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BB10005 > Cell membranes > Flashcards

Cell membranes Flashcards

1
Q

What is the primary function of a membrane?

A

To act as a barrier.

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2
Q

What are the barrier functions of membranes?

A

Preventing the loss of required metabolites, protecting against unwanted outside molecules, storing electrical chemical energy and energy production and electrical signalling.

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3
Q

What are some of the functions of proteins in membranes?

A

Selective permeability, maintaining ionic composition on either side, maintaining cytoplasmic pH, controlling cytoplasmid osmotic pressure, sensing the environment, anchoring cytoskeletal structures, mediating cell/cell and cell extracellular matrix interactions and carrying out membrane requiring enzymatic reaction.s

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4
Q

What are aquaporins?

A

Specialisec ahnnels for water to flow through the cell membrane.

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5
Q

What percentage of total membranes does the plasma membrane make up in a cell?

A

2%.

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6
Q

Lipids are amphipathic. What does this mean?

A

They have a hydrophobic portion and a hydrophilic portion.

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7
Q

What is the energetically favoured structure of phospholipid bilayers?

A

To form sealed compartments (liposome) rather than a planar bilayer as there are no hydrophobic edges in contact with water.

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8
Q

What are glycerophospholipids?

A

They are based on 3 caron glycerol with 2 carbons linked to fatty acids and one linked to a phosphate.

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9
Q

What is the phophatidyl group?

A

Phospholipids that incoorporate choline as a head group.

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10
Q

What other types of molecules are found in membranes?

A

Glycolipids (sphingolipids), sterols and phospholipids - glyceropholipids and sphingolipids.

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11
Q

What does it mean that lipid bilayers are fluid?

A

There can be lateral diffusion, rotation and a “flip flop” movement, even though this is less favourable than lateral diffusion and rotation as there is an energy cost from moving the hydrophilic head group through the hydrophobic interior.

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12
Q

Why is membrane fluidity important?

A

It provides the compromise between rigid, ordered structure and completely fluid non-viscous liquid and allows for interactions to take place in the membrane.

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13
Q

What was an early experiment that showed membrane fluidity?

A

Two cells labelled different were fused together artifically. Originally the different labellings remained separate however they ended up being mixed together.

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14
Q

What factors affect membrane fluidity?

A

Temperature, cholesterol, saturation of acyl chains and length o f acyl chains.

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15
Q

How can a c=c double bond influence membrane fluidity?

A

It produces a kink in the acyl chain which leads to packing defects.

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16
Q

What is cholesterols effect on fluidity of the membrane?

A

It decreases the bilayer fluidity and improve the packing properties.

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17
Q

What is lipid asymmetry?

A

The idea that the two bilayers of the membrane are asymmetrical and have different compositions.

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18
Q

What are the two halves of the lipid bilayer called?

A

The two leaflets.

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19
Q

Why are there so many different lipids?

A

They have important effects of biological properties, fluidity, curvature and fusion properties. They can act as signalling molecules, take part in cell interactions and can effect the activity of membrane proteins.

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20
Q

What molecules can and cannot pass through lipid bilayers?

A

Small hydrophobic molecules and small uncharged, polar molecules can pass through, whereas larger uncharged polar molecules cannot, along with ions that also cannot pass through the membrane.

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21
Q

What different types of membrane proteins are there?

A

Integral membrane proteins, peripheral membrane proteins and lipid anchored membrane proteins.

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22
Q

What are the differences between the types of membrane proteins?

A

Integral span the entire bilayer, peripheral lie on the outer surface and lipid anchored are attached via a lipid molecule.

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23
Q

What are the four different types of R group?

A

Nonpolar aliphatic R groups, Aromatic R groups, Polar uncharged R groups and charged R groups.

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24
Q

What R groups are most suited to the hydrophobic environment of the lipid bilayer?

A

Nonpolar side chains are most suited.

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25
Q

Which amino acids contain nonpolar aliphatic R groups?

A

Glycine, alanine, valine, leucine, methionine and isoleucine.

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26
Q

What joins amino acids together?

A

Peptide bonds.

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27
Q

What is released when two amino acids are joined together?

A

A water molecule.

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28
Q

How is the problem of the polar peptide bonds not being energetically favoured in the hydrophobic core overcome?

A

There is hydrogen bonding between the partial negative charge in the carbonyl oxygen and the partial positive charge of the amide hydrogen which neutralises the negative charge.

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29
Q

What groups are involved in the formation of a peptide bond?

A

The amino group of one amino acid and the carboxyl group of another.

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30
Q

What is another secondary structure with a regular pattern of hydrogen bonding?

A

The formation of a beta sheet.

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31
Q

What is the average total width of the lipid bilayer?

A

50 angstroms.

32
Q

How many amino acids are required to span the bilayer in an alpha helical conformation?

A

Around 20 residues.

33
Q

How many amino acids are required to span the bilayer in an extended conformation?

A

Around 8-9 residues.

34
Q

How can membrane protein structure be predicted from the sequence?

A

Hydrophobicity analysis.

35
Q

Give examples of some of the hydrophobicity scales?

A

Kyte, Doolittle, Engelmann and Steitz.

