Carbohydrates Flashcards
What is a monosaccharide?
A simple sugar, can be classified by number of carbons they have
Examples of pentose monosaccharides
ribose(RNA) deoxyribose(DNA)
Examples of hexose monosaccharides
fructose- in fruit
galactose- in milk
glucose-can cross blood-brain barrier, nourishes brain
What is an isomer?
Same molecular formula but different atom arrangement. Eg alpha and beta glucose
What is a disaccharide?
They are all crystalline, soluble and sweet
Two monosaccharides joined together EG
both alpha glucose+glucose=maltose
alpha glucose+fructose=sucrose
beta glucose+galactose=lactose
Disaccharides and their functions
Sucrose- Converted from glucose from photosynthesis as its easier to transport in phloem
Maltose- Found in grains eg Barley, usually formed during hydrolysis of starch in germination
Lactose- Found in milk, main source of energy for babies. When you cant make lactase you get lactose intolerance.
How are disaccharides condensation reactions?
The bonding of 2 monosaccharides forms a disaccharide and water
What is a polysaccharide?
When 3 or more monosaccharides are joined together
They are generally insoluble not crystalline or sweet.
Examples of polysaccharides
Starch, glycogen, cellulose
What is starch?
An alpha glucose polymer.
Made by plants to use up excess glucose to be used later. Done because its insoluble, meaning it doesn’t affect the osmotic potential of cells.
There are 2 types, amylose and amylopectin
What is amylose?
Straight, unbranched helix chain of glucose with 1:4 glycosidic bonds, they coil up in a compact spiral.
Best for long term storage
What is amylopectin?
Branched chains with 1:4 and 1:6 glycosidic bonds, coil up and store compactly
Best for accessible storage as easily released
What is glycogen?
Polymer of alpha glucose found in mammals.
Way to store excess glucose in muscles and liver
Insulin and glycogon control its storage and breakdown
Its highly branched structure makes it easy to be released. More branched than ampylopectin
What is cellulose?
Polymer of beta glucose found in cell walls.
Provides strength and flexibility, limits vol of water in cell
Molecules flip over, creating straight chains rather than coils. allows hydrogen bonds=more strength.
What is the test for carbohydrates?(reducing)
BENEDICTS TEST, reacts with cu ions
- Add sample to boiling tube with equal vol of Benedict’s reagent
2.Heat mix gently for 5mins in water bath
RESULTS- negative=blue
MID=green/orange
POSOTIVE=Brick red
What is the test for non-reducing sugars?
Add hydrochloric acid them heat in water bath then neutralise using sodium hydrogencarbonate then carry out benedicts test
