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MCB 2020 > 1.4 Lipids and Carbohydrates > Flashcards

1.4 Lipids and Carbohydrates Flashcards

1
Q

What are the three broad functions of lipids in biology?

A
  • Storage
  • Structural
  • Signals
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2
Q

What specific lipids are the storage lipids?

A

Fatty acids

Triacylglycerol

Waxes

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3
Q

What specific lipids are the membrane lipids?

A

Phospholipids

Glycolipids

Cholesterol

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4
Q

What specific lipids are the signalling and cofactor lipids?

A
  • Phospholipid derivatives (inositol phospholipids)
  • Steroid hormones (cholesterol derivatives)
  • Eicosanoids (paracrine hormones eg. prostaglandins)
  • Lipid soluble vitamins (vitamin A)
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5
Q

What defines a fatty acid?

A

Carboxylic acids with hydrocarbon chains containing between 4 to 36 carbons. Usually even number of carbons and unbranched naturally

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6
Q

Types of fatty acids

A
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7
Q

What is the trend seen with increasing length of the carbon backbone of fatty acids for melting point and solubility in water?

A

Melting point increases and solubility decreases

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8
Q

How are saturated fatty acids able to pack more closely?

A
  • The fully saturated C backbone is usually in a fully extended conformation
  • Saturated fatty acids can therefore pack into a nearly crystalline array, stabilised by extensive hydrophobic interactions of the hydrocarbon chain
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9
Q

How are the dobule bonds usually found in unsaturated fatty acids?

A

The double bond is usually in the cis form and is usually NOT conjugated

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10
Q

How is the double bond affected by unsaturated fatty acids?

A
  • Unsaturated cis fatty acids pack less orderly due to the kink
  • Less extensive favourable interactions
  • It takes less thermal energy to disrupt disordered packing of unsaturated fatty acids so they have a lower melting point
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11
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A
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12
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13
Q
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14
Q

What is the difference between simple and mixed fatty acids?

A

Simple = all three fatty acids are identical (triolein, tripalmitin)

Mixed = fatty acids differ

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15
Q

Why are fatty acids advantageous as storage lipids?

A
  1. Higher energy yield than oxidation of other fuel sources such as glycogen or starch
  2. Not hydrated so they weigh less
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16
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A
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17
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18
Q

When drawing a model of the fluid mosaic model what components should you include?

A
  • Glycolipid
  • Oligosaccharide
  • GPI anchored protein
  • Sterol
  • Integral protein
  • Phospholipid
  • Sphingolipid
  • Peripheral protein
  • Peripheral protein covalently linked to lipid
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19
Q

How can phospholipids be further classed?

A

Glycerophospholipids are based on the glycerol molecule

Sphingolipids are based on sphingosine

Each has a polar head group and two non polar tails

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20
Q

What is the most common glycerophospholipid and its structure?

A

Phosphatidylcholine

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21
Q

What is the simplest example of a glycerophospholipid?

A

Phosphatidic acid where X = H

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22
Q
A
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23
Q

What is the simplest example of a sphingolipid?

A

Ceramide where X of the alcohol = H

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24
Q

How else can the structure of sphingolipids be changed apart from this?

A
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25
Q

What is the role of sphingolipids?

A

They perform distinctive structural and signalling roles (not simply redundant with phospholipids)

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26
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A
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27
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28
Q

How can glycolipids contribute to recognition?

A

Glycolipids, as components of the outer membrane leaflet, can contribute to sites of biological recognition, as seen for the use of glycosphingolipids as determinants of the blood groups A, B and O

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29
Q

What is the structure of sterols?

A
  • Have 4 fused carbon rings (A, B & C = 6 carbon rings, D = 5 carbon ring)
  • The fused ring structure constrains their conformation
  • almost planar and relatively rigid
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30
Q

What is the role of cholesterol?

A
  • Structural role in membranes
  • Role in signalling acting as a precursor for steroid hormones
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31
Q
A
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32
Q

What shapes do fatty acids with one tail form vs those with two tails?

A
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33
Q

What shapes do fatty acids form vs phospholipid bilayers?

A

Fatty acids form MICELLES
Phospholipids form BILAYERS

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34
Q

How does a bilayer convert to a liposome?

A
  • Hydrophobic regions at the edges of the bilayer are exposed to water and therefore unstable
  • Bilayers fold back on itself to form a hollow vesicle
  • Continuous bilayer with aqueous cavity
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35
Q

What factors influence the fluidity of the membrane?

A
  • Fatty acid composition
    • Length of fatty acyl chains
    • Degree of unsaturation
    • More unsaturated more fluid
  • Cholesterol content
    • moderates membrane fluidity
    • Low cholesterol breaks up the packing making it more fluid
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36
Q
A
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37
Q

What happens to the lipid bilyaer as temperature increases?

