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The Human Cell > Cell Membranes > Flashcards

Cell Membranes Flashcards

1
Q

What does the world amphipathic mean

A

It means that the membrane lipid has both hydrophilic and hydrophobic parts

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2
Q

Why do membrane lipids act as a permeability barrier

A

It is difficult for most solutes to simply diffuse through

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3
Q

How would you describe the general structure of membrane lipids

A

water hating fatty acyl chains associate with each other and water loving polar head groups interface with the water

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4
Q

What enzyme is involved in the synthesis of fatty acyl chains

A

Fatty acid synthase

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5
Q

Describe roughly how a fatty acid chain is synthesised

A

a two carbon unit joins with a three carbon unit, the loss of carbon occurs, you get a 4c unit and this is repeated until you obtain a long fatty acid chain

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6
Q

what is the two carbon molecule involved in fatty acyl synthesis

A

acetyl coA

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7
Q

what is the three carbon molecule involved in fatty acyl synthesis

A

malonyl coa

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8
Q

how many carbons does palmitic acid have and how many double bonds

A

it is fully saturated because it has no double bonds and it has 16 carbons

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9
Q

what is a fatty acid desaturase

A

A fatty acid desaturase is an enzyme that removes two hydrogen atoms from a fatty acid, creating a carbon/carbon double bond.

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10
Q

what is the carboxyl end of a fatty acid referred to as

A

carboxyl end

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11
Q

what is the methyl end of a fatty acid referred to as

A

the omega end

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12
Q

when delta is used to describe a fatty acid chain what does it mean

A

delta - indicating that the double bond is created at a fixed position from the carboxyl group of a fatty acid (for example, Δ9desaturase creates a double bond at the 9th position from the carboxyl end).

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13
Q

when omega is used to describe a fatty acid chain what does it mean

A

omega (e.g. ω3desaturase) - indicating the double bond is created between the third and fourth carbon from the methyl end of the fatty acid.

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14
Q

is cis or trans commonly found in nature

A

cis

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15
Q

if two hydrogen atoms are removed from the same side in a fatty acid how would you describe the fatty acid

A

it would be cis

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16
Q

if two hydrogen atoms are removed from opposite sides in a fatty acid, it would be referred to as

A

trans

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17
Q

trans fatty acids have what kind of shape

A

they are straight

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18
Q

what does polyunsaturated mean

A

Polyunsaturated fats are lipids in which the constituent hydrocarbon chain possesses two or more carbon–carbon double bonds.

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19
Q

what are the two essential fatty acids

A

Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).

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20
Q

why must we obtain the two essential fatty acids from our diet

A

this is because we do not have the desaturase enzymes to remove the hydrogens from omega3 or omega6 carbons

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21
Q

why are essential fatty acids referred to as essential

A

because we must get them from our diet

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22
Q

what is the actual name for omega-6 fatty acid

A

linoleic acid

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23
Q

what is the actual name for omega-3 fatty acid

A

alpha-linolenic acid

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24
Q

what are the essential fatty acids omega3 and omega6 required for

A

they are important precursors in a pathway to arachidonic acid and eicosapentaenoic acid

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25
Q

what is the function of arachidonic and eicosapentaenoic acid

A

they are used in paracrines so cell-cell communication

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26
Q

what is the enzyme used to convert arachidoni and eicosapentaenoic acid into paracrines

A

cyclo-oxygenase 2 (cox-2)

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27
Q

list three paracrines

A

leukotrienes, prostaglandins and thromboxanes

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28
Q

what is the function of leukotrienes, prostaglandins and thromboxanes

A

they are mediators of inflammation, pain, fever, immunosuppresion, clotting, blood vessel constriction, airway constriction

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29
Q

which three drugs inhibit cox-2 and therefore do not allow the production of paracrines and therefore don’t allow pain to be felt

A

aspirin, ibuprofen and indomethicin

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30
Q

what is the enzyme that converts linoleic acid and alpha linolenic acid into the arachidonic acid and the eicosapentraenoic acid

A

elongases desaturases

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31
Q

elongases desaturase enzymes convert omega6 into what

A

into arachidonic acid

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32
Q

elongases desaturase enzymes convert omega3 into what

A

eicosapentaenoic acid

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33
Q

what are fatty acids primarily stored as

A

triglycerides

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34
Q

why are triglycerides in fat droplets efficient

A

because 1g of triglyceride is 6x energy store of 1g of glycogen and it occupies less volume

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35
Q

which cell type has loads of triglycerides in fat droplets

A

adipocytes

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36
Q

why are the fatty acids in phospholipids describes as amphiphillic

A

due to the polar hydrophillic headgroup and the non polar hydrophobic tail

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37
Q

*label this structure of a fatty acid in a phospholipid

A

there

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38
Q

what are two of the hydroxyls of the glycerol molecule on a fatty acid coupled to

