Carbohydrates Flashcards
What happens in a condensation reaction?
a chemical bond forms between 2 molecules and a molecule of water is produced
What happens in a hydrolysis reaction?
a water molecule is used to break a chemical bond between 2 molecules
What’s the difference between a disaccharide and polysaccharide?
disaccharide - 1 chemical bond and 2 monomers
polysaccharide - many chemical bonds and multiple monomers
What’s the name for 1 chemical bond and 2 monomers?
disaccharide
What’s the name for many chemical bonds and multiple monomers?
polysaccharide
What type of bond forms between monosaccharides?
glycosidic (1,4 or 1,6)
How do disaccharides form?
When a condensation reaction forms a glycosidic bond between 2 monocsaccharides
What are 3 disaccharides?
maltose, sucrose, lactose
What monosaccharides make up maltose?
glucose + glucose
What monosaccharides make up sucrose?
glucose + fructose
What monosaccharides make up lactose?
glucose + galactose
Draw the structure of alpha-glucose
(look at notes)
Draw the structure of beta-glucose
(look at notes)
What is starch?
storage polymer of alpha-glucose in plant cells
What are 2 functions of starch?
insoluble - no osmotic effect on cells
large - does not diffuse out of cells
What are the 2 types of starch?
amylose and amylopectin
What is the structure of amylose?
1,4 glycosidic bonds
H-bonds = compact
Describe amylopectin
1,4 and 1,6 glycosidic bonds
branches = many terminal ends for hydrolysis into glucose
What is glycogen?
main storage polymer of alpha-glucose in animal cells (also found in plant cells)
What bonds does glycogen contain?
1,4 and 1,6 glycosidic bonds
What are the structures related to their functions of glycogen?
branched = many terminal ends for hydrolysis
insoluble = no osmotic effect
large = does not diffuse out of cells
compact
What is cellulose?
polymer of beta-glucose
What is the function of cellulose?
keeps plant cell walls rigid as it:
- prevents bursting under turgor pressure
- holds stem up
H-bond crosslines between parallel strands form microfibrils = high tensile strength
What is the structure of cellulose?
1,4 glycosidic bonds
straight-chained, unbranched molecule
alternate glucose molecules are rotated 180 degrees
What is the test for reducing sugars?
benedict’s test
What is the benedict’s test for reducing sugars
1) add an equal volume of benedict’s reagent to a sample
2) heat mixture in an electric water bath at 100 degrees for 5 mins
3) positive result = blue to orange/brick-red
What is the test for non-reducing sugars?
benedict’s test
What is the benedict’s test for non-reducing sugars?
1) hydrolyse non-reducing sugars by adding 1cm3 of hydrochloric acid
2) heat in boiling water bath for 5 mins
3) neutralise mixture using sodium carbonate solution
4) proceed with benedict’s test as usual
How do you test for starch?
1) add iodine solution
2) positive result = orange to blue-black
How can colorimetry be used to show presence of sugars and starch?
(5 points)
1) make standard solutions with known concentrations
2) record absorbance or % transmission values
3) plot calibration curve (y = absorbance/% transmission, x = concentration)
4) record absorbance or % transmission values of unknown samples
5) use calibration curve to read off concentration
How do beta-glucose and alpha-glucose differ structurally?
alpha-glucose OH group on C1 is below plane whilst beta-glucose OH group on C1 is above plane
