BIOL1152-02 Fall 2024 Cell Biology Handouts PDF

BIOL1152-02 Fall 2024 MSVU BIOL1152 02 Handouts Part 3 The Cell;...

BIOL1152-02 Fall 2024 MSVU BIOL1152 02 Handouts Part 3 The Cell; The Basic Unit of Life 1 The Cell; The Basic Unit of Life 2 Copyrighted Material for In-class Use! No Publication or Distribution! 1  BIOL1152-02 Fall 2024 Cell Theory ALL ORGANISMS ARE COMPOSED OF CELLS !!! The Cell is the Basic Unit of Life => Cell Theory! - Cells, with few exceptions, are smaller than 100 µm - All Living Organisms are Composed of at Least One Cell - All Cells arise by Division of a Previously Existing Cell - Processes of “Life” such as Metabolism and Heredity are Seated in Cells 3 Cell Structure To Study Cells, we need Technical Aids Different technologies and methods give access to cells to solve different questions Method/Tool of choice depends on the question we need to answer - Microscopes (to “see” cell anatomy) - Light Microscope => => Structures ≥ 1 µm - Electron Microscope => Structures ≥ 1nm - Chemical and Physical Methods (physiology, biochemistry and biophysics) - Electronics (biophysics and physiology) 4 Copyrighted Material for In-class Use! No Publication or Distribution! 2  BIOL1152-02 Fall 2024 Cell Structure Microscope: Device to view (scope) small (micro) things Magnification: Makes small things look bigger Physical limit for magnification is the wavelength of light, i.e. limit is ~1000x – 1500x optical magnification. Resolution: Ability to see fine details “Resolution: how close to each other can two dots be that we still can see them as two distinct dots and not as one” Physical limit are refractive properties (quality) of the optical lens system and the wavelength of light. More Magnification without More Resolution is Pointless We don’t see more details we just see them bigger => Empty Magnification Higher Resolution shows More Details! 5 Info slide: The cost of being able to see details! expensive < Cost > cheaper Pollen grains photographed with 40x N.A. 0.65 ($800) and 40x N.A. 0.75 ($1500) cheaper < Cost > expensive 40x N.A. 0.9 ($3000) 40x N.A. 1.3 ($13000) Same Magnification! Higher N.A. = Higher Resolution Different Resolution! Different Price ! 6 Copyrighted Material for In-class Use! No Publication or Distribution! 3  BIOL1152-02 Fall 2024 Cell Structure Light Microscope - Resolution is Limited by Wavelength of Light - ”Useful” Magnification of Light Microscopes ~1000x - Objective is the Important Part, Ocular (“Eyepiece”) can only Magnify what Objective shows - Resolution Limit of Light Microscopes ~ 200 nm, insufficient to resolve most intracellular structures To show intracellular structures we use: - special illumination techniques (dark-field, phase-contrast, filters ….) - staining techniques (chemical dyes, fluorescence markers coupled to antibodies or injected in cells 7 A Word on Magnification Image was taken with the camera attached to a dissecting microscope. Objective 4x, Eyepiece 10X = 40x How big was the spider? The image was taken with 40x magnification, add to this: - magnification by cropping the negative (unknown) - magnification by printing or projecting it (unknown) - information about magnification alone is pretty much useless 8 Copyrighted Material for In-class Use! No Publication or Distribution! 4  BIOL1152-02 Fall 2024 A Word on Magnification Image was taken with the camera attached to a dissecting microscope. Objective 4x, Eyepiece 10X = 40x How big was the spider? A Scale Bar is much more useful! No matter how the image is presented and scaled, we can always tell the size of the spider! 9 Cell Structure Electron Microscopes: Electron Beam and Magnetic Fields (Electromagnets) allow Higher Magnification and Resolution - Scanning Electron Microscope; shows Surface Structures by collecting Electrons Reflected from the Object Surface - Transmission Electron Microscope; Specimen must Be VERY Thin to be electron “translucent”, i.e. to permit Electrons passing through specimen Interpretation of Image requires Experience 1 µm = 1 x 10-6 m 1 µm = 0.001 mm 500 nm 500 nm = 0.5 µm 10 Copyrighted Material for In-class Use! No Publication or Distribution! 5  BIOL1152-02 Fall 2024 Cell Structure Maximal Cell size is limited; usually to ≤ 100µm! T - Efficient Surface to Volume Ratio R A - Efficiency of Diffusion (decreases with distance) N - Ability to Synthesize and Distribute Required S P Metabolites and proteins O R - Ability to Dispose Waste Products in a timely manner T Larger Cells Exist: Larger Size Requires Adaptations to Cell Anatomy and Physiology - Muscle cells/Muscle fibers can be > 30 cm long, i.e., muscle fibers reach from one muscle attachment point to the other - Neurons can cover distance between periphery and the central nervous system without synaptic relay (> 100 cm) 11 All Cells Share Basic Structural Similarities 1) DNA, the genetic material is centrally located - Prokaryotes: single circular DNA molecule located in center of cell, region called nucleoid, not separated from cell lumen - Eukaryotes: DNA is confined in Nucleus, physically separated from cell lumen by double layer membrane, Nuclear Envelope 2) RNA, transcript of genetic information required for protein synthesis 3) Cytoplasm, semi-fluid aqueous intercellular matrix contains macromolecules and in eukaryotes cell organelles 4) Plasma Membrane, phospholipid bilayer membrane with embedded proteins enclosing entire cell 5) Ribosomes, proteins required for protein biosynthesis ( translation) 12 Copyrighted Material for In-class Use! No Publication or Distribution! 