carbohydrates Flashcards
monosaccharides
monomers from which larger carbohydrates are made
glucose, galactose and fructose are common monosaccharides
bonding in carbohydrates
condensation reaction between monosaccharides forms a glycosidic bond
1,4 or 1,6 glycosidic bond
disaccharides
maltose - 2 glucose
sucrose - glucose + fructose
lactose - glucose + galactose
alpha vs beta glucose
H on top - alpha
OH on top - beta
polysaccharides
glycogen and starch - condensation of alpha
cellulose - condensation of beta
starch
(alpha) glucose monomers
energy in plants
- amylose - linear, unbranched, only 1,4 glycosidic bonds - coiled and compact (helix shape) coiled for storage - compact storage molecule
- amylopectin - 1,6 and 1,4 glycosidic bonds - branched - hydrolysed more efficiently, insoluble in water, does not affect water potential of cell,
broken by amylase
blue-black with iodine
glycogen
energy store in animals - liver and muscles
(alpha) glucose monomer
- 1,4 and 1,6 glycosidic bonds
- more branches than amylopectin
- easily hydrolysed - ends available for enzymes to hydrolyse - phosphorylase kinase and glycogen phosphorylase
- insoluble in water - does not affect water potential of cells - efficient storage molecule
- coiled thus compact
cellulose
(beta) glucose monomer
1,4 bonds - no coiling or branching
- every chain forms hydrogen bonds with neighbouring chain, holding the chains together - microfibrils - resist turgor pressure
- gives rigidity to plant cell walls
- every other glucose molecule flipped 180
reducing sugars
Test for Reducing Sugars - capable of donating an electron
all (not sucrose)
• Add Benedict's reagent / solution and heat. • If reducing sugar is present, solution changes from blue to green to yellow to orange to red to brick-red / brown (depending on the concentration).
non-reducing sugars
sucrose - not capable of donating an electron
• Do the Ben test - you get a negative result. • Take a fresh sample, add dilute hydrochloric acid and heat. • Neutralise the sample by adding NaOH / NaHCO3. (Use a pH paper to ensure pH 7 is reached.) • Add Benedict's reagent / solution and heat. • If non-reducing sugar is present, solution changes from blue to green to yellow to orange to red to brick-red / brown (depending on the concentration).
For comparing solutions to determine which is more concentrated - sugar tests
• Take same volume of each sample.
• Add same volume of Benedict’s solution
• Heat at the same temperature for the same length of time.
• Compare the colours - red is more concentrated than green.
monosaccharide functions
a. alpha-glucose is the primary respiratory substrate.
b. Other monosaccharides can be isomerised to glucose and used in respiration.
c. Pentose sugars (ribose and deoxyribose) are used to synthesise nucleic acids.
d. Triose sugars (eg. Triose phosphate and glycerate phosphate) are intermediates in Respiration and Photosynthesis reactions.
e. Monosaccharides can be condensed to form disaccharides and polysaccharides.
disaccharide functions
a. Sucrose is transported to different parts of the plant in the phloem tissue.
b. Disaccharides (and polysaccharides) can be hydrolysed to release glucose for respiration.
Different mono, di and polysaccharides are used in different parts of the plant or animal for energy storage (eg. starch in root tubers like carrots; sucrose and fructose in fruit; glycogen in animals, etc)
polysaccharide functions
a. Starch (plants) and Glycogen (animals): energy storage molecules. Can be hydrolysed to release glucose for respiration.
b. Starch and Glycogen have 1,6-glycosidic bonds, therefore have branches, so efficient hydrolysis can take place.
c. Cellulose has high tensile strength: plant cell walls.
sugar functions
can be added to proteins to form glycoproteins. Glycoproteins are present on cell membrane for cell-to-cell recognition and communication.
