Unit 2b: Cell Membrane Dynamics

Question 1

intracellular fluid (ICF

Answer 1

2/3 of fluid in the body

Question 2

Extracellular fluids (ECF

Answer 2

1/3 of the fluid in the body

Question 3

Interstitial fluid (ISF)

Answer 3

ECF
– surrounds the cells of a tissue; makes
up 75% of ECF volume

Question 4

Intravascular fluid (IVF)

Answer 4

– includes blood plasma and lymph which make up 25% of ECF volume

Question 5

All body fluids are

Answer 5

a solution consisting of a solvent (water) that contains solutes (ions, nutrients, gases, proteins, wastes
like urea, etc)

Question 6

osmotic equilibrium

Answer 6

ECF and ICF are in this

meaning there is no
net movement of water because the two compartments have
the same concentration of solutes.

The concentration of
solutes is equivalent to a 0.9% NaCl solution, or 290 mOsm

Question 7

How are the ECF and ICF in a chemical and electrical disequilibrium?

Answer 7

While the overall concentration is equal between
compartments, the composition and proportion of
different solutes is NOT the same

Question 8

Which compartment has the highest concentration of protein? In which
compartment are proteins absent?

Answer 8

highest= blood plasma and ICF
ISF= lowest

Question 9

concentration gradients

Answer 9

, some solutes are more concentrated in
certain compartments than others. This sets up

Question 10

What does it mean for solutes to “ move down their concentration gradient”

Answer 10

from an area of high
concentration to an area of low concentration

Question 11

What does it mean for solutes to “ move against their concentration”

Answer 11

from an area of
low concentration to an area of high concentration

Question 12

Passive processes

Answer 12

move solute or solvent molecules
down their concentration gradient until equilibrium is
reached and do not require energy.

For example
moving Na+ from the ECF into the ICF; or movement of
water molecules

Question 13

Describe what net movement means

Answer 13

molecules cross a
semipermeable membrane in both directions, but overall more are moving from the area on the left (high concentration) to the area on
the right (low concentration).

Question 14

Active processe

Answer 14

move solute molecules against their
concentration gradients or move large molecules that
would otherwise be unable to cross the membrane
(vesicular transport).

All active transport processes require
the use of energy, which is usually obtained from ATP.

Ø For example moving Na+ from the ICF into the ECF.
Ø Na+ has a low concentration (15 mM) in the ICF, and a high
concentration (145 mM) in the ECF. In order to move Na+
against its concentration gradient, energy is required.

Question 15

Describe the relative concentrations of key substances (ions, etc.) in the plasma, interstitial fluid, and cytoplasm inside of a cell

Answer 15

Blood plasma= high Na+ low K+ high Cl- high protein high HCO3-

ICF= low Na+ high K+ low Cl- high protein low HCO3-

ISF= high Na+ low K+ high Cl- low protein high HCO3-

Question 16

List what is able to freely pass thru the membrane

Answer 16

hydrophobic lipid soluble molecules small polar molecules

ex; o2 co2 water urea

Question 17

List what isn’t able to freely pass thru the membrane

Answer 17

large polar molecules; glc proteins amino acids

charged ions; Na+ K+ Cl-

Question 18

How do large polar molecules and charged ion enter the cell?

Answer 18

require transport proteins

Question 19

Name the types of transport proteins

Answer 19

a. channel proteins

b. carrier proteins

Question 20

channel proteins

Answer 20

Ø is a water filled pore that can be open to both sides.

Ø each channel protein is specific for a particular solute (e.g. Na+
channel, K+ channel, .etc).

Question 21

aquaporins

Answer 21

Channels specific for water

Question 22

List the different types of channel proteins

Answer 22

1. open channels
2. gated channels

Question 23

Open channels (pores)

Answer 23

always open (like a doorway with no
door)

Also called “leak channels”, as they allow the solute they
are specific for to continuously leak into/out of the cell

Question 24

Gated channels

Answer 24

can open and close in response to a stimulus
(signal). Each gated channel type has a specific stimulus:

Question 25

Describe the different types of gated channels

Answer 25

i. Chemically gated channels – open in response to a chemical signal (e.g. a hormone or neurotransmitter) ii. Voltage-gated channels – open in response to to a change in the electrical state of the cell. iii. Mechanically gated channels – respond to physical forces (temperature or pressure

Question 26

Carrier proteins

Answer 26

Never form an open channel between the ECF and ICF. Are open to one side at time. Ø Solute enters carrier protein and binds to it causing a conformational change (change in protein shape) that cause the protein to close on one side and open on the other. The solute is then released

Question 27

List and describe the different types of carrier proteins

Answer 27

a. Uniport – transport only one type of solute e.g. glucose transporters (GLUT) in red blood cells. b. Symport – transports 2 or more types of solute in the same direction. E.g. Na+/glucose transporters (SGLT) in cells of the small intestine that absorb glucose from the digestive tract. c. Antiport – transports two or more types of solute in the opposite directions. E.g. Na+/K+ - ATPase pump – carries 3 Na+ out of the cell and 2 K+ into the cell.