6  BIOL1152-02 Fall 2024 Prokaryotic Cells (pro = before & karyon = nucleus) Prokaryotic organisms, Bacteria and Archaea, are Unicellular! - Significantly Smaller than Eukaryotic Cells (> 1µm) - No Nucleus - No Internal Membrane System - No Cell Organelles - No Interior Compartments - Only Basic Peripheral Cytoskeleton - Rigid Cell Wall Bacterial Cell Wall made from Peptidoglycan, Not Cellulose (=> Plant Cells) - Gram-positive Bacteria; thick single layer wall, stained by Gram staining - Gram-negative Bacteria; multilayered cell wall, not stainable by Gram dye - Some Bacteria secrete additional protective Polysaccharide Capsule 13 Prokaryotic Cells (pro = before & karyon = nucleus) - One or more long locomotive Flagella - Flagella move by Rotary Movement of the Flagellum - Flagellum Motor Fueled and Driven by Transmembrane Proton Gradient Prokaryotic Flagella are a Very Different from Eukaryotic Flagella and Cilia 14 Copyrighted Material for In-class Use! No Publication or Distribution! 7  BIOL1152-02 Fall 2024 Eukaryotic Cells (eu = with & karyon = nucleus) Only Bacteria and Archaea are Prokaryotes, All Other Organisms are Eukaryotes Eukaryotic Cells show High Degree of internal Compartmentalization! - Nucleus with DNA organized in Chromosomes - Intracellular Membrane Systems - Cell Organelles - Cytoskeleton (intra- and extracellular) - Some Eukaryotes have Cell Walls (plants, fungi, protists), other lack cell walls (animals, protists) - Cell Walls composed of Cellulose (plant), or Chitin (fungi) 15 Eukaryotic Cells (eu = with & karyon = nucleus) 16 Copyrighted Material for In-class Use! No Publication or Distribution! 8  BIOL1152-02 Fall 2024 Cell Structure Eukaryotic Cells: The Nucleus Nucleus contains the Genetic Material (DNA) - Every Eukaryotic Cell has One Nucleus - Nucleolus, dense area in Nucleus (region of ribosomal RNA synthesis) - Separated from Cytoplasm by Bilayer Membrane (Nuclear Envelope) Nuclear envelope is part of the Intracellular Membrane System (Endoplasmic Reticulum) Nuclear Pores in the Nuclear Envelope allow Controlled Molecule Exchange between the Nucleus and Cytoplasm! 17 Eukaryotic Cells: Nucleolus and DNA Nucleolus; Ribosome Assembly Area inside the Nucleus - Ribosomes are Cell Organelles Required for Protein Synthesis - Ribosomal RNA (rRNA) transcribed from DNA, ribosomal proteins are synthesized and assembled in nucleolus => Exported to Cytoplasm Chromosomes; Eukaryotic DNA organized in Linear Chromosomes - DNA and Proteins form Chromatin Scaffold with Regulatory Proteins controlling Gene Expression (mRNA synthesis) and DNA Replication 18 Copyrighted Material for In-class Use! No Publication or Distribution! 9  BIOL1152-02 Fall 2024 Eukaryotic Cells: Ribosomes - Ribosomes = Protein Synthesis “Factories” of Pro- and Eukaryotic Cells - Complex Organelles with Two Subunits - Ribosome Subunits are composed of Proteins and Ribosomal RNA (rRNA) - Ribosome Subunits only joined during Protein Synthesis (=> mRNA present) - Protein Synthesis happens Outside of Nucleus Free in Cytoplasm or Associated with Endoplasmic Reticulum - Free Ribosomes synthesize cytoplasmic, mitochondrial and nuclear proteins; Associated with the ER proteins for Export 19 Eukaryotic Cells: Endoplasmic Reticulum (ER) Endoplasmic Reticulum (ER); part of the intracellular membrane system of phospholipid membranes, dividing intracellular space into compartments. Compartmentation: key inventions of eukaryotic cells that creates reaction spaces ER is part of the cell’s “Shipping Department” 20 Copyrighted Material for In-class Use! No Publication or Distribution! 10  BIOL1152-02 Fall 2024 Eukaryotic Cells: Endoplasmic Reticulum (ER) Ratio of Rough ER (rER) and Smooth ER Varies between Cell Types Secretory cells have more rER - Rough ER (rER) associated with Ribosomes and major Site of Protein Synthesis - Proteins are Synthesized into ER Lumen for Export from Cell, Transport to Vacuoles and Lysosomes, or for Inculsion into Cell Membrane - In Cysternal Space of ER proteins are Sorted for Transport to Destination - Smooth ER (sER or just ER) has multiple functions => Synthesis of Cytosolic Carbohydrates and Lipids, and Steroid Hormones - Smooth ER Stores Ca2+, keeping intracellular [Ca2+] low (Ca2+ = intracellular messenger) - Smooth ER plays role in Detoxification of the Cell (“liver of the cell”), by modifying and neutralizing toxins 21 Eukaryotic Cells: Golgi Apparatus Golgi Apparatus consists of Golgi Bodies (yes, named after the Italian guy) - 1 – 100s per cell, depending on cell type (Secretory cells have more, WHY?) - Golgi Bodies are Flattened Membrane Stacks, associated with ER “Fake” colored Electron Micrograph Golgi Apparatus is ”Handling and Shipping Department” of the Cell 22 Copyrighted Material for In-class Use! No Publication or Distribution! 