Carbohydrates - monosaccharides Flashcards
Compounds containing the elements C, H and O in the ratio:
e.g.
(CH2O)n
C6H12O6
Can be defined as sugars and their derivatives
5 points
- Deoxy-sugars
- Sugar acids
- Amino-sugars
- Phospho-sugars
- Acetyl-sugars, etc
Functions
Structural:
3 points
- cellulose, hemicelluloses in plants
- chitin in insects
- components of cell membranes + sub-cellular organelles
Functions
Cell Recognition:
cell surface carbohydrates enabling cells to recognise each other
Functions
Metabolism:
metabolic intermediates, energy substrates
Functions
Energy store:
starch in plants and glycogen in animals
Carbohydrate groups - Sugars
Monosaccharides:
- Single sugars
2. Basic units of carbohydrates
Carbohydrate groups - Sugars
Oligosaccharides:
2 points
- 2-10 residues
2. Di-, tri-, tetra-, penta-, hexa-, octa-, nona-, deca-saccharides
Carbohydrate groups - ‘Poly’-sugars
Polysaccharides:
2 points
- > 20 residues
2. Macromolecules with long chains
Aldehyde
R-CHO
Ketone
R-COR
carbonyl
C=O
Sugars - polyhydroxy carbonyl compounds
- polyhydroxy = 2 or more hydroxyl (-OH) groups
2. carbonyl = C=O
Monosaccharides
3 points
- simplest units of carbohydrates
- Cannot easily be broken down to simpler compounds
- Basic ‘building’ blocks -other classes of carbohydrates are derived from them
Monosaccharides are classified according to:
2 points
- number of C atoms in their structure: trioses (3), tetroses (4), pentoses (5), hexoses (6)
- whether an aldehyde (aldose) R-CHO or ketone (ketose) R-COR
drawing monosacharides
convention to draw the C atoms in monosaccharides in a vertical line (chain with the lowest numbered carbon atom at the top of the chain)
e.g. of naming monosaccharide
H - C = O H - C - OH H - C - OH H - C - OH | H
Tetrose and aldose = aldotetrose
general name for aldose with 4 carbons… aldopentose, aldohexoses, aldotrioses
Common aldoses
where groups found
2 points
- All have the aldehyde (-CHO) group on the top C (C1) and
2. CH2OH on the lowest C (the highest numbered C, e.g. C6)
Common aldoses
general formula and e.g.
Within a group, individual monosaccharides have the same general formula, but differ in the arrangement of their -OH groups
e.g. hexoses,
C6H12O6,
common aldroses
triose
Glyceraldehyde
common aldroses
tetrose
Erythrose
common aldroses
pentose
Ribose
common aldroses
hexose
Glucose
Common ketoses
groups
2 points
- All have the ketone (-C=O) group on the second top C (C2)
- CH2OH on first and last C
Common ketoses
general formula and arrangement of OH groups
3 points
Within a group, individual mono-saccharides have the same general formula,
but differ in the arrangement of their -OH groups
eg. hexoses,
C6H12O6
‘D’ Ketose family
general names
6 points
no of Cs 3 - Ketotriose 4 - Ketotetrose 5 - Ketopentoses 6 - Ketohexoses
what structure is this
CH2OH C=O HO - C - H H - C - OH H - C - OH CH2OH
D - Fructose
a ketohexose
What structure is this
CHO H C OH HO C H H C OH H C OH CH2OH
D - (+) - glucose
Aldohexose
What structure is this
CHO HO C H HO C H H C OH H C OH CH2OH
D- (+) - mannose
aldohexose
What structure is this
CHO H C OH HO C H HO C H H C OH CH2OH
D- (+) - galactose
aldohexose
Aldose and ketose names
3 points
- aldose names end in -ose
- ketose names end -ulose
- related aldose and ketose only have -OH arranged differently on C atoms 1 and 2
Epimers
3 points
- Different compounds (structures) with the same molecular formula
- differ by configuration at only one carbon
- Important because biological systems can differentiate between them
Epimer e.g.
2 points
- Glucose and galactose differ from each other only in respect to the arrangement of atoms in space
- Have the same atoms joined to the same atoms but the opposite configuration at C4
Memorising sugar epimers
see desktop
james bond, swear, bruce lee
Reactions of –OH groups of monosaccharides (part 1)
3 points and e.g.
- Intramolecular (taking place within the same molecule):
- a hydroxyl (-OH) group will react with a carbonyl (C=O) group
- form a hemiacetal
e.g.
R - OH + CORH
=
C OH R H RO
Reactions of –OH groups of monosaccharides
Monosaccharides with 5 or more C atoms form
4 points
- internal hemiacetals
- Results in a ring structure
- Forms a new chiral (asymmetric) C
(a C atom with four different groups bonded to it) - bonded to 2 O atoms – called anomeric C
Reactions of –OH groups of monosaccharides
In a ring form, the –OH attached to the anomeric C1 can point
4 points
- below the ring (a)
OR
above the ring (b)
(this applies only to D-sugars) - a and b structures called anomers
3 5-membered rings are furanoses
- 6-membered rings are pyranoses
Glucose (Glc)
4 points
- Most abundant monosaccharide; aldose
- Central to cell metabolism
- Building block for the most abundant polysaccharide - cellulose
- Found in monosaccharide form in plants, fruits, honey, blood, lymph and cerebrospinal fluid
Fructose (Fru)
3 points
- Most biologically important ketose
- Found in the free form in leaves, fruit and honey
- Major function is as component of sucrose
(commercially extracted from sugarcane or beetroot)
Building block of fructan (storage polysaccharide)
Ribose (Rib)
2 points
- Aldopentose; component of ribonucleic acid (RNA)
2. Its reduced form - deoxyribose – important in deoxyribonucleic acid (DNA)
Galactose (Gal)
4 points
- Major function is as component of lactose (Glc+Gal)
- Present in milk products
- Building block of galactans (structural cell wall polysaccharides from plants)
- Component of the antigens present on blood cells that determine blood group
Mannose, Xylose and Arabinose are
not normally found in the free form but are important components of polysaccharides
(e.g. plant hemicelluloses)
Summary
Aldoses have an aldehyde group on
top C (C1)
Summary
Ketoses have a keto group on the
second C (C2)
Summary
aldoses and ketoses can both exist as
trioses, tetroses, pentoses and
hexoses
Summary
Epimers e.g.
mannose, glucose and galactose
Summary
Anomers e.g.
a glucose
b glucose
Summary
The most common monosacharides:
4 points
- Glucose – the most abundant aldose central to the metabolism, building block of cellulose in plants
- Fructose – a component of disaccharide sucrose
- Ribose – a component of RNA and DNA
- Galactose – component of lactose and many structural polysaccharides found in the plant cell walls
