transport mechanisms Flashcards

1
Q

define homeostasis

A

refers to any process that living things use to actively maintain fairly stable conditions necessary for survival
coined by walter cannon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

how to preserve constancy of milieu interieur and the homeostasis

A

exchange nutrients, salts, gases and waste in and out of the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is the cell membrane highly permeable to

A

H2O
lipid soluble substances
dissolved gasses (O2 and CO2)
small uncharged molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is the cell membrane less permeable to

A

larger molecules
charged particles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is the cell membrane impermeable to

A

very large molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

describe the cell membrane (plasma membrane)

A

6-10nM thick (very thin)
bimolecular phospholipid layer (phospholipid bilayer)
amphipathic = polar hydrophilic heads on outside and non polar hydrophobic tails in center

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

how much of the plasma membrane is phospholipids (by weight)

A

40-50%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

is cholesterol hydrophobic

A

slightly amphipathic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

describe what happens when cholesterol is inserted into the phospholipid bilayer

A

reduces packing of fatty acid tails
tends to increase membrane fluid it keeping fatty acid tails apart

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

describe what cholesterol may also be involved in

A

formation of vesicles that pinch off the plasma membrane in lipid rafts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what does cholesterol do at high temps

A

acts to stabilize the cell membrane and add firmness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what does cholesterol do at low temps

A

inserts into phospholipids and prevents them from interfering with each other to avoid aggregation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

describe proteins

A

most diverse macromolecules
25-75% membrane by weight

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

name the 2 types of proteins

A

integral and peripheral

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

describe integral proteins

A

closely associated with phospholipids
mostly cross cell membrane
trans membrane and amphipathic
embedded transverse the whole membrane
not easily removable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

describe peripheral proteins

A

more loosely associated
mostly on cytoplasmic side
easily removable
located on cell surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is glycocalyx (describe it)

A

layer of carbs formed by chain of monosaccharides
extend from extracellular surface of the cell membrane bound to proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is glycocalyx associated with

A

glycoproteins and glycolipids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is the purpose of glycocalyx

A

provides protection from infection
enables cells to identify each other and interact

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

describe fluid mosaic model or cell membrane

A

proteins are fixed and can move around
not a stable situation
membrane is always being replenished and so there’s much more turnover

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

name the functions of plasma membrane proteins (6)

A

selective transport channel
enzyme
cell surface receptor
cell surface identity marker
cell adhesion
attachment to the cytoskeleton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

describe selective transport channel (functions of plasma membrane)

A

channels (ion channels) and transporters (ions and other molecules)

transport and diffusion of specific molecules into and out of cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

describe enzyme (functions of plasma membrane)

A

amino acid transport Na-K pumps
enzymes like ATPase
act as enzymes that catalyze membrane associated reactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

describe cell surface receptor (functions of plasma membrane)

A

G protein coupled receptors
insulin receptors
ACh receptors
for signaling within cells

