Carbohydrates Overview Quiz

Carbohydrates

• Carbohydrates are categorized into monosaccharides, disaccharides, and polysaccharides.
• Monosaccharides are simple sugars, disaccharides are formed from two monosaccharides, and polysaccharides are long chains of monosaccharides.
• Photosynthesis is a process where plants use sunlight to convert carbon dioxide and water into glucose and oxygen (6CO2 + 6H2O + hv → C6H12O6 + 6O2).
• Respiration is a process where cells break down glucose to release energy, producing carbon dioxide and water (C6H12O6 + 6O2 → 6CO2 + 6H2O + energy).
• Biomass stores energy as a combination of covalently bonded biomolecules and oxygen. An example is glucose.

Monosaccharides

• Monosaccharides are 3-6 carbons long and have a formula of CnH2nOn.
• They exist in various isomeric forms.
• They contain a carbonyl group (aldehyde or ketone) and several OH groups.
• Complex stereochemistry requires specialized drawing conventions.
• The n-1 carbon consistently exhibits D stereochemistry (typically R configuration).
• Examples are glucose, fructose, and galactose.
• Fischer projections are a way to represent the structure of monosaccharides.
• Haworth projections are used to represent the cyclic forms of monosaccharides.

Identifying Sugars

• Convert the molecular structure to Fischer projections to identify a sugar.
• Determine the stereochemistry of the ring by breaking the anomeric bond and rotating C6 into the ring. This identifies the spatial arrangement of the sugars

Cyclization of Monosaccharides

• Monosaccharides can convert to ring forms (5 or 6 membered).
• The conversion is reversible, creating an equilibrium in a solution.
• The cyclic forms are represented easily via Haworth projection.
• For glucose, the β-furanose form is predominately the most stable structure.
• Ribose is commonly found in nucleotides.
  • The 5-membered furanose form is more stable in Ribose than Glucose.

Nucleotides

• Ribose is a central component in nucleotides, forming the backbone of RNA and DNA.
• Nucleotides are connected via phosphate esters.

Glycosidic Bonds

• Monosaccharides link via glycosidic bonds (most common are C1-C2, C1-C4, and C1-C6).
• Two sugars can link to form disaccharides.
• Glycosidic bonds can also connect sugars to bases (nucleotides) or proteins/peptides (glycoproteins, glycopeptides).
• Examples include: the α-1,2 linkage in sucrose or the β-1,4 linkage in lactose.

Polysaccharides

• They act as energy stores and structural components.
• Examples include amylose (a plant starch)
  • Amylose is a polymer of α-glucose molecules connected by α-1,4 glycosidic bonds. The linear structure contributes to its spiral structure
• Cellulose is another important polysaccharide
  • Cellulose forms the rigid cell walls in plants.
  • It's a polymer of β-glucose molecules arranged in a straight chain via β-1,4 glycosidic bonds.
  • Cellulose is not digestible by humans, making it a significant component of dietary fiber
• Other examples include glycogen (mammals) and amylopectin (plant starch).
  • These have 1,6 linkages branching the molecules.
• Chitin is a structural polysaccharide in crab shells and fungal cell walls.
  • Chitin’s structure resembles cellulose, but it has acetamide groups on the glucose monomers.

Metabolism

• Glucose is a vital carbohydrate, used as an energy carrier and energy storage.
• Glucose metabolism (i.e., respiration) results in the production of ATP, powering various cellular processes.
• Glucose levels are controlled by specific regulatory mechanisms to avoid diabetes.