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cardiovascular lectures > movement across membranes > Flashcards

movement across membranes Flashcards

1
Q

what are channel proteins

A

integral - span across membrane

make hydrophillic tunnels for target molecules to pass through
form a narrow aqueous pore

very specific; depends on
- size
- charge

passive - no energy needed for movement

may be gated (voltage or ligand)

usually ions move through them (eg Na+, K+) or water (aquaporins)

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2
Q

what are carrier proteins

A

have specific binding sites

carrier undergoes a conformational change

involved in facilitated diffusion and active transport so can be passive OR active

3 types

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3
Q

what are the 3 types of carrier proteins

A
  1. uniport
  2. symport
  3. antiport
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4
Q

what are uniport carrier proteins

A

transport a single substance

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5
Q

what are symport carrier proteins

A

transport 2 substances in same direction

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6
Q

what are antiport carrier proteins

A

transport 2 substances in the opposite direction

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7
Q

what are the 3 main forces that drive substances into or out of cells

A

chemical
electrical
electrochemical

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8
Q

what determines the direction in which substances move into/out of cells

A

based on the presence of a gradient

substances either move with the gradient or against it with help

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9
Q

what is Nernst equation/diffusion potential details

A

E ion = In

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10
Q

how do chemical drives work

A

based on conc differences across the membrane
all substances have a conc gradient
force is directly proportional to the conc gradient

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11
Q

what is RT In

A

how do you describes ion diffusion work done as a ratio

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12
Q

how do electrical driving forces work

A

also known as membrane potential
based on the distribution of charge across the membrane
only charged substances eg Na+ , K+
force depends on size of membrane potential and charge of ion

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13
Q

what is zFW

A

descrives electrical work done (V = EIon)

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14
Q

how do electrochemical driving forces work

A

combines chemical and electrical forces
net direction is equal to the sum of chemical and electrical forces
only charged substances eg Na+ , K+

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15
Q

describe membrane equilibrium

A

when diffusional and electrical forces balance
RTIn = zFEion
Eion = In

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16
Q

what are the 2 types of membrane transport

A

passive and active

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17
Q

what are 2 types of passive transport

A

simple diffusion
active diffusion

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18
Q

what are two types of active transport

A

primary
secondary

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19
Q

what is passive transport

A

does not require an input of energy
substance moves down its gradient from high to low

simple diffusion - gases
facilitated diffusion - mediated by proteins (channel or carrier)

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20
Q

describe glucose movement

A

GLUT 4 carrier protein
expressed in skeletal muscle and adipose tissue
glucose is taken up by facilitated diffusion
expression is unregulated by insulin

in the absence of insulin, glucose cannot enter cell
insulin signals the cell to insert GLUT 4 transporters into the membrane, allowing glucose to enter cell

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21
Q

what is GLUT 1

A

the glucose carrier protein

it is present in many cells, including the brain
it transports glucose across the blood-brain barrier via facilitative diffusion

22
Q

what is GLUT1 deficiency syndrome

A

very rare disorder
mutations in gene that encodes GLUT 1
less functional GLUT 1- reduces the amount of glucose available to brain cells
symptoms include seizures, microcephaly, developmental delay

23
Q

what is active transport

A

the movement of solutes from a region of low concentration to a region of high concentration against the concentration gradient.
Need transmembrane carrier protein and ATP is required.
2 types - primary and secondary

24
Q

describe primary active transport

A

directly uses a source of energy, commonly ATP

25
Q

example of primary active transport

A

Na+/K+-ATPase

pumps 3 Na+ out of the cell and 2K+ into the cell
utilises the hydrolysis of ATP to ADP and Pi

26
Q

what is wilsons disease

A

rare disorder

caused by mutation ins ATP7B gene - this is a protein that is a Cu2+-ATP present in the liver that transports copper into bile

results in deposition of copper in liver and other tissues eg brain, eyes

symptoms include liver disease, tremor,

27
Q

describe secondary active transport

A

transport of a substance against its gradient coupled to the transport of an ion usually Na+ or H+, which moves down its gradient

uses energy from the generation of the ions electrochemical gradient (usually by primary active transport)

28
Q

example of secondary active transport

A

eg Na+/glucose cottransporter proteins (SGLT)

  • present in intestinal lumen and renal tubules
  • transports glucose from low to high concentration
  • Na+/K+ATPase generates a sodium gradient to enable co transport of sodium and glucose
29
Q

what is glucose - galactose malabsorption

A

rare disorder caused by mutation in SGLT 1

SGLT1 transports glucose and galactose from the intestinal lumen

less functional SGLT 1 - inability to transport glucose and galactose - resulting in their malabsorption

symptoms include severe, chronic diarrhoea, dehydration

30
Q

what is cellular signalling

A

communication between cells takes place via signalling molecules eg hormones, neurotransmitters and growth factors

signalling molecules bind to to receptors

31
Q

what are two types of receptors

A

intracellular - eg steroid hormones

cell surface - eg peptide hormones

32
Q

what are second messegers

A

affect gene expression in the nucleus either directly or through signalling cascades

eg cAMP, IP3, DAG, Ca2+ amplification

33
Q

what are Gateway to intracellular signals:

A

Examples; open a channel, activate a intracellular
enzyme, induce second messenger (peptide hormone binds to receptor) & migrate
nucleus to receptor-ligand complex

34
Q

what is enzyme linked receptor

A

e.g. tyrosine kinase - transfers a phosphate group from ATP to a protein in a cell thus acts like an on/off switch

lead to protein and receptor phosphorylation

35
Q

what is ion channel linked receptor

A

participate in rapid signalling events found in electrically active cells like neurons, also referred to as ligand gated ion channels,

lead to changes in membrane potential or ionic concentration within cell
eg cholinergic nicotinic receptors

36
Q

what are G protein-coupled receptors

A
  • sense molecules outside the cell and activate inside signal transduction pathways to ultimately illicit a cellular response

lead to protein phosphorylation

mutations in G subunit can lead to cholera

37
Q

what do intracellular receptors lead to

A

protein phosphorylation and altered gene expression

38
Q

what is endocytosis

A

energetic process to absorb/engulf molecules into a cell. Some extracellular fluid is usually engulfed too along with the molecule etc. - a portion of the membrane is invaginated to form a membrane-bound vesicle called an endosome

39
Q

where can endocytosis occur

A

in neutrophils and macrophages - they implement phagocytosis (eating)
whereby they engulf entire cells/macromolecules to form a phagosome

40
Q

what is pinocytosis

A

fluid endocytosis
involves taking in dissolved solutes via vesicles

41
Q

how does pinocytosis work

A

is receptor mediated - specific

found in depressed areas (coated pits) - allows the cell to get the molecules it needs.
1. Ligands bind to receptor
2. this complex is engulfed -releasing the ligand into the cytosol (fluid portion of the cytoplasm outside the cell
organelles)

42
Q

what is exocytosis

A

Vesicle from the golgi apparatus, fuse with the plasma cell membrane, resulting in the expulsion of waste or the secretion of enzyme/hormones

43
Q

what is cystic fibrosis

A

caused by mutation in CFTR protein
chloride channel
found in many tissues eg gut, pancreas, lungs and skin
“secretory epithelium”
abnormal function results in sticky viscous mucus
no osmotic drag

44
Q

drugs that target membrane transporters

A

cardiac glycosides
proton pump inhibitors
loop diuretics
thiazide diuretics

45
Q

what do cardiac glycosides do

A

eg digoxin
act on Na+/ K+Atpase in cardiac muscle cells
indirect action to increase intra cellular (Ca2+)

46
Q

what do proton pump inhibitors do

A

eg omeprazole
act on H+/K+-Atpase in gastric parietal cells

47
Q

what do loop diuretics do

A

eg furosemide
act on NKCC2 cotransporter in thick ascending limb of loop of henle

48
Q

what do thiazide diuretics do

A

eg bendroflumethiazide
act on NCC cotransporter in distal tube

49
Q

what is facilitated diffusion

A

the movement of solutes from a region of their high concentration to a region of their low concentration through protein channels
(WITHOUT CARRIER PROTEINS).
This continues until dynamic equilibrium is reached.

50
Q

example of where facilitated diffusion is used

A

Glucose - protein assisted which is regulated by insulin. Voltage gate
channels activated by action potentials

51
Q

what is wilsons disease

A

rare disorder

caused by mutation ins ATP7B gene - this is a protein that is a Cu2+-ATP present in the liver that transports copper into bile

results in deposition of copper in liver and other tissues eg brain, eyes

symptoms include liver disease, tremor,

cardiovascular lectures (15 decks)

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