12: cell membrane transport

what are cells mostly composed of

water ~80%

what is the ranking of abundance of macromolecules by mass in cells

1. proteins ~10-20%

2. nucleic acids ~5-7%

3. lipids ~2-3%

4. carbohydrates ~1-3%

components of hydrophilic head

phosphate and glycerol 

how many hydrophobic tails in a phospholipid 

2 fatty acid tails

what makes the cell membrane selectively permeable

membrane proteins

ranking of components of cell membrane in terms of abundance

1. protein ~55%

2. phospholipid ~25%

3. cholesterol ~13%

4. other lipids ~4%

5. carbohydrates ~3%

components of cytoskeleton 

• microtubules

• actins

• intermediate filaments 

what are microtubules made of 

tubulin 

function of microtubules

cell movement, cell division, transport molecules

kinesin, dynein

what are microfilaments made of

actin

function of microfilaments 

cell division, cell motility, cytoplasmic streaming, part of muscle cells (actin + myosin) 

what are intermediate filaments made of

keratins, vimentin

function of intermediate filaments

maintain shape, bear tension, provide support

function of tight junctions 

selective barrier 

function of adherens

no transcellular communication

function of desmosomes

spot welds formed by cadherins - no communication

function of gap junctions

channels for passage of ions and other small molecules between cells 

structure of a gap junction

• 6 connexins make 1 hemichannel

• 2 hemichannels aligned make 1 channel

• several channels together form gap junction

molarity 

mol/L

osmolarity

osmoles of all solute particles/L of solvent

tonicity

• influenced only by solutes that cannot cross membrane

• solutes able to freely cross have no affect because concentration will always equilibrate

osmosis 

movement of water that follows osmotic pressure 

osmotic pressure

pressure that must be applied to stop osmosis when it’s due to solution containing non-penetrating solutes on one side and pure water on other side of semi-permeable membrane

what happens to RBC in hypotonic solution

lysis

what happens to RBC in hypertonic solution

crenates

osmolality

concentration of solute particles expressed as total number of solute particles per kg of solution

types of channel proteins

• voltage activated

• ligand or receptor activated

• mechano-sensitive

what does ouabain do

cardiac glycoside that binds to potassium binding site and blocks sodium potassium pump if introduced

secondary active transport

uniport co and counter transport due to concentration gradient set up by primary active transport