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neuromembrane biology > Lecture 1 - plasma membrane and transport across membranes > Flashcards

Lecture 1 - plasma membrane and transport across membranes Flashcards

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1
Q

Describe the structure of the plasma membrane

A
  • 3 layers - inner, middle and outer
  • contains a phospholipid bilayer ( hydrophobic tail and hydrophilic head)
  • contains integral and peripheral membrane proteins
  • Contains cholesterol between each phospholipid molecule
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2
Q

What are the functions of the plasma membrane?

A
  • encloses contents of the cell
  • separates cell from external environment
  • cell communication
  • import and export of molecules
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3
Q

How are proteins organized in the plasma membrane?

A
  • Integral proteins - go across membrane that serve as membrane transporters
  • peripheral proteins are loosely attached to membrane, act as enzymes shaping the cell
  • lipid anchored proteins on surface of cell membrane, the lipd anchors the protein on membrane
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4
Q

What are the 4 mechanisms of transport across plasma membrane?

A
  1. passive diffusion
  2. facilitated diffusion
  3. active transport
  4. bulk transport
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5
Q

what does the rate at which a molecule passes the membrane depend on?

A
  • size of molecule
  • solubility of molecule
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6
Q

What is passive diffusion?

A
  • does not require energy to move molecules across the membrane
  • it relies on the concentration gradient across the membrane
  • eg 02 c02 & small molecules pass freely
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7
Q

How do ions travel across the membrane?

A

ions travel across the membrane via ion channels, pumps, exchangers or co-transporters (eg sec active transport)

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8
Q

How is osmosis facilitated in the membrane ?

A
  • by a family of membrane proteins called aquaporins that form a channel for water to flow through
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9
Q

What are the 4 types of ion channels present in the membrane?

A
  1. gated channels (open or closed)
  2. voltage gated channels (conformational change depends on difference of charge on both sides of membrane)
  3. Ligand gated channels ( depends on binding of ligand molecule)
  4. mechanically gated (physically stretching the membrane may cause it to open eg)
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10
Q

What is facilitated diffusion?

A
  • concentration gradient dependent
  • requires gated channels /transmembrane integral proteins
  • eg glucose
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11
Q

What is active transport?

A
  • Movement of molecules across a membrane from low- high conc against the concentration gradient
  • requires energy - ATP
  • occurs through transport protein pumps
  • Eg) Na-K+ - ATPase pump
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12
Q

How does Na-K+ ATPase pump work?

A
  • A transmembrane protein that pumps k+ into cells while also pumping Na+ out of cells
  • Against both of their conc gradients
  • ATP converted to ADP
  • 3 Na3+ out and 2 K+ in
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13
Q

Describe bulk transport

A
  • Transport of large molecules or small particles into cell, requires energy
  1. Phagocytosis
  2. endocytosis
  3. exocytosis/secretion out of cell
  4. Pinocytosis
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14
Q

What are gap junctions?

A

Sites between cells that are specialised for intercellular communication

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15
Q

Give examples of gap junctions

A
  • Tight junctions
  • Adherens junctions
  • desmosomes
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16
Q

what are the different types of ‘channels’ on the membrane?

A
  • ion channels that are selective for specific ions eg Na+, K+, Ca2+
  • mixed cation channels - permeable to more than 1 ion - eg Na+ and K+
  • membrane transporters eg ATPase pumps, ion exchangers (egNa+Ca2+ exchanger) & co-transporters - NB THESE ARE ACTIVE - REQUIRE ENERGY
17
Q

What do the ion exchangers & cotransporters rely on?

A

they rely on ion gradients that are set up by ATPase pumps

18
Q

what are the specialized functions of ion channels?

A
  • control the release of neurotransmitters & hormones
  • initiate muscle contraction
  • mediate the generation, conduction & transmission of electrical signals in the nervous system
19
Q

what are ion channels made up of?

A
  • made up of subunits
  • if they have different subunits - hetero-oligomers
  • if they have the same subunits - homo-oligomers
  • also auxiliary subunits eg in some voltage gated ion channels
20
Q

what are the 3 basic functional properties of ion channels?

A
  1. selection - ie certain channels only allow one type of ion to pass eg Na+ or K+
  2. gating - what regulates ion channel opening/closing eg stretch or binding of neurotransmitter or change in membrane potential
  3. conduction - the channels allow ions to flow down their electro-chemical gradients
21
Q

what are the 3 main families of ‘ion channels’?

A
  1. ligand gated ion channels
  2. gap junction ion channel
  3. voltage gated ion channels
22
Q

What did the patch clamp method discover when studying Na+ channels?

A
  • Na+ has a specific threshold for opening to allow Na+ to enter the cell
  • only opens when the membrane depolarizes to approx. -50mv
  • the channel opens and closes rapidly
23
Q

What did the patch clamp method discover about K+ channels?

A
  • K+ channels open as the membrane depolarises and they stay open while the membrane is depolarised
  • they close when the when the membrane potential returns to a more negative value than at rest
  • K+ channels have delayed closing
24
Q

what is myotonia congenita?

A
  • an inherited neuromuscular disorder - difficulty in mobility
  • caused by a mutant voltage gated chloride channel CLCN
  • adrenaline makes the condition worse
25
Q

what types of stimuli control gating of ion channels?

A
  • ligand gated - eg GABA or glutamate neurotransmitters present
  • protein phosphorylation
  • changes in membrane voltage
  • stretch or pressure changes
26
Q

what are examples of voltage gated channels?

A
  • Na+ channels
  • Ca2+ channels
  • K+ channels
27
Q

what are examples of ligand gated ion channels?

A
  • neurotransmitter receptors
  • Ca2+ activated K+ channel
28
Q

what is an ‘inward rectifying’ channel?

A
  • a channel that passes positive charge more easily into the cell (inward direction) than in the outward direction (ie out of the cell)

neuromembrane biology (14 decks)

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