Cell Transport

Question 1

Diffusion

Answer 1

mvmt along concentration gradient (high to low); no ATP required

Question 2

Simple diffusion

Answer 2

• direct passage through membrane
• kinetic mvmt of molecules/ions provides motion
• high to low conc
• in cells, diffusion occurs directly through the cell membrane or through protein pores in the cell membrane (channel protein)

Question 3

Faciliated diffusion

Answer 3

utilizes membrane protein for import/export

Question 4

Active Transport

Answer 4

requires energy (hence active)
typically moving against conc gradient
2 types: primary and secondary active transport

Question 5

Endo and exocytosis

Answer 5

specialized transport mechanisms

Question 6

Membrane Transport-General

Answer 6

• Lipid soluble molecules pass directly through phospholipid bilayer: O2, CO2, alcohol
• Some H2O soluble molecules pass through the cell membrane using channel protein pores: H2O, PRO, some ions, lipids bound to PRO
• Many substances are transported against their conc. gradient (active transport)

Question 7

General Permeability rules

Answer 7

Small HydroPHOBIC molecules: (O2, CO2, N2, benzene) simple diffusion
Small uncharged POLAR molecules:( H20, glycerol, ethanol) simple diffusion
Larger uncharged POLAR molecules: (AA, Glucose, nucleotides) facilitated
Ions: (H+,Na+, HCO-3, K+,Ca2+,CL-,Mg2+) facilitated

Question 8

Intracellular//Extracellular composition

Answer 8

Na+= 140mEq/L (E)/ 10 mEq/L (I)
K+= 4mEq/L (E)/ 140 mEq/L (I)
Cl-= 103mEq/L (E)/ 4 mEq/L (I)
Glucose= 90mg/dL (E)/ 0-20mg/dL (I)
Proteins= 2g/dL (E)/16 g/dL (I)

Question 9

Factors affecting simple diffusion

Answer 9

• amount of substance available
• lipid solubility of diffusing substance
• # and size of membrane openings (channels)
• velocity of kinetic motion of molecules (greater temp=faster difusion)
• molecular weight-smaller particles move more rapidly
• distance-shorter distance=faster diffusion

Question 10

Facilitated Diffusion “carrier mediated diffusion”

Answer 10

• requires interaction of carrier protein
• carrier protein binds the transported molecule (ion) and shuttles the molecule through membrane w/o energy source
• conformational change in carrier protein causes molecule to move through membrane
• molecule must be moving along its conc gradient

Question 11

Factors affecting facilitated diffusion

Answer 11

• rate is regulated by ability of carrier protein to complete the transport
• once carrier proteins are “saturated” no increase in diffusion rate is possible
• molecules can move in either direction using the same carrier protein-(depending on conc gradient)

Question 12

Simple vs. Facilitated

Answer 12

Facilitated: limited by number of available transport PROs in membrane
Simple: occurs at all parts of the membrane
-limited only by conc. gradients

Question 13

Osmosis

Answer 13

net mvmt of water along its conc. gradient

–requires a semi-permeable membrane separating fluid compartments

Question 14

Osmotic pressure

Answer 14

driving force for osmosis across a membrane

• -directly related to the solute conc. of the two fluid compartments
• -water tends to move from low to high

Question 15

Hydrostatic pressure

Answer 15

fluid pressure

• -force that water transmits via its weight (i.e. water tower) or via its flow through a vessel (blood flow)
• -tends to equalize with the osmotic pressure to prevent too much loss/gain of water from cells & tissues

Question 16

Active transport

Answer 16

transport of substances across the cell membrane which requires energy expenditure

• –molecule move against the conc. gradient
• Ions (Na, K, Ca, Cl, H)
• Large molecules (glucose, PRO)

both types utilize carrier proteins

Question 17

Primary active transport

Answer 17

direct utilization of ATP as energy source

Question 18

Secondary active transport

Answer 18

energy for transport comes from stored energy of ionic conc. gradient b/w intracellular and extracellular environments
—ionic conc. gradient is initially created by primary active transport of the ion of interest

Question 19

Na+/K+ pump: active transport

Answer 19

• Membrane protein actively pumps 3Na+ ions OUT of cell and 2K+ ions INTO cell using ATP
• responsible for setting up ionic conc. gradients b/w intra and extra cellular spaces
• important for maintaining a voltage across the cell membrane (- inside, + outside)

Question 20

Co-transport

Answer 20

method of transport for glucose and AAs

• -AAs are transported into cell against conc. gradient; sugars move w/ conc. gradient
• -transport occurs in conjxn w/ Na athat move down their CG and into cell
• -Carrier PRO is specific for sugars and AAs
• -both the transported molecule and Na+ must be bound to the carrier protein for transport to occur

Question 21

Counter transport

Answer 21

Transport of molecules in opposite directions across the cell membrane; uses energy of conc. gradient of one of the transported molecules

• –example: Ca+ moving out of cell using Na+ moving into cell
• –maintains overall ionic balance of intra and extra cellular space

Question 22

Endocytosis

Answer 22

Passage of material into a cell moving through cell membrane; requires energy use by cell

Question 23

Phagocytosis: endocytosis

Answer 23

uptake of particulate material; only “recognized” particles are engulfed

Question 24

Pinocytosis: endocytosis

Answer 24

uptake of soluble molecules (water); non-specific engulfment of molecules

Question 25

Receptor mediated endocytosis

Answer 25

• -uptake of specific molecules using specific membrane proteins (clathrin)
• -ingested particle first binds to clathrin
• -binding to clathrin activates invaginations of cell membrane, bringing particle into cell
• -vesicle brought in disassembled by cell; ingested material retrieved and protein receptor is recycled back to cell membrane

Question 26

Exocytosis

Answer 26

Process of secreting/releasing most proteins made by cells
vesicles from Golgi app move toward cell membrane and fuse with it
as fused membranes flatten out the vesicle contents are released into the interstitial space