Transmembrane Transport of Small Molecules and Ions PDF

Pumping 3 Na⁺ out and 2 K⁺ in (both against the Allows Essential molecules like nutrients can...

Pumping 3 Na⁺ out and 2 K⁺ in (both against the Allows Essential molecules like nutrients can enter the cell gradiant) for every ATP hydrolyzed ** It is Semi-permeable (selectively allows **Na⁺-K⁺ Pump** Plasma Membrane certain molecules to pass through while Keeps intermediate metabolites inside the cell Maintains membrane potential, regulates cell volume (high keeping others out)** Na⁺ concentration outside the cell and high K⁺ inside) Excretes waste products for cell health Maintains low intracellular Ca²⁺ concentration **Calcium Pump** **Primary Active Transport**: Regulates acidity in stomach cells follows the concentration gradient, meaning molecules **Proton Pump** move from areas of high concentration to low concentration and organelles like lysosomes Largest family of ATP hydrolysis-coupled Small or hydrophobic molecules move through transporters Simple Diffusion the lipid bilayer without assistance (O₂, CO₂, **Passive Transport (movement without energy steroids) Import nutrients (amino acids, peptides) input)** Importers & Exporters: Larger or charged molecules use transport proteins Facilitated Diffusion Export toxins, drugs, antibiotics (channels or carriers) (glucose, amino acids) **ABC Transporters** (ATP-binding cassette) Active Transport - Key Concepts Overexpressed in tumor cells Osmosis The movement of water through the membrane Example: **MDR transporter** (multidrug Types of Transport resistance) This process requires energy (usually ATP) to move Pumps drugs out → **Drug resistance** molecules against their concentration gradient Example: **CFTR** (Cystic Fibrosis Na⁺-K⁺ pump Transmembrane Conductance Regulator) **Active Transport** **Primary Active Transport**: Direct use of **Symporters**: Molecules move in same Calcium pump energy (ATP) direction (eg; Na⁺/glucose co-transporters in But then Na+ accumulates in the cell and their is no more to realise secondary transport. We then need atp to pump na+ out of the cell. SO the intestines) the movement of one solute drives the **Coupled Transport (Secondary Active Transmembrane Types: Proton pump movement of another. There are two types: Transport)**: undirectly secondary transport use ATP **Antiporters**: Molecules move in opposite directions (e.g., Na⁺/Ca²⁺ exchanger in cardiac Transport of Small **Secondary Active Transport** (Coupled Transport) (Uses the energy from the movement Symporters (Na⁺/glucose co-transporter) cells) Molecules and Ions of one molecule down its gradient to move another molecule up its gradient) Antiporters (Na⁺/Ca²⁺ exchanger, Na⁺/H⁺ exchanger) Hydrophobic molecules pass easily This selectivity is achieved through narrow Smaller molecules diffuse faster **Simple Diffusion**(O₂, CO₂, steroids) pores that act as size filters, and by interactions between the ion and specific components of The larger the gradient, the faster the diffusion the channel, such as carbonyl oxygens Ion channels and carrier proteins **They are Selective**:based on size and charge **Na⁺ channels**: More selective for Na⁺ over K⁺ Passive Transport - Key Concepts Example: **GLUT-1** glucose transporter **K⁺ channels**: More selective for K⁺ over Na⁺ Allow specific ions to pass rapidly through the Ion Channels Open in response to changes in membrane Voltage-gated membrane potential **Facilitated Diffusion** Voltage-gated, ligand-gated, mechanosensitive Channels: Eg: the acetylcholine receptor at **Types of ion channels**: Ligand-gated Open when a specific molecule (ligand) binds neuromuscular junction with na+ **Na⁺ and K⁺ channels**: Ion selectivity Mechanosensitive Respond to mechanical forces (e.g., stretching) Bind to the molecule and undergo conformational changes Carriers to transport it across the membrane the movement of water across a membrane down its osmotic gradient Osmosis and Aquaporins **Osmosis**: Have narrow pores that allow water to pass in single file moves through specialized channels called aquaporins, which: Completely block ions