Chapter 4 cell membrane transport

endocytosis: pinocytosis

"cell drinking" -cell makes a hollow pit in its membrane and ECF and molecules fill it up -pinches shut and traps a sample of the ECF inside an endosome -no pseudospods are used

passive transport: diffusion through channels

-can be regulated to be OPEN or CLOSED -substances are diffused down their concentration gradient through pores in the plasma membrane. -ion channels or aquaporins (water)

concentration of solutes

1 mole solute= 1 osmolar 1 milliosmol= 1/1000 osmole

hypertonic

a cell placed in a hypertonic solution shrinks as water flows out of the cell and into its surroundings

isotonic

does not change in volume

secondary active transport

the movement is powered by a concentration gradient generated by the primary active transport. As one substance moves passively down its gradient, it drives the active movement of another substance against its own gradient. ATP is not directly used to move a substance, but it was once used to create the potential energy in a concentration gradient.

Endocytosis: Phagocytosis

-"cell eating" -cell membrane stretches out its pseudopods and eats the material outside the cell -phagosome pinches off into the cytosol once pseudopods completely surround it -phagosome then fuses with the lysosome inside the cell called a phagolysosome to break down the material

primary active transport

-ATP is used directly to transport substances -pumps that are transporters sometimes also act as ATPase enzymes--enzymes that are involved in ATP hydrolysis. The removal of a phosphate group from ATP releases energy which can be used in primary active transport. -sodium potassium pump is an example

hypo-osmotic

-a solution whose osmolarity is lower than another -a solution that is hypo-osmotic to another solution has a lower concentration of solute and a higher concentration of water than the other solution

leak channels

-always open and allow Na+ and K+ to move passively down their electrochemical gradients. -this passive transport will happen until diffusional equilibrium occurs. -if there were only leak channels present, then there would be an even distribution of Na+ and K+ ions on both inside and outside the cell= NOT good physiologically, which is why we have sodium potassium pump to counteract -presence of leak channels and Na+/K+ pumps helps to keep the ECF and ICF stable and different concentrations from one another.

diabetes mellitus

-causes high blood sugar because their body cannot produce insulin or their cells do not react to it -high blood sugar therefore causes hyperosmotic plasma -water moves out of the blood cells and into the plasma, causing the cells to shrink -this can negatively impact the ability of red blood cells to carry oxygen of white blood cells to perform their normal immune function

sodium potassium pump

-example of primary active transport -one sodium-potassium pump cycle pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell steps: 1. pump is open to the intracellular fluid and 3 Na+ ions bind to the active sites 2.ATP is broken down (phosphorylated) releasing energy that can be used to pump ions against their concentration gradient 3. sodium is pushed out of the cell and into the extracellular fluid 4. conformation of the sodium-potassium pump changes, reducing the affinity of the sodium-binding sites and increasing the K+ binding sites 5. 2 potassium ions bind to their active sites and then the potassium is pushed into the intracellular fluid 6. sodium is "picked up again" and the cycle repeats pumpkin

solutes that dissociate into multiple particles

-glucose does not dissociate, so 0.1 mole of glucose has an osmolarity of 0.1 osmolar -NaCl dissociates into Na+ and Cl- particles, so 0.1 mole of NaCl has an osmolarity of 0.2 osmolar

Endocytosis: Receptor-mediated endocytosis

-molecule binds to a receptor protein on the plasma membrane -coated pit is formed with clathrin proteins -membrane then invaginates and pinches off forming a vesicle

cotransport

-movement of two substances in the same direction, such as sodium linked glucose transport. -movement of sodium into the cell down its electrochemical gradient releases energy that powers glucose to move into the cell against its concentration gradient (actively transported)

steady state

-occurs when the concentration gradient offsets the action of the pump -the pump keeps moving molecules across the membrane until the concentration on the other side is too great, and no more molecules can come across.

osmotic pressure

-total solute concentration of a solution -osmotic pressure increases when the total solute concentration increases and it decreases when the total solute concentration decreases -while water tends to move down its concentration gradient, it travels up its osmotic pressure/osmolarity gradient -water follows the solute movement from low to high concentration

passive transport: facilitated diffusion

-transmembrane (carrier) protein required to transport substances down the concentration gradient -following a conformational change, a molecule could be taken back across the membrane -net flux depends on the concentration gradient: active transport has a specific way that it moves; facilitated diffusion does not, it goes where-ever the concentration gradient goes.

active transport - pumps

-transmembrane proteins (carriers) that use energy to drive molecules in a preferred direction -different from passive carriers: passive carriers have equal affinity for molecules on either side of the membrane -pumps are transmembrane proteins that use energy in the form of ATP to move molecules in a preferred direction, normally against the concentration gradient. They have a greater affinity for a molecule on one side relative to the other side

important roles in exocytosis

1. adding to the plasma membrane- endocytosis involves "pinching off" a portion of the plasma membrane to form transport vesicles -the portions of the plasma membrane that were pinched off have to be periodically replaced, or the cell would get so tiny that there would be no room for organelles 2. recycling receptors- receptors that are removed from the cell membrane during endocytosis have to be replaced and can be reinserted into the plasma membrane through exocytosis and the fusion of a secretory vesicle containing the receptor to the plasma membrane 3. secretion of substances- exocytosis is used to secrete substances such as neurotransmitters into the extracellular fluid

factors to consider with membrane permeability

1. lipid solubility (whether the lipid is lipophobic or lipophilic) 2. size and shape of the molecule: smaller molecules can easily pass through 3. temperature: increased temperature generally increases the random movement of molecules, which causes them to diffuse faster 4. membrane thickness: diffusion across the single-celled layer of epithelium in alveolar walls is fast because that tissue is very thin

Identify the three general factors that influence the rate at which a substance can be passively transported across a membrane.

