Permeability of Cell Membrane

Advanced Biology

Transport Vocabulary

Concentration gradient Difference in the concentration of a

substance throughout across a space (inside vs. outside of the cell)

Equilibrium Concentration of a substance is equal

throughout a space

Cell Membrane

Responsible for regulating what goes in and out of the cell Can go through the phospholipids

Small, uncharged molecules Oxygen, water, carbon dioxide Non-polar molecules diffuse much faster than polar

molecules Can go through membrane proteins

Ions and large molecules Macromolecules-sugars, proteins, etc.

Types of Transport Passive transport

Molecules are able to pass through the phospholipids on their own or may need the assistance of a membrane protein

Doesn’t use chemical energy (ATP) Goes with concentration gradient (high low)

Active transport Molecules need assistance by using a membrane protein Uses chemical energy (ATP) Goes against concentration gradient (low high)

Passive Transport Diffusion

Simplest form of passive transport Movement of molecules continues until they reach

equilibrium (distributed equally inside and outside the cell)

Only a few types of molecules will go across the cell membrane this way (oxygen into the bloodstream)

Temperature, pressure, electrical current, and molecule size can affect rate at which diffusion occurs

Passive Transport

Osmosis Diffusion of water molecules across a

membrane Osmotic pressure occurs when pressure

develops in a system (cell) due to osmosis; necessary for osmosis to occur

Osmotic Solutions

Isotonic Concentration of water (solvent) and the solute are

the same inside and outside the cell Hypotonic

Concentration of water is greater outside the cell than inside the cell (high solute inside, low outside)

Water moves inside causing cell to swell (lyse) Hypertonic

Concentration of water is greater inside the cell than outside the cell (low solute inside, high outside)

Water moves outside causing cell to shrink (plasmolysis)

Osmotic Solutions

Plants need a hypotonic environment Cell wall prevents cell from lysing Creates turgor pressure (pressure of the

cell’s contents against the cell wall due to osmosis, determined by how much water is in the central vacuole); provides additional support for cell

Passive Transport with Carrier Proteins

Facilitated diffusion is a form of passive transport that uses carrier proteins to carry large or charged molecules across the cell membrane Proteins are specific to what they

transport Proteins will change shape as they allow

the molecule to pass

Facilitated Diffusion with Carrier Proteins

Passive Transport with Channel Proteins

Channel proteins act as “pores” in the cell membrane which allow ions to pass through Also specific as to what they allow through Don’t change shape as the molecule

passes through Transport occurs at a much faster rate than

with carrier proteins

Transport using Channel Proteins

Active Transport Uses membrane proteins (pumps) to

move molecules across the cell membrane Pumps are integral proteins Most proteins will change shape as the

molecule passes through Some bind with only one type of molecule,

others bind with two different types May move molecules in same direction May move molecules in opposite directions

Active Transport

Sodium-potassium pump (nerve cells) Pumps three sodium (Na+) ions out and two

potassium (K+) ions in Usually more Na+ ions outside the cell and more K+

ions inside the cell Na+ is toxic to the cell (drives osmosis) K+ important for chemical reactions in cell

Proton pumps Move protons (hydrogen ions) out of the cell

(typically across mitochondria during cellular respiration)

Active Transport

Endocytosis Cells take in larger substances by forming a

vesicle around the substance Pinocytosis: intake of smaller substances and

fluids Phagocytosis: intake of large molecules and

entire cells (bacteria) White blood cells use endocytosis to get rid

of foreign molecules (bacteria, viruses, etc.)

Endocytosis

Active Transport

Exocytosis Vesicles fuse with cell membrane to

release substances outside the cell Electrical impulses are converted into

chemical messages and then are “exported” out of your cell through this process

Exocytosis

Active Transport Receptor proteins

Bind to specific signal molecules which enables cell to respond Usually allows for another molecule to pass

through the channel protein Causes receptor protein to change shape to allow

molecule to enter/exit cell Causes an intermediate protein to activate which

activate an enzyme which forms a second messenger

Receptor Proteins

Learning Targets

I can name the two types of movement through the cell membrane.

I can explain differences between active and passive transport.

I can describe examples of active and passive transport.