molecular_trafficking.pptx gggwywgwgwiwhfhn

For studying

1. Membrane transport Details: read the link: https://bio.libretexts.org/Bookshelves/Human_Biology/Human_Biology_(Wakim_and_Grewal)/05%3A_Cells/5.07%3A_Cell_Transport

2. Introduction The needs to take substances in and out depending on conditions: Proteins: hormones, enzymes, membrane receptors etc Non protein polymers: sugars, exopolysaccharides (EPS), PHA, NAs etc Lipids: lipoproteins, hormones, PGs PGX etc Drugs, metabolites and toxins: antibiotics, anticancer, etc Small molecules: Ions, amino acids, electrolytes Organisms: bacteria, fungi etc

3. Why take in or out? Metabolic needs: energy, excess substances etc Synthesis and biogenesis: membrane components Homeostasis: electrolytes, enzymes etc Communication with neighbors: adhesion, inflammation, biofilm formation etc Defense: pathogen recognition and processing

4. Membrane properties Semipermeabililty      only certain materials may freely cross  large and charged substances are typically blocked Selectivity Regulates what to pass Selected substances will pass. Relies on chemical and physical properties

5. Recap

6. Types of membrane transport

7. Passive transport Simple diffusion Only conc. gradient No need of another molecule eg ., ethanol and carbon dioxide Facilitated diffusion Need for a supporting molecule Protein channel carrier protein e.g. GLUT4 –facilitated Glu transport

8. Membrane channels Are integral lipoproteins with a pore through which ions may cross from one side of the membrane to the other Are selective to ions and may be gated Transport along the conc gradient e.g. potassium channels for facilitated diffusion in axons K+ channels are voltage gated Open and close depending on membrane potential gradient Channel Proteins

9. Active transport Molecules move against conc gradient Primary: ATP hydrolysis Secondary: Energy coupled to another molecule along its gradient Eg . Na+/K+ pump The pump hydrolyzes ATP and changes conformation Allowing the solute to translocate

10. Assignment Describe the steps in the Na + /K + pump

11. Basics of trafficking Endocytosis Exocytosis

12. The direct hydrolysis of ATP ( primary active transport ) By coupling with the transport of another molecule moving along its electrochemical gradient ( secondary active transport ) Co-transport

13. Plasma Membrane Vesicles containing materials destined for extracellular use will be transported to the plasma membrane The vesicle will fuse with the cell membrane and its materials will be expelled into the extracellular fluid Materials sorted by the Golgi apparatus may be either: Released immediately into the extracellular fluid (constitutive secretion) Stored within an intracellular vesicle for a delayed release in response to a cellular signal (regulatory secretion

14. Golgi Apparatus The vesicle is then transported to the Golgi apparatus and fuses to the internal ( cis ) face of the complex Materials move via vesicles from the internal  cis  face of the Golgi to the externally oriented  trans  face While within the Golgi apparatus, materials may be structurally modified (e.g. truncated, glycosylated, etc.) Material sorted within the Golgi apparatus will either be secreted externally or may be transported to the lysosome )

15. Endoplasmic Reticulum A membranous network responsible for synthesizing secretory substances RER is embedded with ribosomes and synthesizes proteins required for membrane or extracellular export SER functions:   lipid synthesis   carbohydrate metabolism To transport substances ER membrane bulges and buds to form a vesicle around the cargo Vesicular transport

16. Bulk transport Endocytosis Large substances enter the cell No crossing the membrane Membrane invaginates to form a tube-like depression to enclose the cargo Types: Phagocytosis Pinocytosis Exocytosis  The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis

17. Question: Write short notes on receptor-mediated endocytosis

18. Exocytosis Large substances or large quantities (bulk) of small substances exit the cell without crossing the membrane Vesicles fuse with the plasma membrane to expel their contents into the extracellular environment Exocytosis adds vesicular phospholipids to the cell membrane replacing those lost when vesicles are formed via endocytosis