Question 28

Osmosis

Answer 28

passive process Movement of water molecules (solvent) down their own concentration gradient due to kinetic energy of water molecules. Ø From an area of high [H2O] (lots of water molecules) to an an area of low [H2O] (few water molecules) Adding solutes to pure water lowers the concentration of water molecules. So the more solute in a solution the less concentrated the water is in that solution.

Question 29

How does H20 get across the cell membrane

Answer 29

Movement of water molecules occurs directly across the cell membrane OR through cell membrane protein channels call aquaporins

Question 30

osmotic pressure

Answer 30

Movement of water can cause pressure The pressure/force required to stop the flow of water from one solution/compartment to another

Question 31

Osmolarity

Answer 31

(mOsm/ L) The concentration of a solution based on the total number of solute particles per liter (includes both penetrating and non-penetrating solutes)

Question 32

What is a penetrating solute vs a non penetrating solute?

Answer 32

Penetrating solutes – are capable of freely crossing cell membranes Ø Small, polar and non-polar molecules Ø E.g. urea, glycerol, ethanol Non-penetrating solutes – cannot freely cross cell membranes Ø Ions and larger polar (hydrophilic) molecules that cannot cross the hydrophobic region of the phospholipid bilayer Ø E.g. Na+, glucose, amino acids

Question 33

Isosmotic

Answer 33

have the same osmolarity as another solution

Question 34

hyperosmotic

Answer 34

have a higher osmolarity than another solution

Question 35

Hypoosmotic

Answer 35

have a lower osmolarity than another solution

Question 36

crenation

Answer 36

Movement of water out of the cell causes it to shrink/shrivel

Question 37

tonicity

Answer 37

how a solution will affect the volume of a cell compares a solution to a cell’s intracellular solution. Specifically tells you whether or not a cell will swell or shrink Depends ONLY on the concentration of non- penetrating solutes * Water will always go to high non penetrating solute

Question 38

Hypertonic

Answer 38

causes cell to lose water and shrink ( higher concentration of water inside the cell than outside and lower concentration of non penetrating solutes)

Question 39

Isotonic

Answer 39

does not change cell shape (no net osmosis)

Question 40

Hypotonic

Answer 40

causes cell to swell and may burst. (higher concentration of water outside the cell than inside and lower concentration of non penetrating solutes outside)

Question 41

Hyposmotic solutions are always.....

Answer 41

hypotonic

Question 42

What is diffusion?

Answer 42

Movement of solutes down a concentration gradient (from an area of high concentration to an area of low concentration) Ø Does not require energy. Ø Occurs as a result of the kinetic energy (random motion) of ions/molecules. Ø Process continues until equilibrium is reached. Ø Fast over short distances, slow over long distances. Ø The time it takes to get from A to B is a “distance squared” relationship. If the distance travelled doubles from 1 to 2, then the time it takes for diffusion to occur quadruples from 1 to 4 (=2^2 ) Ø Rate of diffusion is faster at high temperatures (increases kinetic energy/random motion of molecules) Ø Rate of diffusion is slower across a membrane

Question 43

List the different types of diffusion

Answer 43

simple diffusion facilitated diffusion

Question 44

simple diffusion

Answer 44

molecules pass directly through the phospholipid bilayer - lipophilic substances can pass right thru

Question 45

What does Fick’s Law of Diffusion say

Answer 45

the diffusion rate increases with increasing SA concentration gradient and mem. permeability

Question 46

i

Answer 46

a. Surface area of membrane: ↑ surface area = ↑ rate of diffusion (basically there is more space over which diffusion can occur) b. Concentration gradient: ↑ gradient = ↑ rate of diffusion Ø the larger the gradient the more molecules will move into/out of the cell in an attempt to establish equilibrium

Question 47

What does the permeability of the cell membrane to the molecule depend on?

Answer 47

i. Size (and shape) of molecules. ↑ molecular size = ↓ permeability ii. Lipid solubility of the molecule. ↑ lipid solubility= ↑ permeability iii. Composition of the membrane Ø Relative proportions and types of phospholipids, sphingolipids affect rate as does the amount of cholesterol. Ø For example ↑ cholesterol = ↓ permeability (cholesterol gets in between fatty acid tails and blocks movement of molecules through the membrane)

Question 48

Facilitated diffusion

Answer 48

protein mediated transport Ø Movement of a molecule across the cell membrane via a channel protein or a carrier protein. The protein facilitates diffusion of the solute down its concentration gradient. ØDoes not require ATP ØThis process alone cannot accumulate a solute against a concentration gradient

Question 49

channel-mediated facilitated diffusion

Answer 49

Ø uses a channel protein to move the solute down its concentration gradient. Ø E.g. Na+ leak channels

Question 50

Carrier-mediated facilitated diffusion

Answer 50

Ø uses a carrier protein to move the solute down its concentration gradient . Ø E.g. facilitated diffusion of glucose into skeletal muscle or liver cells via glucose transporters (GLUT) Ø Low concentration of glucose inside of cell are maintained because any glucose entering the cell is immediately converted to glucose-6-phosphate. Prevents equilibrium from being reached.

