Cell Membranes

Question 1

What does the world amphipathic mean

Answer 1

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

Question 2

Why do membrane lipids act as a permeability barrier

Answer 2

It is difficult for most solutes to simply diffuse through

Question 3

How would you describe the general structure of membrane lipids

Answer 3

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

Question 4

What enzyme is involved in the synthesis of fatty acyl chains

Answer 4

Fatty acid synthase

Question 5

Describe roughly how a fatty acid chain is synthesised

Answer 5

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

Question 6

what is the two carbon molecule involved in fatty acyl synthesis

Answer 6

acetyl coA

Question 7

what is the three carbon molecule involved in fatty acyl synthesis

Answer 7

malonyl coa

Question 8

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

Answer 8

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

Question 9

what is a fatty acid desaturase

Answer 9

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

Question 10

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

Answer 10

carboxyl end

Question 11

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

Answer 11

the omega end

Question 12

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

Answer 12

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).

Question 13

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

Answer 13

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

Question 14

is cis or trans commonly found in nature

Answer 14

cis

Question 15

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

Answer 15

it would be cis

Question 16

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

Answer 16

trans

Question 17

trans fatty acids have what kind of shape

Answer 17

they are straight

Question 18

what does polyunsaturated mean

Answer 18

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

Question 19

what are the two essential fatty acids

Answer 19

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).

Question 20

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

Answer 20

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

Question 21

why are essential fatty acids referred to as essential

Answer 21

because we must get them from our diet

Question 22

what is the actual name for omega-6 fatty acid

Answer 22

linoleic acid

Question 23

what is the actual name for omega-3 fatty acid

Answer 23

alpha-linolenic acid

Question 24

what are the essential fatty acids omega3 and omega6 required for

Answer 24

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

Question 25

what is the function of arachidonic and eicosapentaenoic acid

Answer 25

they are used in paracrines so cell-cell communication

Question 26

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

Answer 26

cyclo-oxygenase 2 (cox-2)

Question 27

list three paracrines

Answer 27

leukotrienes, prostaglandins and thromboxanes

Question 28

what is the function of leukotrienes, prostaglandins and thromboxanes

Answer 28

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

Question 29

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

Answer 29

aspirin, ibuprofen and indomethicin

Question 30

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

Answer 30

elongases desaturases

Question 31

elongases desaturase enzymes convert omega6 into what

Answer 31

into arachidonic acid

Question 32

elongases desaturase enzymes convert omega3 into what

Answer 32

eicosapentaenoic acid

Question 33

what are fatty acids primarily stored as

Answer 33

triglycerides

Question 34

why are triglycerides in fat droplets efficient

Answer 34

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

Question 35

which cell type has loads of triglycerides in fat droplets

Answer 35

adipocytes

Question 36

why are the fatty acids in phospholipids describes as amphiphillic

Answer 36

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

Question 37

*label this structure of a fatty acid in a phospholipid

Answer 37

there

Question 38

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

Answer 38

to two acyl chains

Question 39

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

Answer 39

the third hydroxyl is coupled to a phosphate

Question 40

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

Answer 40

a cis- doulbe bond

Question 41

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

Answer 41

makes the acyl chain more bulky

Question 42

the amphiphilicity of membrane lipids means what happens when they

Answer 42

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

Question 43

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

Answer 43

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

Question 44

what do fatty acids form when in water

Answer 44

they would form a lipid micelle

Question 45

what is a liposome

Answer 45

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.

Question 46

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

Answer 46

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

Question 47

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

Answer 47

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

Question 48

what is special about the membrane surrounding a fat droplet

Answer 48

it is surrounded by a membrane lipid monolayer

Question 49

why does the membrane surrounding a fat droplet have a monolayer

Answer 49

because the contents are hydrophobic

Question 50

what do fat droplets form from

Answer 50

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

Question 51

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

Answer 51

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.

