Biophysics for Dentistry (PHY113) Lecture Notes Fall 2024/2025 PDF

Biophysics for Dentistry ( PHY113 ) Fall 2024/2025 Lecture 2 Prof. Radwa Hassan Abou-Saleh [email protected]  PHY113--Lec 1 About The Course Course content...

Biophysics for Dentistry ( PHY113 ) Fall 2024/2025 Lecture 2 Prof. Radwa Hassan Abou-Saleh [email protected]  PHY113--Lec 1 About The Course Course content No. of weeks 1. Introduction 2. Cell Structure 3. Cell Dynamics 15 weeks 4. Transport across cell membrane. (Passive) 5. Transport across cell membrane. (Active) 6. Membrane potential. 7. Nernest potential 8. Electrochemical driving force of ions across cell membrane 9. Action potential 10.Neurons and signal transmission 11.Mechanism of muscle contraction 12.Electromyogram 13.Electrocardiogram 2  PHY113--Lec 2 Eucaryotic cells Structure: 1.Nucleus 2.Mitochondria 3.Organelles 4.Cytoplasm 5.Plasma membrane 3  PHY113--Lec 2 Eucaryotic cells Nucleus The nucleus is the most distinguished organelle in eukaryotic cells It is enclosed within a nuclear envelope. Mitochondria One of the prominent organelles in all eukaryotic cells Generate most of the chemical energy needed by the cell and store it in the form of ATP Individual mitochondria are found to be enclosed in two separate membranes, with the inner membrane formed into folds that project into the interior of the organelle 4  PHY113--Lec 2 Eucaryotic cells Organelles Lysosomes: Membrane bounded organelle Destruction of unwanted or excess cell parts Ribosomes: Tiny particles responsible for synthesis of proteins Endoplasmic Reticulum: (ER) Continuous series of flattened sacs, found in all eukaryotic cells. Rough ER Smooth ER 5  PHY113--Lec 2 Eucaryotic cells Cell membrane Function: Protective barrier Contain the cytoplasm Selective permeability: Regulate in and out transport Allows cell recognition Provide anchoring sites for filaments Provide binding sites for enzymes 6  PHY113--Lec 2 Eucaryotic cells Cell membrane Glycocalix (40nm) Plasma membrane (4nm) Actin cortex (400nm) The cell membrane is composed of 3 layers: Glycocalix: facing the extracellular space. formed by the head groups of cell adhesion molecules (CAMs), receptors binding polysaccharides (PSs) of the extracellular matrix, and glycolipids (GLs). Plasma membrane: Central lipid-protein bilayer. Basic components are; phospholipids, cholesterol and proteins. Actin cortex: The actin filaments (diameters ~8 nm) are thicker than the lipid-protein bilayer (~5 nm) (i.e. not shown to scale). 7  PHY113--Lec 2 Eucaryotic cells Cytoplasm Viscous fluid containing organelles Components of cytoplasm Cytoskeleton: Interconnected filaments & fibers Cytosol: The fluid surrounding the organelles Organelles Storage substances 8  PHY113--Lec 2 Cytoskeleton Nuclei – blue, MTs – green, Actin - red Cytoskeleton is the system of protein filaments that are usually observed anchored to the plasma membrane Provides the main structural and mechanical support for the cell and the cytoplasmic components. It also control the motion of cells, cell division and act as monorail for the transport of organelles and materials. 20 um 9  PHY113--Lec 2 Cytoskeleton The cytoskeleton consists of three major biopolymer component (filament types), made of protein polymers: 10  PHY113--Lec 2 Cytoskeleton The cytoskeleton consists of three major biopolymer component (filament types), made of protein polymers: A: Microtubules: Diameter is ~25 nm outer, and 15nm inner. Made of tubulin protein. Straw shaped B: Intermediate filaments: ~ 10 nm diameter. made of a number of different subunit proteins. C: Actin filaments: ~7 nm diameter. made of actin protein. 11  PHY113--Lec 2 Cytoskeleton A: Microtubules polymerisation: Nucleation Elongation Dynamic instability process: a process that respond to the cell needs. Energy is imparted to the tubulin subunits. Part of this energy is stored in MTs in the form of stacking energy which, when a critical amount is exceeded, can be released in the form of an earthquake-like collapse of the entire MT structure. Another part of the energy is stored to increase flexability, Elastic energy 12  PHY113--Lec 2 Cytoskeleton A: Intermediate Filaments: ▪ Generally, rope like, strong filaments. ▪ Some cells have multiple types of intermediate filaments, and some intermediate filaments are associated with specific cell types. For example, neuro-filaments are found specifically in neurons. Function: 1.They are less dynamic than the other 2 types, they are primarily mechanical. 2.Intermediate filaments commonly work in tandem with microtubules, providing strength and support for the fragile tubulin structures. 3.Keeps organelles (nucleus) in position, guide organelles 13  PHY113--Lec 2 Cytoskeleton A: Actin Filaments: Function: networks of actin filaments are found beneath the cell cortex, which is the meshwork of membrane-associated proteins that supports and strengthens the plasma membrane. These networks allow cells to hold and move and support variety of specialized shapes. Actin filaments are involved in cytokinesis and cell movement Actin filaments can associate with myosin for muscle contractions 14  PHY113--Lec 2 Cytoskeleton Dynamic instability: a process that respond to the cell needs. Actin filament is the most active type with the highest rate of dynamic instability Actin polymerisation: https://youtu.be/VVgXDW_8O4U 15  PHY113--Lec 2 Cytoskeleton A: Actin Filaments: Neurons are specialized eukaryotic cells that extend long processes to form connections in the nervous system. 20µm The axon is a long membrane-bounded extension: Neurofilaments (class of intermediate filament) form a structural matrix that embeds microtubules. Microtubules transport materials from the cell body to the axon terminals at the synapse. The growth cone contains dendritic actin filament networks and parallel actin filament filopodia Microtubule Intermediate Actin filaments filaments 16 PHY113--Lec 1 17