Question 51

Primary Active Transport

Answer 51

Directly uses ATP (i.e. the transport protein that breaks down ATP is the same protein that will transport the solute) b. Establishes concentration gradients. c. Carrier proteins involved are sometimes called pump

Question 52

Give an example of active transport

Answer 52

Na+/K+ ATPase is the most widely known example (found in all cells). Ø Pumps 3 Na+ out of the cell and 2 K+ into the cell (antiport). * CREATES THE NA+ AND K+ GRADIENT THAT EXISTS BETWEEN ECF AND ICF Ø Carrier protein hydrolyzes ATP and undergoes several conformational changes

Question 53

Secondary Active Transport

Answer 53

Indirectly uses ATP Ø the transport protein that breaks down ATP creates a concentration gradient of one solute (solute A). Ø The kinetic energy stored in this concentration gradient is then used to move another solute (solute B) against its concentration gradient using a separate carrier protein.

Question 54

Give an ex of 2 active transport

Answer 54

Example: Na+-glucose secondary active transporter (SGLT-protein) used to absorb glucose from lumen of intestine into intestinal cells. i. Na+ binds to SGLT carrier protein (moving down its concentration gradient) ii. Na+ binding creates a high-affinity site for glucose iii. Glucose binding changes the conformation of the protein so that protein is open to the inside of the cell. iv. Na+ is released moving down its concentration gradient v. Release causes decreases affinity of glucose binding site vi. Glucose is released into the cytosl

Question 55

Specificity

Answer 55

The transporter is specific for a particular substrate/solute or a particular group of related substrates/solutes ØE.g. GLUT proteins are specific for 6-carbon sugars, with a preference for glucose (but can also move galactose and fructose

Question 56

Competition

Answer 56

several substrates/solutes compete for the binding sites on the carrier. This reduces the transport rate. E.g. glucose and galactose compete for the same binding sites, so when both are present, the transport of glucose decreases. Some competitors are not transported across the membrane, but simply block the binding site of the preferred solute (competitive inhibitor)

Question 57

Saturation

Answer 57

if there are not enough carriers for the amount of substrate/solute, the binding sites become saturated At this point the rate of transport cannot increase with any further increase in substrate/solute concentration and so a transport maximum is reached ØCells can avoid reaching the transport maximum by building new protein carriers and inserting them in the membrane. ØE.g. Insulin acts on muscle cells to increase the number of GLUT4 protein carriers in their membranes

Question 58

List the different types of active transport

Answer 58

primary secondary vesicular

Question 59

Vesicular transport

Answer 59

Used for large molecules that cannot be transported by membrane channels or carriers

Question 60

Phagocytosis

Answer 60

movement of a very large particle (e.g. bacterium) into the cell in a large vesicle. ”Cell-eating” Ø Cell uses cytoskeleton (microfilaments made of actin) and myosin motor proteins to extend the cell membrane and wrap it around the particle. Creates a membrane bound space within the cell called a phagosome Ø E.g. a white blood cell surrounding a bacterium

Question 61

Endocytosis

Answer 61

movement of large particles into the cell in small vesicles Ø Cell membrane surface indents and forms vesicles

Question 62

Pinocytosis

Answer 62

a on-selective form of endocytosis (cell takes in all particles – water and solutes – in the area where the vesicle forms). “Cell-drinking”.

Question 63

Exocytosis

Answer 63

movement of large particles OUT of the cell in small vesicles Ø Intracellular vesicles move to membrane and merge with it (vescicle membrane becomes part of cell membrane,; vesicle contents exit the cell). Ø Transport of large lipophobic molecules (e.g. some proteins) Ø Requires ATP Ø Usually triggered by an increase in cytosolic Ca++ concentration

Question 64

Absorption

Answer 64

transport from the outside of the body to the inside.

Question 65

Secretion

Answer 65

transport from the inside of the body to the outside

Question 66

Apical surface

Answer 66

f aces the outside of the body (e.g. the lumen of the intestine or the lumen of a kidney tubule (nephron)). Common location for SLGT proteins in intestinal cells.

Question 67

Basolateral surface/membrane

Answer 67

aces the ISF,. Common location for Na+/K+ ATPase pumps

Question 68

Paracellular transport

Answer 68

Through junctions between adjacent cells

Question 69

Transcellular transport

Answer 69

Through cells themselves – substance being absorbed or secreted must pass through two membranes Ø Involves a combination of active and passive transport processes

Question 70

Describe transcellular transport of glucose and Na+, including direction of movement, relevant membrane proteins, additional ions, and concentration gradients.

Answer 70

a. A Na+/Glucose symporter (SGLUT) in the apical membrane that moves glucose into the cell using the concentration gradient for Na+ (secondary active transport). b. GLUT transporter that transports glucose out of the cell into the ECF (first into the ISF, then into the plasma) using carrier mediated facilitated diffusion (passive). c. Na+/K+ ATPase pump in the basolateral membrane that pumps Na+ out of the cell in exchange for K+, thereby keeping [Na+] low inside the cell (allows for (a) to keep happening). – primary active transport