Carbohydrates and Monosaccharides Overview

Carbohydrates

• Carbohydrates have similar atomic compositions (CnH2nOn) but varying sizes and functions.
• Their structure involves carbon bonded to hydrogen atoms and hydroxyl groups.
• Key biochemical roles include storing energy, transporting stored energy, and serving as carbon skeletons.
• Categories based on monomer number: monosaccharides (one), disaccharides (two), oligosaccharides (3-20), and polysaccharides (hundreds/thousands).

Monosaccharides

• General formula CnH2nOn; cannot be hydrolyzed further.
• Properties include sweetness, colorlessness, and crystallinity at room temperature.
• Structure: linear carbon skeleton with a carbonyl group (C=O) and hydroxyl groups (OH).
• Carbon atoms numbered from the carbonyl end.
• Classified as aldoses (aldehyde at position 1) or ketoses (ketone between carbons).
• Vary in the number of carbon atoms (trioses, tetroses, pentoses, hexoses, etc.).
• Simplest: glyceraldehyde (a triose aldose).
• Chiral centers (C atom with 4 distinct atoms bonded) lead to optical isomers (D/L).
• Multiple chiral carbons in larger monosaccharides create many stereoisomers (2^n where n is the number of chiral carbons).
• Structural isomers (same formula, different structure) are possible, with altered properties.

Hexoses

• Group of structural isomers (C6H12O6).
• Glucose: an aldohexose, existing in linear and cyclic forms.
• Cyclic forms: hemiacetals (from aldehydes) or hemiketals (from ketones).
• Two types of glucose ring: α (OH group down) and β (OH group up).
• Fructose: a ketohexose, forming a cyclic structure through a hydroxyl attack on the ketone.

Pentoses

• Ribose: component of RNA.
• Deoxyribose: component of DNA (lacks oxygen at carbon 2).

Reactions of Monosaccharides

• Fehling's Reaction: A reducing sugar reacts with an oxidizing agent (copper) to form a reduced product.

Glycosidic Linkages

• Disaccharides, oligosaccharides, and polysaccharides are formed from monosaccharides linked by glycosidic linkages.
• Formed via condensation reactions (water released) when an hydroxyl group attacks an anomeric carbon, creating an acetal linkage.
• Acetal linkage is less reactive, thus making disaccharides more stable.

Disaccharides

• Formed by linking monosaccharides via glycosidic bonds.
• Common linkages between C1 of one monosaccharide and C4 of the adjacent.
• Specific examples: maltose (α-1,4 link between two α-glucose), cellobiose (β-1,4 link between two β-glucose), sucrose (glucose + fructose), lactose (galactose + glucose).

Oligosaccharides

• Contain 3 to 20 monosaccharides linked by glycosidic bonds.
• Often covalently bonded to proteins and lipids.

Lipids

• Diverse group of non-polar molecules soluble in nonpolar solvents.
• Categorized into saponifiable (contain hydrolyzable fatty acids) and nonsaponifiable (no fatty acids).
• Hydrophobic nature leads to aggregation in nonpolar environments.
• Key roles in energy storage, structure, light capture, hormone/vitamin roles, and nervous system insulation.

Triglycerides

• Fats and oils composed of glycerol and three fatty acids linked by ester linkages.
• Fatty acids: carboxyl group and a long hydrocarbon chain.
• Saturated: single bonds, tightly packed, high melting point.
• Unsaturated: one or more double bonds, causing kinks, low melting point.
• Melting point/fluidity influenced by chain length and saturation level.

Phospholipids

• Contain glycerol, two fatty acids, and a phosphate group linked by ester linkages.
• Phosphate head is hydrophilic; fatty acid tails are hydrophobic.
• Form bilayers in water, with tails facing inward and heads outward.

Carotenoids

• Light-absorbing pigments; β-carotene converts to Vitamin A.
• Contribute colors to plants and animals.
• Involved in light trapping/photosynthesis.

Steroids

• Four interconnected carbon rings; cholesterol is an example.
• Synthesized by animal cells and serve various functions.

Vitamins

• Essential organic molecules not synthesized by the body.
• Examples include Vitamin A (derived from β-carotene), D, E, K.

Waxes

• Secreted by glands to coat hair, repelling water and maintaining flexibility.
• Composed of a saturated fatty acid and a saturated alcohol joined by an ester linkage.

Nucleic Acids

• Polymers for storage, transmission, and use of genetic information.
• Two types: DNA and RNA.

Nucleotides

• Building blocks of nucleic acids, each comprising a nitrogenous base, a pentose sugar, and one to three phosphate groups.
• Bases categorized as pyrimidines (single ring) or purines (double ring).
• Formation of nucleic acids through phosphodiester linkages between the 5' carbon of one nucleotide and the 3' carbon of the next.
• Directionality of nucleic acid growth is 5' to 3'.

DNA and RNA

• DNA: double helix structure, with complementary base pairing (A-T, C-G).
• RNA: single-stranded, with complementary base pairing (A-U, C-G), though base pairing within the same molecule can also occur.
• Different types (mRNA, tRNA, rRNA) with varied roles.

Other Nucleotides

• ATP and GTP: energy carriers in biochemical reactions.
• cAMP: involved in signal transduction.

This quiz covers the fundamental concepts of carbohydrates, highlighting their structure, biochemical roles, and classifications. Special focus is given to monosaccharides, including their properties, structures, and types based on the number of carbon atoms. Test your knowledge on these essential biomolecules.