Transport Mechanisms

Question 1

Permeability of Cell Membrane

Answer 1

Permeable to water, lipid soluble substances, gases, non-polar molecules
Impermeable to large particles

Question 2

Cell Membrane composition

Answer 2

Phospholipid Bilyaer
Cholesterol
Proteins
Glycocalyx

Question 3

Cholesterol Role

Answer 3

Increase membrane fluidity
Helps pinch of vesicles
High temps: stabilize cell membrane

Question 4

Proteins

Answer 4

Integral: transmembrane, amphipathic
Peripheral: cytoplasmic side

Question 5

Glycocalyx

Answer 5

Carbs on the extracellular surface
Helps protect from infection and identification between cells

Question 6

Protein Functions

Answer 6

Transport
Enzymes
Receptors
Identification markers
Cell adhesion
Attachement to cytoskeleton

Question 7

Passive Transport

Answer 7

Diffusion
Carrier Mediated Facilitated Diffusion
Osmosis

Question 8

Active Transport

Answer 8

Carrier-mediated active transport
Pinocytosis
Phagocytosis

Question 9

Diffusion

Answer 9

Movement of molecules from one location to another due to thermal motion
Follows concentration gradient (high –> low)

Question 10

Diffusion Equilibrium

Answer 10

Net flux = 0
Must be permeable to diffused molecules

Question 11

Fick’s Law (Rate of Diffusion)

Answer 11

J = PA(Co - Ci)
- Diffusion time increases in proportion to square of distance travelled by solute (so only efficient over small distances)

Question 12

Factors influencing diffusion

Answer 12

1. Mass of molecules
2. Concentration gradient
3. Lipid solubility
4. Electrical charge
5. Availability

Question 13

Ion Channels

Answer 13

Selectivity based on diameter and distribution of charges lining channel

Question 14

Mediated Transport Systems

Answer 14

Movement of ions by integral proteins
1. Specific to certain molecules
2. Saturation: rate decreases when all binding sites are full
3. Competition: available binding sites

Question 15

Factors Determining Flux Magnitude

Answer 15

1. Solute concentration
2. Affinity of transporter for solute
3. Number of transporters
4. Rate of transporter conformation change

Question 16

List transports that are mediated systems

Answer 16

1. Facilitated Diffusion
2. Active transport
   a) Primary active transport
   b) Secondary active transport

Question 17

Facilitated Diffusion

Answer 17

Diffusion with transporter (high–> low concentration)
a) solute binds to transporter
b) transporter changes conformation
c) solute releases on other side
d) transporter returns to original conf

Question 18

Primary Active Transport

Answer 18

Hydrolysis of ATP by carrier
a) phosphorylation of transporter changes its conformation
sodium-potassium pump: 2K+ go in, 3 Na+

Question 19

Secondary Active Transport

Answer 19

movement of Na+ down its concentration gradient is coupled to transport other molecules against their concentration gradient

Question 20

Steps of secondary active transport

Answer 20

1. Na+ binds to transport protein outside cell, allowing glucose to bind to same carrier
2. Change in configuration transporter delivers Na+ and glucose to other side
3. Transporter returns to original conformation

Question 21

Endocytosis

Answer 21

membrane invaginates + pinches off to form a vesicle (enters)

Question 22

Exocytosis

Answer 22

intracellular vesicle fuses with membrane + releases product to ECF

Question 23

Constitutive (exocytosis)

Answer 23

Non-regulated, replaces membrane, delivers membrane proteins and gets rid of substances inside

Question 24

Regulated (exocytosis)

Answer 24

Triggered by extracellular signals + increase of cytosolic Ca2+
Responsible for secretion of hormones, digestive enzymes and neurotransmitters

Question 25

Pinocytosis (endocytosis)

Answer 25

Fluid endocytosis = vesicle engulfs extracellular fluid (w/ solutes)
Non-specific

Question 26

Phagocytosis (endocytosis)

Answer 26

Cells bind + internalize particle matter = forms a phagosome vesicle in cytoplasm –> lysosome binds and degrades content
Specific and triggered

Question 27

Receptor Mediated Endocytosis

Answer 27

Ligands bind w/ high affinity to protein receptors on membrane

Question 28

Clathrin-Dependent Receptor Mediated Endo.

Answer 28

Ligands bind to receptors at membrane surface
Clathrin coats the inside
Clathrin coated pit vesicle forms
Clathrin is released from vesicle
Endosome binds with pit, separating the receptors and ligands = different ends, and breaks appart
Receptors return to surface
Ligand transport vesicle binds with lysosome = breaks them down into smaller pieces and released in cytoplasm

Question 29

Potocytosis

Answer 29

Molecules are sequestered and transported by caveolae
Transported to cytoplasm or endoplasmic reticulum
Only low molecular weight molecules i.e: vitamins

Question 30

Osmosis

Answer 30

Net diffusion of water across semipermeable membrane
- only water moves

Question 31

Aquaporins

Answer 31

Proteins that facilitate the diffusion of water across membranes

Question 32

Osmotic pressure

Answer 32

Opposes water movement
- pressure required to prevent water from moving across the membrane
- difference in hydrostatic pressures of solutions encourages water movement

Question 33

Osmolarity of Cell

Answer 33

300 mOsm

Question 34

Hypo osmotic

Answer 34

Osmolarity lower than 300 mOsm

Question 35

Hyper osmotic

Answer 35

Osmolarity higher than 300 mOsm

Question 36

Non Penetrating solutes

Answer 36

Unable to cross the membrane (they maintain the osmotic pressure)
Na+ is non penetrating

Question 37

Isotonic Solution

Answer 37

300 mOsm of non penetrating solute

Question 38

Hypotonic Solution

Answer 38

Less than 300 mOsm of non penetrating solute
- Causes water to enter cell = cell swells

Question 39

Hypertonic Solution

Answer 39

Greater than 300 mOsm of non penetrating solute
- Causes water to leave = cell shrinks

Question 40

Capillary wall transport

Answer 40

1. Diffusion: through channels
2. Transcytosis: ???
3. Bulk flow: distributes ECF volume between plasma and ISF