serve as receptors for receiving and transducing chemical signals from the cell environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
describe cell surface identity marker (functions of plasma membrane)
proteins or cells give each a marker/target for therapeutics ex = CD4 T lymphocytes CD45 leucocytes CD68 monocytes
26
describe cell adhesion (functions of plasma membrane)
CAMs cadherins integrins cell-cell adhesion
27
describe attachment to the cytoskeleton (functions of plasma membrane)
proteins involved in attachment and stability actin microtubules septins
28
name the 2 transmembrane transport pathways
via phospholipid bilayer via interaction with protein cluster (channel or carrier)
29
name the 2 transport mechanism across cell membrane
passive active
30
describe passive transport mechanism across cell membrane and name types
energy independent diffusion carrier mediated facilitated diffusion osmosis
31
describe active transport mechanism across cell membrane and name types
energy dependent carrier mediated active transport (primary and secondary) pino/phagocytosis
32
what is diffusion
simple diffusion is the movement of molecules from one location to another as a result of random thermal movement
33
what is flux
amount of particles crossing a surface per unit time net flux is from high concentration to lower concentration from high to low
34
at equilibrium describe diffusion fluxes and net flux
diffusion fluxes are equal net flux is zero (molecules don’t stop moving but it’s equal and opposite movement)
35
does diffusion occur even in the presence of a mechanical partition (membrane)
yes as long as it is permeable to the diffusing particles
36
describe the movement from high to low
downhill until both are equal
37
describe flux from high to low
high to low = one way flux from high to low (large amount) one way flux from low to high (small amount) net flux = from high to low (medium amount)
38
describe what happens to intracellular concentration with constant extracellular concentration
intracellular concentration eventually equals extracellular concentration equilibrium reached when evenly distributed across cell membrane
39
how to calculate rate of diffusion
ficks law of diffusion J=PA(Co-Ci) J=mol/cm^2/sec
40
describe ficks law of diffusion equation - J
J = net flux (rate of diffusion) - moles of solute crossing
41
describe the relationship between diffusion time and distance
diffusion time increases in proportion to the square of the distance travelled by the molecules
42
describe ficks law of diffusion equation - P
permeability or diffusion coefficient constant based on the ease that a molecule moves through a membrane with (property of the solute that is moving through the medium)
43
describe ficks law of diffusion equation - A
surface area of the membrane cm^2 or area of whole cell
44
describe ficks law of diffusion equation - Co-Ci
concentration gradient of the diffusing molecule across the membrane driving force - concentrations change on both sides and this drives the diffusion
45
T or F: diffusion is very inefficient over short distances
FALSE diffusion is an effective transport method only over short distances einsteins approximation equation
46
describe diffusion of glucose (distance and time)
diffusion is good over short distances 1um = 1 m sec 10 um = 100 m sec 100 um = 10000 m sec
47
name factors that affect diffusion across the membrane (5)
1- mass of the molecule 2- concentration gradient across cell membrane 3- lipid solubility (if going across lipid portion of cell membrane 4- electrical charge 5- availability of selective ion channels or membrane carriers
48
how do diffusion particles penetrate cell membrane - 2 ways
1 - dissolving in lipid component - for non polar molecules like O2 CO2 and fatty acids 2 - diffusing through channels for ions
49
what is needed for movement (diffusion of particles across cell membrane)
depends on existence of a concentration gradient
50
describe ion channels
consist of a single protein or clusters of proteins show selectivity based on their diameter and the distribution of charges lining the channel has hole down middle, subunits around it
51
what else is the movement of ions affected by
electrical gradient simultaneous existence of an electrical and a concentration gradient for a particular ion = electrochemical gradient
52
what charge are the inside of cells
always negative
53
what determines membrane potential
concentration gradient
54
describe electrical gradient (movement of K+)
intracellular - K is high -90mV extracellular - K is low so K is moved out of cell and negatives are moved into cell
55
describe the states ion channels can exist in
open or closed state as they undergo conformational changes = gating
56
name the 3 ways channels may be gated
ligan gated - cooper voltage gated - hanrahan, lukacs shrier mechanically gated - sharif
57
name and explain the 2 ways ion channels can be open or closed
conformational change - activation = open and gate closes = inactivation, physically closed off occlusion of channel pore = blocking or closing with a gate - actual thing that blocks end of channel pore
58
describe voltage gated ion channels
cell undergoes action potential and cell membrane depolarizes
59
describe ligand gated channels
ligand that can bind to receptor and inactivate channel ex= acetylcholine neurotransmitter
60
describe mechanically gated channels
transform mechanically into another type - pain receptors
61
name the main voltage gated ion channels
Na+ K+ Ca+ Cl-
62
what does the total number of ions that flow through these channels (generating ionic current) depend on - 3
channel conductance (how open it is = small/big) how often channel opens how long channel stays open
63
what is mediated transport
movement of ions and other molecules like amino acids and glucose by integral membrane proteins (transporters/carriers)
