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Question

what are trans-SNARE complexes

Answer 1

t-snare + v-snare make this complex: coiled-coil complex ensuring specific fusion of vesicle with target membrane, allowing delivery of vesicle's contents to correct location (driven by energy released when forming trans-SNARE complex)

Answer 2

1. cisternal maturation model - dynamic: cisternae mature from cis face to trans face (entry to exit of Golgi) *cisterna change themselves over time* - newly formed cis cisternae mature as they move through the Golgi and acquire enzymes, modifying proteins as they move, as they matural, they go from cis > medial > trans cisternae, fuzing with the next, proteins are modified without moving cisternae between them. 2. vesicular transport model - static: proteins are moved from one cisterna to the next via transport vesicles *discrete veiscles move contents from one cisterna into another, not maturing* - proteins are packed into vesicles at one cisterna, bud off and fuse with the next to transfer contents, each retains its identity throughout transport process and vesicles carry specific enzymes required for process

Answer 3

1. integral: moves molecules across membrane, across membrane, contain channels and carriers to facilitate selective transport (include ion channels, pumps, receptors) 2. peripheral: attaches to the membrane's inner and outer surface temporarily, doesn't embed across the lipid bilayer, interacts with integral membrane proteins and phospholipids (i.e. spectrin, ankyrin) 3. lipid-anchored: embeds in the lipid bilayer via a covalently bonded lipid molecule (i.e. GPCRs, prenyl, fatty-acid anchored)

Answer 4

P-type ATPase pump, that relies on phosphorylation of an intracellular aspartic acid residue (amino acid) and ATP hydrolysis to establish and maintain sodium and potassium gradients across the plasma membrane (consumes 2/3 of cell's ATP, contributing to membrane potential by exporting 3 Na+ ions out for every 2 K+ in)

Answer 5

used for selective passage of potassium ions across cell membrane to contibute to the generation of a cell membrane potential composed of 4 subunits, each with 2 transmembrane helices (M2 helix and M1 helix), where M2 is responsible for controlling the gating mechanism, has a pore-forming segment made of a helix and non-helical loop to form a selectivity filter (which allows only potassium ions to pass through, excluding others and M2 controls opening and closing of the channel)

Answer 6

made of 5 rings within a pore, each with a diameter of 3Å (0.3 nanometres), closely corresponding to the size of K+ ions (2.7Å or 0.27 nanometres) - lined with oxygen atoms to interact with K+ ions, but not smaller molecules (when K+ interacts, it loses its hydration cell, interacts with oxygen all the way through, allowing it to flow rapidly)

Answer 7

glutamate activates both ionotropic and metabotropic receptors, both are permeable to Na+ and K+, but NMDA receptors also require glycine for activiation which are also permeable to Ca2+ (req. for intracellular signalling). they are regulated by factors like voltage-dependent Mg2+ to block channels at resting to prevent Ca2+ influx, and Mg2+ expelling to allow receptors to open and permit Ca2+ entry upon membrane depolarization This chain of events leads to NMDA receptors integrating signals from presynaptic glutamate release and postsynaptic membrane potential changes

Answer 8

1. ionotropic receptors: multiple subunits that form ion channels, directly bind to neurotransmitters and allow ions to cross the cell membrane, alter the membrane potential and produce rapid-immediate short-term responses 2. metabotropic receptors: protein with 7 transmembrane domains (GPCRs), don't form channels, but instead activate intracellular signaling cascades by binding to neurotransmitters to produce slow, long-term signals (control ion channel activity via second messengers)

Answer 9

underlies learning and memory, strengthens synaptic connections between neurons. 1. presynaptic activation: a high frequecy stimulus leads to sustained release of glutamate which then binds to NMDA and non-NMDA glutamate receptors 2. postsynaptic activation: that binding allows for an influx of Na+, and opening of NMDA receptors, but Mg2+ blocks Ca2+ from entering depolarizing the post-synaptic membrane 3. NMDA receptor activation: if depolarization is sufficient, Mg2+ releases its block on NMDA and allows Ca2+ to enter, the influx triggers a second message and the intracellular signalling cascades 4. the potential is brought back to pre-synaptic potential and non-NMDA receptor expression is increased

Answer 10

composed of 3 subunits (alpha, beta, gamma), alpha subunit acts as the binding site and is responsible for signalling, beta and gamma subunits are anchored to the plasma membrane and stabilize the complex

Answer 11

gtp binding proteins, serve as molecular switches that relay signals from GPCRs to target ion channels or enzymes - ligand binds to GPCR on cell membrane - activates GPCR and causes it to interact with the g-protein - alpha subunit phorphorylates GDP --> GTP, activating the g-protein - activated alpha subunit, with beta-gamma complex, modules target proteins - deactivated by hydrolyzing GTP --> GDP to turn off the signal and reassemble the original complex

Answer 12

involves rhodopsin 1. one rhodopsin molecule absorbs one photon 2. five hundred transducin molecules are activated 3. 500 phophodiesterase molecules are activated 4. 10^5 cyclic GMP molecules are hydrolyzed 5. 250 Na+ channels close 6. 10^6-10^7 Na+ ions per second are prevented from entering the cell in ~1 second 7, rod cell membrane is hyperpolarized by 1 mV

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