Cell Junctions and Substance Movement PDF

8/27/24, 8:22 PM Platform | Study Fetch Cell Junctions and Substance Movement Cell Junctions (00:00:40 - 00:01:52) Cell junctions are cellular structures of protein complexes that link cells together or cells with their extrace...

8/27/24, 8:22 PM Platform | Study Fetch Cell Junctions and Substance Movement Cell Junctions (00:00:40 - 00:01:52) Cell junctions are cellular structures of protein complexes that link cells together or cells with their extracellular matrix. They play a role in the movement of substances between cells and in cell-cell communication. Types of Cell Junctions: Tight Junctions Provide a tight seal to prevent leakage Found in areas with a lumen, like the intestinal tract, to isolate the epithelium Prevent leakage from the lumen into the intracellular space Adherens Junctions Provide mechanical stress protection Allow the connection of structural long proteins to give tissue integrity and structure Desmosomes Not covered in this video Gap Junctions Not covered in this video Hemidesmosomes Not covered in this video Movement of Substances (00:00:28 - 00:00:40) Cell junctions play a role in the movement of substances between cells and in cell-cell communication. Key Points: Cell junctions are classified according to their function Tight junctions provide a tight seal to prevent leakage Adherens junctions provide mechanical stress protection by connecting structural proteins Cell junctions facilitate movement of substances between cells and cell-cell communication Structural Connections in Cells (00:01:52 - 00:02:11) Actin filaments create tight connections between cells https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bcee81bb65113fe36ae/document?go=note 1/6 8/27/24, 8:22 PM Platform | Study Fetch These are more structural connections, versus the "water type" connections Desmosome vs. Hemidesmosome (00:02:11 - 00:02:22) Desmosomes connect two cells next to each other, like in an epithelial layer Hemidesmosomes attach the basolateral side of a cell to the extracellular matrix, typically via integrins Gap Junctions (00:02:33 - 00:02:49) Gap junctions allow rapid communication and diffusion between cells, especially important in muscle cells They form a ring-like structure that can be open or closed, creating a small pore between cell membranes Plasmodesmata (00:02:49 - 00:03:14) Narrow channels between plant cells that allow exchange of fluids and signaling molecules Facilitate cell-cell communication in plants Movement of Substances (00:03:14 - 00:03:47) Solute Concentrations Hypertonic solution has higher solute concentration outside the cell than inside Hypotonic solution has lower solute concentration outside the cell than inside Isotonic solution has equal solute concentration inside and outside the cell Osmosis Movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration Can lead to cell swelling (in hypotonic solution) or shrinking (in hypertonic solution) Diffusion Movement of substances from an area of higher concentration to an area of lower concentration Driven by random thermal motion of molecules Active Transport Requires energy (ATP) to move substances against their concentration gradient Allows cells to maintain concentration differences between inside and outside https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bcee81bb65113fe36ae/document?go=note 2/6 8/27/24, 8:22 PM Platform | Study Fetch Osmosis and Tonicity (00:03:47 - 00:04:02) Osmosis is the movement of water molecules across a semipermeable membrane from an area of lower solute concentration (higher water concentration) to an area of higher solute concentration (lower water concentration). This osmotic force can cause cells to shrink and shrivel up as water is pulled out of them into the extracellular solution. Isotonic, Hypotonic, and Hypertonic Solutions (00:04:02 - 00:04:16) Isotonic solution: the extracellular and intracellular spaces have the same solute concentration, so there is no net movement of water. Hypotonic solution: the extracellular space has a lower solute concentration than the intracellular space, causing water to move into the cell, leading to swelling and potential bursting. Hypertonic solution: the extracellular space has a higher solute concentration than the intracellular space, causing water to move out of the cell, leading to shrinkage. Passive and Active Transport (00:04:16 - 00:04:58) Passive Transport: Diffusion: the movement of substances (e.g., steroids, gases) down their concentration gradient across the cell membrane without the use of energy. Ion channels: allow for the passive flow of ions (e.g., potassium) down their concentration gradient across the cell membrane. Active Transport: Requires the use of energy, typically in the form of ATP, to move substances against their concentration gradient. An example is the transport of hydrogen ions into the mitochondria. Mitochondrial Transport (00:04:58 - 00:05:16) The cell transports hydrogen ions into the mitochondria using active transport mechanisms. This is an important process for the production of ATP, the cell's primary