64
is ion movement across membranes via transporters slower or faster than through ion channels
transporters are MUCH slower than through ion channels
65
name types of mediated transport
facilitated diffusion active transport (primary active and secondary active)
66
name the characteristics of mediated transport systems (3)
specificity saturation competition
67
describe specificity (characteristics of mediated transport systems)
systems usually transport one particular type of molecule only
68
describe saturation (characteristics of mediated transport systems)
rate of transport reaches a mx when all binding sites on all transporters are occupied Tm = exists for a given substance across a given membrane ex: seats on a bus analogy
69
the greater the gradient...
the higher the flux
70
describe competition (characteristics of mediated transport systems)
happens when similar substance compete for the same binding site on a membrane carrier
71
name the 4 factors that determine the flux magnitude of mediated transport system
1 - solute concentration 2 - affinity of transporter for the solute 3 - number of transporters 4 - rate of transporter conformational change
72
describe facilitated diffusion
involves presence of a transporter or carrier molecule enables a solute to penetrate more readily than simple diffusion molecule must associate with carrier to cross driven by concentration gradient can flip back and do opposite if conformations switch
73
describe steps of facilitated diffusion
solute binds transporter transporter changes configuration solute is delivered to other side of membrane transporter resumes original configuration
74
describe facilitated diffusion (method, energy and flux?)
transporter/carrier mediated passive - no energy net flux from high to low concentration
75
name and explain systems that use facilitated diffusion
hormones may increase the number and/or affinity of transporters in some membranes glut-4 transports glucose in muscle that is increased by insulin
76
describe active transport - 4 statements
transporter mediated requires supply of chemical energy - usually derive from enzymatic hydrolysis of ATP/GTP susceptible to metabolic inhibitors can transport solute against its concentration gradient - uphill transport
77
describe primary active transport
active transport involves hydrolysis of ATP by a transporter/carrier phosphorylation of transporter changes the conformation of the transporter and its solute binding affinity
78
name and describe a very important active transporter
Na+/K+-ATPase changing in the binding site affinity for a transported solute are produced by phosphorylation and dephosphorylation of Na+/K+-ATPase
79
describe Na+/K+-ATPase steps/changes in conformation
intracellular fluid - 3 binding sites for Na+ hydrolysis ATP conformation change and loses affinity for K+ sodium diffuses off 2 K+ binding sites then back to first change in conformation againn
80
name some active transporters and their functions
Ca2+-ATPase = maintain low intracellular Ca2+ levels H+-ATPase = maintain low lysosomal pH H+/K+-ATPase = acidification of stomach
81
is an ion channel a carrier
NOOOOO ion channels allows ions to permeate down the concentration gradient a carrier can transport ions but does not pass through a channel - it is a conformational change of a protein
82
describe secondary active transport
movement of Na+ down concentration gradient is coupled to the transport of another solute molecule (ion, glucose, amino acid) up hill against its concentration gradient
83
what energy does secondary active transport use
energy stored of the electrochemical gradient to move both Na+ and transported solute creation and maintenance of electrochemical gradient depends on primary active transport
84
describe 3 steps of secondary active transport
1 - sodium binds to a transporter outside the cell (high sodium concentration) allowing glucose or amino acids or ions to bind to the same carrier 2 - through a change in configuration transporter delivers both sodium and glucose or amino acid into cell 3 - transporter then reverts to its original configuration and the sodium is extruded from cell by Na+/K+-ATPase
85
what is cotransport
when solute is transported in the same direction as sodium aka symport Na+-aas
86
what is countertransport
when solute is transported in opposite direction to Na+ aka antiport Na+-Ca2+
87
name secondary active transport mechanisms (5)
Na+/H+ exchanger - antiport Na+/Ca2+ exchanger - antiport Na+/HCO3- symporter Na+-amino acid symporter Na+-glucose symporter (sodium-glucose linked transporter SGLT like glut4)
88
briefly describe endocytosis and exocytosis
active transport mechanisms energy dependent involves participation of the cell membrane itself
89
describe endocytosis (brief - process)
cell membrane invaginates and pinches off to form a vesicle
90
describe exocytosis (brief - process)
intracellular vesicle fuses with the cell membrane and it’s contents are released into ECF
91
describe and name the 2 types of exocytosis
exocytosis is the process of moving material from the inside to outside of cell 1- constitutive exocytosis 2 - regulated exocytosis
92
name the 3 types of endocytosis
pinocytosis phagocytosis receptor mediated endocytosis
93
describe pinocytosis
fluid endocytosis involves endocytotic vesicle that engulfs extracellular fluid including solutes present vesicles travel info cytoplasm and fuse with other vesicles like endosomes or lysosomes
94
describe phagocytosis
cells bind and internalize particulate matter (>0.75um), like small dust, cell debris and microorganisms specific and triggered extensions of cell membrane (pseudopodia) fold around particle and fully engulf it pseudopodia fuse to form large vesicles (phagosomes) phagosomes migrate and fuse with lysosomes where contents of phagosome are degraded defends against infection and scavenge senescent and dead cells involves macrophages, neutrophils and dendritic cells
