Cell Membrane Structure and Function
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Questions and Answers

How does the amphipathic nature of phospholipids contribute to the selective permeability of the cell membrane?

The hydrophobic tails form a barrier to charged or polar molecules, restricting their passage, while the hydrophilic heads interact with water, allowing small polar molecules to pass.

Explain how the Na+/K+ ATPase contributes to maintaining cellular integrity, and what type of transport does it utilize?

It maintains the electrochemical gradient necessary for cell volume, secondary transport, and nerve and muscle function. This pump uses active transport.

Describe how microfilaments and microtubules contribute differently to cell movement and structural support?

Microfilaments, made of actin, support cell shape and movement via interactions with motor proteins like myosin. Microtubules, composed of tubulin, provide tracks for intracellular transport and contribute to the structure of cilia and flagella, enabling movement.

How does cholesterol affect membrane fluidity at different temperatures?

<p>Cholesterol reduces fluidity at high temperatures by limiting phospholipid movement and prevents solidification at low temperatures by disrupting tight packing of phospholipids.</p> Signup and view all the answers

Describe the role of the cell membrane in cell signaling. Please give an example.

<p>The cell membrane contains receptors that bind to signaling molecules, initiating a cascade of intracellular events. For instance, a growth factor binding to its receptor tyrosine kinase and activating downstream signaling pathways ultimately affecting the cell's genetic expression or behaviour.</p> Signup and view all the answers

Briefly explain how co-transport mechanisms utilize existing ion gradients to facilitate the movement of other molecules across the cell membrane. Provide an example.

<p>Co-transport uses the electrochemical gradient of one molecule (e.g., Na+) moving down its concentration gradient to 'pull' another molecule (e.g., glucose) across the membrane, even against its own concentration gradient. SGLT-1 and SGLT-2 are examples.</p> Signup and view all the answers

Describe the key structural features common to most cell membrane receptors that bind extracellular signals, and briefly explain how these features contribute to signal transduction.

<p>Most receptors have hydrophobic domains spanning the lipid bilayer, an extracellular domain for signal binding, and an intracellular domain for signal amplification. These domains enable the receptor to receive, transmit, and amplify the signal into the cell.</p> Signup and view all the answers

In the context of cellular function, explain why it is advantageous for organelles to be enclosed by membranes rather than being 'open' to the cytosol.

<p>Membranes allow for the creation of specific micro-environments within the organelle, optimizing conditions (e.g., pH, ion concentration) for its unique functions and preventing interference with cytosolic processes. It also compartmentalizes harmful substances.</p> Signup and view all the answers

Differentiate between co-transport and counter-transport, highlighting the directional movement of molecules and the energy source driving each process. Provide an example of counter-transport.

<p>Co-transport moves two molecules in the same direction, driven by the gradient of one molecule. Counter-transport moves two molecules in opposite directions, with one molecule's gradient powering the other's movement. An example is the Cl-/HCO3- exchanger.</p> Signup and view all the answers

Explain how a cell's response to a specific extracellular signal is determined, even when multiple cell types are exposed to the same signal, and give an example.

<p>A cell's response to a hormone depends on whether it expresses the specific receptor for that signal. Different cell types express different receptors, leading to varied responses even when exposed to the same signal. For example, only cells with a receptor for growth hormone will respond to it.</p> Signup and view all the answers

Describe how the high concentration of sodium ions ([Na+]) in the extracellular fluid (ECF) contributes to both passive and active transport mechanisms in cells.

<p>The diffusional force from the high [Na+] in the ECF drives Na+ into the cell, which can be used in co- or counter-transport mechanisms for active transport of other substances. Simultaneously, the movement of these charged particles across the membrane changes the charge across the membrane and can change cellular activity – more later.</p> Signup and view all the answers

Explain the difference between facilitated transport and co-transport, highlighting the role of membrane proteins in each process.

<p>Facilitated transport involves a protein carrier binding to a single substance for transport along its concentration gradient. Co-transport uses a single protein to couple the transport of two substances, leveraging the concentration gradient of one to move the other.</p> Signup and view all the answers

Consider a cell that needs to import glucose against its concentration gradient. Describe a mechanism involving both active and passive transport that could accomplish this.