Question 52

*label this diagram of the rough er

Answer 52

there

Question 53

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

Answer 53

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

Question 54

describe the flip flop motion in the fluid mosaic model

Answer 54

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

Question 55

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

Answer 55

there

Question 56

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

Answer 56

outside

Question 57

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

Answer 57

rest of the cell

Question 58

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

Answer 58

biologically important molecules

Question 59

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

Answer 59

they are permeable

Question 60

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

Answer 60

impermeable

Question 61

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

Answer 61

impermeable

Question 62

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

Answer 62

impermeable

Question 63

what are the three major lipids present in the cell membrane

Answer 63

phosphoglycerides, sphingolipids and sterols

Question 64

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

Answer 64

cholestrol

Question 65

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

Answer 65

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

Question 66

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

Answer 66

phosphatidylserine

Question 67

name the two amino phospholipids

Answer 67

phosphatidylethanolamine and phosphatidylserine

Question 68

name the two choline phospholipids

Answer 68

phosphatidylcholine and sphingomyelin

Question 69

name the two glycolipids

Answer 69

cerebrosidase and gm1-ganglioside

Question 70

name the three sphingolipids

Answer 70

sphingomyelin, cerebrosidase and gm1-ganglioside

Question 71

what is the difference between sphingolipids and glycerophospholipids

Answer 71

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

Question 72

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

Answer 72

asymmetrically

Question 73

*describe the structure of a cholesterol molecule

Answer 73

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

Question 74

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

Answer 74

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

Question 75

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

Answer 75

the head group of the glycerophospholipid

Question 76

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

Answer 76

the steroid ring and the acyl chain of the cholesterol molecule

Question 77

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

Answer 77

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

Question 78

what affect does cholesterol have on membranes made of sphingolipid

Answer 78

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

Question 79

what is a lipid raft

Answer 79

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.

Question 80

what is the overall function of lipid rafts

Answer 80

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

Question 81

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

Answer 81

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

Question 82

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

Answer 82

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

Question 83

what are bile salts for

Answer 83

solubilisation of dietary fat and lipophilic vitamins

Question 84

name two steroids cholesterol acts as a substrate for

Answer 84

cortisol and aldosterone

Question 85

name three hormones cholesterol acts as a steroid for

Answer 85

progesterone, oestrogen and testosterone

Question 86

what is the main structural component that glycolipids are based on

Answer 86

ceramide

Question 87

what type of head groups do glycolipids contain

Answer 87

sugar head groups

Question 88

name a glycolipid which carries a negative charge

Answer 88

NANA - sialic acid

Question 89

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

Answer 89

the cholera toxin

Question 90

what is the overall function of glycolipids, list three

Answer 90

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

Question 91

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

Answer 91

because of differing functions

Question 92

explain why hepatocyes are enriched in phosphatidylcholine

Answer 92

because they secrete phosphatidylcholine into bile

Question 93

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

Answer 93

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

Question 94

explain why e.coli lacks cholestrol

Answer 94

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

Question 95

why is myelin enriched in glycolipids

Answer 95

to insulate the nerve axons for nerve impulse conductivity

Question 96

what does the fluid mean when describing the fluid mosaic model

Answer 96

fluid describes the motions of the lipids and the proteins

Question 97

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

Answer 97

mosaicity describes the membrane proteins embedded in the bilayer

Question 98

label/describe the following membrane protein, 1 and 2

Answer 98

there

Question 99

label/describe the following membrane protein, 3

Answer 99

there

Question 100

label/describe the following membrane protein, 4

Answer 100

there

Question 101

label/describe the following membrane protein, 5 and 6

Answer 101

there

Question 102

label/describe the following membrane protein, 7&8

Answer 102

there

Question 103

what are lipid anchors

Answer 103

they are long chain fatty acids

Question 104

what can lipid anchors be used for

Answer 104

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

Question 105

lipid anchors are reversible by what process

Answer 105

de-esterification

Question 106

what enzyme is involved in the detachment of lipid anchros

Answer 106

lipid transferase

Question 107

why are transmembrane a helices enriched in hydrophobic amino acids

Answer 107

because they pass through the hydrophobic core of the membrane

Question 108

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

Answer 108

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

Question 109

can lipid anchored membrane proteins associate and dissociate from the membrane

Answer 109

yes

Question 110

can lipid anchored membrane proteins diffuse laterally

Answer 110

yes

Question 111

can lipid anchored membrane proteins change conformation

Answer 111

yes

Question 112

can integral membrane proteins associate and dissociate from the membrane

Answer 112

no

Question 113

can intergral membrane proteins diffuse laterally

Answer 113

yes

Question 114

can integral membrane proteins change conformation

Answer 114

yes