1.2 Carbohydrates Flashcards
What are carbohydrates?
Carbohydrates are molecules which consist of only carbon, hydrogen and oygen. They are long chains of sugar units called saccharides
What are monosaccharides?
Monosaccharides are the monomers from which larger carbohydrates are made
Name the 3 hexose monosaccharides
Glucose
Fructose
Galactose
Name the type of bond that forms when monosaccharides react
(1,4 or 1,6) glycosidic bond
What are disaccharides?
Disaccharides are formed when a condensation reaction forms glycosidic bond between 2 monosaccharides
Name the 3 disaccharides
Maltose: glucose + glucose
Sucrose: glucose + fructose
lactose: glucose + galactose
Describe alpha glucose
Alpha glucose has the H molecule above
Describe beta glucose
Beta glucose has the H molecule below
What are polysaccharides?
Combining many monosaccharides results in the formation of a polysaccharide
What polysaccharides are formed from alpha glucose?
Glycogen and starch
What polysaccharide is formed from beta glucose?
Cellulose
Describe the function of glycogen
Glycogen is the main storage polymer of alpha glucose in animal cells and is formed from many molecules of a-glucose joined together by 1,4 and 1,6 glycosidic bonds
Describe the structure of glycogen
- Large number of side branches = terminal ends for hydrolysis
- Insoluble = no osmotic effect and does not diffuse out of cells
- Compact = maximising the amount of energy it can store
Describe the function of starch?
Starch stores energy in plants and is a mixture of two polysaccharides: amylose and amylopectin
Describe the structure of starch
- Insoluble = no osmotic effect on cells
- Large = does not diffuse out of cells
Describe the structure of amylose
- Unbranched chain of glucose molecules joined by 1,4 glycosidic bonds
- Coiled, therefore very compact = storing lots of eneryg
Describe the structure of amylopectin
- Made up of 1,4 and 1,6 glycosidic bonds
- Branched = many terminal ends for hydrolysis into glucose
Describe the function of cellulose
Cellulose is a polymer of beta glucose which gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stems up)
Describe the structure of cellulose
- Made from 1,4 glycosidic bonds
- Straight-chain, unbranched molecule
- H-bond crosslinks between parallel strands form microfibrils = high tensile strength
Describe the Benedict’s test for reducing sugars
- Add an equal volume of Benedict’s reagent to a food sample
- Heat the mixture in an electric water bath at 100 degrees Celsius for 5 minutes
- Positive result: colour change from blue to orange and brick-red precipitate forms
Describe the Benedict’s test for non-reducing sugars
- Negative results: Benedict’s reagent remains blue
- Hydrolyse non-reducing sugars e.g. sucrose into their monomers by adding 1cm3 of HCl. Heat in a boiling water bath for 5 minutes
- Neutralise the mixture using sodium carbonate solution
- Proceed with the Benedict’s test as usual
Describe the test for starch
- Add iodine solution
- Positive result: colour change from orange to blue-black
Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch
- Make standard solutions with known concentrations. Record absorbance or % transmission values
- Plot calibration curve: concentration (x-axis)
- Record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration
