Carbohydrates and lipids
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Draw the ring structure of α-glucose.
The α-glucose ring has the -OH group on carbon 1 pointing DOWN. Note the positions of other -OH groups and the CH₂OH group.
Define the terms 'monomer', 'polymer', and 'macromolecule'.
A monomer is a small repeating unit. A polymer is a large molecule made of many monomers joined together. A macromolecule is a very large molecule, often a polymer, with a high molecular weight (
What are monosaccharides, disaccharides and polysaccharides? Provide an example of each.
Monosaccharides are simple sugars (
What type of bond joins smaller molecules to form polymers, and how is this bond formed?
Covalent bonds join smaller molecules (monomers) to form polymers. These bonds are formed through condensation reactions, where a water molecule is removed.
Which of the following are reducing sugars: glucose, fructose, maltose, sucrose?
Glucose, fructose, and maltose are reducing sugars. Sucrose is a non-reducing sugar.
Describe the formation of a glycosidic bond.
A glycosidic bond forms between two monosaccharides by a condensation reaction. An -OH group is removed from each monosaccharide, releasing a water molecule and linking the sugars together through an oxygen atom.
Give an example of the formation of a glycosidic bond with reference to sucrose.
Sucrose is formed from glucose and fructose. A glycosidic bond forms between carbon 1 of glucose and carbon 2 of fructose, with the removal of a water molecule.
Give an example of the formation of a glycosidic bond with reference to polysaccharides.
Starch is formed from many α-glucose molecules. Glycosidic bonds form between carbon 1 and carbon 4 of adjacent α-glucose molecules, linking them into a long chain with the release of water molecules.
Describe the process of hydrolysis in the context of breaking down polysaccharides and disaccharides.
Hydrolysis is the breaking of a glycosidic bond by the addition of water. A water molecule (H₂O) is added, with -H attaching to one monosaccharide and -OH to the other, separating them. This process is key in digestion and is tested for with a non-reducing sugar test (
Describe the molecular structure of starch, including amylose and amylopectin, and relate their structures to their function in energy storage.
Starch is a polysaccharide composed of glucose monomers. Amylose is a long, unbranched chain of α-glucose linked by α-1,4-glycosidic bonds, forming a helical structure. Amylopectin is branched, with α-1,4-glycosidic bonds and α-1,6-glycosidic bonds at the branch points. The compact structure allows for efficient storage of glucose.
Describe the molecular structure of glycogen and relate its structure to its function in energy storage.
Glycogen is a highly branched polysaccharide of α-glucose, similar to amylopectin but with more frequent α-1,6-glycosidic branches. This branching allows for rapid hydrolysis and release of glucose when needed, important for maintaining blood sugar levels.
Describe the molecular structure of cellulose and explain how its arrangement contributes to the function of plant cell walls.
Cellulose is a linear, unbranched polysaccharide of β-glucose linked by β-1,4-glycosidic bonds. Many cellulose chains run parallel and are cross-linked by hydrogen bonds, forming strong microfibrils. These microfibrils provide tensile strength and rigidity to plant cell walls.
Explain why triglycerides are described as non-polar and hydrophobic.
Triglycerides are non-polar due to the even distribution of electrons in their hydrocarbon chains of fatty acids. This lack of polarity makes them hydrophobic, meaning they are insoluble in water because they cannot form hydrogen bonds with water molecules.
Describe the molecular structure of a triglyceride, including its components and the type of bond formed.
Triglycerides consist of a glycerol molecule bonded to three fatty acids. The bonds are ester bonds, formed by the reaction of the glycerol's hydroxyl (-OH) groups with the carboxyl (-COOH) groups of the fatty acids, releasing three water molecules.
Relate the structure of triglycerides to their function as energy stores and insulation.
The long hydrocarbon chains of fatty acids in triglycerides are rich in chemical energy. Their non-polar nature allows them to be stored without dissolving in the aqueous cytoplasm, and their low density provides insulation.
Describe the molecular structure of phospholipids, highlighting the hydrophilic and hydrophobic regions.
Phospholipids consist of a glycerol molecule linked to two fatty acids and a phosphate group. The phosphate group is polar and hydrophilic (water-loving), forming the 'head,' while the fatty acid tails are non-polar and hydrophobic (water-repelling).
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