movement across membranes

Question 1

what are channel proteins

Answer 1

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)

Question 2

what are carrier proteins

Answer 2

have specific binding sites

carrier undergoes a conformational change

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

3 types

Question 3

what are the 3 types of carrier proteins

Answer 3

1. uniport
2. symport
3. antiport

Question 4

what are uniport carrier proteins

Answer 4

transport a single substance

Question 5

what are symport carrier proteins

Answer 5

transport 2 substances in same direction

Question 6

what are antiport carrier proteins

Answer 6

transport 2 substances in the opposite direction

Question 7

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

Answer 7

chemical
electrical
electrochemical

Question 8

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

Answer 8

based on the presence of a gradient

substances either move with the gradient or against it with help

Question 9

what is Nernst equation/diffusion potential details

Answer 9

E ion = In

Question 10

how do chemical drives work

Answer 10

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

Question 11

what is RT In

Answer 11

how do you describes ion diffusion work done as a ratio

Question 12

how do electrical driving forces work

Answer 12

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

Question 13

what is zFW

Answer 13

descrives electrical work done (V = EIon)

Question 14

how do electrochemical driving forces work

Answer 14

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

Question 15

describe membrane equilibrium

Answer 15

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

Question 16

what are the 2 types of membrane transport

Answer 16

passive and active

Question 17

what are 2 types of passive transport

Answer 17

simple diffusion
active diffusion

Question 18

what are two types of active transport

Answer 18

primary
secondary

Question 19

what is passive transport

Answer 19

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)

Question 20

describe glucose movement

Answer 20

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

Question 21

what is GLUT 1

Answer 21

the glucose carrier protein

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

Question 22

what is GLUT1 deficiency syndrome

Answer 22

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

Question 23

what is active transport

Answer 23

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

Question 24

describe primary active transport

Answer 24

directly uses a source of energy, commonly ATP

Question 25

example of primary active transport

Answer 25

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

Question 26

what is wilsons disease

Answer 26

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,

Question 27

describe secondary active transport

Answer 27

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)

Question 28

example of secondary active transport

Answer 28

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

Question 29

what is glucose - galactose malabsorption

Answer 29

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

Question 30

what is cellular signalling

Answer 30

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

Question 31

what are two types of receptors

Answer 31

intracellular - eg steroid hormones cell surface - eg peptide hormones

Question 32

what are second messegers

Answer 32

affect gene expression in the nucleus either directly or through signalling cascades eg cAMP, IP3, DAG, Ca2+ amplification

Question 33

what are Gateway to intracellular signals:

Answer 33

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

Question 34

what is enzyme linked receptor

Answer 34

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

Question 35

what is ion channel linked receptor

Answer 35

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

Question 36

what are G protein-coupled receptors

Answer 36

- 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

Question 37

what do intracellular receptors lead to

Answer 37

protein phosphorylation and altered gene expression

Question 38

what is endocytosis

Answer 38

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

Question 39

where can endocytosis occur

Answer 39

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

Question 40

what is pinocytosis

Answer 40

fluid endocytosis involves taking in dissolved solutes via vesicles

Question 41

how does pinocytosis work

Answer 41

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)

Question 42

what is exocytosis

Answer 42

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

Question 43

what is cystic fibrosis

Answer 43

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

Question 44

drugs that target membrane transporters

Answer 44

cardiac glycosides proton pump inhibitors loop diuretics thiazide diuretics

Question 45

what do cardiac glycosides do

Answer 45

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

Question 46

what do proton pump inhibitors do

Answer 46

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

Question 47

what do loop diuretics do

Answer 47

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

Question 48

what do thiazide diuretics do

Answer 48

eg bendroflumethiazide act on NCC cotransporter in distal tube

Question 49

what is facilitated diffusion

Answer 49

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.

Question 50

example of where facilitated diffusion is used

Answer 50

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

Question 51

what is wilsons disease

Answer 51

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,