11  BIOL1152-02 Fall 2024 Eukaryotic Cells: Golgi Apparatus Golgi Apparatus Collects, Modifies, Packages, and Distributes Molecules (not limited to proteins) Synthesized in other Compartments (ER!). - Some molecules (polysaccharides!) are synthesized in the lumen of the Golgi Apparatus - cis-Face; Receiving End, facing the ER - trans-Face; Discharge/Shipping End - Loaded Transport Vesicles fuse with Golgi cis-Face Membrane, releasing contents into the Golgi Apparatus - Molecules are modified during passage of Golgi Apparatus on way to trans-Face - Secretory Vesicles form on trans-Face, carrying products and are transported to their target regions in the cell 23 Eukaryotic Cells: ER and Golgi Apparatus Collaborate Proteins, Lipids, Carbohydrates and other molecules are required in locations distant from synthesis site - Cell needs to transport them there => Trafficking - Packing into Transport Vesicles protects product from premature breakdown and protects cell from product (think about digestive enzymes) - Membrane Proteins on Vesicle Surface are “Shipping Labels”, recognized by Receptors in the cis-face of the Golgi Apparatus. - Membrane of Vesicle and cis-Face Membrane fuse, releasing Vesicle Contents into lumen (Cisternae) of the Golgi Apparatus! - Molecules are modified before re-packaging into Secretory Vesicles on the Golgi trans-face. 24 Copyrighted Material for In-class Use! No Publication or Distribution! 12  BIOL1152-02 Fall 2024 Eukaryotic Cells: Lysosomes Lysosomes are the “Cell’s Stomach” - Lysosomes contain Digestive Enzymes, produced in the ER and repacked in the Golgi Apparatus Digestive Enzymes must be Contained in Vesicles or Lysosomes otherwise the Cell would Digest Itself - Lysosomes fuse with Damaged or Expired Cell Organelles - Lysosomes fuse with Vesicles containing Food Particles (collected by Endocytosis or Phagocytosis) - Lysosome Enzymes break down Organic Molecules, providing cell with metabolites for synthesis or energy 25 Eukaryotic Cells: Vacuoles Only Plant Cells have Vacuoles, membrane enclosed Storage Compartments - Central Vacuole is found in all Plant Cells, size varies - Vacuole Membrane aka Tonoplast, a Phospholipid Bilayer Membrane - Vacuoles play important roles in cell’s Osmotic Balance, Tonus Maintenance (internal pressure), Cell Growth (vacuole volume increases, not cytoplasm volume) and Storage of Solutes (sugars, ions, pigments, waste products) 26 Copyrighted Material for In-class Use! No Publication or Distribution! 13  BIOL1152-02 Fall 2024 Vacuoles: Plasmolysis and Deplasmolysis Passive Transmembrane Transport Plasmolysis and Deplasmolysis in a plant cell demonstrates osmotic water exchange between central vacuole, cytoplasm and extracellular space In Protists Contractile Vacuoles allow organism to osmoregulate (see Video Clip on Moodle) 27 Eukaryotic Cells: Endosymbiont Theory x 10-9 years Two Types of Cell Organelles are the Result of Endosymbiosis, a relationship that offers all partners Advantages Incorporation of Prokaryotic Cells into Eukaryotic Cells, forming a Mutualistic Beneficial Relationship. Prokaryotic Cells become Organelles of Eukaryotic Cells! Mitochondria: former aerobic prokaryotes (heterotroph bacteria) Chloroplasts: former autotroph prokaryotes, (photosynthetic active bacteria) 28 Copyrighted Material for In-class Use! No Publication or Distribution! 14  BIOL1152-02 Fall 2024 Eukaryotic Cells: Endosymbiont Theory x 10-9 years Supporting Evidence Endosymbiont Theory, the Endocytosis of Prokaryotic Cells as origin of Eukaryotic Mitochondria/Chloroplasts Both Types of Cell Organelles enclosed by Two Double Layer Membranes, resulting from Endocytosis - One from Prokaryote Ancestor - One from Eukaryote Host Ancestor Size with ~ 1 µm close to Prokaryote Cells Own Circular DNA, => bacterial DNA Own Prokaryote-type Ribosomes Multiply by Fission / Division, not synthesized by eukaryotic cells 29 Curiosity Fact: Mitochondria are Maternal Inheritance Nuclear DNA is inherited from both parents, mitochondria and mitochondrial DNA (mDNA) is inherited only from mothers. Both oocyte and sperm cells contain mitochondria with mDNA, but during fertilization only paternal nuclear DNA is transferred from sperm to oocyte, not the sperm’s mitochondria and mDNA. All mitochondria in the cells of an individual originate from the mitochondria of the oocyte. Mitochondrial DNA changes very little across generations, so it is used to trace maternal lineage through hundreds of generations. Studies used mitochondrial DNA of modern-day populations to determine migration patterns of early humans. 30 Copyrighted Material for In-class Use! No Publication or Distribution! 15  BIOL1152-02 Fall 2024 Eukaryotic Cell Organelle: Mitochondria “Power Plants” of the Cell Aerobic Respiration harvests energy by breaking down Organic Molecules, stores it in ATP (universal energy currency) ATP stays in cell. No ATP exchange between Cells. - Varying Numbers in All Eukaryotic Cells - Own “prokaryotic” circular mDNA and Ribosomes - Double Membranes; Inner membrane shows Lots of Folding to Increasing Surface Area for Catabolic Reactions of Aerobic Respiration. 