Monomers, Polymers and Carbohydrates

• Monomers are smaller units that join together to form larger molecules, including monosaccharides (glucose, fructose, galactose), amino acids, and nucleotides.
• Polymers are molecules formed when many monomers join together, including polysaccharides, proteins, and DNA/RNA.
• In a condensation reaction, a chemical bond forms between two molecules and a molecule of water is produced.
• In a hydrolysis reaction, a water molecule is used to break a chemical bond between two molecules.
• The three hexose monosaccharides are glucose, fructose, and galactose, all with the molecular formula C6H12O6.
• The type of bond formed when monosaccharides react is a (1,4 or 1,6) glycosidic bond.
• Disaccharides form through a condensation reaction that forms a glycosidic bond between two monosaccharides.
• The molecular formula of sucrose, maltose, and lactose are all C12H22O11.
• Colorimetry can be used to give qualitative results for the presence of sugars and starch by making standard solutions with known concentrations, recording absorbance or % transmission values, plotting a calibration curve: absorbance or % transmission (y-axis), concentration (x-axis), recording absorbance or % transmission values of unknown samples, and using the calibration curve to read off concentration.
• The test for starch involves adding iodine solution, if there is a colour change from orange to blue-black, it is positive, if not, it is negative.
• Benedict’s test for non-reducing sugars involves heating a sample in an electric water bath at 100 ℃ for 5 mins, if there is no colour change, it is negative, if there is a colour change, it is positive.
• Amylose is a storage polymer of α-glucose in plant cells, it has 1,4 glycosidic bonds, is helix with intermolecular H-bonds, and is compact.
• Cellulose is a polymer of β-glucose that gives rigidity to plant cell walls, prevents bursting under turgor pressure, and holds stem up.
• Amylopectin is a storage polymer of α-glucose in plant cells, it is insoluble, does not diffuse out of cells, and has 1,4 & 1,6 glycosidic bonds.
• Glycogen is the main storage polymer of α-glucose in animal cells and is also found in plant cells.
• Benedict’s test for reducing sugars involves heating a sample in an electric water bath at 100 ℃ for 5 mins, if there is a colour change from blue to orange and a brick-red precipitate forms, it is positive, if not, it is negative.
• Disaccharides are formed from two monosaccharide units joined together by glycosidic bonds, which can be cleaved to form the original monomers.