A

There is a phase transition temperature

  • Temperature at which the membrane goes from paracrystalline state to fluid state
  • At 37o all biological membranes are fluid
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38
Q

What are the two types of lipid movement in membranes?

A
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39
Q

How can lateral diffusion be measured?

A

Experimentally by Fluorescence Recovery After Photobleaching FRAP experiments

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40
Q

How does the flip flop lipid movement occur?

A
  • It occurs very slowly if at all
  • Catalysis is essential
  • Use of specialised proteins embedded in the bilayer providing an energetically favourable path that is faster than uncatalysed movement
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41
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42
Q
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43
Q

Is the lipid composition the same on the inside and outide of the lipid bilayer?

A
  • No there is an asymmetry
  • The exact composition dictates the packing of the lipids within each membrane leaflet
  • Spontaneous flip flop is not favoured
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44
Q

What is seen to be a marker of cell death in the lipid bilayer?

A

Phosphatidylserine is usually found on the inner monolayer of the cell membrane so disruption which exposes the inside contents to the outside suggests there are dead cells

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45
Q

What are membrane rafts?

A

Where sterols and sphingolipids cluster together in microdomains of the membrane

46
Q
A
47
Q

What roles do membrane proteins play?

A
  1. Permit selective entry and exit of molecules from cell via transporters
  2. Provide recognitions signals. eg receptors for growth factors
  3. Provide structural support to the cell
48
Q

What are the two types of proteins that interact with the membrane?

A
  1. Intergral membrane protein
  2. Peripheral protein
49
Q

How do peripheral membrane proteins associate with membranes?

A

Ionic interactions and H bonding with:

  • Polar head groups of lipids
  • Integral membrane proteins
50
Q

How do integral membrane proteins interact with the membrane?

A

Hydrophobic interactions with acyl chains of membrane lipids

51
Q

How are peripheral membrane proteins released from the membrane?

A

By reagants that disrupt ionic interactions

  1. high salt
  2. change of pH
  3. Chelating agent
52
Q

How are integral membrane proteins released from the membrane?

A

By reagants that disrupt hydrophobic interactions

eg detergents such as SDS - sodium dodecyl sulphate

53
Q

How can we determine the arrangement of membrane proteins?

A

Protease sensitivity of proteins from intact cells

54
Q

How can protease be used to determine trypsin sensitivity?

A
  • Trypsin cleaves on the carbonyl side of lysine and arginine but only has access to the outside part of the protein
  • After trypsin digestion analysis of remaining protein identifies the domains of protein buried in the bilayer or exposed on the inner surface
55
Q

How can we predict that there will be a transmembrane protein domain based on the sequence?

A

We look at if there is hydrophobic amino acids in the sequence with alpha helix conformation and if this spans the width of the membrane (20 amino acids)

56
Q

WHat does the hydropathy index tell us about an amino acid?

A

It is a measure of the polarity of each amino acid.

The free energy change required to move from an organic solvent to water.

57
Q

What does a positive hydropathy value indicate?

A

It is hydrophobic if it is a positive value

58
Q
A
59
Q

What are the two classes of membrane transport proteins?

A

Carriers (transporters) and channels

60
Q
A
61
Q

What define a carrier protein?

A

Carriers undergo a conformational change during the transport process

62
Q
A
63
Q

What is the mechanism of glucose transport inside the cell?

A
  • Glucose transporter exists in two conformations (T1 and T2)
  • Binding of glucose (from blood plasma) may induce a conformation change from T1 to T2
  • net transport of solute down its concentration gradient
64
Q

What is one example of anctive transporters that transport ATP?

A

One class of membrane proteins that uses ATP hydrolysis to pump ions across membranes are the ubiquitous P-type ATPases

65
Q

What are some examples of the P type ATPases?

A
  • Na+/K+ ATPase (pumps Na+ out, increase K+ in cell)
  • H+/K+ ATPase (pumps H+ out, K+ in; acidifies stomach)
  • Ca2+ ATPase (pumps Ca2+ out of cytosol)
66
Q

What is the mechanism for P type ATPases?

A
67
Q

What is the funciton of Na+/K+ ATPase?

A

Na and K gradient in animal cells is important to maintain cell volume and create transmembrane electrical potential

68
Q

What are the three different roles of sugars in biology?

A
  1. Source of energy/stored fuels
  2. Provide structure to cells and organism
  3. Cell biology as part of the cell surface, influencing protein function or specific recognition interactions
69
Q

What are some examples of carbohydrates providing structure to cells and organisms?

A

Cellulose in plants

CHitin in arthropods

70
Q

What is the basic definition of monosaccharides?

A

Aldehydes or ketones that have two or more hydroxyl groups

Formula [CH2O]n “carbon hydrate”

71
Q

What is the difference between an aldose and a ketose sugar?

A

It is aldose because it contains an aldehyde group

72
Q

What stereoisomer is seen in naturally occuring sugars?

A

D rather than L

73
Q
A
74
Q

What does the D in D aldose indicate?

