Transport Across Membranes

Question 1

2 main categories of transport across membranes:

Answer 1

1) Passive Transport
2) Active Transport

Question 2

Passive Transport

Answer 2

The diffusion of a substance across a membrane with NO energy investment

Question 3

Types of passive transport

Answer 3

1) Diffusion
2) Osmosis
3) Facilitated diffusion

Question 4

Diffusion

Answer 4

Transport of a solute down a concentration gradient

–> Solute goes from areas of high conc. to low conc.

Question 5

In diffusion, all molecules move___________ but as a population move ___________

Answer 5

RANDOMLY, but as a population diffusion becomes DIRECTIONAL

Question 6

Each substances diffuses down…

Answer 6

ITS OWN gradient

–> Unaffected by the gradient of others

Question 7

Equilibrium

Answer 7

Molecules are still moving but concentrations remain constant

Question 8

Osmosis

Answer 8

The diffusion of free water across a selectively permeable membrane

Question 9

Osmosis is helpful when…

Answer 9

solute cannot diffuse through a membrane

–> H2O will then move through the membrane to attempt to dilute the more concentrated side

Question 10

Tonicity

Answer 10

The ability of a surrounding solution to cause a cell to gain or lose water

–> Depends largely on concentration of solutes that cannot cross the membrane

Question 11

Isotonic

Answer 11

Concentrations are ~ equal on either side of membrane

= NO NET MOVEMENT of water across membrane

Question 12

Hypertonic

Answer 12

A solution that has > conc. of solute than other solution across a membrane

= Water moves INTO hypertonic solution

Question 13

Hypotonic

Answer 13

A solution that has < conc. of solute than another solution across a membrane

= Water moves OUT OF hypotonic solution

Question 14

Most animals have their cells in a ______________ extracellular fluid

Answer 14

ISOTONIC: to maintain a stable cell volume

Question 15

Osmotic Pressure

Answer 15

The tendency for a solution to take up water when separated from pure water by a selectively permeable membrane

Question 16

Animal Cell in Hypotonic Solution

Answer 16

= LYSED

–> Too much water entering cell causes it to swell and then burst

Question 17

Animal Cell in Isotonic Solution

Answer 17

= NORMAL

–> Maintains proper cell volume

Question 18

Animal Cell in Hypertonic Solution

Answer 18

= SHRIVELED

–> Too much water leaves cell causing it to shrink in on itself

Question 19

Plant Cell in Hypotonic Solution

Answer 19

= TURGID (ideal condition) – Very firm

–> More water entering cell creates turgor pressure that pushes up against cell wall

–> Keeps plants “perky”

Question 20

Plant Cell in Isotonic Solution

Answer 20

= FLACCID (limp)

–> Not enough water to produce the turgor pressure needed

Question 21

Plant Cell in Hypertonic Solution

Answer 21

= PLASMOLYZED

–> Cell inside shrinks but cell wall maintains shape (too much water leaving cell)

Question 22

Facilitated Diffusion

Answer 22

Diffusion aided by transport proteins (“to make faster”)

Question 23

Facilitated diffusion can allow for…

Answer 23

polar/charged molecules to diffuse through a membrane using the transport proteins as a “door”

Question 24

2 types of transport proteins:

Answer 24

1) Channel Proteins
2) Shuttle/Carrier Proteins

Question 25

Channel Proteins

Answer 25

Provide hydrophilic pathways to allow for very fast diffusion

Question 26

Carrier Proteins

Answer 26

AKA Shuttle Proteins --> Undergo a subtle change in shape that translocates molecules across a membrane

Question 27

Facilitated diffusion still...

Answer 27

MOVES DOWN CONC GRADIENT (cannot go against the gradient)

Question 28

Active Transport

Answer 28

"pumping" a solute/molecule across a membrane going AGAINST the conc. gradient -->*Requires energy input to do so

Question 29

Active transport enables a cell to...

Answer 29

maintain internal concentrations of small solutes that differ from concentrations in its environment

Question 30

Sodium-Potassium Pump

Answer 30

Import K+ and Exports Na+ --> Cells want high conc. of K+ and low conc. of Na+

Question 31

Sodium-Potassium Pump is also known as...

