B.4. Carbohydrates Flashcards
What functional groups do Monosaccharides contain?
+ Carbonyl group (>C=O)
+ At least 2 Hydroxyl groups (-OH)
How do Monosaccharides differ?
In orientation of the hydroxyl group
What happens to straight chain forms of sugars in solutions?
Cyclise to form ring structures containing an ether linkage.
What does the ‘Haworth Projection’ represent ?
Cyclic structures of Monosaccharides that give the 3D perspectives.
In glucose which carbon does the numbering start at?
The carbon of the carbonyl group (is C1)
In Harworth Projection the groups that appear on the LHS of the straight chain = appear____the ring
Above
In Harworth Projection the groups that appear on the RHS of the straight chain = appear____the ring
Below
What is the difference between the structure of galactose and glucose?
The orientation of the H and OH around the C4
How many chiral carbon atoms are there in glucose and galactose? and which are they?!
4
C2, C3, C4, C5
(C1 and C6 = non chiral!)
Why do monosaccharides form rings?
Because the straight chain form is unstable due to the presence of a carbonyl group and several hydroxyl groups.
Aldose
Aldehyde sugar
= when the carbonyl group of a monosaccharide is connected to the terminal C atom.
Ketose
Ketone sugar
= When the carbonyl group of a monosaccharide is connected to the 2nd C.
Disaccharides
2 simple sugars linked together with a glycosidic bond. C-O-C
Which carbons usually from the glycosidic bond?
1,4
Properties of Monosaccharides and Disaccharides (4)
1) Low Molar masses
2) Sweet
3) Readily Soluble in water
= because of H-bonding between water and the -OH groups
4) Readily taken up by cells
Why do monosaccharides and disaccharides form crystalline solids?
Due to the INTRAmolecular H-bonds between the -OH groups
Reducing sugars
Aldose Monosaccharides
= because Aldehydes are easily oxidised (to carboxylic acids)
What do polysaccharides differ in? (4)
1) Nature of their recurring monosaccharides units
2) The bonds connecting the units
3) Length of their chain
4) Degree of branching
Structure of starch amylose
+ straight chain joined by α-1,4 glycosidic bonds
+ coiled helix structure due to the intramolecular H-bonding of some -OH groups on diff glucose units
Properties and function of starch amylose
+ Other -OH groups on outside form H-bonding w, water = making it somewhat water soluble
+ can be hydrolysed by amylase
+ stored as energy reserve
Structure of starch amylopectin
+ α-1,4 linkages
+ branches formed by α-1,6 linkages of glucose
+ Interactions of water w, polymeric chains = restricted
Properties and functions of starch amylopectin
+ INsoluble in water
+ can be hydrolysed by amylase
+ stored as energy reserve
Structure of Cellulose
+ much longer chains
+ ALL glycosidic linkages in 1,4 position = LINEAR
+ Allows side-by-side alignment of cellulose chains = extensive H-bonding betw, chains = gives strength and rigidity
+ Can be hydrolysed by cellulase (absent in humans = unable to digest)
= Cows and many animals have bacteria that produce cellulase
Properties and functions of Cellulose
+ structural component in plants
+ INsoluble in water due to extensive INTERmolecular H-bondings betw, chains
= not enough water molecules can H-bond w, cellulose to separate the chains
+ important dietary fibre
