MCAT Biochemistry: Mastering Carbohydrate Structures and Functions

Carbohydrates are classified based on the number of carbon atoms they contain, with trioses, tetroses, pentoses, and hexoses representing carbohydrates with 3, 4, 5, and 6 carbon atoms respectively. Heptoses, octoses, and nonoses do not exist as classifications for carbohydrates.

Maltose is composed of two glucose molecules linked together in an α-1,4 glycosidic bond. Fructose, sucrose, and lactose have different chemical structures and compositions.

A ketose is a type of carbohydrate that contains a ketone as its most oxidized functional group, distinguishing it from aldose which contains an aldehyde group.

A glycosidic linkage specifically refers to a bond involving carbohydrates, not proteins, lipids, DNA, or RNA.

Hemiacetals are formed when aldehydes react with alcohols. The correct term for the hemiacetal formed from an aldehyde is glycoside. Ketone, ester, and amide refer to different functional groups and are not applicable in this context.

Acetals are formed when an aldehyde reacts with an alcohol, resulting in the formation of a new carbon-oxygen-carbon linkage. This differentiates them from ethers, ketones, and hemiacetals.

A furanose ring is a term commonly used in biochemistry to describe the five-membered ring structure that is commonly found in carbohydrates such as sugars. The ring is formed when a hydroxyl group from the fifth carbon in a six-carbon sugar molecule reacts with the aldehyde or ketone group on the first carbon, resulting in the formation of the cyclic structure. This unique ring structure plays a crucial role in the biological functions of carbohydrates.

Aldonic acids specifically refer to oxidized aldoses, not monosaccharides with sulfur-containing functional groups, carbohydrates that have undergone polymerization, or lipids that have been enzymatically hydrolyzed.

Lactone specifically refers to the formation of a cyclic ester from an aldose in ring formation. The cyclic ester formed has a carbonyl group on the anomeric carbon due to oxidation.

Phosphorylation is a chemical reaction that involves the addition of a phosphate group to a molecule, typically a sugar molecule with the help of ATP. It is not the addition of a lipid molecule to a protein, removal of a phosphate group, or the conversion of a sugar into a lipid molecule.

Sucrose is composed of one molecule of glucose linked to one molecule of fructose through an α-1,2-glycosidic bond.

Lactose is a disaccharide composed of one galactose and one glucose molecule linked by a β-1, 4 glycosidic bond.

Mutarotation is a specific phenomenon observed in cyclic compounds involving the shift between different anomeric forms, typically with the straight-chain form as an intermediate. It is not a general term for chemical reactions, rearrangement of atoms, or changes in state of matter.

D-glucose and L-glucose are enantiomers because they are non-superimposable mirror images of each other, with opposite configurations at every chiral center.

The correct formula for calculating the number of possible stereoisomers (enantiomers & diastereomers) of a compound is 2^n, where n is the number of chiral centers in the compound. This formula is derived from the fact that each chiral center can exist in two possible configurations, giving rise to 2^n stereoisomers. The three incorrect answers provided do not accurately represent the relationship between the number of chiral centers and the number of possible stereoisomers.

In a hemiketal, one of the alcohol groups is derived from the ketone, while the other alcohol group is added during the formation process.

When a ketal is formed from a ketone, it is known as an acetal. Acetals are formed by the reaction of a ketone or aldehyde with a diol.

A pyranose ring is a common structure found in carbohydrates, specifically in monosaccharides like glucose and fructose. It is essential for understanding the structure and function of sugars in biochemistry.

Anomers are a type of epimer, which are diastereomers that differ in configuration at a single stereogenic center. In the case of α-anomer and β-anomer, the key difference lies in the orientation of the hydroxyl (OH) group at the anomeric carbon (C-1).

Absolute Configuration refers to the specific spatial arrangement of atoms or groups in a chiral molecule, particularly around a chiral carbon atom. It is crucial in understanding the stereochemistry of organic molecules.

Deoxy sugars are sugars in which a hydroxyl group (-OH) is replaced by a hydrogen atom (-H). This modification results in a different structure and properties compared to regular sugars.

A homopolysaccharide is made up of a single type of sugar units, while a heteropolysaccharide consists of multiple types of sugar units.

In biochemistry, chiral molecules are typically designated as D or L based on their stereochemistry, rather than using the R & S system commonly used in organic chemistry.

Epimers are specifically defined as diastereomers that differ in configuration at only one chiral center, distinguishing them from other types of stereoisomers.

Glycoside formation is essential for the construction of complex carbohydrates by linking the anomeric carbon of a sugar molecule to another sugar molecule. This process plays a crucial role in creating the structural diversity of carbohydrates in living organisms.

An aldose is a type of carbohydrate characterized by the presence of an aldehyde group as its most oxidized functional group. This differentiates aldoses from ketoses, which have a ketone functional group as their most oxidized group.

Tollen's and Benedict's reagents are commonly used in detecting reducing sugars through oxidation reactions. Litmus reagent, Barfoed's reagent, and Fehling's reagent are not specifically designed for detecting reducing sugars in the same way.

Sugars can form esters by reacting with carboxylic acids and their derivatives through an esterification reaction. Carboxylic acids have a -COOH functional group that reacts with the hydroxyl group (-OH) in the sugar molecule to form an ester bond.

The correct answer refers to the orientation of the OH group on the bottom chiral center of a carbohydrate molecule, which determines whether it is classified as D or L.

Reducing sugars are carbohydrates that have a free aldehyde group or free ketone group. Monosaccharides with hemiacetal rings have a free aldehyde group, making them reducing sugars.