A

D designates the configuration of the asymmetric carbon furthest from the aldehyde group

75
Q

What are epimers? Give an example

A
76
Q

How do hexoses cyclise to form pyranose rings?

A

The C1 aldehyde reacts with the C5 hydroxyl group to form an intramolecular hemiacetal

Results in 6 membered ring called pyranose

77
Q

Why is the chair conformation favourable?

A

Pyranose rings adopt an energetically favourable chair form.

Results in bulky hydroxy groups orientated in less hindered periphery of the sugar

78
Q
A
79
Q

Name these common disaccharides

A
80
Q

How many different ways can two D glucose units be linked?

A

11

81
Q

What is the structure of glycogen

A
82
Q

How can monosaccharides be used as reducing agents?

A
  • Ring opens up and the free aldehyde reduces the copper.
  • Itself is oxidised to carboxylic acid.
  • Cu2O is a product andc measuring this tells you sugar concentration for blood glucose levels in diagnosing diabetes
83
Q

What defines the reducing end?

A

If the anomeric carbon can open up and expose the aldehyde carbon to becoming a reducing sugar

84
Q
A
85
Q

How does the structure of glucose depend on its linkage?

A

–Glucose residues are linked by (B 1→4) glycosidic bonds

– structure is stabilized by H bonds
– Results in a long flat molecule

86
Q

How does the properties of cellulose between chains give rise to its structure?

A
  • Chains of cellulose can form interchain hydrogen bonds
  • Many chains pack together
  • Results in stable supramolecular fibres of great strength
87
Q

What is the structure of chitin?

A
  • Linear homopolymer of N-acetylglucosamine residues
  • Linked B 1,4
  • The only difference between it and cellulose is the presence of acetylated amino group at C2
88
Q

What is the structure of glycogen/starch in terms of the linkage?

A
  • Homopolymer of glucose residues
  • Linked alpha 1,4
  • Open helix structure rather than linear so that it is an accessible store of sugar
89
Q
A
90
Q

What are the two ways carbohydrates can be linked to proteins?

A
  1. Via asparagine residues (N glycans)
  2. Via serine or threonine residues (O glycans)
91
Q

What is the structure of an N glycan linkage between protein and carbohydrate?

A

Sugars are linked to the amide side chain of asparagine

Therefore called N linked oligosaccharides or N glycans

92
Q

What does the O glycan linkage between proteina and carbohydrate involve>

A
  • Sugars linked to the O atom in the side chain of serine or threonine residues (O linkage)
  • Called O linked oligosaccharides or O glycans
93
Q

How is an oligosacchatide assembled/added to the acceptor?

A
94
Q

To what end of the carbohydrate acceptor is the monosaccharide added to?

A

The monosaccharide is transferred from the nucleotide sugar to the NON reducing end of the carbohydrate acceptor

95
Q

How is the disaccharide lactose synthesised?

A
96
Q

What is the structure of the human ABO antigens

A

They are glycosphingolipids and A,B differ from O by adding one extra monosaccharide

97
Q

Which antigen is this?

A

O antigen

98
Q

Which antigen is this?

A

A antigen

99
Q

Which antigen is this?

A

B antigen

100
Q

Genetically what gives rise to the different ABO blood groups?

A
  • There is a single gene encoding the synthesis of ABO blood groups.
  • This gene encodes a glycosyltransferase (enzyme) and three forms of it exist.
  • An individual inherits one allele from each parent.
101
Q

How does the glycosyltransferase encode different ABO antigens?

A
102
Q

WHat are lectins?

A

A broad family of proteins which recognise carbohydrates, found in animal plants and microbes

103
Q
A
104
Q

How is the specificity of C type lectins achieved?

A
  • DifferentC-type lectins have different carbohydrate binding specificities
  • Changes in residues that interact with the sugar alter the carbohydrate binding specificity of the lectin
105
Q

What are selectins?

A
  • They are C type Lectins
  • Involved in cell to cell adhesion
  • Bind white blood cells to sites of injury and allow movement of cells from blood stream to site of infection
106
Q

How do viruses attach to host cells in terms of binding?

A
  • To infect host cell viruses need to bind to receptors on the cell surface, which may be carbohydrates
107
Q

How does the influenza virus bind to the host cell?

A
  • Recognises the sialic acid residues present on cell surface glycoproteins
108
Q

What is the mechanism of anti viral drugs for such as relenza?

A
  • It is an analogue for sialic acid and attacks the sugar binding site of sialic acid binding proteins
  • It inhibits the enzyme neuriminidase so that there is no cleavage of sialic acid and the virus remains stuck
  • Virus can’t leave the infected cell stopping propagation
109
Q

What is the structure/conformation of the GLUT transporters?

A
  • 2 states changing from T1 to T2
  • 12 transmembrane alpha helices each 20 residues long
110
Q

What are the common GLUT transporters?

A

MCB 2020 (38 decks)

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