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BIOSCI 107 (modules 4-7) > 4. cellular processes > Flashcards

4. cellular processes Flashcards

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1
Q

explain the steps involved in usual chloride secretion

A
  1. tight junctions create distinct apical and basolateral domains
  2. Na/K ATPase primary transporter pumps three Na+ out of cell against its gradient
  3. Entry step at basal membrane is sodium moving down gradient, bringing in 1K+ and 2Cl-
  4. Cl- in the negative cell interior wants to leave, which it does through passive diffusion through a CTFR at the apical surface
  5. Na+ exits the cell by a pump to maintain the gradient for it to continue entering, drawing in Cl-, and K+ diffuses out via a channel to maintain negative environment inside cell
  6. Cl- transport across cell induces movement of Na+ and fluid via the paracellular pathway to maintain osmolarity and charge
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2
Q

CFTR stands for

A

cystic-fibrosis transmembrane conductance regulator

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3
Q

how does CFTR work/open?

A

the gate is regulated by protein kinase A dependent phosphoryaltion of the R-domain. This causes ATP to bind to the nucleotide binding domain (NBD), causing conformational changes that open the gate and allow chloride to diffuse down its electrochemical gradient

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4
Q

what are the direct effects of a defective CFTR

A

cell can’t secrete chloride, which increases sodium absorption, therefore osmosis draws water into the cell rather than pumping it out -> dry cell surface

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5
Q

pathology of cystic fibrosis in the lungs

A

lack of fluid causes thick, sticky mucous. this traps bacteria, leading to accumulation of immune cells which damages healthy lung tissue and causes infection. affects lung’s ability to perform gas exchange.

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6
Q

CF symptoms in the liver

A

blocking of small ducts of bile tubes

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7
Q

CF symptoms in the pancreas

A

occlusion of ducts leading to lack of digestive enzyme secretion, pancreatitis

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8
Q

symptoms of CF specific to males

A

the reproductive ducts are affected, leading to infertility due to insufficient fluid for ejaculation

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9
Q

symptoms of CF in small intestine

A

thick stool blocks the gut, resulting in intervention required in some newborns

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10
Q

main organs/areas affected by CF, and what they have in common

A

all epithelial-lined; airways, liver, pancreas, small intestine, skin/sweat glands, reproductive tract

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11
Q

where in the gut are the secretory cells

A

crypts, alternating with microvilli, in small intestine and colon

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12
Q

two causes of secretory diahrrea

A

abnormally high concentration of endogenus secretagogues, or enterotoxins secreted from bacteria

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13
Q

bacterua that secretes the cholera toxin

A

vibrio cholerae

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14
Q

what are endogenus secretagogues, what can cause these to be in high concentration

A

naturally produced substances like neurotransmitters and hormones that stimulate secretion
can be put in high concentration by tumors and inflammation

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15
Q

where does glucose absorption occur

A

in the villi of the epithelial cells in the gastrointestinal tract

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16
Q

what is the first stage of sweat formation

A

acinar cells in sweat glands secrete a primary isotonic fluid, driven by chloride secretion which pulls water and sodium along (same NaCl concentration as blood plasma)

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17
Q

what are the two chloride channels in sweat glands, how are they activated

A

CFTR activated by noradrenaline, and Ca2+ activated chloride channels regulated by acetylcholine/IP3 and CLCAs

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18
Q

how does the second stage of sweat formation work

A

reabsorption of NaCl creates a hypotonic solution, due to Na+ absorption down its concentration gradient into the cell through which depolarises the membrane potential (lumen is more negative), drawing Cl- into the cell through CFTRs, but not water, as cells are impermeable to water (lack aquaporins).