31 Eukaryotic Cell Organelles: Chloroplasts Chloroplasts Key for (Photo)Autotrophy - Photoautotroph; Using Light Energy to Fixate Carbon into Organic Molecules (Glucose) - Double Membrane Shell, own DNA and Ribosomes Thylakoid Disks carry Chlorophyll to => Endosymbiont Theory harvest Light, surrounded by fluid - Internal Membrane Stacks Stroma with Enzymes Required for form Thylakoid Disks Glucose Synthesis 32 Copyrighted Material for In-class Use! No Publication or Distribution! 16  BIOL1152-02 Fall 2024 Eukaryotic Cells: Cytoskeleton Intracellular Network of Protein Fibers, Supporting the Cell Shape, Anchor Cell Organelles, Intracellular Transport and Cell Movements - Dynamic System of Protein Polymer Fibers, constant Formation and Disassembly of Fibers by Polymerization and Depolymerization Three Types: - Actin Filaments, two Chains made from globular Actin Molecules - Microtubules tubes of 13 circular arranged Tubulin protofilaments - Intermediate Filaments, made from a variety of proteins 33 Eukaryotic Cells: Extracellular “Cytoskeleton” Extracellular Structures to Maintain Cell Shape and Orientation; Essential for Many Specialized Cell Functions Cell Walls of Plant Cells, Fungi Cells, and Protists - Eukaryotic Cell Walls are very different from Prokaryotic Cell Walls - Eukaryotic Cell Walls are made from Structural Polysaccharides Cellulose (plants, protists) and Chitin (fungi) Animal Cells Don’t Have Cell Walls - Secrete Extracellular Matrix of Glycoproteins (Collagen, Elastin and Proteoglycans) - Integrins (transmembrane proteins) Connect Extracellular Matrix with Elements of the Cytoskeleton 34 Copyrighted Material for In-class Use! No Publication or Distribution! 17  BIOL1152-02 Fall 2024 Eukaryotic Cells: Cell Wall of Plant Cells Cell Wall of Plant Cells - Cells are held together by sticky Middle Lamellae (secreted by cell membrane) - Primary Cell Wall: formed by Secretion of Cellulose Fibers between Membrane and Middle Lamella - Secondary Cell Wall formed after Cell Stops Growing by Cellulose Secretion between Primary Wall and Membrane Secondary Wall allows for Specializations giving Plant Tissues specific Properties - Stability - Water Proofing - ……….. 35 Eukaryotic Cells: Locomotion Flagella and Cilia give Protists mobility and give Cells in Tissues Ability to Move Substrate - Structure of Eukaryotic Flagella and Cilia is Very Different from Prokaryotic Flagella (ATP-driven microtubule sliding vs. protein filament driven by rotary, H+-gradient driven “motor”) - Eukaryotic Flagella and Cilia are Built from Microtubules (MTs) in “9 + 2” Arrangement - MT sliding makes them Undulate, not rotate like prokaryotic filament - MT sliding based on Motile Proteins (Dynein) and ATP to move MTs past each other 36 Copyrighted Material for In-class Use! No Publication or Distribution! 18  BIOL1152-02 Fall 2024 Eukaryotic Cells: Locomotion Some Cells without Flagella or Cilia “Crawl” or “Grow in one Direction and Pull Rest Along” Amoeba (protists) and White Blood Cells use Directional Polymerization of Actin Filaments to “Grow” into Direction of Movement, MTs will secondarily stabilize cell shape. Depolarization of Actin and MTs on opposite cell side will let cell follow (Video on Moodle!) its “Growth Cone”* *Mechanism is also used by cells that show directional growth in a tissue/body => Neurons Innervating Targets 37 Structure of Membranes Phospholipid bilayer is the structural foundation of all biological membranes Phospholipid: hydrophilic head (polar) - glycerol - phosphate group - additional rest (polar) hydrophobic tail (unpolar) - two (or more) fatty acids - in aqueous environment phospholipids spontaneously form bilayers, impermeable for water-soluble substances 38 Copyrighted Material for In-class Use! No Publication or Distribution! 19  BIOL1152-02 Fall 2024 Cell Membranes The Cell Membrane Creates a Compartment, aka The Cell, with an Intracellular Environment VERY Different from Extracellular Space! Cell Membranes are: - Hydrophobic Phospholipid Bilayer Barrier, Impermeable for Solutes - Embedded Membrane Proteins make Bilayer Barrier Selectively Permeable for Solutes, allowing Controlled Exchange of Solutes between Cell and Environment, and Cellular Compartments Intracellular Membrane Systems (ER, nuclear envelope …) Create Compartments Within the Cell! - Compartments allow for different Microenvironments, enabling chemical reactions requiring specific conditions - Increase Available Surface Area (even more so by folding) for Membrane Bound Biochemical Reactions and Exchange between Compartments 39 Membrane Structure Biological membranes consist of four component groups, arranged in a Fluid Mosaic Membrane (model proposed 1972 by Singer and Nicolson) - Foundation: Phospholipid Bilayer; hydrophilic “heads” of molecules face outside / inside and their hydrophobic tails face each other - Transmembrane Proteins floating in phospholipid bilayer make it selectively permeable for solutes and H2O - Membrane-integrated Glycolipids and Glycoproteins are Receptors that make Cells Excitable and are markers that identify cells to other cells (antigens “a cell’s business card”) - Interior Protein Network (cytoskeleton) provides structural support for lipids and membrane proteins 40 Copyrighted Material for In-class Use! No Publication or Distribution! 