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PHGY 209 > Transport Mechanisms > Flashcards

Transport Mechanisms Flashcards

1
Q

Permeability of Cell Membrane

A

Highly permeable to:
H2O,
lipid-soluble substances, dissolved gasses (O2, CO2),
small uncharged molecules

Less permeable to:
Large molecules
charged particles

Impermeable to:
Very large molecules

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2
Q

Plasma membrane composition

A

Phospholipid bilayer (40-50% of plasma membrane)

Membrane is 6-10 nM thick

Amphipathic: polar (hydrophilic heads) and nonpolar ends (Hydrophobic tails)

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3
Q

Role of Cholesterol

A

Inside bilayer, slightly amphipathic

Acts as buffer and ensures fluidity

temp is low = keeps fluidity
temp is high = prevents to much fluidity

involved in forming vesicles and lipid rafts

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4
Q

Types of proteins in plasma membrane

A

most diverse macromolecule 25-75% of membrane weight

Integral: mostly cross membrane (trans-membrane), associated with phospholipids

Peripheral: mostly on cytoplasmic side and next to polar heads of phospholipids

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5
Q

What is Glycocalyx

A

Coating surrounding cell membrane formed of glycans, glycoproteins and glycolipids.

helps in cell-cell recognition
communication
adhesion
protection
permeability

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6
Q

Fluid mosaic model

A

Things are not completely stuck in place in the membrane.
Fluidity can be changed with cholesterol
some proteins are created and others are removed
proteins move or stay attached to cytoskeleton

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7
Q

Functions of plasma membrane proteins (6)

A
  1. Selective transport:
    channels and transporters
  2. Enzyme Catalyst
  3. Cell surface receptor
  4. Cell surface identity marker:
    CD4 T lymphocytes, CD proteins are important for cell recognition during immune response,
    markers can help detect cancerous cells
  5. Cell adhesion: CAMs, integrins, cadherins
  6. Attachment to cytoskeleton: actin, microtubules, septins
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8
Q

Types of passive transport

A

(energy independent)

  1. diffusion channels
  2. facilitated diffusion (carriers, transporters)
  3. osmosis
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9
Q

Types of active transport

A

Energy dependent

  1. Active transport
    primary
    secondary
  2. Endocytosis Pino/Phagocytosis, receptor-mediated endocytosis
  3. Exocytosis
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10
Q

Diffusion

A

Thermal motion makes molecules move from a location to another until equilibrium is reached
(net flux is 0)

net flux:
high => low concentration
down concentration gradient

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11
Q

Why is diffusion effective on very short distances

A

diffusion time increases in proportion to the square of the distance travelled by solute
1um = 1msec
10 um = 100 msec
100 um = 10 000 msec

Very slow as distance is increased
(explain why we have a lot of capillaries across body, to have diffusion everywhere)

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12
Q

Ion channels distinctions

A

Show ion selectivity

movement of ion is affected by electrical gradient in addition to concentration gradient

Combination = electrochemical gradient

ions go where they are smaller in concentration, but at the same time some are sent back because the charge is different where they come from

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13
Q

Types of gating (3)

A

some ion channels can be closed by conformational changes

Ligand-gated
voltage-gated
mechanically-gated

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14
Q

Voltage gated ion channels depend on

A

channel conductance
channel open time
frequency of opening

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15
Q

What is mediated transport

A

Movement of ions and molecules by integral membrane proteins (transporters or carriers)

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16
Q

Types of mediated transport

A

Facilitated diffusion (passive)

Active transport
1. primary
2. secondary

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17
Q

Specificity of Mediated transport

A

system usually transports one particular type of molecule

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18
Q

Saturation of mediated transport

A

rate of transport can increase but reaches a maximum velocity once each binding sites are occupied

Transport maximum (Tm) is the limit of the rate at which substance cross the membrane

Increasing concentration of solute does not increase rate of transport

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19
Q

Competition in mediated transport

A

similarly structured molecules can compete for the same binding site of a carrier.

can slow rate of transport of desired molecule

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20
Q

Factors that determine mediated transport efficiency

A

solute concentration

affinity of transporter to solute

numbers of transporters

rate of transporter conformational change

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21
Q

What is Facilitated diffusion

A

presence of transporter or carriers enable solute to move across membrane from high to low concentration without use of energy

down concentration gradient

solutes binds
binding changes configuration
solute is delivered on other side
transporter resumes original config.

