86 lines
3.8 KiB
Markdown
86 lines
3.8 KiB
Markdown
[[Cell Structure and Function]]
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Membrane transport is how cells move materials across the nuclear membrane.
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Passive transport includes simple diffusion, facilitated diffusion, and osmosis.
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Active transport and bulk transport, including endocytosis and exocytosis use ATP to move substances against gradients or move large amounts of material.
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# Summary
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* Selective permeability comes from hydrophobic membrane interior.
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* Passive transport moves molecules down a concentration with no metabolic energy. Active transport uses ATP.
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* Concentration gradients store potential energy and let cells keep internal conditions different from outside.
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* Endocytosis and exocytosis move a lot of material and require energy.
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* Direction of movement (high to low/low to high) is the fastest clue to if it's using active or passive.
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* Cells use multiple transport types to maintain levels of solute and water.
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Larger movements of water require proteins called aquaporins.
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| Molecule Type | Examples | Can Cross Freely? | Needs Transport Protein? |
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| --------------------- | -------------------- | ------------------- | ------------------------ |
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| Small nonpolar | O₂, CO₂, N₂ | Yes | No |
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| Small polar uncharged | H₂O, NH₃ | Yes (small amounts) | Yes (large amounts) |
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| Large polar | Glucose, amino acids | No | Yes |
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| Ions | Na⁺, K⁺, Cl⁻, Ca²⁺ | No | Yes |
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# Concentration Gradients
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Selective permeability allows cells to build concentration gradients, which exist when a substance has different concentrations of a substance on either side.
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Allows for storing potential energy, drive passive transport, and maintain internal conditions separate from the outside.
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# Passive Transport
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1. Simple Diffusion
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* Molecules move straight through the membrane
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* Works for small non-polars
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2. Facilitated Diffusion
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* Still moves down gradient (high to low)
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* Requires transport or channel proteins
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* Used for polar molecules or ions
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3. Osmosis
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* Diffusion of water across the selectively permeable membrane
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* Moves from low to high (refers to solute concentrations)
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* Aquaporins speed up water movement
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# Active Transport
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Requires direct input of energy (usually ATP).
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* Uses membrane proteins, often called pumps
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* Important for processes like nerve function and nutrient absorption
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* Uses ATP
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* Can create concentration gradients
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|Transport Type|Energy Required?|Direction|Examples|
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|---|---|---|---|
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|Simple Diffusion|No|High to Low|O₂, CO₂|
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|Facilitated Diffusion|No|High to Low|Glucose, amino acids|
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|Active Transport|Yes (ATP)|Low to High|Na⁺/K⁺ pump, calcium pumps|
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1. Selective permability creates control
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2. Active transport allows for creating concentration gradients
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3. Passive transport allows for equilibrium
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4. Maintaining water and solute levels is vital to an organism
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# Transport of Large Molecules
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![[Pasted image 20260817123835.png]]
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Exocytosis (moving stuff out):
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* Internal vesicles fuse to plasma membrane
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* Requires energy
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* Is then secreted outside
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* Used for secreting things like hormones
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Endocytosis (bringing stuff in):
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* Plasma membrane folds inwards and create vesicle
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* Requires energy
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* Vesicle pinches off and enters
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Three main types of endocytosis:
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1. Phagocytosis
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* Cell engulfs large molecules or microorganisms
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* Creates food vacuoles
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* Common for white blood cells that take in bacteria
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2. Pinocytosis
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* Cell takes in liquid with dissolved substances
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* Non specific: brings in whatever is liquid
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3. Receptor-Mediated Endocytosis
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* Specific: only brings in molecules that bind to receptors
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* Receptors clustered in coated pits that form vesicles
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* Examples: cholesterol uptake, insulin uptake |