Membrane transport Flashcards
What are the symptoms of cholera
- severe diarrhoea
- vomiting
What is the prevalence of cholera
- 3-5m cases year
- >100000 deaths year
What is the cause of cholera
- vibrio cholerae bacteria
- cholera toxin
What is the treatment for cholera
ORT: water, salts & glucose
What is the function of the membrane
- selectively permeable
- maintain constant internal environment eg pH
What are the two types of passive transport
- simple diffusion
- facilitated diffusion
What are the two types of active transport
- ATP-driven
- Ion-driven
Describe simple diffusion
- no energy required
- small molecules
- co specificity
- conc. gradient
Describe facilitated diffusion
- conc. gradient
- no energy
- depend on integral proteins, temp., pH, etc
- specific
What is an ionophore
Ion carrier
Why is ionophore produced by bacteria & how does it do that
- antibiotic, destroy rival bacteria
- discharge ion gradients of target cell
Give an example of carrier ionophore
- valinomycin
- hydrophobic molcules —> carry ions
- specific to transport K+ —> down its conc. gradient
Give an example of channel-forming ionophore
- gramicidin A
- made of alternating L & D amino acids
What is the function of ion channels
- rapid and gated passage of anions & cations
- highly selective
- allow ion flow
- maintain osmotic balance
- signal transduction
- nerve impulse
Describe glucose transport
- facilitated diffusion
- integral protein, GLUT 1
What is the structure of GLUT1
12 transmembrane a-helices
What happens to glucose once entering the cell
- glucose —> glucose-6-phosphate
- hexokinase
- maintain conc. gradient
What is the relationship between Km and affinity of transporter for molecule
- lower Km —> greater affinity
What are aquaporins
- water channels for bulk H2O flow
What is the structure of aquaporins
- 28 kDa protein
- 6 transmembrane a-helices
- 4 pores for H2O
Where are aquaporins abundant
- erythrocytes
- kidney cells
What is the Na+/K+ gradient
- high K+
- low Na+
- in cell
What is the mechanism of ATP-driven active transport maintained by
Na+/K+ ATPase
What is the function of ATP-driven active transport
- control cell volume
- make nerve & muscle cells excitable
- facilitate ion-driven a-transport of amino acid & sugar
Describe the structure of Na+/K+ ATPase
Tetramer: 2a, 2b
What is the mechanism of Na+/K+ ATPase
- 3Na+ out
- 2K+ in
- polarises cell membrane
- ATP hydrolysis —> conformational change
- Na+ and K+ pumped against conc. gradient
- coupled system
What’s coupled system
ATP not hydrolysed unless Na+ and K+ are transported
Give the two examples of ion-driven active transport
- symport
- antiport
Describe the symport
- Na+ conc. gradient
- movement of glucose with Na+
- Na+/glucose transporter
Describe the antiport
- Na+ In
- Ca2+ out
- Na+/Ca2+ exchanger
(- low Ca2+ Maintained)
What does digitalis cause in healthy ppl
Heart failure
What does digitalis cause in patients of congestive heart failure
Strengthen heart
What is digitalis replaced by nowadays
ACE inhibitors & diuretics
What is the mechanism of digitalis
- inhibit Na+/K+ ATPase
- increase [Na+] inside
- decrease Na+ grad
- decrease Na+/Ca2+ exchange
- increase [Ca2+] inside
- enhance contraction of heart
What is the lining of the lumen
Epithelial cells
What does polarised epithelial cells mean
- apical membrane
- basolateral surface
Describe glucose transport in lumen
- Na+/glucose symport transporter transport glucose into epithelial cells through apical membrane down conc. gradient
- glucose diffused across basolateral membrane through glucose transporter, facilitated diffusion
- Na+ level is maintained low due to Na+/K+ ATPase in basolateral membrane
- increases osmotic pressure, water flow follows glucose diffusion
What are the different types of exocytosis
- constitutive: all cells, proteins
- regulated: specialised cells, Ca2+ dependant
Explain exocytosis in nerve terminal
- nerve stimulation —> depolarisation —> activated voltage-gated ion channels —> Ca2+ enter nerve terminal rapidly —> synaptic vesicles with neurotransmitters fuse with synaptic membrane —> content released in synaptic cleft —> stimulate receptors in post-synaptic clefts
What are the three types of endocytosis
- phagocytosis
- pinocytosis
- receptor-mediated endocytosis
Explain receptor-mediated endocytosis
- selective
- chain-coated pits & vesicles
- good for contracting low levels of macromolecules
