Ap Bio- Cell Membrane Structure & Cell Transport

Membrane Carbohydrates (oligosaccharides):

• important for cell recognition

Integral Protein:

• Embedded inside the membrane

Peripheral Protein:

• Not embedded inside the membrane

Phospholipid Tails:

• Hydrophobic

Phospholipid Head:

• Hydrophilic

Passive Transport:

• Does not require energy (no ATP is needed)

• Moves substances from an area of high concentration to an are of low concentration (down concentration radian)

Diffusion (type of passive transport): 

• Moves non polar substances through the phospholipids into or out of the cell (ex. O2, CO2)

Facilitated Diffusion (types of passive transport):

• Moves polar or charged substances through transport proteins (integral proteins)

• ex: glucose, amino acids

• ions: H+, Na+, K+

Examples of channel proteins:

• Ion channels that open or close in response to a stimulus (gated channels)

Carrier proteins change_:

• Shape, to allow molecules to cross membrane

Osmosis (Passive Transport):

• Diffusion of H2O through a selectively permeable membrane

• H2O moves quickly through aquaporins in cell membrane, moves through phospholipids slowly 

Aquaporins:

• Diffusion of water

• Proteins that form channels in cell membranes to facilitate the rapid transport of water.

Isotonic: 

• Iso = same or equal

• Has same solute concentration as environment

• No net movement of H2O

Hypotonic: 

• Hypo = under, below, less

• Has lower solute concentration than environment

• Cell loses H2O

Hypertonic:

• Hyper = more or above

• Has higher solute concentration than environment 

• Cell gains H2O

Tonicity:

• The ability of a surrounding solution to cause a cell to gain or lose water

Cytolysis:

• Cell swells and may burst

Crenates:

• Cell Shrinks

Plasmolysis:

• Cell membrane pulls away from cell wall

Active Transport:

• Requires energy (ATP or other energy source is needed)

• Moves substances from an area of low concentration to an area of high concentration (against concentration gradient)

Protein Pumps:

• Transport protein moves ions into or out of cell against concentration gradient

Sodium/Potassium Pump:

• Important in animal cells: Nerve cells (neurons)

• Pumps 3 Na+ ions out of cell - 2 K+ ions into cell

Proton Pump: 

• Important in mitochondria, chloroplast, cell membranes

• Pump H+ across membrane with help of a energy source

• H+ gradient can be used to do work (ex. make ATP)

Contransport: 

• Uses a carrier protein along with a proton pump to move molecules into the cell

• Combines active + passive transport

• Ex. Sucrose- H+ are pumped

Exocytosis: 

• Large molecules leave cell by vesicle fusing with the cell membrane.

• Also called secretion

Endocytosis: 

• Brings large molecules into cell by forming vacuoles or vesicles from cell membrane

Phagocytosis:

• “Cell eating”

• Cell membrane moves around substance forming a vacuole 

• Vacuoles fuse with a lysosome to digest contents

Pinocytosis:

• “Cell drinking”

• Cell membrane folds inward forming a vesicle, taking in extracellular fluid

Receptor-Mediaited Endocytosis:

• Specific

• When a specific molecule binds to a receptor on cell surface, cell membrane folds inward forming a vesicle to bring molecule into cell

• This is how cholesterol enters the cell