carbohydrate notes
Carbohydrates
Monosaccharides:
General formula: , indicating a 1:2:1 ratio of carbon, hydrogen, and oxygen atoms. These are the simplest form of carbohydrates, containing either an aldehyde or a ketone functional group. They serve as the building blocks for more complex carbohydrates.
Aldolases: Monosaccharides containing an aldehyde group. The anomeric carbon in aldoses is C1, the carbon derived from the aldehyde. Examples include glucose and galactose, which play crucial roles in energy metabolism.
Ketoses: Monosaccharides containing a ketone group. The anomeric carbon in ketoses is C2, the carbon derived from the ketone. Fructose, found in fruits and honey, is a common example, often sweeter than glucose.
Anomeric Carbon: The carbon derived from the carbonyl carbon (aldehyde or ketone) in the open-chain form of a monosaccharide. It is the carbon with two bonds to oxygen within the cyclic form, making it a reactive site for glycosidic bond formation.
Phosphosugars: Monosaccharides that have been phosphorylated, typically by the attachment of a phosphate group to one of the hydroxyl groups. Phosphorylation often activates sugars for further metabolic reactions, such as in glycolysis where glucose-6-phosphate is formed.
Deoxysugars: Monosaccharides in which one or more hydroxyl groups have been replaced by a hydrogen atom. A common example is deoxyribose, a component of DNA, where the 2' hydroxyl group of ribose is removed.
Aldonic Sugars: Sugars formed via the oxidation of the aldehyde group on the aldose anomeric carbon to a carboxylic acid. Gluconic acid, derived from glucose, is an example, often used in cleaning products.
Amino Sugars: Sugars in which one or more hydroxyl groups have been replaced with an amino group. Often found in glycoproteins and glycolipids, such as N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc) that are components of cell surfaces.
Configuration:
Determined by the orientation of the hydroxyl group on the second to last carbon in the linear structure; this determines whether a sugar is D or L.
D sugars: Have an R absolute configuration at the last chiral center. Most naturally occurring sugars in mammals are D-isomers.
L sugars: Have an S absolute configuration at the last chiral center. L-sugars are less common but can be found in some microorganisms and synthetic compounds.
Anomer vs Epimer:
Anomer: A specific type of stereoisomer that differs in configuration only at the anomeric carbon; this is relevant in cyclic forms of monosaccharides.
Epimer: Stereoisomers that differ in configuration at only one chiral center (other than the anomeric carbon). Examples include glucose and galactose, which differ only at the C-4 position.
Mutarotation:
The change in optical rotation because of the interconversion of α and β anomers in solution, until equilibrium is achieved. This process occurs spontaneously in water.
Alpha Anomer: The -OH group on the anomeric carbon is trans to the CH2OH group; points down on Haworth projection. In glucose, the α anomer has the -OH group at C1 pointing down.
Beta Anomer: The -OH group on the anomeric carbon is cis to the CH2OH group; points up on Haworth projection. In glucose, the β anomer has the -OH group at C1 pointing up.
Reducing vs Nonreducing Sugars:
Reducing Sugar: Sugars with a free anomeric carbon that can reduce oxidizing agents, such as silver ions in Tollens' reagent or cupric ions in Benedict's reagent. These sugars can open to form an aldehyde or ketone in solution.
Nonreducing Sugar: Sugars in which all anomeric carbons are involved in glycosidic bonds and cannot act as reducing agents. Sucrose is a common example where both anomeric carbons of glucose and fructose are involved in the glycosidic bond.
Glycosides/Glycosidic Bonds:
Glycosides/Glycosidic Bonds: Covalent bonds that link the anomeric carbon of a carbohydrate to another molecule (which may or may not be another carbohydrate). These bonds are crucial for forming disaccharides, oligosaccharides, and polysaccharides.
Formation: Formed through a reversible condensation reaction, where a molecule of water is eliminated. This reaction is catalyzed by enzymes known as glycosyltransferases.
Breaking: Broken via a reversible hydrolysis reaction, where a molecule of water is added. This reaction is catalyzed by glycosidases or hydrolases.
Disaccharides:
Carbohydrates composed of two monosaccharides linked via a single glycosidic bond. They must be broken down during digestion to be absorbed.
Examples: maltose (glucose + glucose), sucrose (glucose + fructose), lactose (galactose + glucose). Each is digested by a specific enzyme: maltase, sucrase, and lactase, respectively.
Polysaccharides:
Complex carbohydrates consisting of multiple monosaccharides linked together to form long chains; this decreases glucose molarity and osmotic effects within cells, making them suitable for storage and structural roles.
Types: amylose, amylopectin, glycogen, starch, cellulose. These differ in the types of glycosidic bonds, the degree of branching, and their overall structure.
Glycogenin: A protein that serves as the primer for glycogen synthesis; glucose molecules are attached to glycogenin, which then extends the glycogen chain. Glycogenin remains at the core of the glycogen granule.
Amylose: A linear polymer of glucose units linked by α-1,4 glycosidic bonds; it forms a helical structure and is one of the two main components of starch.
Amylopectin: Highly branched polymer of glucose units, with α-1,4 glycosidic bonds in the main chain and α-1,6 glycosidic bonds at the branch points. The branching allows for quicker glucose release.
Glycogen: The main storage form of glucose in animals; similar