95
describe receptor mediated endocytosis and name 2 types
molecules in extracellular fluid (ligands) bund with high affinity to specific protein receptors on the plasma membrane clathrin dependent receptor mediated endocytosis potocytosis
96
describe clathrin dependent receptor mediated endocytosis
when ligand binds receptor undergoes conformational change clathrin recruited to plasma membrane adaptor proteins link ligand receptor to clathrin complex forms a cage like structure that leads to aggregation of ligand bound receptors then clathrin stuff (ex = LDL receptor)
97
describe LDL receptor
clathrin coated pit formed then invaginates and forms clathrin coated vesicle vesicle pinches off and sheds clathrin coat vesicles can dude with membrane of cellular organelles like endosomes and lysosomes or they can fuse with membrane on another side of cell (transcytosis) receptors and clathrin protein are recycled back to cell membrane
98
describe potocytosis
molecules are sequestered and transported by tiny vesicles (caveolae) vesicles are clathrin independent caveolae can deliver contents directly into cell cytoplasm and to ER and other organelle and to plasma membrane on opposite side of cell (transcytosis) implicates in uptake of low molecular weight molecules like vitamins
99
describe diffusion of water
water diffuses freely across most cell membranes facilitated by groups of proteins called aquaporins that form permeable channels
100
describe osmosis
net diffusion of water across a semipermeable membrane (permeable to solvent but not all solute) must be able to calculate molarity (moles of solvent) also note that if solute then must account for that in moles
101
describe osmotic pressure
pressure required to prevent movement of water across a semi permeable membrane pressure is equal to the difference in hydrostatic pressure of the two solutions
102
describe relationship between osmotic pressure and gas
osmotic pressure is related to temp in the same way as pressure of a gas pv=nrt osmotic pressure is proportional to the number of particles in the solution/unit volume and not their size/configuration/charge
103
what is osmolarity
total solute concentration of a solution osmotic pressure is proportional to osmolarity (Osm) 1 osmol = 1 mole of solute particles osm = osmol/litre must consider dissociation (NaCl = 2 osmol of solute)
104
describe how to determine osmotic pressure of physiological saline 3
determine molarity determine osmolarity calculate osmotic pressure (osm to atm to mmHg)
105
describe isosmotic
solutions have the same osmolarity (concentration of osmotically active particles) as normal intracellular or extracellular solution 300 mOsm
106
describe hypoosmotic
solutions with osmolarity lower than 300 mOsm
107
describe hyperosmotic
solutions with osmolarity greater than 300mOsm
108
describe particles needed to be effective in exerting a sustained osmotic pressure
particles must not be able to cross the membrane referred to as non penetrating extracellular sodium = non penetrating bc sodium that moves into cell is pumped out by Na-K ATPase
109
describe what happens when you put rbc in isotonic extracellular solution
when solution has concentration of 300mOsm of non penetrating solute particles no net shift of water if penetrating - solute goes in and water goes in and then cells with burst
110
describe what happens when you put rbc in hypotonic extracellular solution
concentration of no penetrating solute less than 300mOsm water will enter cells and they will swell
111
describe what happens when you put rbc in hypertonic extracellular solution
if solution has a concentration of solute non penetrating particles greater than 300mOsm then water will leave cell and it will shrink
112
where does main exchange take place
at level of the capillaries
113
describe capillaries physically
adult had ~40km of capillaries capillaries contain ~5% of total circulating blood each capillary is ~1mm long and has inner diameter of ~8um
114
describe capillary wall
single layer of flattened endothelial cells and a supporting basement membrane
115
name and briefly describe capillary structure and permeability characteristics (4)
1 - small water voluble substances pass through the pores 2 - lipid soluble substances pass through endothelial cells 3 - exchangeable proteins are moved across by vesicular transport 4 - plasma proteins cannot cross capillary wall
116
describe transport across capillary wall (1,2-diffusion)
across cell membrane very important also occurs through water filled channels (intracellular clefts and fused vesicle channels)
117
describe transport across capillary wall (3-transcytosis)
endocytosis on the luminal side followed migration of the vesicle across the cell and then exocytosis on the interstitial side
118
describe transport across capillary wall (bulk flow)
distributes extracellular fluid volume between plasma and ISF magnitude of bulk flow is proportional to hydrostatic pressure difference between plasma and ISF capillary wall acts as filter that permits protein free plasma to move from capillaries to ISF (difference in hydrostatic pressures)
119
describe constitutive exocytosis
non regulated functions to replace plasma membrane deliver membrane proteins to cell membrane get rid of substances from the cell
120
describe regulated exocytosis
tends to be triggered by extracellular signals and increase of cytosolic calcium responsible for secretion of hormones, digestive enzymes and neurotransmitters ex= synapses and vesicles with acetylcholine
121
how is cholesterol transported in blood
lipid protein particles known as LDL lipoprotein is recognized by PM LDL receptors and endocytosis follows