gen bio-cell membrane and transport

structure of the membrane

phospholipids, membrane proteins, and carbohydrates

phospholipids

main structural components of membrane. Glycerol + 2 fatty acid tails (hydrophobic) + phosphate group (hydrophilic). forms phospholipid bilayer

membrane proteins

Can be on one side or transmembrane. Some membrane proteins can move within membrane, others are attached to extracellular matrix or cytoskeleton. responsible for transport, enzymes, signaling, and structure

carbohydrates (membrane)

Polysaccharides attached to protein (glycoprotein) or lipid (glycolipid). responsible for cell identification

fluid mosaic model

describes the cell membrane as a flexible, dynamic two-dimensional liquid where various molecules move laterally

Fluid – membrane components can move laterally within the membrane

Mosaic – emergent properties of membrane as a whole due to combination and arrangement

of components

passive transport

spontaneous and Does not require metabolic E(ATP). movement from high to low concentration (down the concentration gradient). results in dynamic equilibrium

simple diffusion

tendency for molecules of a substance to fill available space. all molecules in constant random motion, eventually evenly distributed.

dynamic equilibrium

no net movement at equilibrium

what can cross a membrane via simple diffusion

small nonpolar molecules and VERY small polar molecules. ex. gases (O2, CO2, N2), small hydrocarbons, and water. NO ions or charged molecules

osmosis

Diffusion of water across selectively permeable membrane

solvent

a substance that can dissolve other substances. water is the universal one

solute

substance that gets dissolved

how is direction of osmosis determined

total solute concentration

how does water diffuse

regions of lower solute concentration to regions of higher, which Equalizes solute concentration

tonicity

Ability of a solution to cause a cell or gain or lose water

isotonic solution

amount of solute on the inside of the cell is equal to the amount on the outside. no net water movement

hypertonic solution

amount of solute outside of the cell is greater than the solute on the inside. cell loses water

hypotonic solution

amount of solute outside of the cell is less than the amount of solute inside the cell. cell gains water

what can’t diffuse directly across a membrane

Large molecules – just too big, not small polar molecules (hydrophilic); ions (charged-even H+). Transported by proteins across lipid bilayer instead

facilitated diffusion

passive transport through a transport protein that does not require ATP. Transport proteins are specific to the substance being transported. Two types: channel (does not change shape), carrier (does change shape)

active transport

requires ATP, works against the concentration gradient, transports through a carrier protein

bulk transport

transports many molecules at once using vesicles, but not carrier mediated. enters/exits cell without crossing bilayer

exocytosis

Vesicle containing waste or secretory products fuses with plasma membrane. Releases content from cell

endocytosis

Material taken into cell by forming vesicles derived from plasma membrane

phagocytosis

the cellular process where a cell uses its outer membrane to engulf and digest large food particles

pinocytosis

a cell engulfs extracellular fluids and dissolved solutes by folding its membrane inward to form tiny internal vesicles