Glicídios ou carboidratos - Aula 04 - Módulo 1: Bioquímica - Prof. Guilherme

Understanding Lactose Intolerance and Carbohydrates

The Evolution of Lactose Tolerance

• The discussion begins with the historical context of lactose tolerance, noting that around 9,000 years ago, humans primarily consumed breast milk until about two years old. After this age, lactase production (the enzyme that digests lactose) typically ceased.

• With the advent of agriculture and domestication of animals for milk production, some adults began consuming milk. However, most humans lost the ability to produce lactase after childhood.

• Individuals who could digest lactose had a survival advantage due to access to nutritious milk, while those who were intolerant faced severe health issues like dehydration from diarrhea.

• Genetic predisposition plays a role in lactose intolerance; those unable to digest lactose are descendants of populations that historically struggled with dairy consumption.

Introduction to Carbohydrates

• The speaker introduces themselves as Guilherme, a biology teacher, and connects the topic of lactose back to carbohydrates since lactose is classified as a carbohydrate or sugar.

• Clarification is provided on terminology: carbohydrates can also be referred to as sugars. This includes common sugars like table sugar and structural components like cellulose.

Understanding Sugars and Carbohydrates

• It’s emphasized that not all carbohydrates taste sweet; for example, cellulose is a carbohydrate but not sweet. The definition encompasses any compound made up of carbon and water.

• A key point is made regarding nomenclature in biochemistry: many carbohydrates end with "ose," indicating their classification as sugars (e.g., glucose, galactose).

Functions of Carbohydrates

• The speaker highlights the importance of understanding functions over rote memorization for exams like ENEM.

• One primary function of carbohydrates is energy provision; they serve as the first source cells utilize when ATP (energy currency in cells) is needed.

• Various forms of carbohydrates can be converted into glucose for energy use; examples include galactose and fructose which must be transformed before utilization.

Energy Storage in Organisms

• Carbohydrates also play a role in energy storage but are less durable than lipid reserves. They can be stored as glycogen in animals or starch in plants.

• Glycogen consists of long chains of glucose molecules stored mainly in the liver; it serves as an energy reserve when immediate sources are unavailable.

Understanding Carbohydrates and Their Functions

The Role of Energy in Germination

• A plant without leaves can still generate energy to form roots, utilizing stored starch from its seed for germination.

• Carbohydrates are often associated with weight gain; the balance between energy intake and expenditure is crucial for maintaining body weight.

Energy Sources and Weight Management

• Consuming high-energy foods like hot dogs, pizza, and soda leads to excess glucose in the bloodstream.

• When glycogen stores in the liver are full, excess glucose can be converted into fat, emphasizing the importance of physical exercise to maintain energy balance.

Structural Functions of Carbohydrates

• Carbohydrates also serve structural roles; cellulose provides rigidity to plant cell walls, while chitin forms exoskeletons in arthropods.

• These structural carbohydrates allow cells to connect and support overall plant structure.

Molecular Composition of Nucleic Acids

• Sugars are integral components of DNA and RNA, which are essential nucleic acids involved in genetic information storage.

• ATP (adenosine triphosphate), a key energy currency in cells, contains ribose sugar as part of its structure.

Classification of Carbohydrates

• Carbohydrates are classified based on their molecular size: monosaccharides (single units), disaccharides (two units), oligosaccharides (2–20 units), and polysaccharides (more than 20 units).

• Monosaccharides serve as building blocks for more complex carbohydrates; they can polymerize to form larger carbohydrate structures.

Understanding Monosaccharide Structure

• Monosaccharides have a general formula represented as CnH2nOn where n varies typically between 3 and 7.

• Examples include trioses (n = 3), tetroses (n = 4), pentoses (n = 5); these sugars play significant roles in biological processes.

Importance of Pentoses

Understanding RNA and DNA Structures

The Basics of RNA

• RNA, or ribonucleic acid, contains ribose sugar, which is crucial for its structure. It forms adenosine triphosphate (ATP), consisting of adenine linked to ribose and three phosphate groups.

Introduction to DNA

• DNA stands for deoxyribonucleic acid, which features deoxyribose sugar. This sugar is a modified form of ribose that lacks one oxygen atom (C5H10O4), contributing to the stability of the DNA structure.

• The absence of an oxygen atom in deoxyribose allows DNA to form a more stable double helix structure compared to the single-stranded nature of RNA.

Importance of Glucose

• Glucose is highlighted as the primary energy source for organisms. Its molecular formula is C6H12O6, indicating six carbon atoms, twelve hydrogen atoms, and six oxygen atoms.