<p>The cell could use a sodium-glucose co-transporter. Sodium ions flow down their concentration gradient (passive), providing the energy for the co-transporter to move glucose against its concentration gradient (active).</p> Signup and view all the answers

If a drug inhibits the function of the Na+/K+ ATPase, how might this indirectly affect the transport of other molecules into the cell? Give one specific example.

<p>Inhibiting the Na+/K+ ATPase reduces the sodium gradient. This will reduce the energy available for the import of other molecules, such as glucose, via co-transport mechanisms.</p> Signup and view all the answers

Explain why small hydrophobic molecules can diffuse directly across the cell membrane, while larger or charged molecules require the assistance of membrane proteins.

<p>Small hydrophobic molecules can dissolve in the lipid bilayer and pass through due to their compatibility with the nonpolar environment. Larger or charged molecules are repelled by the hydrophobic core and require channels or transporters to facilitate their passage.</p> Signup and view all the answers

Describe how the semi-permeable nature of cell membranes contributes to the necessity of energy expenditure by the cell.

<p>Since the cell membrane is impermeable to larger solutes on the inside of the cell compared to the outside, cells must expend energy to regulate the solute concentration and cell volume.</p> Signup and view all the answers

How does the Na+/K+ ATPase contribute to preventing cell swelling due to osmosis?

<p>By pumping 3 Na+ ions out of the cell and 2 K+ ions into the cell, the Na+/K+ ATPase maintains a solute gradient that prevents excessive water influx and subsequent swelling.</p> Signup and view all the answers

Explain how the sodium gradient, established by the Na+/K+ ATPase, can be used to transport other substances across the cell membrane.

<p>The sodium gradient created by the Na+/K+ ATPase provides potential energy that can be coupled with the transport of other molecules across the membrane, such as in secondary active transport mechanisms.</p> Signup and view all the answers

What would happen to the concentration gradient of sodium and potassium ions if a cell's ATP production was significantly reduced? Why?

<p>The concentration gradients of sodium and potassium would dissipate because the Na+/K+ ATPase requires ATP to function. Without ATP, the pump cannot actively transport ions against their concentration gradients.</p> Signup and view all the answers

If a cell suddenly loses its ability to produce ATP, explain why the cell starts to swell.

<p>With reduced ATP, the Na+/K+ ATPase cannot function properly, leading to a buildup of ions inside the cell. This increases the intracellular solute concentration, causing water to enter the cell via osmosis, resulting in swelling.</p> Signup and view all the answers

Describe the significance of aquaporins in maintaining cellular homeostasis, and explain how they function in conjunction with osmosis.

<p>Aquaporins are integral membrane proteins that act as channels to facilitate the rapid movement of water across the cell membrane, increasing water conductance. In conjunction with osmosis, they allow water to move down its concentration gradient quickly, helping cells regulate volume and respond to changes in solute concentration.</p> Signup and view all the answers

How would a drug that inhibits aquaporin function affect cells in a hypotonic solution?

<p>In a hypotonic solution (lower solute concentration outside the cell), water would still enter the cell due to osmosis, but at a significantly slower rate. This could lead to a slower rate of cell swelling (or eventual lysis) compared to normal.</p> Signup and view all the answers

Explain how the Na+/K+ ATPase contributes to establishing a gradient of charge across the cell membrane, and why this is important for the cell.

<p>The Na+/K+ ATPase pumps 3 positive sodium ions out for every 2 positive potassium ions in. This unequal exchange of charge results in a net positive charge outside the cell and a net negative charge inside, establishing an electrochemical gradient. This is crucial for nerve impulse transmission, muscle contraction, and other cellular processes.</p> Signup and view all the answers

How do microtubules contribute to cellular organization, and what is the role of the MTOC in this process?

<p>Microtubules form a cellular scaffolding that positions cellular structures and determines cell polarity. The MTOC, containing centrioles, organizes and anchors these microtubules.</p> Signup and view all the answers

Describe how dyneins and kinesins facilitate cellular movement using microtubules, and what is the key difference in their movement?

<p>Dyneins and kinesins are motor proteins that move along microtubules, causing the 'whipping' movements of cilia and flagella. Dyneins and kinesins move in opposite directions along microtubules.</p> Signup and view all the answers

What are the structural differences between centrioles and the microtubules that radiate from the MTOC?