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19
Q

how does sodium enter the cell for reabsorption in the reabsorption duct

A

through ENaC, epithelial sodium channel, via facilitated diffusion

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20
Q

what is an electrogenic transport process

A

A transport process that moves ions in a way that creates a net movement of electric charge across a membrane

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21
Q

composition of the lipid bilayer

A

about 50% proteins and 50% lipids by mass. the lipid bilayer contains 3 different types of lipids; 75% phospholipids, as well as glycolipids and cholesterol

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22
Q

how would transmembrane proteins be removed from the bilayer

A

with a detegerent to allow them to come free of the hydrophobic region

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23
Q

what do hydrophobic regions of membrane proteins typically consist of

A

non-polar amino acids coiled into alpha helices

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24
Q

lipids in the bilayer can move where…

A

within their leaflet of the membrane, but cannot switch leaflets

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25
what factors influence the fluidity of the membrane
lipid tail length: longer = less fluid cholesterol concentration: more cholesterol = less fluid saturation (double bonds): more saturated (less double bonds) = less fluid
26
factors affecting rate of diffusion
size of gradient: steeper gradient = faster diffusion size of molecule: smaller molecule = faster diffusion distance to travel: smaller distance = faster diffusion temperature: greater temperature = faster diffusion surface area: more surface area = faster diffusion
27
need for diffusion sets a limit on cell size of about____, because:
20 um (micrometers), because otherwise the diffusion rate would be too slow to sustain cell life and activity
28
the need for diffusion has consequences on:
cell size, membrane thickness, cell membrane folding (for surface area)
29
how do cell membranes operate like a dam
they create electrical gradients essentially of stored energy, which can be selectively released if the membrane allows ions through, creating a flow of energy
30
what is a condition for osmosis
that the membrane is permeable to water, but not to other solutes
31
equation for membrane water permeability
Pw= Pd + Pf Pd = water permeability via diffusion Pf = water permeability via aquaporins (water channels)
32
how many, and what are, isoforms of aquaporins
9. isoforms are different versions of a protein resulting from the same gene/gene family
33
characteristics of Pf
large amount of water insensitive to temp sensitive to mercury
34
characteristics of Pd
small amount of water sensitive to temp insensitive to mercury
35
mercury inhibits the function of:
some aquaporins
36
sodium ion electrochemical gradients and net movement
chemical gradient: favours entry, as extracellular sodium concentration is far greater than intracellular electrical gradient: also favours entry as inside cell is negative (attracts) net: sodium wants to move into the cell
37
potassium ion electrochemical gradients and net movement
chemical: favours exit, as extracellular concentration of potassium is much lower electrical: favours entry, as inside cell is slightly negative (attracts) net: slight outward movement, but mostly balanced/at equilibrium
38
chloride electrochemical gradients and net movement
chemical: favours entry, as extracellular chloride concentration is much higher electrical: favours exit, as inside of cell is negative (repels) net: minimal net movement, near equilibrium
39
why is oxygen able to cross the cell membrane
it is small, non-polar, and lipid-soluble.
40
a typical cell uses ____ of its ATP energy for active transport
30%
41
secondary active transport uses energy from...
energy stored in ion concentration gradients
42
glucose transport occurs until:
all binding sites are saturated
43
what enzymatic characteristics do transport proteins demonstrate
1. specificity 2. competition 3. inhibition 4. saturation
44
differences and relative speeds of ion channels vs carrier-mediated transporters
ion channels do not interact directly with the ions, and don't undergo a conformational change. carrier-mediated transport interacts directly with its substrate. therefore ion channels are much faster.
45
how do ion channels mediate the movement of charged ions through the hydrophobic cell membrane
the outer surface of the channel is lined with hydrophobic amino acids to allow it to embed into the membrane, while the interior of the actual channel is lined with hydrophilic amino acids so that ions can flow through.
46
different stimuli for ion gates:
voltage ligand binding ion volume phosphorylation pH
47
how do ion channels allow for specificity
selectivity filter: an amino acid ring in the channel creates a selective filter that discriminates against certain ions, e.g negative amino acids repel cl- size: channel shaped like an hourglass to only allow certain sizes of ions through
48
why can pH cause opening if ion channel gates
