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BMSC 220 > Topic 10: Plasma Membrane and Cell Surface > Flashcards

Topic 10: Plasma Membrane and Cell Surface Flashcards

1
Q

Plasma Membrane

A
  • defines the boundary of all cells
  • separates the internal contents from the external environment surrounding cells
  • phospholipid bilayer, which forms a stable barrier
  • contain proteins which control cell to cell signalling, mediating interactions between cell and environment by acting as sensors
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2
Q

Red Blood Cells

A
  • first evidence of lipid bilayers

- contain no organelles, no internal membranes

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3
Q

Fluid Mosaic Model

A
  • model of membrane structure
  • basic paradigm for the organization of all biological membranes
  • “proteins afloat in a sea of lipids”
  • two basic categories of membrane proteins (peripheral and integral)
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4
Q

Peripheral Membrane Proteins

A
  • dissociate from the membrane following treatments with polar reagents
  • solutions of extreme pH or high salt concentration that do not disrupt the phospholipid bilayer
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5
Q

Integral Membrane Proteins

A
  • can be released by experimental treatments
  • amphipathic detergents, that disrupt the phospholipid bilayer
  • part of protein spans the hydrophobic region of the lipid bilayer
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6
Q

Mobility of Plasma Membrane Proteins

A
  • mobility of integral membrane proteins is critical to proper functioning
  • membrane proteins and phospholipids can diffuse laterally within membrane with some restrictions
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7
Q

Restrictions of Mobility

A
  1. membrane proteins can’t move back and forth spontaneously between inner and outer leaflets at an appreciable rate, can’t reverse orientation
  2. association with cytoskeletal anchors regions of membranes to defined location and help determine cell shape
  3. lipids rafts to make functional domains in plasma membrane
  4. cells with specialized functions need to be anchored in place to maintain function of cell
    - orientation and separation of membrane domains occurs through specialized junctions between cells
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8
Q

Glycophorin

A
  • associated with cytoskeleton at actin/spectrin junctions via Protein 4.1
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9
Q

Band 3

A
  • bicarbonate (HCO3-) and chloride (Cl-) transporter critical for CO2 uptake by red blood cells
  • associated with spectrum via Ankyrin
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10
Q

Lipid Rafts

A
  • clusters of cholesterol, sphingomyelin, glycolipids
  • form semisolid patches of membrane
  • transient structures
  • # of diff. integral membrane proteins involved in signalling, movement, endocytosis are localized within lipid rafts
  • create specialized functional domains within plasma membrane
  • first visualized using super-resolution light microscopy
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11
Q

Epithelial Cells

A

are polarized cells

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12
Q

Polarized Cells

A
  • refers to specific molecules (amino acids) not charges
  • have different structural and functional faces at opposite ends of cell (apical and basolateral)
  • movement and separation maintained by specialized junctions
  • tight junction in intestinal epithelial cells
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13
Q

Apical Domain

A
  • nutrient uptake from lumen
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14
Q

Basolateral Domain

A
  • nutrient transfer to capillaries
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15
Q

Tight Junctions

A
  • prevents protein diffusion
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16
Q

Passive Diffusion

A
  • unassisted, direct movement of membrane-permeable molecules across membrane along a concentration gradient
  • for small, non-polar molecules
  • non-selective, no energy required
17
Q

Facilitated Diffusion

A
  • assisted transport for molecules that are not soluble in phospholipid bilayer
  • carrier proteins, channel proteins
18
Q

Carrier Proteins

A
  • bind specific molecules to be transported on one side of membrane and then transported to opposite side
19
Q

Channel Proteins

A
  • ion channels form open pores through membrane allowing free diffusion of any molecule of appropriate size and charge
  • aquaporins, ion channels
20
Q

Glucose Transporters

A
  • conformational changes are reversible
  • glucose can more either direction
  • most cells: inward movement (low intracellular concentration)
  • glucose-generating cells (liver, basolateral domain of intestinal epithelial cells): outward movement (high intracellular concentration)
21
Q

Aquaporins

A
  • water channel proteins
  • allow for more rapid movement of water across membrane
  • passive diffusion
  • impermeable to any charged ions or small molecules
  • process of sweating uses aquaporins
22
Q

Ion Channels

A
  • allow for movement of selected ions down electrochemical gradient
  • many ion channels are gated and open in response to a specific signalling molecule or change in membrane polarity
23
Q

Gated Ion Channel

A
  • very rapid movement of ions across channel
  • highly selective (recognize specific target molecules)
  • open/close in response to specific types of signalling
  • -> ligand gated, voltage gated
24
Q

Active Transport

A
  • driven by ATP hydrolysis
  • process in which energy is provided by another coupled reactions
  • used to drive the “uphill” transport of molecules across the plasma membrane in an energetically unfavourable direction
25
Q

Ion Pumps

A
  • responsible for maintaining gradients of ions across plasma membrane
  • provide important examples of active transport driven directly by ATP hydrolysis
  • important for transmission of nerve impulses which specifically uses Na+/K+ pumps
26
Q

Ion Gradients

A
  • high concentrations of macromolecules in the cell needs to be counterbalanced to maintain the osmotic balance of the cell
27
Q

Na+/K+ Pump

A
  • active transport mechanism
  • establishes the gradient of Na and K ions across plasma membrane of diff. cell types
  • established ion gradient allows for facilitative diffusion of K+ through voltage gated channel
  • 3 Na+ out for every 2 K+ in
28
Q

Resting Membrane Potential

A
  • the electrical charge maintained when a membrane is resting = equilibrium charge
29
Q

Nerve Impulses

A
  • action potentials
  • rapidly depolarize membranes (changing voltage)
    release neurotransmitters which bind specific receptors which open specific ion-gated channels
30
Q

Active Transport Driven by Ion Gradients

A
  • molecules transported against their concentration gradients using energy derived not from ATP hydrolysis, but from the coupled transport of a second molecule in the energetically favourable direction
  • ions transported down electrochemical gradients established by ion pumps
  • Symport and Antiport
31
Q

Symport

A
  • both molecules transported in same direction across membrane
32
Q

Antiport

A
  • molecules transported in opposite directions across membrane
33
Q

Endocytosis

A
  • process where material to be internalized is surrounded by an area of plasma membrane
  • buds off inside cells to form a vesicle containing the invested material
34
Q

Pinocytosis

A
  • cell drinking

- uptake of fluids or macromolecules in small vesicles

35
Q

Receptor-Mediated Endocytosis

A
  • form of pinocytosis

- relies on specific cell surface receptors that recognize molecules/particles to be taken up

36
Q

Phagocytosis

A
  • cell eating
  • ingestion of large particles such as bacteria
  • contact of bacterium with the cell membrane stimulates the extension of pseudopodium
  • bacterium is engulfed and broken down in a phagolysosome
37
Q

LDL

A
  • low density lipoprotein

- particle used to transport cholesterol through the bloodstream to target cells

38
Q

LDL Structure

A
  • cholesterol esters in core
  • surrounded by phospholipids and cholesterol
  • 1 molecule of ApoB protein on surface
  • transported through blood to target cells
39
Q

Uptake of LDL Particles

A
  • by receptor-mediated endocytosis
  • LDL receptors: on cell surface
  • LDL and receptor undergo endocytosis and are incased in a Cathrin coated vesicle and moved through endosomes
  • LDL and receptor sorted in an early endoscope
  • LDL receptor is recycled back to plasma membrane
  • LDL moved to lysosome where cholesterol is released

BMSC 220 (6 decks)

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