Chapter 3 - carbohydrates Flashcards
what is the structure of glucose?
- composed of six carbons (hexose monosaccharide)
- alpha and beta glucose (hydroxyl group on opposite positions)
- polar and soluble in water (hydrogen bonds)
- 2 glucose molecules bond to form a glycosidic bond
other hexose sugars?
- fructose - naturally occurs in fruit, combines with glucose forming disaccharide sucrose
- galactose -combine with glucose to form disaccharide lactose
what is a condensation reaction?
- a water molecule is formed and removed from the reaction
- bond between carbons 1 and 4
pentose sugars?
- contain 5 carbon atoms
- ribose = sugar present in RNA nucleotides
- deoxyribose = sugar present in DNA nucleotides
what is starch?
- formed from 2 slightly different polysaccharides made from alpha glucose
what is amylose?
- energy storage molecule in plants
- a polysaccharide in starch
- formed by 1-4 glycosidic bonds between alpha glucose
- twists to form a helix stabilised by hydrogen bonds
- compact and less soluble than glucose
what is amylopectin?
- energy storage molecule in plants
- a polysaccharide in starch
- formed by 1-4 and 1-6 glycosidic bonds between alpha glucose
- branched structure
- insoluble
what is glycogen?
- energy storage molecule in animals
- more branched than amylopectin: more compact and takes up less space, ideal for storage
- many free ends for glucose molecules to be added or removed
- insoluble
what is a hydrolysis reaction?
a reaction requiring the addition of a water molecule
what is cellulose?
- beta glucose molecules
- alternating beta glucose molecules turned upside down
- unable to coil or form branches (straight chain molecule)
how are cellulose fibres formed?
- cellulose molecules form hydrogen bonds with eachother to form microfibrils
- microfibrils combine to form macrofibrils
macrofibrils combine to form fibres
what are the properties of cellulose?
- strong
- insoluble
- very hard to break down
- forms ‘fibre’ or ‘roughage’ necessary for a healthy digestive system
what is Benedicts test for reducing sugars?
1) place sample in a boiling tube
2) add an equal volume of Benedicts reagent
3) heat the mixture gently in a boiling water bath (80) for five minutes
- positive = brick red layer
how can you use Benedicts test for non reducing sugars?
non reducing sugars don’t react so the solution will stay blue
what is iodine test for starch?
1) mix a few drops of iodine dissolved in potassium iodide solution
- positive = colour change from yellow/brown to purple/black