A

to two acyl chains

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39
Q

what is the final hydroxyl of the glycerol molecule - excluding the two hydroxyl groups that are coupled to two acyl chains -attached to

A

the third hydroxyl is coupled to a phosphate

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40
Q

what type of double bond is present in one of the acyl chains attached to one of the hydroxyls of the glycerol

A

a cis- doulbe bond

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41
Q

what does the cis double bond in one of the fatty acid acyl chains result in

A

makes the acyl chain more bulky

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42
Q

the amphiphilicity of membrane lipids means what happens when they

A

the amphiphilicity of membrane lipids means that they readily self associate in water

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43
Q

membrane lipids form a bilayer of two leaflets rather than a micelle, why is this

A

membrane lipids have a cyclindrical shape therefore they favour a bilayer of two leaflets, rather than a micelle

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44
Q

what do fatty acids form when in water

A

they would form a lipid micelle

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45
Q

what is a liposome

A

A liposome is a spherical vesicle having at least one lipid bilayer. The liposome can be used as a vehicle for administration of nutrients and pharmaceutical drugs.

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46
Q

why is a sealed compartment formed by the phospholipid bilayer when making liposomes more energetically favourable compared to a planar phospholipid bilayer with edges exposed to the water

A

The closed structure is stable because it avoids the exposure of the hydrophobic hydrocarbon tails to water, which would be energetically unfavorable.

47
Q

list two uses of liposomes, in terms of future study and cures

A

they can be used to study the behaviour of lipid membranes and because they are readily taken up by cells they have also been used to deliver drugs and dna to patients

48
Q

what is special about the membrane surrounding a fat droplet

A

it is surrounded by a membrane lipid monolayer

49
Q

why does the membrane surrounding a fat droplet have a monolayer

A

because the contents are hydrophobic

50
Q

what do fat droplets form from

A

They are thought to form from discrete regions of the endoplasmic reticulum membrane where many enzymes of lipid metabolism are concentrated.

51
Q

how would you describe how fat droplets are formed from the er

A

Neutral lipids are deposited between the two monolayers of the endoplasmic reticulum membrane. There, they aggregate into a three-dimensional droplet, which buds and pinches off from the endoplasmic reticulum membrane as
a unique organelle, surrounded by a single monolayer of phospholipids and associated proteins.

52
Q

*label this diagram of the rough er

A

there

53
Q

the fluid mosaic model describes the phospholipids being able to move in three ways within the bilayer, what are these three types of movements

A

phospholipids can rotate within the bilayer, they can diffuse laterally within the leaflet, flip-flop

54
Q

describe the flip flop motion in the fluid mosaic model

A

the movement of phospholipid from one leaflet to the other - this is rate but can occur rapidly in certain cell types under certain conditions

55
Q

*label this diagram of the movements occuring in the fluid mosaic model

A

there

56
Q

finish off the sentence, membranes separate the cell contents from the

A

outside

57
Q

finish off the sentence, membranes separate the contents of different organelles from the

A

rest of the cell

58
Q

finish off the sentence, membranes form a permeability barrier to many

A

biologically important molecules

59
Q

are gases such as co2, n2 and o2 permeable or impermeable through the cell membrane

A

they are permeable

60
Q

are large uncharged polar molecules such as glucose and fructose permeable or impermeable through the cell membrane

A

impermeable

61
Q

are ions such as k+, mg2+ permeable or impermeable through the cell membrane

A

impermeable

62
Q

are charger polar molecules such as amino acids, atp, proteins and nucleic acids permeable or impermeable through the cell membrane

A

impermeable

63
Q

what are the three major lipids present in the cell membrane

A

phosphoglycerides, sphingolipids and sterols

64
Q

what is the sterol present in the cell membranes of animal cells

A

cholestrol

65
Q

list the five phospholipids and what makes them fit under this category

A
  1. phosphatidylinositol 2. phosphatidylethanolamine 3. phosphatidylserine 4. phosphatidylcholine 5. sphingomylein - they fit under this category because they all have a phosphate group present
66
Q

what is the only lipid component in the cell membrane which has an overall negative charge

A

phosphatidylserine

67
Q

name the two amino phospholipids

A

phosphatidylethanolamine and phosphatidylserine

68
Q

name the two choline phospholipids

A

phosphatidylcholine and sphingomyelin

69
Q

name the two glycolipids

A

cerebrosidase and gm1-ganglioside

70
Q

name the three sphingolipids

A

sphingomyelin, cerebrosidase and gm1-ganglioside

71
Q

what is the difference between sphingolipids and glycerophospholipids

A

sphingolipids are built from sphingosine rather than with glycerol as the ‘back-bone’

72
Q

how are the major lipid components of most biological membranes arranged between the two leaflets of the bilayer

A

asymmetrically

73
Q

*describe the structure of a cholesterol molecule

A

a polar head group at the top, a rigid steroid ring structure and a nonpolar hydrocarbon tail