36
Q

What are some of the functions of membrane proteins?

A

Transporters, linkers, receptors and enzymes.

37
Q

What is the difference between carrier proteins and ion channels?

A

Carrier proteins allow solutes to cross by passive or active transport, whereas ion channels are selective and gated.

38
Q

What happens when substrates bind to membrane proteins?

A

There is a conformational change that results in the substrate being released on the other side of the membrane.

39
Q

What are the three types of transport across the membrane?

A

Uniport, symport and antiport.

40
Q

What is coupled transport?

A

The transport of 2 different types of molecules that are interdependent on one another for transport.

41
Q

What is symport?

A

Transport of two different molecules in the same direction.

42
Q

What is antiport?

A

The transport of two different molecules in the opposite direction.

43
Q

Give an example of a passive facilitative transporter.

A

GLUT1, a glucose transporter.

44
Q

What is an example of a symporter and how does it work?

A

Lactose permease, a bacterial membrane protein that transporters lactose and protons in the same direction.

45
Q

What is membrane potential?

A

The charge difference between the two sides of the membrane.

46
Q

What makes up an electrochemical gradient?

A

The concentration gradient and the membrane potential.

47
Q

What are examples of active transport?

A

The glucose sodium symporter and the Na/K ATPase antiport.

48
Q

please do the extra reading lol

A

transporter thing

49
Q

What is Nexium?

A

One of the biggest selling prescription drugs that is effective against heartburn and stomach ulcers as it inhibits the stomachs H+/K+ ATPase.

50
Q

What is patch clamp recording?

A

A way of measuring ion channels. An area of membrane is removed from a membrane and seals the end of a glass capillary.

51
Q

How does patch clamp recording work?

A

Current can only flow through when the ion channels are open, which can be used to measure ion channel activity.

52
Q

What is gating?

A

When the opening and closing of ion channels is dependent on a stimulus. Can be due to voltage differences, ligands or mechanics.

53
Q

What is the mechanism for signalling in neurones?

A

A stimulus causes depolarisation which causes Na+ channels to open. Na+ enters the cell and depolarises the membrane further to cause more Na+ channels to open. The channels then become inactivated.

54
Q

How does the propagation of action potentials only occur in one direction?

A

The ion channels behind the action potential become inactivated and can therefore only move in one direction.

55
Q

What happens at nerve terminals?

A

When an action potential reaches nerve terminals voltage gated Ca2+ channels open and Ca2+ enters the cell which causes fusion of vesicles with the plasma membrane and the release of neurotransmitters.

56
Q

What is an example of an inherited disease caused by defects in ion channels and what is the result of this disease?

A

Cystic fibrosis due to a defect in a chloride channel and leads to lung congestion and infections.

57
Q

What are three types of cell surface receptors?

A

Ion channel linked, G-protein linked and enzyme linked.

58
Q

What are G protein coupled receptors?

A

They are 7 transmembrane spanning receptors that have a huge potential as drug targets. They have a G protein attached to them that can cause downstream effects when the receptor is activated. The binding of the ligand causes conformational changes.

59
Q

What is an example of an enzyme receptor?

A

The insulin receptor. The binding of insulin activates enzyme activity - tyrosine kinase.

60
Q

What amino acids contain aromatic R groups?

A

Phenylalanine, tyrosine, tryptophan.

61
Q

What amino acids contain polar, uncharged R groups?

A

Serine, threonine, cysteine, proline, asparagine and glutamine.

62
Q

What amino acids contain charged R groups?

A

Lysine, arginine, histidine, aspartate and glutamate.

63
Q

How is an antiparallel beta sheet formed?

A

Adjacent beta strands run in opposite directions - every other side chain extends above or below the sheet.

64
Q

What length of the lipid bilayer is made up of the hydrophobic tails?

A

30 angstroms.

65
Q

What is the total width of the lipid bilayer?

A

50 angstroms.

66
Q

In an extended conformation what is the length of one residue?

A

3.5 angstroms.

67
Q

In an alpha helix residue what is the length of one residue?

A

1.5 angstroms.

68
Q

What are porins?

A

Beta barrel membrane proteins that cross a cell membrane and act as a pore through which molecules can diffuse.

69
Q

What are carrier proteins needed for?

A

To transport nearly all small organic molecules, such as nucleotides, sugars and amino acids.

70
Q

What is another example of a symporter?

A

The glucose-sodium symporter.

71
Q

What is required for symporters to work?

A

An ion gradient that is generated by active transport.

72
Q

What type of electrochemical gradient will result in the most movement across the membrane?

A

A very large concentration gradient and a very large membrane potential - very positive on the outside and negative on the inside.

73
Q

What is secondary active transport?

A

The idea that the membrane potential in the symporter has to be generated using active transport.

74
Q

What other sources of energy can be used to drive pumps?

A

Light energy - bacteriorhodopsin uses light energy to pump protons across a membrane.

75
Q

What is the difference between a kinase and a phosphatase?

A

A kinase adds phosphate groups whereas a phosphatase removes phosphate groups.

76
Q

What is an example of a membrane protein that has another function not previously mentioned?

A

Linkers - create cell to cell contacts and are involved in adhesion.

BB10005 (22 decks)

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