20  BIOL1152-02 Fall 2024 Membrane Structure Fluid Mosaic Model describes Non-static Nature of Membrane, Elements can Move and are Unevenly Distributed in Bilayer - There are Microdomains on the Membrane with distinct Lipid and Protein Compositions (“Islands”) - “Islands” float in membrane Two cells, each labeled with different marker bilayer and can change location proteins in their membranes are fused into a Hybrid cell! Example: Specializations of the membrane in neurons (“nerve cells”)! Axonal membrane of neuron After short time the different marker proteins specialized for information are evenly distributed over the membrane, an transport, Dendritic membrane observation supporting the Fluid Mosaic Model specialized to receive information from other cells 41 42 Copyrighted Material for In-class Use! No Publication or Distribution! 21  BIOL1152-02 Fall 2024 Membrane Proteins Membrane-associated Proteins determine functional properties of cell membrane and cell - Transporter and Channel Proteins determine selective permeability of the membrane - Membrane-bound Enzymes enable chemical reactions - Receptor Proteins, detect chemical messengers or markers of cells and vesicles, allow cell response to those signals - Surface Identity Markers (“antigens”) are unique ID-tags of cells, recognized by other cells - Anchor Proteins attach cell membrane or proteins of the cell membrane to the cytoskeleton - Cell-to-Cell Adhesion Proteins “glue” cells together 43 Membrane Proteins Membrane Proteins Interact with Phospholipid bilayer Membrane Binding of Protein to Anchoring Molecules tethers it to Lipids Anchoring Molecules are Modified Phospholipids - Nonpolar (lipophilic) Region embedded into membrane bilayer “Anchor” - Protein-binding (lipophobic) Region binds to a matching protein Examples: Membrane-bound Enzymes, Structural Proteins of the Cytoskeleton, Surface Marker Proteins 44 Copyrighted Material for In-class Use! No Publication or Distribution! 22  BIOL1152-02 Fall 2024 Membrane Proteins Integral Membrane Proteins span across Phospholipid Membrane - Nonpolar Amino Acids in primary protein structure (lipophilic/hydrophobic) form protein domains or motifs that pass through the membrane in the form of helices or β–pleated sheets (secondary protein structure) - Nonpolar, hydrophobic protein regions keep this section of the protein within the membrane Proteins have multiple Transmembrane Domains forming 3D channels, pores or tunnels through the membrane (tertiary and quaternary structure) Transmembrane Domains are interconnected by Hydrophilic Domains Examples: Ion channels, Receptors, Transporter 45 Transmembrane Transport Transporter and Channel Proteins determine Membrane Permeability by Allowing Solutes to Cross Membrane Barrier - Ion-Channels Passive Transport along Solute Gradient - Carrier Proteins Passive Transport along Solute Gradient - Transport Proteins Active Transport Utilizing Energy - Primary Active Transport using ATP as energy - Secondary Active Transport using gradients as energy source 46 Copyrighted Material for In-class Use! No Publication or Distribution! 23  BIOL1152-02 Fall 2024 Transmembrane Transport Cell membranes are Barriers that Create and Separate Compartments (extracellular/intracellular, cytoplasm/organelle lumen ….) Solutes must Cross Membranes to Allow Cells to Create and Maintain Working Conditions required for all processes Life requires Gradients! Solute Exchange Across Membranes Must Be Controlled to Form and Maintain Vital Transmembrane Gradients Transmembrane Transport Mechanisms - Passive Transport: no energy investment required, only Gradient Can only go “downhill”, follow existing gradient - Active Transport: energy investment required (ATP or other form) Can go “uphill”, against gradient / form a gradient 47 Transmembrane Transport Passive Trans-Membrane Transport: Costs NO Energy! Solutes can move ONLY “Downhill” along an existing gradient, e.g. from side with higher solute concentration to side with lower solute concentration! Active Trans-Membrane Transport: Costs Energy! Solutes move “Uphill” against an already existing gradient, e.g. from side with lower solute concentration Modified from: to side with solute higher concentration! www.quora.com 48 Copyrighted Material for In-class Use! No Publication or Distribution! 