Plasma membranes Flashcards

1
Q

What is a Plasma membrane

A

Basically the cell surface mmebrane of all cells and organelles

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2
Q

Describe the fluid-mosaic model of membrane structure

A

● Molecules free to move laterally in phospholipid bilayer
● Many components - phospholipids, proteins,
glycoproteins and glycolipids

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3
Q

Describe the arrangement of the components of a cell membrane (7)

A

● Phospholipids form a bilayer - fatty acid tails face inwards, phosphate heads face outwards
● Proteins
○ Intrinsic / integral proteins span bilayer eg. channel and carrier proteins
○ Extrinsic / peripheral proteins on surface of membrane
● Glycolipids (lipids with polysaccharide chains attached) found on exterior surface
● Glycoproteins (proteins with polysaccharide chains attached) found on exterior surface
● Cholesterol (sometimes present) bonds to phospholipid hydrophobic fatty acid tails

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4
Q

How does the phospholipid bilayer affect entry and exit of substances in and out of the cell? (4)

A
  • It allows the movement of lipid soluble and non charged molecules
  • Prevents the movement of Water soluble/Polar molecules
  • Membrane is partially permeable
  • Large molecules do not move through;small molcecules do
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5
Q

Explain the role of cholesterol (sometimes present) in cell membranes

A

● Restricts movement of other molecules making up membrane
● So decreases fluidity (and permeability) / increases rigidity

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6
Q

What is the importance of cholesterol

A
  • Makes the membrane less fluid at high temps
  • Prevents water and dissolved ions leaking out of the cell
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7
Q

What is the difference between Peripheral/extrinsic and Integral/intrinsic proteins?

A
  • Peripheral/extrinsic do not extend completely across the membrane
  • Integral/Intrinsic spans across from one side of the bilayer to the other
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8
Q

What is the function of the peripheral/extrinsic proteins

A
  • To provide mechanical support
  • They connect to proteins or lipids to make glycoproteins and glycolipids—> act as receptors,cell recognition,
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9
Q

What is the function of integral/intrinsic proteins

A

Transport molecules across the membrane through carrier and channel proteins

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10
Q

What is the function of glycoproteins/lipids

A

Cell recognition ;act as receptors

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11
Q

What do channel proteins do

A

Form tubes that fill with water to enable water soluble ions to diffuse

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12
Q

What do carrier proteins do

A

Bind with larger molecules, such as glucose and amino acids and change shape to transport them to the other side of the membrane

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13
Q

What are the factors allowing substances to pass through the membrane (simple diffusion)

A

Lipid soluble substances e.g. some hormones: estrogen
Very small molecules e.g. O2 CO2 H2O

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14
Q

What are the factors that do not allow molecules to pass through the membrane in Simple diffusion

A

Water soluble (polar) substances
Sodium ions
Large molecules e.g. glucose

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15
Q

Explain the limitations imposed by the nature of the phospholipid bilayer

A

● Restricts movement of water soluble (polar) & larger substances eg. Na
+/ glucose

● Due to hydrophobic fatty acid tails in interior of bilayer

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16
Q

Explain the arrangement of phospholipids in a cell membrane (3)

A

● Bilayer, with water present on either side
● Hydrophobic fatty acid tails repelled from water so point away from water / to interior
● Hydrophilic phosphate heads attracted to water so point to water

17
Q

What features of a particle would allow it to diffuse directly through the phospholipid bilayer

A

Small and non polar (uncharged)

18
Q

What structure in the membrane has the function ‘to allow the facillitated diffusion of large or charged particles’

A

Channel proteins

19
Q

Suggest how cell membranes are adapted for other functions

A

● Phospholipid bilayer is fluid → membrane can bend for vesicle formation / phagocytosis
● Glycoproteins / glycolipids act as receptors / antigens → involved in cell signalling / recognition