74
Q

how does the absence of cholesterol molecules in the cell membrane impact the cell membrane

A

it makes it more fluid. the more cholesterol molecules in the cell membrane, the more gel-like/ rigid the cell membrane becomes

75
Q

focusing in on the membrane structure, the head group of a cholesterol molecules associates with what part of the neighbouring glycerophospholipid

A

the head group of the glycerophospholipid

76
Q

what part of the cholesterol molecule intercalates with the acyl chains of the glycerophospholipids

A

the steroid ring and the acyl chain of the cholesterol molecule

77
Q

describe the structure of the membrane when there is more cholesterol - 3 points

A

the membrane is more densely packed, less fluid and less permeable

78
Q

what affect does cholesterol have on membranes made of sphingolipid

A

cholesterol intercalation reducing the packing density of sphingolipids and keeps the membrane more fluid

79
Q

what is a lipid raft

A

the self association of sphingomyelin and cholesterol to form ‘rafts’ - OR Lipid rafts are subdomains of the plasma membrane that contain high concentrations of cholesterol and glycosphingolipids. They exist as distinct liquid-ordered regions of the membrane that are resistant to extraction with nonionic detergents.

80
Q

what is the overall function of lipid rafts

A

they bring together proteins that work together, for example proteins for endocytosis or signalling may be bought together

81
Q

which part of the cell membrane is enriched with cholesterol along with spingholipids

A

membrane invaginations (caveolae and clathrin coated pits) important for endocytosis

82
Q

cholesterol is not just a membrane lipid, list four other places it is found

A

precursor for bile salts, vitamin d, steroids, sex hormones

83
Q

what are bile salts for

A

solubilisation of dietary fat and lipophilic vitamins

84
Q

name two steroids cholesterol acts as a substrate for

A

cortisol and aldosterone

85
Q

name three hormones cholesterol acts as a steroid for

A

progesterone, oestrogen and testosterone

86
Q

what is the main structural component that glycolipids are based on

A

ceramide

87
Q

what type of head groups do glycolipids contain

A

sugar head groups

88
Q

name a glycolipid which carries a negative charge

A

NANA - sialic acid

89
Q

gm1 ganglioside is a glycolipid found in the cell membrane, what is it a receptor for

A

the cholera toxin

90
Q

what is the overall function of glycolipids, list three

A

protection from hostile environment, important in cell-cell contact, localise to and may be important in lipid raft generation

91
Q

different organisms/cells/organelles have different lipid composition, why is this

A

because of differing functions

92
Q

explain why hepatocyes are enriched in phosphatidylcholine

A

because they secrete phosphatidylcholine into bile

93
Q

explain why the er is low in cholesterol and its lipids are asymmetric

A

in order to make the er more fluid for membrane protein insertion

94
Q

explain why e.coli lacks cholestrol

A

because gram negative bacteria already have a double membrane, with peptidoglycan to provide stability

95
Q

why is myelin enriched in glycolipids

A

to insulate the nerve axons for nerve impulse conductivity

96
Q

what does the fluid mean when describing the fluid mosaic model

A

fluid describes the motions of the lipids and the proteins

97
Q

what does the world mosaicity describe when discussing the fluid mosaic model

A

mosaicity describes the membrane proteins embedded in the bilayer

98
Q

label/describe the following membrane protein, 1 and 2

A

there

99
Q

label/describe the following membrane protein, 3

A

there

100
Q

label/describe the following membrane protein, 4

A

there

101
Q

label/describe the following membrane protein, 5 and 6

A

there

102
Q

label/describe the following membrane protein, 7&8

A

there

103
Q

what are lipid anchors

A

they are long chain fatty acids

104
Q

what can lipid anchors be used for

A

can be used to recruit proteins to or detach proteins from the membrane

105
Q

lipid anchors are reversible by what process

A

de-esterification

106
Q

what enzyme is involved in the detachment of lipid anchros

A

lipid transferase

107
Q

why are transmembrane a helices enriched in hydrophobic amino acids

A

because they pass through the hydrophobic core of the membrane

108
Q

give three examples of hydrophobic amino acids which would be found in the transmembrane a helices

A

any three - glycine (Gly), alanine (Ala), valine (Val), leucine (Leu), isoleucine (Ile), proline (Pro), phenylalanine (Phe), methionine (Met), and tryptophan (Trp).

109
Q

can lipid anchored membrane proteins associate and dissociate from the membrane

A

yes

110
Q

can lipid anchored membrane proteins diffuse laterally

A

yes

111
Q

can lipid anchored membrane proteins change conformation

A

yes

112
Q

can integral membrane proteins associate and dissociate from the membrane

A

no

113
Q

can intergral membrane proteins diffuse laterally

A

yes

114
Q

can integral membrane proteins change conformation

A

yes

The Human Cell (11 decks)

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