Biological Molecules- Carbohydrates Flashcards
(25 cards)
What are polymers?
Large complex molecules composed of long chains of monomers
What are monomers?
Small basic molecular units
What are examples of monomers?
Monosaccharides, amino acids, nucleotides
What elements do carbohydrates contain?
Carbon, hydrogen and oxygen
What is glucose?
A hexose sugar
What are examples of monosaccharides?
Glucose, fructose, galactose
What are the two isomers of glucose?
Alpha and beta
What’s the difference between an alpha and beta glucose molecule?
Alpha glucose- H at top, OH at bottom
Beta glucose- OH at top, H at bottom
What happens when a condensation reaction occurs?
Two molecules join together to form a new chemical bond and a molecule of water is released
How are monosaccharides joined together?
Condensation reactions
What bond is formed between two monosaccharides?
Glycosidic bond
How is a disaccharide formed?
Two monosaccharides join together
How is maltose formed?
Two alpha glucose molecules join
How is sucrose formed?
A glucose molecule and a fructose molecule join
How is lactose formed?
A glucose molecule and a galactose molecule join
How can polymers be broken down into monomers?
Hydrolysis reaction
What happens in a hydrolysis reaction?
Breaks chemical bond between monomers using a water molecule
How do you test for reducing sugars?
- Add Benedict’s reagent
- Heat in a water bath that’s been brought to boil
- Positive result= colour change (green/yellow/orange/brick red)
- Higher concentration of reducing sugar, closest to red precipitate colour goes
How can you measure the concentration of reducing sugar?
Dry and weigh the precipitate or use a colorimeter
How do you test for non-reducing sugars?
- Add dilute hydrochloric acid
- Heat in water bath that’s been brought to boil
- Neutralise with sodium hydrogencarbonate
- Carry out Benedict’s test as you would when testing for a reducing sugar
- Positive result= forms coloured precipitate
How are polysaccharides formed?
When more than two monosaccharides are joined together by a condensation reaction
What is the structure and function of starch?
- Plants store excess glucose as starch
- Mix of amylose and amylopectin
- Amylose is a long, unbranched chain of alpha glucose, coiled structure which makes it compact so good for storage
- Amylopectin is a long, branched chain of alpha glucose, side branches allow enzymes that break down molecule to easily get at glycosidic bonds so glucose can be released quickly
- Insoluble in water and doesn’t affect water potential so water doesn’t enter cells by osmosis
How do you test for starch?
Iodine test
- Add iodine dissolved in potassium iodide solution
- Positive result= colour change to blue-black
What is the structure and function of glycogen?
- Animals store excess glucose as glycogen
- Similar structure to amylopectin
- Lots more side branches so glucose can be released quickly
- Very compact so good for storage