22
Q

Characteristics of active transport

A

Needs energy supply, ATP

susceptible to metabolic inhibitors

Transport solute against concentration gradient
low to high

23
Q

Primary active transport

A

Involves hydrolysis of ATP by carrier (becomes ADP + P)

P binds to carrier = phosphorylation, which changes conformation and binding affinity to solute

against concentration gradient

24
Q

Na+/K+-ATPase, sodium potassium pump

A

outside high [Na+], low [K+]

inside, ATP binds to carrier, 3 Na+ ions bind to carrier

Phosphorylation occurs P ions attached to carrier and ADP leaves = conformation change

3 Na+ ions leave cell and 2 K+ ions attach to carrier

P ion detaches from carrier to form ATP molecule => conformation change

2 K+ ions are released in cell where [K+] is high, [Na+] is low

25
Active transports to remember
Ca2+-ATPase maintain low intracellular Ca2+ levels H+-ATPase maintain low lysosomal pH H+/K+-ATPase acidification of the stomach
26
What is secondary active transport
Primary active transport creates an electrochemical gradient. Secondary transport uses this gradient to send Na+ down its concentration gradient while being coupled with another solute molecule (ion, glucose, amino acid) on the carrier conformation change delivers Na+ and other into cell Transporter reverts to original configuration and Na+ leaves cell with Na+/K+ATPase
27
What are some kinds of transport (directions)
Symport, cotransport two solutes transported in same direction Antiport, Counter transport Two solutes are transported in opposite directions
28
What is Exocytosis
Intracellular vesicle fuses with cell membrane to release content into ECF
29
What is endocytosis
Cell membrane invaginates and pinches off to form a vesicle (inside)
30
2 Types of Exocytosis
Constituitive exo. non-regulated, replace plasma membrane, deliver membrane proteins to cell membrane and get rid of substances Regulated exo. Triggered by extracellular signals (increase of cystolic Ca2+) Does secretion of hormones, digestive enzymes, neurotransmitters
31
Pinocytosis
(cell drinks) vesicle engulfs ECF and everything inside, nonspecific vesicles fuse with other vesicle like endosomes or lysosomes
32
Phagocytosis
(Cell eats) Pseudopodia (extensions of cell membrane) engulfs solid matter, small-sized particles, microorganisms. Pseudopodia fuse into phagosomes which fuse with lysosomes where contents are degraded
33
Receptor-mediated Endocytosis
Molecules in ECF (ligands) bind with protein receptors on plasma membrane when binding occurs, conformational change happens in receptors. Clathrin proteins form a cagelike structure with the receptors Clathrin coated pit (Cage) fuses with lysosome to process substance inside receptors and clathrin are recycled in cell membrane
34
What is potocytosis
molecules are transported by clathrin-independent vesicles (caveolae) Caveolae deliver contents in cytoplasm or endoplasmic reticulum Uptake of vitamins
35
How water diffuses
Aquaporins are water permeable channels across the cell membrane
36
what is osmosis
net diffusion of H2O across semipermeable membrane (solvent can go trough and some but not all solutes) water goes from High to low concentration of water
37
What is osmotic pressure
Pressure to prevent movement of water across semi-permeable membrane Equal to difference in hydrostatic pressures of two solutions Pressure (P) is proportional to number (n) of particles in solution, not their size P = nRT/V
38
What is Osmolarity (Osm)
Total solute concentration of a solution. (number of solute particles per unit of solvent) osmol = mol of solute 1 mol glucose = 1 osmol solute Osm = osmol / unit of solvent 2 mol glucose/L = 2 osmol/L = 2 Osm
39
Isomotic solutions
Solutions with the same osmolarity as normal extracellular or intracellular solutions (which are at 300 mOsm)
40
Hypoosmotic solutions
Osmolarity is lower than 300 mOsm
41
Hyperosmotic
Osmolarity is greater than 300 mOSm
42
Importance of nonpenetrating particles in osmotic pressure
Particles must not be able to cross the membrane freely all the time to allow a difference in solute concentration between each side of the cell membrane Na+ is non penetrating because what goes in is pumped out by the Na-K ATPase
43
Isotonic solution
Solution with concentration of 300 mOsm = no net shift of water
44
Hypotonic solution
Solution concentration is less than 300 mOsm, there is more solute inside the cell water enters cell and it swells
45
Hypertonic Solution
Solution concentration of nonpenetrating solute is greater than 300 mOsm, solute concentration is higher outside cell Water leaves cell and it shrinks
46
Capillaries details
40 km in an adult 5% of total circulating blood each: 1mm long diameter 8 micrometer
47
Capillary wall
Single layer of flattened endothelial cells supporting basement membrane
48
Diffusion across capillary wall
Diffusion across the membrane is most important Also diffusion through water filled channels
49
Transcytosis in capillary wall
Endocytosis on luminal side followed migration of vesicle across cell and exocytosis on interstitial side
50
Bulk flow in capillary wall
Distribution of ECF volume between plasma and ISF Bulk flow: Proportional to hydrostatic pressure difference between plasma and ISF protein free plasma is filtered from capillaries to ISF

PHGY 209 (9 decks)

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