Membrane Transport and Structures

What are important features in Membrane Structure?

• fluid mosaic model

• phospholipid

• proteins

• carbohydrates

Amphipathic

polar/non-polar sides

How are phospholipid bilayers formed?

• spontaneous

• held together by hydrophobic interactions (Van der Waals)

What are membrane proteins?

• determine many membrane functions

• are transmembrane → span the entire membrane

• some can move (from side to side) → laterally

• microfilaments of cytoskeleton and fibers of extra-cellular matrix (ECM)

What are the functions of membrane proteins?

• transport

• enzymatic activity

• signal transduction

• cell-cell recognition

• intercellular joining

• attachment to cytoskeleton and ECM

What are carbohydrates?

• polysaccharides attached to protein → glycoprotein

• or attached to lipid(glycolipid)

What are the functions of Carbohydrates?

cell identification

What is the fluid mosaic model?

The membrane components can move laterally within one layer of the membrane. Consists of Lipids, Carbohydrates, and Proteins.

Types of transport

Active and Passive

Plasma Membrane is…

selectively permeable 

Passive Transport

• does not use metabolic ATP

• moves with the concentration gradient

• results in dynamic equilibrium

Active Transport

• does use metabolic ATP

• moves against the concentration gradient 

  • low to high

• facilitated by proteins (carriers or pumps) or bulk transport molecules

What are different types of Passive Transport?

• simple diffusion

• osmosis

• facilitated diffusion (uses proteins)

What is Diffusion?

The tendency for molecules of a substance to fill available space. Usually involves smaller molecules like O2, CO2, and N2, and other smaller nonpolar molecules and small polar uncharged molecules including H2O. 

What is Osmosis?

Diffusion of water across a selectively permeable membrane which either diffuses from lower to higher concentration of solute or higher to lower concentration of water.  

Isotonic solution

equal concentration of solute inside and outside the cell

Hypotonic solution

Solute concentration outside the cell is greater than the solute concentration inside the cell. Causes the cell to swell

Hypertonic solution

Solute concentration inside the cell is greater than the solute concentration outside the cell. Causes cell to shrivel.

What can’t diffuse directly across a membrane?

• large molecules that are too big

• not small polar molecules → hydrophilic

• charged ions

Facilitated diffusion

• large molecules or charged ions 

• transport proteins → integral proteins 

• channel proteins 

• carrier proteins → specific to what protein needs to be transported

Sodium Potassium Pump

• 3 Na + out, 2 K+ in

• type of active transport

• established electrical gradient

Bulk Transport

Does not move against phospholipid bilayer

Types of Bulk Transport

Exocytosis and Endocytosis

Exocytosis

• waste, proteins, and secretory products

• releases contents from cell

• vesicle fuses with plasma membrane

Endocytosis

• material taken into cell by forming vesicles derived from plasma membrane

Phagocyotsis

• cellular eating

• cell engulfs large particle

Pinocytosis

• cellular drinking

• ingestion of fluid and dissolved material