24  BIOL1152-02 Fall 2024 Transmembrane Transport I) Diffusion - Diffusion / Facilitated Diffusion is Passive Transport of Solutes requiring No Direct Energy Investment - Solutes Move Along / Follow Existing Gradients - Movement of Solute will Eventually Lead to its Even Distribution in Space Even Solute Distribution = No Gradient = No Movement 49 Passive Transmembrane Transport The Cell Membrane is a Selectively Permeable Diffusion Barrier Only Small Nonpolar Molecules can cross the Membrane directly, following existing concentration gradients (O2, CO2, steroid hormones) Note: Solutes Only “Care” About Own Gradient, Not the Gradient of Other Solutes! Small Nonpolar Molecules Require No Specific Transport Mechanisms As Long As Their Gradient Moves Them In The Required Direction! - Large Solutes Cannot Diffuse Directly Across Membrane - Polar Solutes Cannot Diffuse Directly Across Membrane they are repelled by Hydrophobic Membrane Properties - Charged Solutes Cannot Diffuse Directly Across Membrane They are repelled by Hydrophobic Membrane Properties 50 Copyrighted Material for In-class Use! No Publication or Distribution! 25  BIOL1152-02 Fall 2024 Passive Transmembrane Transport The Cell Membrane is a Selectively Permeable Diffusion Barrier Polar, Charged, and Large Solutes need Help to Cross Membranes! Integral Membrane Proteins ALLOW CONTROLLED Transmembrane Transport of Polar, Charged, and Large Solutes by Passive Transport or by Active Transport Integral Membrane Proteins are Highly Selective Transporters for a Specific Type of Solute, providing selective membrane permeability for a particular solute - (Ion) Channel Proteins form Gated Channel (“pole”) in membrane; Size of Channel Pore and Electrical Surface Charges provide Ion Channel with Selective Permeability for a Specific Ion Species, and Gating the Pore (opening / closing) Controls Ion Exchange - Carrier Proteins can bind only Specific Solutes and shuttle them across the membrane without breaking the membrane’s integrity 51 Ion Channels and Carriers are Transmembrane Proteins that Utilize Passive Transmembrane Transport of Solutes Both Represent Passive Transport, Requiring Existing Gradients of “Their” Specific Solute to Drive Transport Direction of Solute Transport is Determined by Gradient, e.g., from the Side with Higher Solute Concentration to the Side with Lower Solute Concentration => Downhill Transport 52 Copyrighted Material for In-class Use! No Publication or Distribution! 26  BIOL1152-02 Fall 2024 Passive Transmembrane Transport Carrier Proteins are Membrane Proteins transporting Solutes like Sugars and Amino Acids Across the Membrane - Depend on Solute Concentration Gradient as driving force, i.e., only works “downhill” from high to low concentration - Called Facilitated Diffusion, as it is facilitated by the carrier protein by binding the solute and shuttling it across the membrane Facilitated Diffusion: - specific, a given carrier transports only a certain type of solute - passive, direction of movement is determined by the concentration gradient of the solute 53 Passive Transmembrane Transport Ion Channels are Membrane Proteins forming a Pore Permeable for Select Ions (cations like Na+, K+, Ca2+, or anions like Cl-) Ion Channel Selectivity Controls What Ion Cross The Membrane Ions Can Cross the Membrane When The Pore is Open Passive Transport by Diffusion: Ions can cross the membrane only “downhill” following an existing gradient Gradient determines direction of ion flow across the membrane through an open ion channel Movement through open ion channel can be driven by ion concentration gradient, electrical gradient, or a combination of both 54 Copyrighted Material for In-class Use! No Publication or Distribution! 27  BIOL1152-02 Fall 2024 Passive Transmembrane Transport Ion Channels are Gated, they can be Open or Closed, allowing Control When Ions Cross the Membrane - 60mV - 50 mV Ligand-gated Channel Voltage-gated Channel gated by binding of Ligand Molecule gated by change in electrical gradient (aka membrane potential) - Ligand-gated Channels (binding of “ligand” opens or closes the gate) - Voltage-gated Channels (gated by change in membrane potential) - Mechanically-gated Channels (mechanical force gates the channel) 55 Passive Transmembrane Transport - Ion Channels form “Hole” in the Membrane, allowing Ions to Pass Across Membrane Through Open Pore , following the Ion’s Concentration Gradient! => Direct Connection between Intracellular Space and Extracellular Space when Pore is Open. Limits Pore Size as Large Pore Would Compromise Membrane Integrity and Kill Cell - Carrier Proteins Shuttle Solute Across the Membrane, following the Solute’s Gradient! => No Direct Connection between Intracellular Space and Extracellular Space. Carriers Do Not Compromise Membrane Integrity and Can Move Large Molecules! 56 Copyrighted Material for In-class Use! No Publication or Distribution! 28  BIOL1152-02 Fall 2024 Passive Transmembrane Transport: Diffusion / Facilitated Diffusion Require Transmembrane Gradients: No Gradient – No Flow OPEN ION CHANNEL No Concentration Gradient, No Electrical Gradient 57 Transmembrane Gradients: I) Chemical Concentration Gradients Solutes (Ions) BLUE (e.g., Na+) and RED (e.g., K+) with higher concentration on one side of the membrane and lower concentration on the other side of the membrane, but even distribution of electrical charges TWO CHEMICAL CONCENTRATION GRADIENTS, but No Electrical Gradient 58 Copyrighted Material for In-class Use! No Publication or Distribution! 29  BIOL1152-02 Fall 2024 Transmembrane Gradients: I) Chemical Concentration Gradients BOTH SOLUTES FOLLOW THEIR GRADIENT! 