<p>Centrioles have a '9x3' structure, consisting of nine tubulin triplets, while the microtubules radiating from the MTOC are typically composed of tubulin dimers arranged in a cylindrical structure.</p> Signup and view all the answers

Explain how the dynamic instability of F-actin and microtubules is related to the function of molecular motors like myosin, dynein and kinesin.

<p>Molecular motors like myosin, dynein and kinesin require dynamic filaments like F-actin and microtubules to move along, which is similar to how a train moves along a track.</p> Signup and view all the answers

How does the structure of intermediate filaments contribute to their stability, and why is this stability important for cells?

<p>Intermediate filaments have a coiled structure and do not hydrolyze GTP or ATP, making them more stable than actin or tubulin. This stability provides structural support and resistance to cellular stress.</p> Signup and view all the answers

Describe the role of the primary cilium in cellular signaling and its importance for cellular function or localization.

<p>The primary cilium senses stimuli in the extracellular environment and helps with cellular localization and function. In other words, it is important for cell signaling.</p> Signup and view all the answers

How do keratins contribute to the properties of epithelial cells, hair, and nails?

<p>Keratins are strong intermediate filaments found in epithelial cells, hair, and nails. They are modified to limit water permeability and provide strength.</p> Signup and view all the answers

Explain the distinct roles of microtubules during cell division.

<p>During cell division, microtubules form the mitotic spindle, which separates chromosomes and pulls them to opposite poles of the dividing cell, ensuring each daughter cell receives the correct genetic material.</p> Signup and view all the answers

What characteristics differentiate intermediate filaments from microfilaments and microtubules, in terms of protein structure and energy requirements?

<p>Intermediate filaments have a more diverse structure, formed by long proteins with an alpha-helix conformation that coil around other monomers. Unlike actin and tubulin, they do not hydrolyze GTP or ATP.</p> Signup and view all the answers

Describe the function of lamins and their location within the cell.

<p>Lamins are a type of intermediate filament that form a network of filaments just under the nuclear membrane, providing structural support to the nucleus.</p> Signup and view all the answers

How do tight junctions contribute to the compartmentalization of tissues, and what is the significance of their varying selectivity?

<p>Tight junctions create distinct apical and basal compartments within tissues by controlling the passage of substances between cells. Their varying selectivity allows for differential regulation of molecule movement, influencing tissue-specific functions and permeability.</p> Signup and view all the answers

Describe the roles of cadherins and intermediate filaments in the structural integrity provided by desmosomes.

<p>Cadherins mediate cell-cell adhesion by interacting with cadherins on neighboring cells, while intermediate filaments anchor to intracellular plaques connected to cadherins. This arrangement distributes mechanical stress, providing robust structural support to tissues.</p> Signup and view all the answers

How do hemidesmosomes differ from desmosomes in terms of their extracellular components and the structures they connect?

<p>Hemidesmosomes utilize integrins to connect to the basement membrane, anchoring epithelial cells to the underlying connective tissue. Desmosomes, in contrast, use cadherins to connect to adjacent cells.</p> Signup and view all the answers

Adherens junctions can connect to another cell via _______, or to a basement membrane via _______?

<p>Adherens junctions can connect to another cell via <em>cadherins</em>, or to a basement membrane via <em>integrins</em>.</p> Signup and view all the answers

Explain how the cytoskeleton contributes to both cellular movement and the organization of intracellular components.

<p>The cytoskeleton enables cellular movement through the dynamic assembly and disassembly of actin filaments and microtubules. It also organizes intracellular components by providing tracks for organelle transport and structural support during processes like cell division.</p> Signup and view all the answers

Describe the roles of microtubules, microfilaments, and intermediate filaments in maintaining the overall structural integrity of a cell.

<p>Microtubules resist compression and provide tracks for intracellular transport, microfilaments support cell shape and drive cellular movement, and intermediate filaments provide tensile strength and stability to the cell.</p> Signup and view all the answers

How does the dynamic nature of the cytoskeleton allow cells to respond to changing environmental conditions or signals?

<p>The dynamic assembly and disassembly of cytoskeletal filaments allow cells to rapidly remodel their shape, move, and reorganize their internal structure in response to environmental cues or intracellular signals.</p> Signup and view all the answers

Explain how the regulation of actin filament assembly and disassembly can influence cell shape and movement.

