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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
Q

Active transports to remember

A

Ca2+-ATPase
maintain low intracellular Ca2+ levels

H+-ATPase
maintain low lysosomal pH

H+/K+-ATPase
acidification of the stomach

26
Q

What is secondary active transport

A

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
Q

What are some kinds of transport (directions)

A

Symport, cotransport
two solutes transported in same direction

Antiport, Counter transport
Two solutes are transported in opposite directions

28
Q

What is Exocytosis

A

Intracellular vesicle fuses with cell membrane to release content into ECF

29
Q

What is endocytosis

A

Cell membrane invaginates and pinches off to form a vesicle (inside)

30
Q

2 Types of Exocytosis

A

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
Q

Pinocytosis

A

(cell drinks)
vesicle engulfs ECF and everything inside, nonspecific
vesicles fuse with other vesicle like endosomes or lysosomes

32
Q

Phagocytosis

A

(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
Q

Receptor-mediated Endocytosis

A

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
Q

What is potocytosis

A

molecules are transported by clathrin-independent vesicles (caveolae)

Caveolae deliver contents in cytoplasm or endoplasmic reticulum

Uptake of vitamins

35
Q

How water diffuses

A

Aquaporins are water permeable channels across the cell membrane

36
Q

what is osmosis

A

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
Q

What is osmotic pressure

A

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
Q

What is Osmolarity (Osm)

A

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
Q

Isomotic solutions

A

Solutions with the same osmolarity as normal extracellular or intracellular solutions (which are at 300 mOsm)

40
Q

Hypoosmotic solutions

A

Osmolarity is lower than 300 mOsm

41
Q

Hyperosmotic

A

Osmolarity is greater than 300 mOSm

42
Q

Importance of nonpenetrating particles in osmotic pressure

A

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
Q

Isotonic solution

A

Solution with concentration of 300 mOsm = no net shift of water

44
Q

Hypotonic solution

A

Solution concentration is less than 300 mOsm, there is more solute inside the cell

water enters cell and it swells

45
Q

Hypertonic Solution

A

Solution concentration of nonpenetrating solute is greater than 300 mOsm, solute concentration is higher outside cell

Water leaves cell and it shrinks

46
Q

Capillaries details

A

40 km in an adult
5% of total circulating blood
each: 1mm long
diameter 8 micrometer

47
Q

Capillary wall

A

Single layer of flattened endothelial cells

supporting basement membrane

48
Q

Diffusion across capillary wall

A

Diffusion across the membrane is most important

Also diffusion through water filled channels

49
Q

Transcytosis in capillary wall

A

Endocytosis on luminal side followed migration of vesicle across cell and exocytosis on interstitial side

50
Q

Bulk flow in capillary wall

A

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 (5 decks)

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