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Michaelmas Term 1 > Carbohydrates for energy, structure, and signals > Flashcards

Carbohydrates for energy, structure, and signals Flashcards

1
Q

What are carbohydrates essential for?

A
  • energy storage
  • structure
  • recognition
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2
Q

Define carbohydrates

A

molecules with molecular formula (CH2O)n (n≥3)

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3
Q

List some monosaccharides

A
  • glucose
  • ribose
  • fructose
  • mannose
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4
Q

List some disaccharides

A
  • sucrose
  • maltose
  • lactose
  • mannose
  • trehalose
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5
Q

List some polysaccharides

A
  • starch
  • glycogen
  • cellulose
  • amylopectin
  • amylose
  • dextran
  • cellulose
  • chitin
  • GAGs
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6
Q

Describe aldose

A

carbohydrate with aldehyde

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7
Q

Describe ketose

A

carbohydrate with ketone

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8
Q

Describe enantiomers

A
  • mirror images
  • stereoisomers)
  • L = left
  • D = right (dextral)
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9
Q

Stereo/chiral center

A

atom with four different attachments

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10
Q

L stereoisomer carbohydrates are

A

very rare

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11
Q

Organisms prefer

A
  • D-carbohydrates
  • L-amino acids
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12
Q

List some aldose pentoses

A
  • D-Ribose
  • D-Arabinose
  • D-Xylose
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13
Q

List some ketose pentoses

A

D-Ribulose

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14
Q

List some aldose hexoses

A
  • D-Glucose
  • D-Mannose
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15
Q

List some ketose hexoses

A

D-Fructose

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16
Q

Enantiomers are

A

rare

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17
Q

Diastereomers

A

stereoisomers that are not mirror images

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18
Q

Epimers

A

diastereomers that differ only at one stereo center

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19
Q

Compare and contrast D-Glucose and D-Fructose

A
  • D-Glucose: aldose
  • D-Fructose: ketose
  • both hexoses
  • differ only in position of carbonyl
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20
Q

Describe Pyranoses

A
  • six-membered sugar rings
  • more stable
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21
Q

Describe Furanoses

A
  • five-membered sugar rings
  • less stable
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22
Q

Four-membered

A

sugar rings are unstable

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23
Q

Describe intramolecular cyclization

A
  • (preferably secondary) hydroxyl can react with carbonyl
  • pentoses and hexoses form rings
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24
Q

What does aldehyde cyclisation result in?

A

hemiacetal with anomeric carbon

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25
Q

What does ketone cyclisation result in?

A

hemiketal with anomeric carbon

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26
Q

Describe cyclisation of aldoses

A
  • α and β are anomers
  • α: OH on C-1 is opposite side of C-6
  • β: OH on C-1 is on same side as C-6
  • equilibrium in solution: 36% α, 64% β
  • <1% linear
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27
Q

anomers

A

type of stereoisomer

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28
Q

Describe Pyranose rings

A
  • chair or boat
  • chair is energetically more favorable
  • less steric hindrance between equatorial groups
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29
Q

Describe cyclisation of fructoses

A
  • α and β are anomers
  • α: OH on C-1 is opposite side of C-6
  • β: OH on C-1 is on same side as C-6
  • Furanose rings have envelope conformations
  • fructose mostly as pyranose via primary OH at C6
30
Q

Compare epimers and anomers

A

epimers are fixed, anomers are dynamic

31
Q

Describe a reduction reaction

A
  • β-D-Deoxyribose from ribose in DNA to D-Mannitol
  • not cyclic
  • from D-mannose
  • fungal energy
32
Q

Describe an oxidation reaction

A
  • β-D-Glucuronic acid
  • detoxification in liver
33
Q

Describe a phosphorylation reaction

A
  • β-D-Glucose-6- Phosphate (G6P) to D-Ribulose-1,5-Biphosphate (RuBP)
  • in glycolysis
34
Q

Describe amino sugars

A
  • α-D-Glucosamine to α-N-acetyl-glucosamine (GlcNac, in chitin)
  • chitin degradation
35
Q

Describe glycosidic bonds

A
  • in acidic conditions, anomeric carbon reacts with alcohols to form O-glycosidic bonds
  • common linkage in di/polysaccharides
36
Q

Disaccharides are often

A

soluble

37
Q

Describe lactose

A
  • Galactose-β(1→4)-Glucose
  • milk sugar: 2-8% in milk
  • hydrolysis by β-galactosidase in bacteria; lactase in humans
  • reducing sugar: carbonyl is still available
  • can act as reducing compound
38
Q