energy currency. The Mitochondrial Membrane Gradient and ATP Production (00:05:16 - 00:05:26) https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bcee81bb65113fe36ae/document?go=note 3/6 8/27/24, 8:22 PM Platform | Study Fetch The space within the mitochondria allows for a gradient to develop across the mitochondrial (internal) membrane. This gradient creates a force that drives the creation of ATP. Passive Transport and Gradients (00:05:26 - 00:05:40) Glucose is typically passively transported, not actively transported, because there is usually a higher concentration outside the cell than inside. Cells will use ATP to establish gradients for things they want to transport. Types of Passive Transport (00:05:40 - 00:06:20)Passive Diffusion: Gases will move across the membrane by passive diffusion. Facilitated Diffusion: Proteins may be needed to transport something against its concentration gradient by exchanging it with something moving down its concentration gradient. Countercurrent Exchange: When two liquids flow past each other in opposite directions, it increases the rate of exchange of anything between them, such as gases. Vesicular Transport: Can involve endocytosis, where something is drawn into the cell, or exocytosis, where something is expelled from the cell. Mitochondrial Membrane Gradient and ATP (00:05:16 - 00:05:26) The space within the mitochondria allows for a gradient to develop across the mitochondrial (internal) membrane. This gradient creates a force that drives the creation of ATP. Passive Transport and Gradients (00:05:26 - 00:05:40) Glucose is typically passively transported, not actively transported, because there is usually a higher concentration outside the cell than inside. Cells will use ATP to establish gradients for things they want to transport. Types of Passive Transport (00:05:40 - 00:06:20)Passive Diffusion: Gases will move across the membrane by passive diffusion. Facilitated Diffusion: https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bcee81bb65113fe36ae/document?go=note 4/6 8/27/24, 8:22 PM Platform | Study Fetch Proteins may be needed to transport something against its concentration gradient by exchanging it with something moving down its concentration gradient. Countercurrent Exchange: When two liquids flow past each other in opposite directions, it increases the rate of exchange of anything between them, such as gases. Vesicular Transport: Can involve endocytosis, where something is drawn into the cell, or exocytosis, where something is expelled from the cell. Vesicular Transport (00:06:20 - 00:06:36) Vesicular transport can involve endocytosis, where something is drawn into the cell, or exocytosis, where something is expelled from the cell. Countercurrent exchange, where two liquids flow past each other in opposite directions, can increase the rate of exchange between them. Countercurrent Exchange (00:06:36 - 00:06:48) Countercurrent exchange, where two liquids flow past each other in opposite directions, can increase the rate of exchange of anything between them, such as gases. Vesicular Transport and Endocytosis/Exocytosis (00:06:48 - 00:07:05) Vesicular transport can involve endocytosis, where something is drawn into the cell, or exocytosis, where something is expelled from the cell. Cell Membrane and Vesicle Transport Cell Membrane (00:07:05 - 00:07:34) The cell membrane envelops the external environment of the cell Substances can be taken up into the cell through a process called endocytosis In endocytosis, the cell membrane forms a small vesicle or "packet" around the substance, bringing it into the cell This vesicle can then be transported to an endosome, where the cell can decide what to do with the contents The cell may break down the contents using lysosomes, or it may use the contents as nutrients Endocytosis is a way for cells to take in materials from their external environment https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bcee81bb65113fe36ae/document?go=note 5/6 8/27/24, 8:22 PM Platform | Study Fetch Exocytosis (00:07:34 - 00:07:49) Exocytosis is the opposite of endocytosis In exocytosis, a vesicle fuses with the cell membrane and releases its contents outside the cell This is how cells can secrete substances, like neurotransmitters, to the extracellular environment Phagocytosis vs. Pinocytosis (00:08:15 - 00:08:27) Phagocytosis is the uptake of large particles by the cell Pinocytosis is the uptake of small substances by the cell The main difference is the size of the material being taken in Key Points: Cell Membrane: Envelops the external environment of the cell Endocytosis: Cell membrane forms a vesicle around a substance, bringing it into the cell Endosome: Vesicle can be transported here, where the cell decides what to do with the contents Lysosomes: Can break down the contents of the endosome Exocytosis: Vesicle fuses with cell membrane to release contents outside the cell Phagocytosis: Uptake of large particles by the cell Pinocytosis: Uptake of small substances by the cell https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce6bcee81bb65113fe36ae/document?go=note 6/6