59 Transmembrane Gradients Typical Cellular Gradients: - high intracellular [K+] - low intracellular [Na+] - low extracellular [K+] - high extracellular [Na+] - cell inside more negative charged than outside (e.g., VM = -90 mV) When We Specify Electrical Transmembrane Gradient, the Membrane Potential (VM), We Use Inside as Reference! If Inside of Cell is More Negative Than Outside then VM is Negative If Inside of Cell is More Positive Than Outside then VM is Positive 60 Copyrighted Material for In-class Use! No Publication or Distribution! 30  BIOL1152-02 Fall 2024 NaCl + H2O Na+ + Cl- + H2O + 61 Transmembrane Gradients: II) Electrical Gradients Solutes Na+ and K+ with Individual Concentration Gradients PLUS ELECTRICAL GRADIENT due to Uneven Distribution of Positive Changes One Side of the Membrane Is Negatively Charged Compared to Other Side ELECTRICAL GRADIENT IS KNOWN AS MEMBRANE POTENTIAL! A + - - 60 mV + - B 62 Copyrighted Material for In-class Use! No Publication or Distribution! 31  BIOL1152-02 Fall 2024 Transmembrane Gradients: II) Electrical Gradients Solutes Na+ and K+ Driven by Individual Concentration Gradient PLUS ELECTRICAL GRADIENT KNOWN AS MEMBRANE POTENTIAL! A + - - 60 mV + - B Movement of Na+ speeds up: Concentration and Electrical Gradient Combine Forces Movement of K+ slows down: Concentration and Electrical Gradient Counteract (K+ rejected by Dominant Positive Charge on Side A) 63 Passive Transmembrane Transport Osmosis, Diffusion of H2O Across Membrane - Cytoplasm and Extracellular Fluid are Aqueous Solutions Solvent = Water (H2O) Solutes = Sugars, Amino Acids, Ions….. If Solute Concentration On Both Sides of the Membrane is Different, but Solutes Can not Cross The Membrane, H2O will Move! - Without Membrane Barrier Solute Gradients would soon even out by Diffusion Moving Solutes - Membrane Barrier Prevents Free Diffusion of Solutes, allowing Formation and Maintenance of Solute Gradients If Solutes Can’t Move Across Membrane Water will Move => Osmosis 64 Copyrighted Material for In-class Use! No Publication or Distribution! 32  BIOL1152-02 Fall 2024 Passive Transmembrane Transport: Osmosis H2O Molecules interact with Solutes Goal of Diffusion: Equal Solute Concentration on Both Sides of the Membrane pressure - Solvents can’t Cross Membrane to Reach this Goal, but H2O can Cross Membrane we observe OSMOSIS OSMOSIS = Movement of H2O to Reach Equal Solute Concentration Movement of H2O on both Sides of Membrane Goal: Isosmotic Conditions Total Solute Concentration Matters, Same Solute Concentration on not Individual Concentration Gradient Both Sides by Moving H2O - Removing H2O from Dilute Side or Size of Different Solutes - Adding H2O to Concentrated Side (number of particles; piece concept) 65 Isosmotic Same Total Solute Concentration on Both Sides No osmotic H2O Movement Hyperosmotic Hyperosmotic Side has Higher Total Solute Concentration than the Other, Hypoosmotic Side Direction of osmotic H2O Movement Hypoosmotic Hypoosmotic Side has Lower Total Solute Concentration than the Other, Hyperosmotic Side Direction of osmotic H2O Movement 66 Copyrighted Material for In-class Use! No Publication or Distribution! 33  BIOL1152-02 Fall 2024 Passive Transmembrane Transport Membranes are HYDROPHOBIC, impermeable for H2O molecules Aquaporins (proteins) are specialized “Water Channels” allowing H2O to Cross the Membrane Aquaporins are not Gated, Cells Insert or Remove them very rapidly from the membrane 67 Most Cells (Organisms) are Not Isosmotic with their Environment - Marine Organisms may adjust their solute concentration till they are isosmotic with the surrounding seawater to avoid water loss – isosmotic regulation – - Freshwater Protists use Contractile Vacuoles to discharge excess water from the cytoplasm. Rate of water discharge is related to the rate of water influx - Animals have Osmoregulatory Organs (kidney etc.) to maintain proper water balance by controlling water gain and loss in cells and tissues - Plant Cells are Hyperosmotic and “pressurized” (hypertonic) to their environment, i.e., under hydrostatic pressure (turgor), with rigid cell walls preventing them from bursting 68 Copyrighted Material for In-class Use! No Publication or Distribution! 34  BIOL1152-02 Fall 2024 Vacuoles: Contractile Vacuoles prevent swelling of freshwater protists (Video on Moodle!) 69 Isosmotic Cytoplasm Blood Plasma Same Total Solute Concentrations, No Osmotic H2O Movement Note: Different Solutes! Hyperosmotic Fish in Freshwater (Hyperosmotic) (Hypoosmotic) Fish Cells have Higher Total Solute Concentration than Freshwater Fish Cells “Swell” due to H2O Uptake Direction of osmotic H2O Movement Hypoosmotic Fish in Saltwater Fish Cells have Lower Total Solute (Hypoosmotic) (Hyperosmotic) Concentration than Saltwater Fish Cells “Shrink” due to H2O Loss Direction of osmotic H2O Movement 70 Copyrighted Material for In-class Use! No Publication or Distribution! 