• Notably, glucose shares the same molecular formula with fructose and galactose; however, their atomic arrangements differ significantly.

Structural Differences Among Sugars

• Fructose has a distinct hexagonal structure compared to glucose's pentagonal shape due to variations in carbon positioning.

• Galactose closely resembles glucose but differs in the orientation of hydroxyl groups (OH), affecting its properties despite having similar structures.

Exploring Oligosaccharides and Disaccharides

Definition and Composition

• Oligosaccharides are carbohydrates formed from a few sugar units (from two up to twenty). The term "oligo" means "few" in Greek.

Key Disaccharides

• Important disaccharides include maltose (glucose + glucose), sucrose (glucose + fructose), and lactose (glucose + galactose).

Maltose Formation

• Maltose results from starch breakdown during germination in grains like barley or wheat. This process involves breaking down long chains of glucose into smaller units.

Sucrose as Table Sugar

• Sucrose is commonly known as table sugar used in cooking; it consists of glucose bonded with fructose.

Lactose in Dairy Products

• Lactose combines glucose with galactose and is found primarily in milk products. The name "galaxy" derives from Greek meaning "milk," referencing the Milky Way galaxy's appearance.

Glycosidic Bonds

Understanding Glycosidic Bonds and Polysaccharides

Glycosidic Bond Formation

• The discussion begins with the importance of glycosidic bonds in carbohydrates, specifically how two glucose molecules can combine to form maltose.

• The process involves a hydrogen atom from one glucose molecule combining with a hydroxyl group from another, resulting in the release of water (H2O).

• This reaction is termed dehydration synthesis, as it synthesizes a new compound while losing a water molecule.

• Conversely, breaking down maltose back into glucose requires hydrolysis, which involves adding water to break the bond.

• Hydrolysis is essential for digestion and occurs when water is introduced to split larger molecules.

Characteristics of Polysaccharides

• Polysaccharides consist of long chains of monosaccharide units, ranging from 500 to 30,000 monomers.

• They are categorized into two groups: storage polysaccharides (like starch and glycogen) and structural polysaccharides (like cellulose).

Storage Polysaccharides

• Starch is commonly found in various plants and serves as an energy reserve; it's often referred to as flour derived from sources like cassava or corn.

• Plants utilize stored starch during periods without sufficient sunlight for photosynthesis, converting it back into energy when needed.

Glycogen as Energy Reserve

• Glycogen acts as an energy reserve in animals, primarily stored in the liver and muscles. It serves as a secondary source of energy when glucose levels are low.

Structural Polysaccharides

• Cellulose is highlighted as the most abundant carbohydrate on Earth, forming cell walls in plants.

• Unlike animal cells that have skeletal structures for support, plant cells rely on their rigid cell walls made up of cellulose for structural integrity.

Comparison with Fungi

Understanding Cellulose and Its Role in Nutrition

The Nature of Cellulose

• Cellulose is a type of dietary fiber that plays a significant role in our daily nutrition, despite not being digestible.

• Composed of multiple glucose units, cellulose cannot be broken down by the human digestive system, meaning it does not provide nutritional benefits directly.

Importance of Fiber in Digestion

• Although cellulose is indigestible, it is crucial for maintaining digestive health; it helps retain moisture in the intestines.

• Consuming sufficient fiber leads to bulkier stools and facilitates peristalsis—the movement that pushes waste through the intestines.

Consequences of Low Fiber Intake

• A diet low in fiber can lead to constipation as water is absorbed from feces, causing them to become hard and difficult to pass.

• Foods rich in cellulose include various vegetables and algae, which contribute positively to intestinal motility.

Chitin: A Key Structural Component

Characteristics of Chitin

• Chitin is a nitrogen-containing polysaccharide found in the cell walls of fungi and exoskeletons of arthropods.

• It differs from keratin (a protein), emphasizing the importance of distinguishing between these two substances.

Applications and Presence

• Arthropods such as insects, arachnids (like spiders), and crustaceans possess chitin-based exoskeletons that provide structural support and protection.

Hyaluronic Acid: Its Role in Aesthetics

Properties of Hyaluronic Acid

• Hyaluronic acid contains nitrogen but has a gelatinous consistency rather than rigidity; it fills spaces between cells.

Use in Cosmetic Procedures

• Commonly used for aesthetic enhancements, hyaluronic acid can smooth out imperfections without invasive surgery. It integrates well with body tissues due to its natural presence within intercellular spaces.

Final Thoughts on Life's Challenges

Perspective on Problems