed of the protein actin  Functions: 1. Aid in cytokinesis(cytoplasm division) 2. Aid in cell Motility 3. Involved in cytoplasmic streaming 4. Involved in muscle contractions 5. Maintenance of cell shape 4 4  b) Microtubules  Functions: 1) Involved in chromosome division 2) Involved in transporting molecules within the cell 3) Maintenance of cell shape 4) Involved in cell motility 5 5  Cilia & Flagella  Flagella, which are “tails” that propel a cell forward  Cilia, which are appendages that allow the cell to move 6 6  c) Intermediate Filaments  Called intermediate because they are in-between the size (8- 10 nm) of microfilaments (25 nm) and microtubules (7 nm)  Made of different proteins such as keratin (found in hair and nails, and also in animals with scales, horns, or hooves), vimentin, desmin, and lamin.  Function: 1) maintain the cell’s shape 2) play some structural or tension-bearing role 3) Provide structural support to the cell 7 7  Cell Membrane  Also known as Plasma Membrane, Contains cell organelles  Structure – Phospholipids form the basic structure of a cell membrane, called the lipid bilayer with embedded proteins  Five functions: 1) Protects the cell by acting as a barrier. 2) Regulates the transport of substances in and out of the cell. 3) Receives chemical messengers from other cell. 4) Acts as a receptor. 5) Cell mobility, secretions, and absorptions of substances. 8 8  Structure of cell membrane 1. Channels or transporters: 4. Enzymes Move molecules in one direction Catalyze production 2. Receptors of substances Recognize certain chemicals 5- Glycoproteins 3. Cholesterol molecules: Identify cell type keep the membrane fluid consistent 9 9  Structure of cell membrane / Phospholipids  Hydrophilic (head): having an affinity for water forming ionic or a hydrogen bond with the water molecule  Hydrophobic (tail): (water-hating) because they bind poorly to water molecules  Interacts with water is important for the evolution of life. 10 10 10  Movement Across the Plasma Membrane A few molecules move through cell membrane such as: Water, Carbon dioxide, Ammonia, Oxygen 11 11 Methods of Molecule Movement into Cells 1. Passive Transport 2. Active Transport 3. Endocytosis (phagocytosis & pinocytosis) 4. Exocytosis 12 12 1. Passive Transport moves biochemicals from areas of high concentration to areas of low concentration; so it does not require energy Move due to gradient: differences in concentration, pressure, charge Move to equalize gradient: moves from High to low concentration 13 13 1. Passive Transport (cont.) They are 3 kinds of passive transport : 1. Diffusion 2.facilitated diffusion 3. Osmosis 14 14 14  1.1. Diffusion The movement of molecules from a high concentration to a low concentration (equalize concentration) 15 15  Diffusion is the movement of small particles across a selectively permeable membrane like the cell membrane until equilibrium is reached. These particles move from an area of high concentration to an area of low concentration. This process is “passive” – i.e. it requires no energy; the gradient is enough to drive the process outside of cell inside of cell 16 16  Diffusion of H2O Across A Membrane High H2O potential Low H2O potential 17 17  2. Facilitated Diffusion is the process of spontaneous passive transport of molecules or ions across a biological membrane via specific transmembrane integral proteins Does not require energy but does require cell membrane proteins which are called carrier proteins to carry the molecules across the cell membrane from high to low concentration area Simple diffusion vs facilitated diffusion Simple diffusion is the movement of molecules through a cell membrane without using the channels formed by integral membrane protein. Facilitated diffusion is the movement of molecules through those channels 18 18  Facilitated Diffusion is the movement of larger molecules like glucose through the cell membrane – larger molecules must be “helped” Glucose molecules outside of cell inside of cell 19 19  3. Osmosis The movement of water across a semi permeable membrane Osmosis is the movement of water (blue dots) through a semipermeable membrane to a higher concentration of solutes (green dots). Semi-permeable membrane is permeable to water only, but not to sugar Low saturated –high saturated 20 20  Osmosis vs diffusion: Osmosis is the movement of solvent particles (water molecules) across a semipermeable membrane from a dilute solution into a concentrated solution.... Diffusion: Diffusion is the movement of particles (such as oxygen in and out cell) from an area of higher concentration to lower concentration. The overall effect is to equalize concentration throughout the medium. 21  How do hypotonic, hypertonic, and isotonic Solutions Affect the Water Movement of a Cell?  Hypotonic: Low conc of solute lower than cell. the water diffuses into the cell, causing the cell to swell and possibly explode.  Hypertonic: High conc of solute greater than cell. Water diffuses out of the cell, causing the cell to shrivel up out of cell Isotonic : Solutes equal inside & out of cell 22 22  Cell in Isotonic Solution Isotonic Solutions: contain the same concentration of solute What is the direction of water movement? When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic. 10% NaCL ENVIRONMENT 90% H2O CELL equilibrium 10% NaCL 90% H2O NO NET MOVEMENT23 23  Cell in Hypotonic Solution What is the direction of water movement? Hypotonic Solutions: contain a low concentration of solute relative to another solution. When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode 10% NaCL 90% H2O CELL 20% NaCL 80% H2O 24 24  Cell in Hypertonic Solution What is the direction of water movement? Hypertonic Solutions: contain a high concentration of solute relative to another solution. When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel. 15% NaCL ENVIRONMENT 85% H2O 5% NaCL 95% H2O CELL 25 25  2. Active Transport  Active transport requires chemical energy because it is the movement of biochemicals from areas of lower concentration to areas of higher concentration  Active Transport creates a charge gradient in the cell membrane.  Active transport uses energy to send substances against the direction they would travel by simple diffusion 26 26  2. Active Transport (cont.) Proteins that work as pumps are called protein pumps. Ex: Body cells must pump carbon dioxide out into the surrounding blood vessels to be carried to the lungs for exhale. Blood vessels are high in carbon dioxide compared to the cells, so energy is required to move the carbon dioxide across the cell membrane from LOW to HIGH concentration. outside of cell Carbon Dioxide molecules inside of cell 27 27  3. Endocytosis Movement of large material into cells – Particles – Organisms – Large molecules Types of endocytosis – bulk-phase (nonspecific) – receptor-mediated (specific): by using phagocytosis and pinocytosis process 28 28 Receptor-Mediated Endocytosis Phagocytosis – cell eating Pinocytosis – cell drinking 29 29 Pinocytosis Cell forms an invagination materials dissolve in water to be brought into cell called “Cell Drinking” 30 30 30  4. Exocytosis Reverse of endocytosis Cell discharges material Vesicle moves to cell surface Membrane of vesicle fuses Materials expelled 31 31  Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane. Inside Cell Cell environment 31 32  Endocytosis and Exocytosis is the mechanism by which very large molecules (such as food and wastes) get into and out of the cell Food is moved into the cell by Endocytosis Wastes are moved out of the cell by Exocytosis 32 33 Second assignment: Q1: What is the difference between prokaryotic and eukaryotic cell in the following: Structure Chromosomes Cell wall Q2: Mention the organelles that is responsible for: 1-indigestion and waste removal 2- synthesis of lipid 3- synthesis of protein 4- produce energy 34 34  35 35 Dr. Omar Bamaga