<p>Regulating actin filament assembly and disassembly controls the formation of structures like lamellipodia and filopodia, which drive cell migration. By modulating the balance between polymerization and depolymerization, cells can dynamically change their shape and move in specific directions.</p> Signup and view all the answers

Actin monomers, known as _______, polymerize to form _______.

<p>Actin monomers, known as <em>G-actin</em>, polymerize to form <em>F-actin</em>.</p> Signup and view all the answers

Describe how ATP hydrolysis affects the stability of F-actin filaments and the likelihood of G-actin monomers dissociating from the filament.

<p>ATP hydrolysis by G-actin within F-actin filaments weakens the binding affinity between monomers. G-actin bound to ADP is more likely to dissociate from the filament, leading to depolymerization.</p> Signup and view all the answers

How do capping proteins influence the stability of actin filaments, and what effect does this have on cell behavior?

<p>Capping proteins bind to the ends of actin filaments, preventing further polymerization or depolymerization. This stabilizes the filament and can influence cell shape, motility, and the formation of specific actin-based structures.</p> Signup and view all the answers

How do the organization and stability of actin filaments differ in muscle cells compared to fibroblasts, and why are these differences important for their respective functions?

<p>Muscle cells have stable, parallel actin filaments for force generation, whereas fibroblasts have dynamic meshes for exploration. Muscle cells need a stable actin system to generate lots of force. Fibroblasts use actin filaments to explore their enviornment to deposit collagen/ECM.</p> Signup and view all the answers

What are the two types of tubulin that form dimers?

<p>Alpha and beta tubulin.</p> Signup and view all the answers

How does GTP hydrolysis affect the stability of microtubules, and what is this phenomenon known as?

<p>GTP hydrolysis by beta-tubulin within microtubules destabilizes the polymer, leading to rapid depolymerization. This phenomenon is known as dynamic instability.</p> Signup and view all the answers

How does dynamic instability contribute to the diverse functions of microtubules in cellular processes?

<p>Dynamic instability enables microtubules to rapidly explore the cytoplasm, attach to chromosomes during cell division, and transport cargo within the cell. This dynamic behavior is essential for processes like mitosis, cell motility, and intracellular trafficking.</p> Signup and view all the answers

Flashcards

Phospholipid Bilayer

A double layer of phospholipids forming the cell membrane's structural foundation, providing barrier and fluidity.

Membrane Proteins

Proteins embedded in the cell membrane serving various functions like transport and signaling.

Na+/K+ ATPase

An enzyme that uses ATP to pump sodium out and potassium into the cell, maintaining cellular integrity.

Diffusion

The passive movement of molecules from an area of higher concentration to lower concentration across a membrane.

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Cytoskeleton

A network of fibers (microfilaments, microtubules, intermediate filaments) providing structure and transport within cells.

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Active Transport

Movement of substances across a membrane against concentration gradient using energy (ATP).

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Passive Transport

Movement of molecules across a membrane from high to low concentration without energy use.

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Facilitated Transport

Movement of substances across a membrane via a protein carrier along its concentration gradient.

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Co-Transport

Coupled transport of two substances through the same protein, either in the same direction or opposite.

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Ion Channels

Proteins that allow charged particles to move across the membrane, critical for signaling.

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Counter-transport

Transport process where molecules X and Y move in opposite directions, using the gradient of one to drive the other's movement.

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Receptor signaling

Process where extracellular signals bind to protein receptors on the cell membrane, causing a response.

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Hydrophobic domains

Parts of protein receptors that extend through the lipid bilayer and interact with membrane lipids.

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Membrane protein functions

Diverse roles of membrane proteins including signaling, protection, transport, and structural support.

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Tight Junctions

Junctions that separate apical and basal compartments and regulate movement across membranes.

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Anchoring Junction - Desmosome

Connects adjacent cells, providing structural integrity through cadherins and intermediate filaments.

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Hemi-desmosome

A type of anchoring junction that anchors cells to the basement membrane using integrins.

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Adherens Junction

Connects cells or a cell to the basement membrane, using a plaque connected to microfilaments.

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Cytoskeleton Functions

Supports cellular movement, organization, structure, and communication within the cell.

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Microtubules

Cytoskeletal structures made of tubulin that organize cell structure and assist in movement.

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Microfilaments

Thin fibers composed of actin important for cellular movement and structure.

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Intermediate Filaments

Cytoskeletal components providing overall structural integrity to a cell.

