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Cell Biology > Biological Membranes > Flashcards

Biological Membranes Flashcards

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1
Q

What are the three properties of a biological membrane?

A
  • Flexible
  • Continuous
  • Self-repairing
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2
Q

What is the point of a membrane?

A

Provides cell boundary/compartmentalisation, selectively permeable

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3
Q

What is the composition of a biological membrane?

A

Mainly lipids (phospholipids, cholesterol…), proteins (pumps, ion channels…) and carbohydrates (glycolipids, glycoproteins…)

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4
Q

Give an example of an amphipathic molecule

A

Phospholipid

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5
Q

How are phospholipids held together?

A

Non-covalent bonds

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6
Q

Wy are phospholipids described as amphipathic?

A

They have a polar head (hydrophilic) and a non-polar tail (hydrophobic)

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7
Q

What makes the fatty acid tails present in phospholipids saturated or unsaturated?

A

Presence of a C=C bond in unsaturated

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8
Q

How is the kink in the tail of a phospholipid caused?

A

C=C

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9
Q

What affects membrane fluidity?

A

How the phospholipids pack against each other so the differences in length and saturation of the fatty acids tails in each individual phospholipid

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10
Q

Structure of phospholipid

A

Choline
Phosphate
Glycerol
Fatty acid tails

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11
Q

What are the four major phospholipids present in mammalian membranes?

A
  • Phophatidylethanolamine
  • Phosphatidylcholine
  • Phosphatidylserine
  • Sphingomyelin
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12
Q

Which major phospholipid present in mammalian membranes has a net negative charge and why?

A

Phosphatidylserine because it has a negatively-charged phosphate group

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13
Q

Which phospholipid is essential for cell-cell signalling?

A

The metabolism of phosphatidylinositol is vital for signalling

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14
Q

Will saturated/unsaturated fatty acids cause more fluidity?

A

Unsaturated as the phospholipids can’t pack together as tightly

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15
Q

What is the role of cholesterol in biological membranes?

A

Modulate the properties of lipid bilayers

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16
Q

Structure of cholesterol

A

Polar head
Rigid steroid ring structure
Non-polar hydrocarbon tail

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17
Q

What part of cholesterol’s structure partly immobilises regions of the hydrocarbon tails on the phospholipid?

A

Rigid steroid ring structure

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18
Q

What is the consequence of more rigid lipid bilayer?

A

Less permeable

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19
Q

How does cholesterol affect the membrane fluidity?

A

Doesn’t affect the membrane fluidity but only the rigidity

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20
Q

What can high concentrations of cholesterol in a lipid bilayer prevent?

A

Can prevent hydrocarbon chains from coming together and crystallising

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21
Q

Examples of movement of phospholipids in a membrane

A
  • Lateral diffusion
  • Flexion
  • Rotation
  • Flip flop
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22
Q

Which phospholipid movement is least common and why?

A

Flip flop because it requires a lot of energy as the hydrophilic head would have to move across the central hydrophobic core

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23
Q

How is it possible that cholesterol flip flips more commonly that phospholipids do?

A

Cholesterol has a smaller polar hydroxyl group so less energy required

24
Q

What are phospholipid bilayers impermeable to?

A

Charged ions and large water-soluble molecules due to the hydrophobic core

25
Q

What kind of molecules can diffuse across membranes freely?

A

Small uncharged polar molecules e.g. CO2

26
Q

Name a method to illustrate lateral diffusion of membrane proteins

A

Fluorescence recovery after photobleaching (FRAP)

27
Q

What is FRAP?

A

Fluorescence recovery after photobleaching illustrates lateral diffusion of membrane proteins. Can’t follow individual proteins

28
Q

What are the 2 types of membrane protein?

A
  • Peripherally associated membrane proteins

- Integral membrane proteins

29
Q

How are peripherally associated membrane proteins part of the membrane?

A

They are non-covalently bonded with integral proteins

30
Q

Main difference between integral membrane proteins and peripherally associated membrane proteins

A

Peripherally associated membrane proteins do not extend into the hydrophobic core of the lipid bilayer

31
Q

How can peripherally associated membrane proteins be removed from the membrane?

A

Mild treatments that disrupt ionic interactions/ hydrogen bonds

32
Q

How are integral membrane proteins part of the membrane?

A

They are directly inserted into the membrane by hydrophobic domain

33
Q

How can one remove integral membrane proteins from a membrane?

A

Use detergents to dissolve them

34
Q

What are the three types of integral membrane proteins?

A
  • α-helices - transmembrane
  • embedded without crossing the bilayer
  • not embedded. lipid-anchored via covalently bound fatty acid
35
Q

What is an example of a lipid anchor? How does it attach the protein to the bilayer?

A

Phosphotidylinositol via fatty acids

36
Q

What are 3 benefits of lipid anchoring?

A
  • Mobility at cell surface
  • Rapid release of protein into extracellular space
  • Regulation of binding and release of proteins to membrane
37
Q

Are membrane proteins fluid?

A

Yes but move less rapidly than phospholipids

38
Q

What are some functions of integral membrane proteins?

A
  • Act as receptor
  • Act as adhesive molecule
  • Amphipathic α-helices interact to form channels
  • Enzymes
  • Intracellular signalling
39
Q

What are some functions of peripherally associated membrane proteins?

A
  • Cell shape determination
  • Communication with internal and external environment
  • Intracellular transport
40
Q

What is a lipid raft?

A

A micro domain which has a higher concentration of cholesterol and sphingolipids

41
Q

What other molecule along cholesterol is found at a lipid raft?

A

Sphingolipid

42
Q

Characteristic of a lipid raft

A

Membrane is slightly thicker and more rigid at rafts

43
Q

What is the glycocalyx?

A

The cell coat

Sugar residues associated with the transmembrane and peripheral proteins

44
Q

Example of glycocalyx

A

Slime on fish scales

45
Q

What is the point of the glycocalyx?

A
  • Protects cell against mechanical and chemical damage

- Prevents unwanted cell-cell interactions

46
Q

What structure makes it harder for bacterium to be engulfed due to an increase in diameter and receptors being covered?

A

The glycocalyx

47
Q

What is the enzyme that drives symmetry in the membrane?

A

Scramblase

48
Q

What does scramblase do?

A

Equilibrate lipid

49
Q

What does flippase do?

A

Ensures membrane asymmetry is maintained

50
Q

Which enzyme drives asymmetry in the membrane?

A

Flippase

51
Q

Do scramblase and/or flippase require ATP?

A

Flippase

52
Q

What 2 (/3) cellular processes does membrane asymmetry have importance?

A
  • Apoptosis
  • Coagulation
    (- Phagocytosis)
53
Q

How is asymmetry of membranes used in coagulation?

A

Phosphatidylserine provides nucleation site on platelets for coagulation cascade
Translocase moves phosphatidylserine to outside of cell

54
Q

In coagulation, phosphatidylserine provides what on platelets for a coagulation cascade?

A

A nucleation site

55
Q

Which enzyme moves phosphatidylserine to the outisde of a cell?

A

Translocase

56
Q

What does translocase do?

A

Transports phosphatidylserine to outside of cell

57
Q

Which phospholipid provides a nucleation site on platelets in coagulation?

A

Phosphatidylserine

Cell Biology (21 decks)

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