35  BIOL1152-02 Fall 2024 Hypertonic Environment (Hypotone Cells): H2O will diffuse out of a cell and cell will shrink until the osmotic concentration inside the cell is isotonic with extracellular environment Hypotonic Environment (Hypertone Cells): H2O will diffuse into a cell and the cell will swell and may eventually burst if isotonic state can’t be reached Isotonic Environment: Flow of H2O out of cell and the cell is balanced, no net water flow and no change of osmotic concentration 71 Membranes Passive Transmembrane Transport Blood Cells shrink in hypertonic environment and swell and burst in hypotonic environment due to inability to osmoregulate! Red Blood Cells (Erythrocytes) White Blood Cells (Leukocytes) (Video on Moodle!) 72 Copyrighted Material for In-class Use! No Publication or Distribution! 36  BIOL1152-02 Fall 2024 Passive Transmembrane Transport: Osmosis Plant Cell with Rigid Cell Wall Extracellular Fluid Hypoosmotic => Cells Swells and is Under Pressure => Turgor Extracellular Fluid with [S] > [S] Hyperosmotic: - Cell loses H2O and Vacuole shrinks - Cytoplasm maintains its volume, cytoplasm and cell membrane detach from cell wall - Plasmolysis continues to the point when [S] of vacuole is equal to extracellular [S] Reversible Process => Deplasmolysis 73 Vacuoles: Plasmolysis and Deplasmolysis (Video on Moodle!) 74 Copyrighted Material for In-class Use! No Publication or Distribution! 37  BIOL1152-02 Fall 2024 Active Transmembrane Transport Passive Transport by Diffusion and Facilitated Diffusion can only follow existing gradients, run “downhill”. Cell must be able to Transport Solutes “Uphill” to Create Gradients, to accumulate desirable molecules, to discharge undesirable molecules against existing gradient ACTIVE TRANSPORT Active Transport Requires Energy Investment - Primary Active Transport directly fueled by ATP - Secondary Active Transport fueled by other Energy Sources 75 Active Transmembrane Transport ACTIVE TRANSPORT Active Transport Requires Energy Investment - Primary Active Transport directly fueled by ATP - Secondary Active Transport fueled by other Energy Sources Transmembrane Proteins are Key Players in Active Transport! - Transporter Proteins bind only to Specific Solutes - High Diversity Required to be able to move all required solutes across membrane barrier 76 Copyrighted Material for In-class Use! No Publication or Distribution! 38  BIOL1152-02 Fall 2024 Active Transmembrane Transport Transmembrane Proteins are Key Players in Active Transport! Transporter Proteins bind only to Specific Solutes High Diversity required to be able to move all required solutes across membrane barrier Modes of Active Transport: Uniporters – single kind of solute Symporters – more than one kind of solute the same way Antiporters – more than one kind of solute in opposite directions 77 Active Transmembrane Transport Example for Primary Active Transport: ATP (energy!) Hydrolysis fuels movement of 3 Na+ Out of the Cell and 2 K+ Into the Cell by Na+/K+- ATPase, aka Na+/K+-Pump! 78 Copyrighted Material for In-class Use! No Publication or Distribution! 39  BIOL1152-02 Fall 2024 Active Transmembrane Transport Activity of Na+/K+-pump Results in Three Transmembrane Gradients: - K+ Concentration Gradient [K+]i > [K+]o by moving 2 K+ into cell - Na+ Concentration Gradient[Na+]i < [Na+]o by moving 3 Na+ out of cell - Electrical Gradient (Membrane Potential) by moving 3+ Out & 2+ In - Speed ~300 cycles / s K+ Na+ ATP => ADP + P + Energy + drives Na+/K+-pump - Na+/K+-pump found in ALL Cells => evolved early K+ Na+ 79 Active Transmembrane Transport ATP is not the only form of energy used in active transport Potential Energy stored in Gradient drives Secondary Active Transport Example: Na+-Gradient created and maintained by the Na+/K+-pump powers Coupled Transport with Na+ movement downhill Na+- Gradient moves Different Solute (e.g. Glucose) Uphill Against Solute Gradient Glucose Transport Protein uses Na+ Concentration Gradient to drive Cotransport of Glucose and Na+ Diffusion of Na+ is Used to Fuel Active Transport of Glucose! Symport; Move in Same Direction Antiport; Move in Opposite Directions Na+ Movement drives Glucose Movement! 80 Copyrighted Material for In-class Use! No Publication or Distribution! 40  BIOL1152-02 Fall 2024 Active Transport Endocytosis and Exocytosis: Bulk Transport Solutes Packed in Membrane Vesicles for Transmembrane Transport Endocytosis transports solutes across the membrane into the cell, solutes remain packed in membrane vesicle once inside the cell! - Phagocytosis: cell “eats” large solutes; way to take in larger food particles, subsequently digested inside the cell (intracellular digestion in lysosomes) - Pinocytosis: cell “drinks” fluid; Vesicle contents is metabolized - Receptor mediated Endocytosis: Target Solutes bind to specific receptor proteins; receptors with solutes are invaginated as vesicle and metabolized 81 Active Transport Endocytosis and Exocytosis: Bulk Transport Exocytosis: Discharge of vesicle contents into the extracellular space by fusion of the vesicle with the cell membrane - Used to secrete cellular products packed in membrane vesicles by Golgi Apparatus (cellulose, enzymes, transmitters, hormones) Exocytosis and Endocytosis are Active Transport, requiring ATP! 82 Copyrighted Material for In-class Use! No Publication or Distribution! 41