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Dynamic Filament Assembly

Filaments can grow and shrink, regulated by intracellular signals.

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G-actin vs F-actin

G-actin is the monomer, F-actin is the filament formed by polymerizing G-actin.

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Dynamic Instability of Microtubules

When tubulin dimers rapidly assemble and disassemble, affecting the stability of microtubules.

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Integrins

Proteins that bind cells to the extracellular matrix, essential for cell anchoring and communication.

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Cadherins

Proteins essential for cell-to-cell adhesion in desmosomes and adherens junctions.

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Basement Membrane

A thin layer that separates epithelial cells from underlying connective tissue, anchoring epithelial cells.

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Microtubule Organizing Centre (MTOC)

A structure composed of centrioles that organizes microtubules for cellular functions.

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Centrioles

Cylindrical structures made of microtubules that form the MTOC.

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Tubulin Triplet Structure

The unique arrangement of three tubulin proteins that make up centrioles.

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Cilia and Flagella

Cellular projections made of microtubules that aid in movement.

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Cell Division

Process where microtubules help separate chromosomes into daughter cells.

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Primary Cilium

A single, non-motile structure that senses stimuli in the environment.

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F-actin

Filamentous actin protein that forms a network within cells.

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Molecular Motors

Proteins (like myosin, dyneins, and kinesins) that move along filaments for cellular transport.

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Types of Intermediate Filaments

Examples include lamins, keratins, vimentin, and neurofilaments with specific functions.

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Osmosis

The diffusion of water through a semi-permeable membrane.

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Semi-permeable membrane

A membrane that allows certain substances to pass through while blocking others.

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Cellular swelling prevention

The mechanism by which cells avoid swelling by regulating ion concentrations.

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Aquaporins

Channel proteins that facilitate the transport of water across the plasma membrane.

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Concentration gradients

Differences in the concentration of substances across a membrane, crucial for signaling and metabolism.

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Study Notes

Physiology 1.04 - Foundational Physiology Cell Membranes in Physiology

  • This course covers foundational cell membrane concepts within physiology.
  • The course is part of BMS 100, a broader study on specific modules within physiology.
  • The Canadian College of Naturopathic Medicine (CCNM) is the provider of this course material.

Learning Outcomes

  • Students will understand the structural components of cell membranes including phospholipids, cholesterol, sphingolipids, and membrane proteins.
  • They will examine the basic structure of the phospholipid bilayer and its function as a molecular barrier for homeostasis.
  • Students will identify different types of transport across the plasma membrane, focusing on diffusion, osmosis, and the Na+/K+ ATPase's role in maintaining cellular integrity.
  • The function of the plasma membrane in cell signaling will also be analyzed.
  • Students will understand the cytoskeleton, including detailed descriptions of microfilaments, microtubules, and intermediate filaments.
  • Cellular motors associated with F-actin and microtubules are to be described.

Overview - Cell Membranes

  • Key lipid components of cell membranes include phospholipids, cholesterol, and sphingolipids.
  • Types of membrane proteins and their function are examined.
  • Comparisons of the plasma membrane and the endomembrane system are made for a deeper understanding.
  • Cytoskeleton components (microfilaments, microtubules, and intermediate filaments) are a key concept.
  • Functions of cell membranes, including molecular partitioning, homeostasis, transport, movement, cellular integrity, and cell signaling, are covered.

The Cell Membrane - General Structure

  • The cell membrane's components, such as glycoproteins, glycolipids, peripheral membrane proteins, integral membrane proteins, cholesterol, and channel proteins, each contribute to its unique function.
  • Diagram of a typical cell membrane showing these components is presented.

Lipid Components

  • Glycerophospholipids: Phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol are the most common glycerophospholipids in the cell membrane. Phosphatidylinositol plays a role in signaling.
  • Sphingolipids: Slightly differing shape compared to glycerophospholipids, and sphingolipids can decrease membrane fluidity. They are involved in cellular signaling and the formation of lipid rafts and myelin. Contribution to glycocalyx.
  • Glycocalyx: Carbohydrates covalently attached to protein and lipid components, which are more prominent on the outer leaflet of the cell membrane. Key roles include protective structures, structural interactions for signaling.

Cholesterol

  • Cholesterol, belonging to the isoprenoid class of lipids, intercalates between phospholipids.
  • It helps stabilize membrane fluidity.

