Fluid Mosiac Model Flashcards

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1
Q

What does the cell membrane being partially permeable mean?

A

Small molecules can pass between the gaps in the phosolipds

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2
Q

What is a phospholipid made of?

A

A tail made up of 2 fatty acids with a phosphate group head attached to it

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3
Q

Is the phosphate head hydrophobic or hydrophillic and why?

A

Hydrophillic

The phosphate group heads are polar so they attract other polar molecules

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4
Q

Are the lipid tails hydrophobic or hydrophillic and why?

A

Hydrophobic

The lipid tails are non-polar so they repel polar molecules

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5
Q

How do the phospholipids molecules in cell membrane arrange themselves?

A

They automatically arrange themselves into a fluid bilayer

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6
Q

Why is the phospholipid bilayer fluid?

A

The phospholipid molecules are constantly moving

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7
Q

Describe the phospholipid bilayer structure

A
  • The hydrophilic phosphate heads face out towards the water (either the aqueous tissue fluid/the aqueous cytoplasm) on either side of the membrane
  • The hydrophobic lipid tails are on the inside, making the centre of the bilayer hydrophobic
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8
Q

What does the centre of the bilayer being hydrophobic mean?

A

Membrane doesn’t allow water-soluble, charged or polar substances e.g ions through it

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9
Q

Why do the phospholipids not form micelles in the membrane?

A

The 2 fatty acids in the tails are too bulky to fit in the micelle’s interior

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10
Q

Where are the proteins in the bilayer?

A

They are scattered throughout the bilayer (like tiles in a mosaic)

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11
Q

Why can some of the proteins move?

A

As the phospholipid bilayer is fluid

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12
Q

Define an “integral” protein

A

Protein that are fully embedded within the phospholipids, some even spanning both layers

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13
Q

Describe the structure of integral protein

A
  • The regions at the end are polar hydrophillic amino acids

- The middle portion is made up of non-polar, hydrophobic amino acids

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14
Q

Define a “peripheral” protein

A

Proteins loosely attached on the outside surface of the cell membrane

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15
Q

What are the two types of protein?

A
  • Integral

- Peripheral

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16
Q

What are the different kinds of proteins found in the cell membrane?

A
  • Glycoproteins
  • Channel proteins
  • Carrier proteins
  • Enzymes
17
Q

What is a glycoprotein?

A

Proteins with a polysaccharide chain attached to them

18
Q

What is the function of a glycoprotein?

A

To act as a receptor for hormones by producing specific shapes

19
Q

What is the function of channel/carrier proteins?

A

Large molecules and ions can only pass through them

20
Q

What are glycolipids?

A

Lipids with a polysaccaride chain attached

21
Q

What is the function of a glycolipid?

A

To provide energy and be markers for cellular recognition

22
Q

What is the function of cholesterol in the cell membrane?

A

To fit in between the phospholipids, making bonds with them and therefore make the membrane more rigid

23
Q

How does the ratio of phosopholipds containing unsaturated fatty acids to those containing saturated fatty acids relate to the fluidity of the membrane?

A

The greater the ratio of phosopholipds containing unsaturated fatty acids to those containing saturated fatty acids, the more fluid the membrane

24
Q

How do unsaturated phospholipds ensure membrane fluidity?

A

The kinks in the hydrocarbon tails of the unsaturated phospholipids prevent them packing too closely together

25
Q

Describe the old model for the cell membrane

A

3 layers - a phospholipid layer between 2 continuous protein layers

26
Q

What was the evidence for the old membrane model?

A

Based on the EM image of 3 layers where the dark outer layers were thought to be proteins and the lighter region within was thought to be the phospholipid layer

27
Q

What 2 things did the old model not allow for?

A

Hydrophillic phosphate heads to be in contact with the water

Hydrophobic non-polar amino acids on the outside of the membrane proteins to be kept away from water

28
Q

How was the EM image re-interpreted for the fluid mosaic model?

A
  • The darker outer layers are the more electron dense phosphate heads
  • The inner lighter layer are the lipid tails
29
Q

Whats was the proof for peripheral and integral proteins?

A

Peripheral proteins could be disassociated from the membrane easily by increasing the ionic strength of a solution it was placed in whereas the integral proteins could only be removed by adding detergents

30
Q

How did freeze/fracture electron microscopy prove the existence of integral proteins?

A
  • Frozen membrane sections were fractured along a weak point between the lipid layers
  • The inner fractured surface was covered in a heavy metal
  • Scanning electron microscopy gave a 3D image revealing a smooth mosaic-like surface interspersed by much larger molecules
31
Q

Describe the plant protein experiment and its results

A

Plant proteins (lectins) that bind to polysaccharides were labelled with feretin which is viewable under the EM

  • These were mixed with membrane samples
  • They only bound to the outer surface and never the inner of the membrane
32
Q

What did the plant protein experiment prove?

A
  • That membranes were asymmetric (the outer surface was different to the inner surface)
  • Showed that polysaccharide chains were only on the outside of the membrane
  • Proved the invalidity of the protein sandwich model as this would have had lectin binding on both sides
33
Q

How was cell membrane fluidity proved?

A
  • A mouse cell and a human cell were fused

- The mouse and human proteins completely mixed throughout the cell membrane

34
Q

Why does a temperature below 0 degrees mean a high membrane permeability? 4

A
  • Phospholipids don’t have much energy, don’t move much
  • Tightly packed together, membrane is rigid
  • But channel proteins and carrier proteins in membrane deform, increase permeability
  • Ice crystals pierce membrane, make it highly permeable when it thaws
35
Q

What happens to the membrane at temperatures between 0 and 45 degrees?

A
  • Phospholipids move around, not as tightly packed together
  • Partially permeable membrane
  • Temperature increases, phospholipids move more, increases permeability of membrane
36
Q

What happens to the membrane at temperatures above 45 degrees?

A
  • Phospholipid bilayer starts to melt and membrane becomes more permeable
  • Water inside cell expands
  • Putting pressure on membrane
  • Channel proteins and carrier proteins deform - can’t control what enters/leaves