Describe maltose

A
  • Glucose-α(1→4)-Glucose
  • malt sugar: starch degradation product
  • malting barley during beer brewing
  • hydrolysis by maltase in small intestine
  • reducing sugar: carbonyl is still available
  • can act as reducing compound
39
Q

Describe sucrose

A
  • Glucose-α(1→2)β-Fructose - table sugar from cane or beet
  • hydrolysis by sucrase/invertase
  • O-Glycosidic bond between anomeric carbons locks carbonyl
  • ‘nonreducing’
40
Q

Describe trehalose

A
  • Glucose-α(1→1)α-Glucose
  • stable: heat/acid resistant
  • antifreeze in plants, bacteria
  • flying insects hydrolysis by trehalase
  • O-Glycosidic bond between anomeric carbons locks carbonyl
  • ‘nonreducing’
41
Q

What happens in non-reducing disaccharides

A

second residue is inverted 180 degrees

42
Q

polysaccharides are … than disaccharides

A

less water soluble

43
Q

Describe glycogen, starch and dextran

A
  • branching α(1→6)
  • glucose polymers
  • accessible, quickly mobilisable energy store
44
Q

Describe glycogen

A
  • animals
  • branching every ~10 units
45
Q

Describe starch

A

mixture of amylopectin and amylose

46
Q

Describe amylopectin

A

branching every ~30 units

47
Q

Describe amylose

A

no branching

48
Q

Describe dextran

A

bacteria; yeast
- only α(1→6) linkages

49
Q

Describe cellulose

A
  • unbranched glucose polymer with β(1→4) glycosidic bonds
  • every second unit turned 180 degrees (extra H-bond)
  • long straight chains assemble into fibers (structural role)
  • plant cell wall: most abundant organic compound in biosphere!
50
Q

Describe chitin

A
  • decorated cellulose
  • 2nd most abundant polymer in biosphere
  • structural role in fungi, anthropods, squid, algae
  • GlcNac instead of glucose
  • carries acetylated amino group at C-2
51
Q

GlcNac

A

N-acetylglucosamine

52
Q

Describe GAG

A
  • major component of ECM in animals
  • Hyaluronan in cartilage of joints
  • inear disaccharide polymer
  • water soluble
  • linked to proteins
53
Q

GAG

A

Glycoaminoglycans (GAG)

54
Q

Describe some possible glycogen conjugates

A
  • to nitrogen bases
  • to proteins
  • to lipids
55
Q

How does glycogen bond to nitrogen bases?

A

N-glycosidic bond

56
Q

How does glycogen bond to proteins?

A

N- and O-glycosidic bond

57
Q

How does glycogen bond to lipids

A

diverse linkages

58
Q

Describe glycogen conjugates with nitrogen bases

A
  • in all (deoxy)nucleotides
  • in many cofactors
  • e.g. adenosine
  • β-(1-N)-Glycosidic bond
59
Q

Describe protein glycosylation

A
  • common for secreted proteins
  • N-glycosylation
  • O-glycosylation
60
Q

Describe N-glycosylation

A
  • on Asn(N) residues in N-x-S/T motifs
  • similar core
  • diverse antenna
  • quality control and trafficking
61
Q

Describe O-glycosylation

A
  • on Ser/Thr residues
  • highly diverse
    and complex
  • roles in recognition
  • e.g. animal proteoglycan (with GAG)
62
Q

Describe lipid glycosyation

A

common and diverse

63
Q

List some glycosylated lipids

A

Ganglioside
GPI anchor
LPS

64
Q

Describe ganglioside

A
  • diverse glycosphingolipids
  • signaling in nervous system
65
Q

Describe GPI anchor

A
  • glycosylphosphatitylinositol
  • anchors membrane proteins
66
Q

Describe LPS

A
  • lipopolysaccharide
  • Gram-negative bacteria
  • antigenic
  • can cause sceptic shock
67
Q

List the 3 main roles of carbohydrates

A
  • energy storage
  • structure
  • recognition
68
Q

Describe the carbohydrates used in energy storage

A
  • mannitol
  • sucrose
  • lactose
  • trehalose
  • mannose
  • glycogen
  • starch
  • dextran
69
Q

Describe the carbohydrates used in structure

A
  • cellulose
  • chitin
  • GAGs
70
Q

Describe the carbohydrates involved in recognition

A

protein/lipid glycosylation

Michaelmas Term 1 (42 decks)

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