Macromolecules - Carbohydrates PDF

Lesson 2: Macromolecules - Carbohydrates Define and identify monosaccharides, disaccharides, and polysaccharides through molecular structures and chemical formulas. - 1. Monosaccharides - Definition: Monosaccharides are the simplest form of carbohydrates, consisting o...

Lesson 2: Macromolecules - Carbohydrates Define and identify monosaccharides, disaccharides, and polysaccharides through molecular structures and chemical formulas. - 1. Monosaccharides - Definition: Monosaccharides are the simplest form of carbohydrates, consisting of a single sugar unit. They are the building blocks of more complex carbohydrates. - Molecular Structure: Monosaccharides typically have a backbone of 3-7 carbon atoms, each with a hydroxyl group (–OH) attached, and either an aldehyde group (–CHO) or a ketone group (C=O) at one end. - Common Examples: - Glucose: C₆H₁₂O₆ – A hexose (6-carbon) sugar and the primary energy source in cells. - Fructose: C₆H₁₂O₆ – Another hexose sugar, structurally different from glucose, found in fruits. - Galactose: C₆H₁₂O₆ – Similar to glucose, it is commonly found in milk. - 2. Disaccharides - Definition: Disaccharides consist of two monosaccharides joined together by a covalent bond known as a glycosidic bond, which forms through a dehydration synthesis reaction (removal of water). - Molecular Structure: Disaccharides are formed by linking two monosaccharides via an oxygen bridge, with the general formula C₁₂H₂₂O₁₁ for most common disaccharides, since a molecule of water (H₂O) is lost during bonding. - Common Examples: - Sucrose (table sugar): C₁₂H₂₂O₁₁ – Formed from glucose and fructose. - Lactose (milk sugar): C₁₂H₂₂O₁₁ – Formed from glucose and galactose. - Maltose (malt sugar): C₁₂H₂₂O₁₁ – Formed from two glucose molecules. - 3. Polysaccharides - Definition: Polysaccharides are large, complex carbohydrates composed of long chains of monosaccharide units. These chains can be linear or branched and can contain hundreds to thousands of monosaccharides. - Molecular Structure: Polysaccharides are formed by repeated glycosidic linkages between monosaccharide units. Their structure varies depending on the type of glycosidic bonds and branching. - Common Examples: - Starch: (C₆H₁₀O₅)ₙ – A storage form of glucose in plants, made of amylose (linear) and amylopectin (branched). - Glycogen: (C₆H₁₀O₅)ₙ – A highly branched storage form of glucose in animals, found mainly in the liver and muscles. - Cellulose: (C₆H₁₀O₅)ₙ – A structural polysaccharide in plant cell walls, with linear chains of glucose units that form strong fibers.  - Each type of carbohydrate plays a unique role in biological systems, from immediate energy sources (monosaccharides) to energy storage (disaccharides and polysaccharides) and structural support (polysaccharides). Explain the role of carbohydrates in providing energy for cells, using examples like glucose and glycogen. - Carbohydrates are essential for providing energy to cells, as they are the primary and most readily available source of fuel. Through various metabolic processes, carbohydrates like glucose and glycogen are broken down to release energy in the form of ATP (adenosine triphosphate), which powers cellular activities. - 1. Glucose: Immediate Energy Source - Role in Cells: Glucose is the most common and primary energy source for cells, particularly in organisms that require quick energy. - Process of Energy Production: When glucose enters a cell, it undergoes glycolysis in the cytoplasm, where it is broken down into two molecules of pyruvate, releasing a small amount of ATP and NADH (an electron carrier). - Example: During intense exercise, muscle cells rapidly use glucose to meet their increased energy requirements. - 2. Glycogen: Stored Energy for Later Use - Role in Cells: Glycogen is a polysaccharide that serves as the main form of stored glucose in animals. It is primarily stored in the liver and muscle tissues. - Process of Energy Release: When blood glucose levels drop, glycogen is broken down into glucose molecules through a process called glycogenolysis. - In the liver: Glycogen breakdown releases glucose into the bloodstream, maintaining stable blood glucose levels, which provides energy for the whole body, including the brain and nervous system. - In muscles: Glycogen is broken down to provide glucose for muscle cells directly, which is critical during sustained physical activity. - Example: During fasting or between meals, the liver breaks down glycogen to release glucose, supplying energy to maintain bodily functions. Demonstrate the process of dehydration synthesis to show how monosaccharides form disaccharides and polysaccharides. - Dehydration synthesis is a chemical process in which two molecules are joined together by removing a molecule of water. This process is fundamental for building larger carbohydrates, as it allows monosaccharides to link and form disaccharides and polysaccharides. - - 1. Forming Disaccharides from Monosaccharides - Process: When two monosaccharides join, one monosaccharide loses a hydroxyl group (–OH), and the other loses a hydrogen atom (H) from its hydroxyl group. These two atoms combine to form a molecule of water (H₂O). - Glycosidic Bond: The bond that forms between the two monosaccharides is called a glycosidic bond, a type of covalent bond. - Example: Glucose + Fructose → Sucrose - Glucose (C₆H₁₂O₆) and fructose (C₆H₁₂O₆) combine, releasing one molecule of water (H₂O). - The resulting disaccharide is sucrose (C₁₂H₂₂O₁₁) with a glycosidic bond connecting the two monosaccharides. - 2. Forming Polysaccharides from Multiple Monosaccharides - Process: When multiple monosaccharides link together, the same dehydration synthesis process occurs repeatedly. Each new bond formed between monosaccharides results in the removal of one water molecule. - Polysaccharide Structure: This chain can be linear or branched, depending on the type of glycosidic bonds formed. - Example: Glucose + Glucose + Glucose … → Starch or Glycogen - Starch: In plants, many glucose molecules link together in a long chain to form starch, which serves as a storage form of glucose. - Glycogen: In animals, glucose molecules form a highly branched polysaccharide known as glycogen, stored mainly in liver and muscle cells for energy. Compare the structures and functions of common polysaccharides such as starch, cellulose, and glycogen, and explain why humans can digest some but not others. - Humans can digest starch and glycogen because both have α-glycosidic bonds, which our digestive enzymes can break down into glucose. - Digestibility in Humans: Humans can digest starch because we produce the enzyme amylase, which breaks down α-1,4-glycosidic bonds in starch. This releases glucose units that can be absorbed and used as energy. - Digestibility in Humans: Humans can digest glycogen easily using enzymes that break α-1,4 and α-1,6 bonds, similar to those in starch. This makes glycogen a readily accessible energy source. - Humans cannot digest cellulose because it has β-glycosidic bonds, which we lack the enzymes to break. Instead, cellulose serves as dietary fiber, which aids in digestive health. - In summary, the structural differences in glycosidic bonding (α vs. β) in these polysaccharides determine whether humans can digest them Describe the role of dehydration synthesis and hydrolysis reactions in the metabolism of carbohydrates - 1. Dehydration Synthesis: Building Carbohydrates - Definition: Dehydration synthesis, or condensation reaction, is the process of joining two molecules by removing a water molecule. This reaction links monosaccharides to form disaccharides and polysaccharides. - Process: In this reaction, one monosaccharide loses a hydroxyl group (–OH), while another loses a hydrogen atom (H). These atoms combine to form a molecule of water (H₂O), and the two monosaccharides are joined by a covalent glycosidic bond. - Role in Carbohydrate Metabolism: Dehydration synthesis allows cells to store glucose as polysaccharides such as glycogen (in animals) or starch (in plants). - 2. Hydrolysis: Breaking Down Carbohydrates - Definition: Hydrolysis is the process of breaking down complex molecules by adding a molecule of water. In carbohydrate metabolism, hydrolysis breaks down disaccharides and polysaccharides into simpler sugars, making them available for cellular energy. - Process: During hydrolysis, a water molecule is added to a glycosidic bond, breaking it and separating the larger carbohydrate into its smaller monosaccharide components. - Role in Carbohydrate Metabolism: Hydrolysis is crucial for releasing glucose from stored carbohydrates, providing energy for cellular processes. - Example: When energy is needed, glycogen in the liver or muscles is broken down into glucose molecules through hydrolysis, which can then be used in cellular respiration to produce ATP.