Biochemistry Quiz On Carbohydrates

Lactose is the main sugar found in milk. It is a disaccharide composed of glucose and galactose. Lactose is digested in the small intestine by the enzyme lactase, which breaks it down into its monosaccharide components for absorption. Lactose is an important source of energy for infants and young mammals. Some people have lactose intolerance, which means they lack sufficient lactase to digest lactose properly, leading to digestive discomfort.

Glucose is the most common monosaccharide found in the human body. It is a primary source of energy for cells and is essential for metabolic processes. Glucose is transported through the bloodstream to provide energy to all body tissues. It is also a building block for more complex carbohydrates like starch and glycogen. Monitoring glucose levels is crucial in managing conditions like diabetes, highlighting its importance in biochemistry and health.

Glycogen is the carbohydrate stored in the liver and muscles for energy. It is a polysaccharide composed of glucose units linked together in a highly branched structure. When the body needs energy, glycogen is broken down into glucose, which is then used in cellular respiration to produce ATP. Glycogen storage allows for quick release of glucose during physical activity or between meals, maintaining blood sugar levels and energy supply.

Amylase is the enzyme responsible for breaking down starch into simpler sugars like maltose and glucose. Amylase is produced in the salivary glands and the pancreas. When we eat starchy foods, amylase in saliva begins the digestion process in the mouth, and pancreatic amylase continues the process in the small intestine. This enzyme plays a crucial role in carbohydrate digestion, ensuring that complex carbohydrates can be converted into a form that the body can use for energy.

Carbohydrates primarily contain carbonyl (-C=O) and hydroxyl (-OH) groups, which contribute to their solubility and reactivity. The ether (-C-O-C-) group is also found in some carbohydrate structures, especially in polysaccharides. However, the sulfhydryl (-SH) group is characteristic of proteins rather than carbohydrates. It plays a key role in forming disulfide bonds in proteins, particularly in stabilizing protein structures. Since sulfur is not a standard component of carbohydrates, the sulfhydryl group is not commonly found in their molecular structure.

Glucose serves as the primary energy source for the brain because it is the most readily available monosaccharide in the bloodstream. The brain consumes about 120 grams of glucose per day, accounting for nearly 20% of the body's total energy use. Unlike other organs, the brain lacks significant energy storage and depends on a continuous glucose supply. During fasting or low carbohydrate intake, the liver converts stored glycogen into glucose. If glucose levels drop, the body shifts to ketone production, but glucose remains the brain’s preferred fuel due to its efficiency in ATP production via glycolysis and oxidative phosphorylation.

The diagram represents sucrose, a disaccharide composed of one glucose molecule and one fructose molecule. Sucrose is the common table sugar found in plants, fruits, and processed foods. It is broken down by the enzyme sucrase in the digestive system, releasing glucose and fructose for metabolism. Unlike maltose (which consists of two glucose units), sucrose has a unique glycosidic bond linking its monosaccharides. This difference in structure gives sucrose distinct chemical and physiological properties.

Chitin is a structural carbohydrate found in the exoskeleton of insects, crustaceans, and the cell walls of fungi. It is a polysaccharide composed of N-acetylglucosamine units linked by β-1,4-glycosidic bonds. Chitin provides mechanical strength and protection due to its rigid, fibrous nature. It has a high tensile strength comparable to collagen in vertebrates. When combined with proteins and calcium carbonate in crustaceans, it forms a hardened exoskeleton. Unlike cellulose, chitin is modified with nitrogen-containing groups, making it less digestible. Its applications extend to medical, agricultural, and industrial uses, including biodegradable plastics, wound dressings, and water purification materials.

Sucrose is not a monosaccharide because it is a disaccharide composed of two monosaccharides, glucose and fructose, joined together by a glycosidic bond. Monosaccharides, on the other hand, are single sugar molecules that cannot be broken down into smaller sugar units. Glucose, fructose, and galactose are all monosaccharides because they consist of a single sugar unit.

The structural diagram represents glucose, a simple sugar and monosaccharide. Glucose is an important carbohydrate in the body and is used as a source of energy. It is a hexose sugar, meaning it has six carbon atoms. The diagram shows the arrangement of the carbon, hydrogen, and oxygen atoms in glucose, with a ring structure formed by five carbon atoms and an oxygen atom.

A glycosidic bond links monosaccharides together in polysaccharides. This covalent bond forms between the hydroxyl group of one monosaccharide and the anomeric carbon of another, releasing a molecule of water. Glycosidic bonds can vary in their position and configuration, leading to different structures and properties of polysaccharides, such as starch, glycogen, and cellulose. Understanding glycosidic bonds is fundamental in biochemistry, as it explains how complex carbohydrates are built from simple sugars.

The diagram represents fructose, a monosaccharide with a five-membered ring structure. Unlike glucose, which forms a six-membered ring, fructose has a different atomic arrangement but still follows the formula C₆H₁₂O₆. Fructose is found in fruits, honey, and high-fructose corn syrup. It is metabolized differently than glucose, primarily in the liver, and has a higher sweetness level. Maltose and sucrose contain more than one sugar unit, making them disaccharides, unlike fructose, which is a single sugar molecule.

Fructose is commonly used as a sweetener in processed foods due to its high sweetness index and low glycemic response. It is about 1.2 to 1.8 times sweeter than sucrose (table sugar), making it an effective sweetener in lower quantities. High-fructose corn syrup (HFCS), a processed form of fructose, is widely used in beverages and snacks because it enhances flavor and shelf life. Unlike glucose, fructose is metabolized in the liver, where excessive intake can lead to fat accumulation, insulin resistance, and metabolic disorders, making its use in food products both beneficial and potentially harmful.

The diagram represents glycogen, the primary storage polysaccharide in animals. Glycogen is composed of highly branched glucose units, allowing for rapid energy release when needed. It is stored mainly in the liver and skeletal muscles, where it can be quickly broken down into glucose during energy demands. Unlike cellulose and chitin, which serve structural roles, glycogen functions in energy storage. Glucagon, on the other hand, is a hormone that regulates glycogen breakdown rather than being a carbohydrate itself.

Starch is the polysaccharide used by plants to store energy. It is made up of glucose units linked together and is stored in plant cells as granules. When energy is needed, plants break down starch into glucose, which can then be used in cellular respiration to produce ATP, the energy currency of cells. Starch is also an important dietary carbohydrate for humans and animals, providing a significant source of energy.

Oxygen’s electronegativity makes carbohydrates polar and water-soluble, not insoluble. Oxygen forms polar covalent bonds with hydrogen, leading to partial charges that allow carbohydrates to dissolve in water. This property enables glucose and other simple sugars to travel in the bloodstream and participate in metabolic reactions. However, large polysaccharides like starch and cellulose have reduced solubility due to extensive hydrogen bonding and structural complexity. Despite this, oxygen’s presence in hydroxyl (-OH) and carbonyl (-C=O) groups contributes significantly to the hydrophilic nature of carbohydrates.

The structural diagram represents maltose because it shows two glucose molecules linked together by a glycosidic bond. Maltose is a disaccharide composed of two glucose units, and the diagram accurately depicts this structure. Glucose is a monosaccharide, fructose is a different monosaccharide, and sucrose is a disaccharide composed of glucose and fructose. Therefore, the correct answer is maltose.