Answer 31

Sodium-Potassium ATPase (Due to hydrolysis of ATP)

Question 32

Sodium-Potassium Pump Process (4 Steps)

Answer 32

1) 3 Na+ bind to pump (INSIDE cell) 2) ATP phosphorylation of pump causes conformation change = Na+ released to environ. 3) 2 K+ bind to pump with new conform. = triggers dephosphorylation = return to old conform. 4) K+ released into cell REPEAT

Question 33

ATP is not the only driver of active transport:

Answer 33

Membrane potential/electrochemical gradient can be coupled to transport molecules

Question 34

Membrane Potential

Answer 34

The voltage across a membrane

Question 35

Membrane potential is due to...

Answer 35

Charge differences between cytoplasmic and extracellular membrane sides --> as a result of unequal cation/anion distribution

Question 36

If inside of cell is negatively charged (which it is), membrane potential favors...

Answer 36

the passive transport of CATIONS INTO cell and ANIONS OUT of cell

Question 37

2 forces driving diffusion of ions:

Answer 37

1) Conc. gradient 2) Membrane potential

Question 38

Electrochemical Gradient

Answer 38

The combination of the forces of conc. gradient and membrane potential acting on an ion --> *Ions diffuse down their electrochemical gradient

Question 39

If conc. gradient and electrical forces oppose...

Answer 39

Active transport may be needed

Question 40

If conc. gradient and electrical forces align...

Answer 40

Ions diffuse down electrochemical gradient

Question 41

Electrogenic Pump

Answer 41

Transport protein that generates voltage across a membrane through the active transport of ions

Question 42

Electrogenic pumps help to store...

Answer 42

ENERGY --> Through generation of the voltage --> This energy can be tapped for cellular work

Question 43

Co-transport

Answer 43

Couples favorable movement of one molecule down its conc. gradient and unfavorable movement of another molecule down its conc. gradient

Question 44

Co-Transport Example with Sucrose

Answer 44

1) H+ it pumped across membrane creating positive charge and high conc. on one side 2) H+ diffuses back through a co-transporter in which sucrose follows along 3) Sucrose is now across membrane

Question 45

Co-Transporter

Answer 45

Transport protein that couples the transport of molecules

Question 46

2 main types of active transport:

Answer 46

1) Co-transport 2) Bulk transport

Question 47

Bulk Transport

Answer 47

A category of transport of large quantities of materials/large molecules/particles across a membrane

Question 48

Types of Bulk Transport

Answer 48

1) Exocytosis 2) Endocytosis a. Pinocytosis b. Phagocytosis c. Receptor-mediated endocytosis

Question 49

Exocytosis

Answer 49

Process of cells secreting (excreting) certain molecules by fusion of vesicles with the plasma membrane (which causes materials inside to release out of cell)

Question 50

Endocytosis

Answer 50

The taking in of molecules and particulate matter by forming new vesicles from the plasma membrane

Question 51

Phagocytosis

Answer 51

The engulfing of a particle (usually food) by extending membrane around it and packaging it within a membranous sac called a food vacuole (NON SPECIFIC)

Question 52

Pseudopodium

Answer 52

The membrane extension in phagocytosis

Question 53

Pinocytosis

Answer 53

The engulfing of liquid droplets by infolding part of the membrane to form "pits" that pinch into the cell as a vesicle (NON SPECIFIC)

Question 54

Clathrin

Answer 54

AKA Coat Protein --> Coats the membrane (on cytoplasmic side) that then form coated vesicles when pinched into cell

Question 55

Receptor-Mediated Endocytosis

Answer 55

SPECIFIC engulfing of substances due to receptors embedded in plasma membrane (vesicle formation process is similar to pinocytosis)

Question 56

Receptor-mediated endocytosis is the...

Answer 56

main type of transport of macromolecules across a membrane

Question 57

Pinocytosis and phagocytosis are...

Answer 57

NON SPECIFIC