Structure and Function of Membrane Lipids

  • The amphipathic nature of lipids in cell membranes leads to bilayer formation.
  • Hydrophobic tails interact with one another, while hydrophilic heads interact with the aqueous environment.
  • The phospholipid bilayer functions as a barrier for certain molecules.
  • The integrity of the plasma membrane is essential for cell survival and function, including maintaining homeostasis, keeping vital molecules within the cell, and cellular movement.

Importance of the Na+/K+ ATPase

  • Na+/K+ ATPase is a critical plasma membrane transporter.
  • Its operation involves 3 sodium ions pumped out and 2 potassium ions pumped in, powered by ATP hydrolysis, regulating cellular volume and charge gradients.
  • It plays a significant role in osmotic balance and transmembrane transport.

Transport and the Cell Membrane

  • Transport across membranes can be passive (e.g., diffusion) or active (requiring energy).
  • Passive transport moves material along concentration gradients; active requires energy.
  • Specific types of transport are discussed including active transport (e.g., Na+/K+ ATPase), passive transport (e.g., aquaporins), facilitated transport (e.g., glucose transporter), cotransport, and countertransport.

Other Cellular Membranes and Gradients

  • Different organelles have specialized membranes that are important for their function.
  • The membrane keeps the organelle's internal components separate from the cytosol.

Plasma Membrane and Signaling

  • Cells respond to extracellular signals, often through receptors on the cell membrane.
  • Extracellular signals, such as hormones and growth factors, bind to receptors, triggering intracellular signaling pathways.
  • Receptors typically have domains that span the lipid bilayer and bind extracellular signals while interacting intracellularly to amplify signals

Membrane Proteins

  • Membrane proteins have a wide range of functions relating to signaling, transport and general homeostasis, protection, and structure/movement.
  • Different proteins have different functions.
  • Membrane proteins can link the cell membrane to both extracellular and intracellular structures and are important for stability.

Tight Junctions

  • Tight junctions separate cells into apical and basal compartments.
  • They regulate the movement of molecules and substances across cell membranes and in other epithelial structures.

Anchoring Junctions

  • Intracellular components of anchoring junctions, such as desmosomes, involve molecules associated with cadherins and intermediate filaments.
  • Extracellular components include cadherins on neighboring cells.
  • Purpose: Structural integrity in cells and tissue.

Anchoring Junction - Hemi-Desmosome

  • Similar to desmosomes, but the extracellular component involves integrins.
  • Typically link epithelial cells to the basement membrane.

Adherens Junction

  • These junctions use a plaque that can connect to another cell or a basement via microfilaments.

The Cytoskeleton

  • The cytoskeleton is crucial for cellular functions like movement, organization, maintenance of cellular structure, and interaction with organelles and vesicles.

Microfilaments

  • Microfilaments are primarily composed of actin.
  • Their structure and function are discussed.
  • Actin filaments are involved in cell movement and force production, such as cell crawling and muscle contraction.

Microtubules

  • Microtubules are more complex structures than actin and are composed of dimers of alpha and beta-tubulin.
  • They are involved in cellular organization, movement (e.g., cilia, flagella), and cell division.

Microtubules - Important aspects

  • Microtubules are composed of alpha and beta tubulin, and are involved in the formation of cilia, flagella, and the cell division process.

Microfilaments, Microtubules, and Cellular Motors

  • F-actin and microtubules, coupled with molecular motors like myosin, dynein, and kinesin, are essential for cellular movement, transport, and overall organization.

Intermediate Filaments

  • Intermediate filaments provide structural integrity to cells and tissues, resisting mechanical stress, including those found in neurons, skin, and other areas.
  • Many different types of intermediate filaments exist with varied, complex structures.

Intermediate Filaments – Some Examples

  • Lamins are found beneath the nuclear membrane, contributing to nuclear structure and stability.
  • Keratins function in epithelial cells, nails, and hair, providing strength and resistance to stress.
  • Vimentin family provides stability in mesenchymal cells.
  • Neurofilaments are found in neurons and support the cell structure there.

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Explore the structure and functions of cell membranes, including selective permeability, transport mechanisms like Na+/K+ ATPase, and the roles of microfilaments and microtubules. Understand how cholesterol affects membrane fluidity and the cell membrane's role in cell signaling. Discover the importance of membrane-bound organelles.

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