cell membranes Flashcards
1
Q
describe the characteristics phospholipids
A
- glycerol + phosphate head + fatty acid chains (lipid tails)
- amphipathic molecule: non-polar end (hydrophobic tails) and polar end (hydrophilic heads)
- bilayer: two layers, in water polar heads seek partners for hydrogen bonding and non-polar tails pack together
- selectively permeable, permeability of molecule affected by lipid solubility, size and charge
- permeable: gases, water, small uncharged polar molecules
- impermeable: charged polar (AA and ATP), ions, large uncharged polar molecules
- fluidity: degree of alignment of tails, cholesterol inserter amongst = maintain fluidity at low temperature
2
Q
describe the movement of substances (diffusion) across a membrane
A
- simple: random thermal motion of substances from regions of high concentration to regions of lower concentration
- conc. gradient: difference in conc. of a substance
- movement direction: high to low, with gradient towards equilibrium
- electrochemical gradient: electrical potential gradient,, +ve ions attracted to -ve ions, vice versa, not linked to number of particles as 1 -ve and 1 +ve = 0, 6+ve and 6-ve = 0
3
Q
describe the different types of cell membrane proteins
A
- integral (1): transmembrane proteins
- peripheral (2): attachment to network of supporting fibres, exterior glycoproteins / glycolipids
- transporters: channels to allow flow (active pumps)
- enzymes: catalyse reactions in cytoplasm (often clustered, work as a team)
- cell surface receptors: binding site with specific shape for messenger chemical (hormone)
- cell surface identity markers: glycoprotein ‘tags’
- cell adhesion markers: junction formation between cells
- cytoskeleton and extracellular attachments: provide support and shape while transmitting messages
4
Q
describe protein assisted transport
A
- passive (facilitated, gradient is favourable but rate is too slow)
- active (unfavourable gradient)
- channels: hydrophilic pores through membrane, not coupled with energy usage, ions diffuse down electrochemical gradient
- carriers: interaction between molecule / carrier protein, passive / active, radical conformational change, slower than channels
5
Q
what is osmosis
A
- net movement of water across a membrane, rapidly moves across selectively permeable membrane
- through bilayer and aquaporins (channels)
- move from high energy (low solute) to low energy (high solute)
- hypertonic: more solute, dilute, water leaves cell = shrinks
- hypotonic: less solute, concentrated, water enters = cell bursts / lysis
- isotonic: same concentrations, cell fluctuates about equilibrium
6
Q
what is active transport
A
- pumping solutes across a membrane against their concentration gradient
- primary AT: carrier protein pumps use energy directly
- essential to maintain required solute conc. in animal cells
7
Q
describe the NaK pump
A
- active movement
- high K inside (overall -ve charge) and high Na outside
- area of protein is non-polar to allow it to sit embedded in membrane
- anchored due to chemical relationship
- affinity: becomes more receptive to either Na or K, changes in shape of receptor sites (domains) in conjunction with these changes
- phosphorylates: ATP to ADP, release and transfer energy to protein, allows Na to be moved against gradient
- 3 Na out and 2 K in (net loss, hence inside if -ve)
- resting membrane potential = difference in charge (-70mV)
8
Q
what is co transport
A
- coupling transport of two solutes (secondary active transport
- accumulates molecules within cells against a gradient
- harness energy from Na or H moving down their conc. gradients
- sugars, AA, transverse up gradient
- use energy from first movement
9
Q
describe co transport of glucose via symport
A
- entering / exiting cell from the same side
1. H pumped out of cell (active)
2. conc. gradient favours re-entry of H (passive)
3. H and sugar bind to symport simultaneously on same side of membrane, H moves down gradient (passive) and sugar moves up gradient (active)
10
Q
describe go transport via antiports
A
- counter transport, enter / exit cell from opposite side of protein
- inward movement of Na coupled with outward movement of solute
- both simultaneously bind to anti port on opposite sides of membrane
- energy captured by Na moving down gradient is used to move solute up its own gradient
- one substance can be transported by many proteins
11
Q
what is cystic fibrosis
A
- genetic disorder
- affect cell singing in lungs. / pancreas, thick sticky mucous, high Cl
- abnormal or absent Cl channels, high extracellular Cl
- daily exercise, strong antibiotics, digestive enzymes, synthesised molecule (reduce symptoms)
12
Q
how is bulk matter moved throughout cells
A
- endocytosis: movement in, plasma membrane extends outwards and envelopes food particles (vesicles), phagocytosis (food), pinocytosis (liquid), receptor mediated
- exocytosis: outward movement, discharge of material from vesicles at cell surface
- transcytosis: endocytosis directly followed by exocytosis (cell uses what is valuable and discharges what is not from cell)
13
Q
what is a neuron
A
- specialised nerve cell
- receive, process and send information
- dendrites (receive), cell body (soma), axon (carries output signal)
14
Q
what is action potential problem and solution
A
- long distance electrical signalling
- problem: due to resistance, the amplitude of an electrical impulses fades the further it travels
- solution: action potential prevent loss / distortion of signal because they are regenerated, all or none response, long distance transmission, voltage gated channels are key to this mechanism (NaK)
15
Q
what are gated channels
A
- open and close in response to stimuli
- chemically ligand: binding of messenger (neurotransmitter)
- voltage gated: change in electrical potential of membrane
16
Q
describe neurons and electrical signals / stimuli
A
- stimuli: neuron is stimulated, polarising / depolarising of cell membrane to different degrees depending on magnitude of stimulus
- action potential: not generated until threshold is reached (-55mV)
17
Q
what is resting neuron potential and what occurs when it is stimulated
A
- cell -ve inside and +ve outside (resting = -70mV)
- polarity: dependent on Na K pumps, anions inside cell and low permeability to their loss (Na K leak channels, more K leakage = -ve charge)
18
Q
describe the process of action potentials
A
- resting state: Na K gated channels are closed
- depolarisation: stimulus leads to few Na+ gated channels open and Na+ rushes into the cell
- trigger = threshold (-55mV) if it doesn’t the membrane returns to resting state
- rapid depolarisation (rising phase): more Na+ channels open, triggers
repolarisation - (falling phase): Na+ channels inactivate (inflow ceases), K+ channels open and outflow begins
- repolarisation of the membrane, potential falls
- hyper-polarisation (undershoot): Na+ channels close, K+ channels remain open, potential falls below the resting state (-80 mV)
- resting state: sodium potassium pump returns the membrane to a polarised state via active transport)
19
Q
what is a synapse / NMJ
A
- action potential arrives at axon terminal of pre-synaptic cell, depolarising the presynaptic membrane
- depolarisation opens voltage gated channels, triggering an influx of Ca ions
- elevated Ca concentration causes synaptic vessels to migrate towards and fuse with the presynaptic membrane
- vesicles release neurotransmitter into the synaptic cleft via exocytosis (chemical messenger)
- neurotransmitter diffuses across synaptic cleft
- neurotransmitters bind to ligand gated ion channels in the postsynaptic membrane and generate an electric current to depolarise the postsynaptic neuron
- neurotransmitter binds to ligand gated channels on muscle and trigger contraction
20
Q
what are two ways you can interfere with impulses
A
- botox: prevents vesicles in pre-synaptic membrane from forming a connection with membrane, no neurotransmitter released
- tetredotoxin: paralyses signal, no rest, stimulus is continuous, prevents normal breakdown of ACh, involuntary muscle contraction, respiratory / cardiac arrest
21
Q
what is the refractory period
A
- when a neuron is stimulated it cannot be stimulated by another stimuli
- inactivated during depolarisation and repolarisation phases