could signal metabolic stress, e.g4 a decrease in oxygen causes more lactate production, which alters pH
49
how does the patch clamp technique work and what does it measure
it measures electrical currents generated by ion channels by using a very small glass micropipette to suction a bit of the cell membrane
50
current fluctuations recorded by the patch clamp technique represent:
changes in protein conformation associated with channel gating
51
the Na/K ATPase maintains:
a high potassium and low sodium concentration in the cytosol
52
what is the pump-leak hypothesis
the idea that 'leaks' let ions in/out of the cell down their concentration gradients, and pumps continuously oppose this to maintain the cells resting membrane potential
53
what is the resting membrane potential
~ -70mV
54
what is meant by 'ATPase' as in Na/K ATPase
inherent ability to hydrolyse ATP
55
how does the Na/K ATPase work
3 Na+ bind, and ATP is hydrolysed to spit it out of the cell, simultaneously pulling in 2 K+
56
two active transporters beside from Na/K ATPase
Ca/K ATPase, important in muscle contraction H/K ATPase, important for regulating stomach pH
57
is Na/K ATPase electrogenic?
yes, it pumps out 3 positive Na+ and in 2 K+, therefore it contributes to negative resting membrane potential
58
what might a sodium antiporter cause movement of
calcium or hydrogen out of the cell, as sodium rushes into the cell down its electrochemical gradient
59
what might a sodium symporter cause movement of
glucose or amino acids into the cell along with sodium as it rushes into the cell down its electrochemical gradient
60
antiporters aka
exchangers
61
symporters aka
contransporters
62
how do tight junctions look in freeze fracture
they appear as a series of interlocking ridges
63
how do tight junctions make the membrane look in electron microscopes
the membranes look fused where the junction is
64
in what ways are tight junctions a barrier and a fence
a barrier to substances through the intercellular/paracellular space a fence for membrane proteins, creating two distinct membrane domains with different compositions (basolateral and apical)
65
leaky epithelium is dominated by:
paracellular transport, as there are less tight junctions therefore less resistance
66
tight epithelium is dominated by:
transcellular transport, as strong tight junction activity restricts paracellular movement
67
explain changes in tilt-junction induced resistance in the GI tract and kidney
at the proximal end: the stomach and small intestine of the GI tract, and proximal tubule of kidney, have lots of leaky epithelium and a low electrical resistance, thus are dominated by paracellular transport. at the distal end: the colon of GI tract and collect duct of kidney nephron, are dominated by tight epithelium and transcellular transport, allowing for hormone-controlled specific transport.
68
what is meant by electrical resistance i.e tight junctions
epithelial tissues can have less or more electrical resistance to ions based on how many tight junctions they have
69
where are primary active transporters typically situated in epithelial cells
the basal surface
70
what is the entry step in epithelial transport, and where
it is usually secondary active transport, and will be at the apical surface for absorption and basal for secretion
71
what is the exit step in epithelial transport and where
often passive diffusion, at the apical surface for secretion and the basal surface for absorption
72
how does glucose absorption in the small intestine work
Na/K ATPase sets up ion gradient for the SGLT symporter to use energy of sodium gradient to actively accumulate glucose in the cell. glucose then exits at basal surface to the blood via facilitated diffusion of GLUT, down its concentration gradient. sodium leaves via Na/K ATPase at basal surface to maintain the gradient for further action of SGLT.
73
where is the SGLT and what does it do (and what type of transporter)
at the apical surface in the small intestine and kidney, it takes sodium into the cell with its concentration gradient and takes in glucose with it. it is a secondary active symporter.
74
why does sugar solution/oral rehydration therapy work to rehydrate?
because glucose enhances na+ and cl- absorption, and therefore draws in water by osmosis
75
what is Glucose-galactose malabsorption syndrome/its effect
mutation to glucose symporter in the small intestine causes glucose retention as it is unable to be absorbed. lumen osmolarity increases, causing water to be taken into the lumen, producing osmotic diarrhoea.
76
how is Glucose-galactose malabsorption syndrome treated
removal of glucose and galactose (6 carbon) from diet and replace with fructose (5 carbon) as carb source
77
how is fructose absorbed
same steps as glucose, but the apical surface transport protein is GLUT5 which allows facilitated diffusion into cell, and the exit step at the basal surface is GLUT2 to facilitate diffusion into blood
78
what is glycosuria and how does it arise
sugar in the urine, arises when not enough glucose is absorbed into the kidney due to SGLT being overwhelmed
79
what is the renal threshold
the transport maximum of SGLT, when all SGLTs are
80

BIOSCI 107 (modules 4-7) (3 decks)

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