Lecture 8 - Transport Flashcards
Membrane transport (passive vs active)
Passive transport:
Substances move down concentration gradient (high to low)
Use no energy
Active transport:
Substances move against a concentration gradient (low to high)
Energy required
Diffusion
Movement of molecules DOWN a concentration gradient
Influenced by:
Mass of molecule
Temp. of molecule
Steepness of gradient
Surface area
Distance to diffuse
Simple diffusion
Diffusion through membrane without channel or carrier
Only done by lipids or very small molecules
Facilitated diffusion
Sugars, amino acids or ions bind to protein carriers in membrane or move through channels
Osmosis
Movement of water through a selectively permeable membrane
Solute molecules cannot cross
Autophagy
“Self eating” cell digests its own structure
Autolysis
Breakdown of cells during own enzymatic action
Auqaporins
Integral membrane proteins that act as a water channel during osmosis
Tonicity
Refers to the ability of a solution to change shape/tone depending on volume of water
Isotonic- same solute concentration
Hypertonic- high solute (crenate)
Hypotonic low solute (lyse)
Active transport processes
Energy required because:
Solute too large for channels
Solute not lipid soluble
Solute not able to move down a gradient
Two major active membrane transport processes:
Active transport
Vesicular transport
Carrier proteins
Bind specifically and reversibly with substance being moved
Anti-porters- Transport one substance into cell while transporting a different substance out of cell
Symporters- transport two different substances in the same direction
Primary vs secondary active transport
Primary active transport:
Required energy comes directly from ATP hydrolysis
Shape change causes solutes to be pumped across the membrane
Secondary active transport:
Required energy comes indirectly from ionic gradients created by primary active
Membrane Potential
A membrane is a voltage across the cell membrane that occurs due to separation of oppositely charged particles
Inside of the membrane is more negatively charged than the outside
Resting membrane potential:
Determined by concentration gradient of potassium ions that move freely out of cell down gradient, but also move into cell along electrical gradient
Vesicular transport (endocytosis, exocytosis, transcytosis, vesicular trafficking)
Vesicular transport: Uses membrane is vesicles to transport large particles, macromolecules and fluids across the membrane or within cell, this requires energy
Endocytosis- is transport into the cell
Exocytosis- Is transport out of the cell
Transcytosis- Is transport into, across and out of the cell
Vesicular trafficking- is transport from one area for organelle in a cell to another
Phagocytosis (cell eating)
Form of endocytosis in which large, solid materials are brought into cell

Pinocytosis (cell drinking)
A form of Endocytosis that takes a small volume of extracellular fluids into the cell
No receptor used, process is non-specific
Receptor mediated endocytosis
Allows cells to concentrate molecules found in small amounts in extracellular fluids
Because it uses receptors, it is HIGHLY SPECIFIC
many cells have receptors embedded in cathrin-coated pits
Enzymes,lipids, iron and insulin taken in this way
Some viruses- diphtheria and cholera toxins trick cells and enter this way
Caveolae are slightly different from clathrin, but still capture specific molecules (folic acid and tetanus toxin) and use transcytosis
Exocytosis
Type of vesicular transport that moves molecules out of cell in a simple vesicle, often used for secretion or removal of waste from the cell
Protein of vesicle —> vSNARE fuses with tSNARE Proteins on membrane, triggers Exocytosis
Exocytosis can expel hormones,neurotransmitters, mucous etc.
