Ch 11 Flashcards

1
Q

What are three actions that the plasma membrane is involved in?

A
  1. receiving information
  2. import / export of small molecules
  3. capacity for movement and expansion
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2
Q

What does amphipathic mean?

A

Both hydrophilic + hydrophobic parts
ex. phospholipids have hydrophilic heads + hydrophobic tails

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3
Q

Examples of membrane lipids?

A

phosphatidylcholine (chloine group in head)
phosphatidylserine (serine group in head)
cholesterol
glycolipids

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4
Q

How / why do hydrophobic molecules avoid water?

A

molecules like to be in a less energetic state –> (i.e more entropic + disordered)

When individual hydrophobic molecules are “caged” by water molecules –> it is highly ordered and requires free energy

–> therefore, they aggregate + cluster together to minimize energy cost

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5
Q

Properties of phospholipids

A
  • lipid bilayer: energetically favorable
  • self-sealing: reverts to bilayer when severed (b/c free edge exposes hydrophobic tails to water)
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6
Q

how do membrane phospholipids move?

A
  1. lateral diffusion
  2. flexion
  3. rotation
  4. flip-flop (from one mono-layer to the next mono-layer)
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7
Q

Purpose of cholesterol

A

stiffen cell membranes by inserting itself between phospholipids and locking / preventing lipid movment

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8
Q

Process of membrane assembly in ER

A
  1. portion of membrane on ER is modified (phospholipid synthesis adds to cystolic half of bilayer)
  2. protein SCRAMBLASE randomly transfers phospholipids to the other monolayer)
  3. results in symmetric growth of lipid bilayer
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9
Q

What happens when vessicles fuse with membrane of other organelles?

A
  1. membrane delivered from ER
  2. protein FLIPPASE transfers specific phospholipids to cytosol monolayer
  3. Golgi apparatus + other cell membranes have asymmetric distributions
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10
Q

How do membrane proteins insert themselves in/on the lipid bilayer?

A

Transmembrane (integral membrane):
1. singlepass (signal receptors) *alpha
2. multipass (channels) *alpha
3. beta barrel (channels)
- often requires 16 beta sheets

Monolayer-associated (integral membrane)

Lipid-Linked (integral membrane)

Protein-Attached (peripheral memrbane)

(transmembrane + mono-layer associated proteins insert themselves directly into membrane)

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11
Q

How to isolate membrane proteins?

A

use detergents: SDS + TritonX-100

  1. detergent monomers have 1 hydrophobic tail + hydrophilic head
  2. separates protein from lipids in homogenous solutions (still difficult to crystalize)
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12
Q

Function of cell cortex

A

meshwork of fibrous proteins that reinforces plasma membrane

  • often made of spectrin –> forms a lattice and helps maintain biconcave shape of RBC
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13
Q

If phospholibds move laterally, how and why do membrane proteins remain stationary?

A

Proteins are tethered:
1. to cell cortex
2. to extracellular matrix
3. to proteins on surface of another cell
4. diffusion barriers (ex. tight junctions)

Why?
proteins serve different functions –> maxmimized function at certain locations
ex. Ca2+ voltge gated channels are localized near the end of a nerve cell axon at presynaptic membrane

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14
Q

Why are cells slimy?

A

coated with sugars
1. glycolipid
2. glycoprotein
3. proteoglycan

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