Brief Summary
This video explains carbohydrates, their definition based on functional groups, and their classification based on hydrolysis and the number of carbon atoms. It clarifies that carbohydrates are polyhydroxy aldehydes or ketones, not just compounds with a 2:1 hydrogen-oxygen ratio. The video also details monosaccharides, their properties, and various types based on carbon number and functional groups, providing examples like glucose, fructose, ribose, and deoxyribose.
- Carbohydrates are defined by their functional groups (polyhydroxy aldehydes or ketones).
- Monosaccharides are the simplest sugars and are classified by carbon number and functional group.
- Examples of monosaccharides include glucose, fructose, ribose, and deoxyribose.
Introduction to Carbohydrates
The term "carbohydrate" literally means "hydrated carbon," referring to compounds of carbon, hydrogen, and oxygen with a hydrogen-oxygen ratio similar to that of water (2:1). However, this definition is not always accurate. Some compounds with a 2:1 ratio are not carbohydrates, such as lactic acid (C3H6O3), while others like deoxyribose (C5H10O4) do not have a 2:1 ratio but are still carbohydrates. The true definition of carbohydrates relies on their functional groups.
Functional Groups of Carbohydrates
Carbohydrates are defined by their functional groups, specifically polyhydroxy aldehydes or polyhydroxy ketones. A functional group gives a compound its properties. A carbonyl carbon (carbon with a double-bonded oxygen) with a hydrogen atom on one side and an R group on the other forms an aldehyde. If there are R groups on both sides of the carbonyl carbon, it forms a ketone. For a compound to be a carbohydrate, it must have many hydroxyl groups (polyhydroxy) in addition to either an aldehyde or ketone group. Examples include glucose (polyhydroxy aldehyde) and fructose (polyhydroxy ketone), which are isomers with the same molecular formula but different structures.
Classification of Carbohydrates
Carbohydrates are classified based on hydrolysis into monosaccharides, oligosaccharides, and polysaccharides. Monosaccharides are the simplest carbohydrates and cannot be further hydrolyzed into simpler sugars. They are the smallest sugar molecules and are the sweetest, with fructose being the sweetest among them. Monosaccharides are easily soluble in water and exist as white crystalline powders in dry form.
Monosaccharides: Carbon Number and Functional Groups
Monosaccharides are further classified based on the number of carbon atoms (from three to seven) and their functional group (aldehyde or ketone). Sugars with an aldehyde group are called aldoses, while those with a ketone group are called ketoses. Examples include:
- Trioses: Aldotriose (glyceraldehyde), Ketotriose (dihydroxyacetone)
- Tetroses: Aldotetrose (erythrose)
- Pentoses: Aldopentose (ribose in RNA, deoxyribose in DNA), Ketopentose (ribulose, important in photosynthesis' dark reactions)
- Hexoses: Aldo hexoses (glucose, galactose, mannose), Ketohexose (fructose)
- Heptoses: Aldoheptoses (glucoheptose, pseudoheptulose)
It is important to remember which sugars fall into each category for exam preparation.