1. magnitude of the driving force (difference between concentration gradient; larger the driving force, the faster the rate) 2. membrane surface area: rate of diffusion is larger when there is a larger membrane surface area (alveoli in lungs have a larger surface area to increases gas exchange) 3. membrane permeability: the more permeable a membrane is to a substance, the faster is will diffuse across

factors that affect the rate of facilitated diffusion

1. transport rate of individual carriers (faster carrier will provide more net flux) 2. magnitude of concentration gradient: the larger the concentration gradient, the larger the net flux. There comes a point where increasing the concentration gradient will not increase the net flux. This is known as the point of saturation, where all the carriers are "busy" transporting substances across the cell membrane. 3. number of protein carriers: when the carrier proteins are fully saturated, the only way to increase the rate of diffusion is to add more carrier proteins.

hypotonic

a cell placed in a hypotonic solution swells as water flows into the cell from its surroundings

membrane potential

a difference in electrical potential across the plasma membrane; sign of the membrane potential is the net charge inside the cell -cells membrane potential is Vm= -70 mV

hyperosmotic

a solution whose osmolarity is higher than another -a solution that is hyper-osmotic to another solution has a higher concentration of solute and a lower concentration of water than the other solution

endocytosis

a type of vesicular transport where materials are brought into the cell with vesicles called endosomes

vesicular transport

active transport of substances across a membrane in vesicles or "pouches"

exocytosis

basically endocytosis in reverse- removal of materials from the cell by secretory vesicles -a secretory vesicle containing materials for secretion is produced within the cell, sent to the plasma membrane and then fuses with the plasma membrane and its contents are released into the extracellular fluid

electrochemical force

combination of the electrical driving force and the chemical driving force -must determine which is stronger

chemical force

created by differences in concentration on either side of a membrane -rate of transport depends on the size of the concentration gradient (greater difference in concentration inside vs outside will create a faster rate of transport)

water intoxication

if you drink an excessive amount of water, the osmolarity of your red blood plasma decreases. -water flows from the plasma and into your red blood cells, causing them to swell -problematic in the brain, where there is little room for swelling

tonicity

measure of the concentration of impermeant solutes in the extracellular fluid relative to the intracellular fluid. -uses a reference point; has to describe a surrounding fluid

equilibrium potential

membrane potential at which the electrical driving force exactly opposes (balances) the chemical driving force -electrochemical gradient= 0 -equilibrium- no net movement of the ion -each ion has its own equilibrium potential -E(Na)= +60 mV -E(K)= -94 mV

countertransport

movement of two substances in opposite directions, such as the sodium-proton exchange, in which the inward flow of sodium powers the movement of H+ to the outside of the cell by increasing the carrier protein's affinity for H+ while it faces the inside of the cell

types of passive transport

net flux is down the electrochemical gradient -simple diffusion, facilitated diffusion, diffusion through channels (pores)

active transport

net flux is up the electrochemical gradient -primary active transport -secondary active transport

difference between tonicity and osmolarity

osmolarity is the total concentration of permeant and impermeant solutes while tonicity only cares about impermeant solutes

electrical force

results from the interaction of charged particles with electrical charges on either side of the membrane -opposite charges attract and like charges repel -larger the magnitude, the greater the attraction or repulsion -Na+ and Ca2+ (Ca2+ will have the greater electrical driving force)

passive transport: simple diffusion

spontaneous transport of molecules across the plasma membrane -includes lipid soluble hormones (thyroid and steroid hormones), small molecules (O2 and CO2), lipid soluble vitamins

excessive sweating

sweat is mostly water and salt and the water in sweat comes from blood plasma. -if you sweat a lot, the osmolarity of your blood plasma increases -water flows out of your red blood cells and into the plasma, and the red blood cells shrink -when the red blood cells shrink, they become less efficient at delivering oxygen

osmolarity

term used to describe the concentration of solutes in solution with water -describes the total solute particle concentration -solution with a high osmolarity has a high solute concentration and something with a low osmolarity has a low solute concentration -water moves from areas of low osmolarity to high osmolarity

what would happen if you put a red blood cell into distilled water, which has very few solutes?

the cell will have a higher osmolarity than the surrounding water -water will rush into the cell -this will cause the cell to expand and potentially burst (hemolysis)

iso-osmotic

two solutions with equal osmolarity -have the same concentrations of solutes and water