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The Cell 

The Cell 

Cellular membranes are fluid mosaics of lipids and proteins 

- The plasma membrane is selectively permeable, meaning it allows some substances to cross more easily than others 

- FLUID MOSAIC MODEL: membrane represented as a fluid with proteins integrated in the phospholipid bilayer

- PHOSPHLIPIDS: provide a hydrophobic barrier that separates the cell from its liquid environment 

    -amphipathic 

    -fluid/ viscous membrane 

    -saturated fatty acids 

        -decreases fluidity 

   -unsaturated fatty acid tails 

       -increases fluidity

- PROTEINS: acts as transport channels by molecular receptors (ligands: 

   -integral

       -transmembrane 

   -peripheral 

- CARBOHYDRATES: crucial for cell to cell recognition 

- CHOLESTEROL: plays a role in membrane fluidity , prevents water soluble molecules from diffusing across 

Membrane structure results in selective permeability 

- NONPOLAR MOLECULES: able to pass the bilayer easily 

- polar and large molecules have to go through transport proteins which it is called facilitated diffusion  

- water is special and in order to cross, have to go through aquaporins 

Passive transport is diffusion of a substance across a membrane with no energy investment 

- PASSIVE DIFFUSION: a substance travels down the concentration gradient and requires no energy 

- the diffusion of water across a selectively permeable membrane is osmosis 

- ISOTONIC: n net movement of water across the plasma membrane 

- HYPERTONIC: the cell will lose water due to its surroundings 

- HYPOTONIC: water will enter the cell faster than it leaves 

Active transport uses energy to move solutes against their gradients 

- ACTIVE TRANSPORT: substances are moved against their concentration gradient, this energy, usually ATP

- SODIUM POTASSIUM PUMP: moves 3 + NA+ out and 2 K+ into the cell to maintain homeostasis 

- MEMBRANE POTENTIAL: is the difference in electric charge across a membrane and is expressed in voltage 

- the inside of the cells is negatively charged, so positively charges molecules are attracted to the cell. The combination of forces forms an electrochemical gradient

- bulk transport across the plasma membrane occurs by exocytosis and endocytosis 

- EXOCYTOSIS: vesicles from the cell's interior fuse with the cell membrane and expel their contents 

- ENDOCYTOSIS: essentially the reverse of exocytosis, the cell forms new vesicles from the plasma membrane 


The Cell 

Cellular membranes are fluid mosaics of lipids and proteins 

- The plasma membrane is selectively permeable, meaning it allows some substances to cross more easily than others 

- FLUID MOSAIC MODEL: membrane represented as a fluid with proteins integrated in the phospholipid bilayer

- PHOSPHLIPIDS: provide a hydrophobic barrier that separates the cell from its liquid environment 

    -amphipathic 

    -fluid/ viscous membrane 

    -saturated fatty acids 

        -decreases fluidity 

   -unsaturated fatty acid tails 

       -increases fluidity

- PROTEINS: acts as transport channels by molecular receptors (ligands: 

   -integral

       -transmembrane 

   -peripheral 

- CARBOHYDRATES: crucial for cell to cell recognition 

- CHOLESTEROL: plays a role in membrane fluidity , prevents water soluble molecules from diffusing across 

Membrane structure results in selective permeability 

- NONPOLAR MOLECULES: able to pass the bilayer easily 

- polar and large molecules have to go through transport proteins which it is called facilitated diffusion  

- water is special and in order to cross, have to go through aquaporins 

Passive transport is diffusion of a substance across a membrane with no energy investment 

- PASSIVE DIFFUSION: a substance travels down the concentration gradient and requires no energy 

- the diffusion of water across a selectively permeable membrane is osmosis 

- ISOTONIC: n net movement of water across the plasma membrane 

- HYPERTONIC: the cell will lose water due to its surroundings 

- HYPOTONIC: water will enter the cell faster than it leaves 

Active transport uses energy to move solutes against their gradients 

- ACTIVE TRANSPORT: substances are moved against their concentration gradient, this energy, usually ATP

- SODIUM POTASSIUM PUMP: moves 3 + NA+ out and 2 K+ into the cell to maintain homeostasis 

- MEMBRANE POTENTIAL: is the difference in electric charge across a membrane and is expressed in voltage 

- the inside of the cells is negatively charged, so positively charges molecules are attracted to the cell. The combination of forces forms an electrochemical gradient

- bulk transport across the plasma membrane occurs by exocytosis and endocytosis 

- EXOCYTOSIS: vesicles from the cell's interior fuse with the cell membrane and expel their contents 

- ENDOCYTOSIS: essentially the reverse of exocytosis, the cell forms new vesicles from the plasma membrane