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
2
Q
Red Blood Cells
A
- first evidence of lipid bilayers
- contain no organelles, no internal membranes
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)
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
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
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
7
Q
Restrictions of Mobility
A
- membrane proteins can’t move back and forth spontaneously between inner and outer leaflets at an appreciable rate, can’t reverse orientation
- association with cytoskeletal anchors regions of membranes to defined location and help determine cell shape
- lipids rafts to make functional domains in plasma membrane
- 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
8
Q
Glycophorin
A
- associated with cytoskeleton at actin/spectrin junctions via Protein 4.1
9
Q
Band 3
A
- bicarbonate (HCO3-) and chloride (Cl-) transporter critical for CO2 uptake by red blood cells
- associated with spectrum via Ankyrin
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
11
Q
Epithelial Cells
A
are polarized cells
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
13
Q
Apical Domain
A
- nutrient uptake from lumen
14
Q
Basolateral Domain
A
- nutrient transfer to capillaries
15
Q
Tight Junctions
A
- prevents protein diffusion
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
Ion Pumps
- 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
Ion Gradients
- high concentrations of macromolecules in the cell needs to be counterbalanced to maintain the osmotic balance of the cell
27
Na+/K+ Pump
- 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
Resting Membrane Potential
- the electrical charge maintained when a membrane is resting = equilibrium charge
29
Nerve Impulses
- action potentials
- rapidly depolarize membranes (changing voltage)
release neurotransmitters which bind specific receptors which open specific ion-gated channels
30
Active Transport Driven by Ion Gradients
- 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
Symport
- both molecules transported in same direction across membrane
32
Antiport
- molecules transported in opposite directions across membrane
33
Endocytosis
- 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
Pinocytosis
- cell drinking
| - uptake of fluids or macromolecules in small vesicles
35
Receptor-Mediated Endocytosis
- form of pinocytosis
| - relies on specific cell surface receptors that recognize molecules/particles to be taken up
36
Phagocytosis
- 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
LDL
- low density lipoprotein
| - particle used to transport cholesterol through the bloodstream to target cells
38
LDL Structure
- cholesterol esters in core
- surrounded by phospholipids and cholesterol
- 1 molecule of ApoB protein on surface
- transported through blood to target cells
39
Uptake of LDL Particles
- 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
