CH3 carbohydrates Flashcards
What is a carbohydrate
- only contain hydrogen, oxygen and carbon
- means ‘hydrated carbon’
- has general formular Cx(H2O)y
Examples of monosaccharides
Glucose, fructose, galactose, ribose
Examples of disaccharides
Lactose, sucrose
Examples of polysaccharides
Glycogen, cellulose, starch
What is glucose
- hexose monosaccharide
- C6H12O6
- two structural variations - alpha and beta
Why is glucose soluble in water
Glucose is polar so hydrogen bonds form between hydroxyl group of glucose and water molecules
What happens when two alpha glucose molecules are side by side
- two hydroxyl groups interact
- a 1,4 glycosidic bond forms
- water molecule produced so is a condensation reaction
- maltose
What is lactose made from
Glucose and galactose
What is sucrose made from
Glucose and fructose
What is starch
Chemical energy store in plants (how glucose is stored)
Starch - amylose
- formed by alpha glucose molecules joined by 1,4 glycosidic bonds
- angle of bond means long chain twists into a helix
- helix further stabilised by hydrogen bonding
- more compact and less soluble than glucose
Starch - amylopectin
- made by 1,4 glycosidic bonds and 1,6 glycosidic bond
- branched structure with 1,6 branching point occurring roughly every 25 glucose subunits
What is glycogen
Energy store in animals and fungi
Glycogen
- more branches form than amylopectin
- free ends where glucose molecules can be added or removed
- compact
What is a hydrolysis reaction
Addition of water molecules to break down bonds
Cellulose
- beta glucose
- every other molecule turned upside down
- long, straight chain molecule
How are cellulose fibres made
- cellulose molecules make hydrogen bonds with each other to form microfibrils
- microfibrils join together to form macrofibrils which combine to form fibres
How do you test for reducing sugars
Benedicts test
How do you carry out benedicts test
- place sample in boiling tube (if solid grind up)
- add equal volume of benedicts reagent
- heat mixture gently in water bath for five minutes
What is a positive benedicts test result
- turns from blue to red
- blue copper 2+ ions are reduced to red copper + ions
- higher concentration = less blue left
How do you test for non-reducing sugars
- boil with hydrochloric acid to hydrolyse
- will then give a positive result with benedicts
How do you test for starch
Iodine test
How do you carry out iodine test
- a few drops of iodine dissolved in potassium iodide solution mixed with sample
- present = yellow to purple/black
