Bio: 4.1-4.5 - Membranes and Transport

Cell Membrane Structure

flexible bonding between the internal and external environments of a cell/organelle

Cell Membrane Function

maintain cellular homeostasis by regulating the entry and exit of molecules

Fluid Mosaic

the membrane is made of many different molecules that are constantly moving

Phospholipid Bilayer

2 layers of phospholipids with fatty acid tails (hydrocarbons) and polar heads on the outside & nonpolar tails attracted to each other on the inside

Saturated

straight C totally surrounded by single bonded H

Unsaturated

bent tail b/c they have a double bond between 2 carbons = more space = fluid

Cellular Homeostasis

balance of molecules between the inside and outside of the cell

Selectively Permeable

allows molecules (based on charge and size) through while keeping others out

Molecules that can cross:

small, nonpolar molecules

Molecules that can't cross:

ions (repelled by charges) and large molecules

Transport Proteins

allow passage of hydrophilic substances across the membrane

Channel Proteins

provide a tunnel through the membrane

Gated Channel Protein

opens after another molecules binds to it

Carrier Protein

binds with specific molecules and changes shape to allow it to pass

Cell Transport

the movement of materials across a cell membrane

Concentration Gradient

tends to move from [HIGH] to [LOW]

Passive Transport

does not require energy, materials move down gradient

Diffusion

when small polar/nonpolar solutes pass through a membrane due to their random movement (incr w/ heat)

Osmosis

diffusion of water molecules across a membrane from [HIGH] to [LOW]

Dynamic Equilibrium

when [H2O] is equal, but continues to move - osmosis

Isotonic Solution

equal [H2O] on either side of the membrane and the cell keeps normal shape

Hypotonic Solution

outside solution has a higher [H2O], cell size incr (like a hippo) and may burst

Hypertonic Solution

outside solution has a lower [H2O], cell size decr

Facilitated Diffusion

molecules use transport proteins to move from [HIGH] to [LOW] (usually large molecules or ions using channel proteins - still passive transport)

Active Transport

needs an input of energy (ATP) to move ions from [LOW] to [HIGH] through transport proteins

Bulk Transport

moves many at once using vesicles and ATP (endocytosis and exocytosis)

Endocytosis

brings materials into a cell by folding the membrane to make a vesicle

Exocytosis

releasing materials out of a cell when a vesicle fuses with the membrane

Cell Size

needs to efficiently bring molecules in/out of a cell and deliver molecules to different locations inside the cell

As a cell grows

V incr faster than SA, so larger cells have a smaller SA:V ratio (and vice versa)

Best Cell Size

small volume, but a large SA:V ratio

Small Cell Benefit

takes less time for materials to diffuse and move materials around in a cell

Eukaryotic Cell Adaptations

folded membranes to incr surface area