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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
What does ketone cyclisation result in?
hemiketal with anomeric carbon
26
Describe cyclisation of aldoses
- 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
27
anomers
type of stereoisomer
28
Describe Pyranose rings
- chair or boat - chair is energetically more favorable - less steric hindrance between equatorial groups
29
Describe cyclisation of fructoses
- 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
Compare epimers and anomers
epimers are fixed, anomers are dynamic
31
Describe a reduction reaction
- β-D-Deoxyribose from ribose in DNA to D-Mannitol - not cyclic - from D-mannose - fungal energy
32
Describe an oxidation reaction
- β-D-Glucuronic acid - detoxification in liver
33
Describe a phosphorylation reaction
- β-D-Glucose-6- Phosphate (G6P) to D-Ribulose-1,5-Biphosphate (RuBP) - in glycolysis
34
Describe amino sugars
- α-D-Glucosamine to α-N-acetyl-glucosamine (GlcNac, in chitin) - chitin degradation
35
Describe glycosidic bonds
- in acidic conditions, anomeric carbon reacts with alcohols to form O-glycosidic bonds - common linkage in di/polysaccharides
36
Disaccharides are often
soluble
37
Describe lactose
- 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
Describe maltose
- 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
Describe sucrose
- 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
Describe trehalose
- 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
What happens in non-reducing disaccharides
second residue is inverted 180 degrees
42
polysaccharides are ... than disaccharides
less water soluble
43
Describe glycogen, starch and dextran
- branching α(1→6) - glucose polymers - accessible, quickly mobilisable energy store
44
Describe glycogen
- animals - branching every ~10 units
45
Describe starch
mixture of amylopectin and amylose
46
Describe amylopectin
branching every ~30 units
47
Describe amylose
no branching
48
Describe dextran
bacteria; yeast - only α(1→6) linkages
49
Describe cellulose
- 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
Describe chitin
- 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
GlcNac
N-acetylglucosamine
52
Describe GAG
- major component of ECM in animals - Hyaluronan in cartilage of joints - inear disaccharide polymer - water soluble - linked to proteins
53
GAG
Glycoaminoglycans (GAG)
54
Describe some possible glycogen conjugates
- to nitrogen bases - to proteins - to lipids
55
How does glycogen bond to nitrogen bases?
N-glycosidic bond
56
How does glycogen bond to proteins?
N- and O-glycosidic bond
57
How does glycogen bond to lipids
diverse linkages
58
Describe glycogen conjugates with nitrogen bases
- in all (deoxy)nucleotides - in many cofactors - e.g. adenosine - β-(1-N)-Glycosidic bond
59
Describe protein glycosylation
- common for secreted proteins - N-glycosylation - O-glycosylation
60
Describe N-glycosylation
- on Asn(N) residues in N-x-S/T motifs - similar core - diverse antenna - quality control and trafficking
61
Describe O-glycosylation
- on Ser/Thr residues - highly diverse and complex - roles in recognition - e.g. animal proteoglycan (with GAG)
62
Describe lipid glycosyation
common and diverse
63
List some glycosylated lipids
Ganglioside GPI anchor LPS
64
Describe ganglioside
- diverse glycosphingolipids - signaling in nervous system
65
Describe GPI anchor
- glycosylphosphatitylinositol - anchors membrane proteins
66
Describe LPS
- lipopolysaccharide - Gram-negative bacteria - antigenic - can cause sceptic shock
67
List the 3 main roles of carbohydrates
- energy storage - structure - recognition
68
Describe the carbohydrates used in energy storage
- mannitol - sucrose - lactose - trehalose - mannose - glycogen - starch - dextran
69
Describe the carbohydrates used in structure
- cellulose - chitin - GAGs
70
Describe the carbohydrates involved in recognition
protein/lipid glycosylation

Michaelmas Term 1 (42 decks)

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