Campbell+Biology+Concepts+and+Connections+9th+Ed

Evolution and Lactose Intolerance

• Lactose Intolerance: A common condition where most adult populations experience difficulty digesting milk due to a lack of lactase enzyme, leading to digestive discomfort.

• Lactase Production: Nearly all infants can digest lactose, but lactase production significantly decreases after age 2 in most populations. In the U.S., about 80% of African Americans and Native Americans, and 90% of Asian Americans, become lactase-deficient in their teenage years.

• Genetic Mutation: Certain populations maintain lactase production into adulthood because of a genetic mutation that proved advantageous in past pastoral cultures, particularly during times when milk was a staple food.

• Evolutionary Advantage: The ability to digest milk allowed specific populations, such as those in northern Europe, to obtain vital nutrients during harsh winters.

• Molecular Interactions: The digestion of lactose involves lactase (protein) acting on lactose (sugar), underpinned by genetic codes from DNA (nucleic acid), demonstrating the importance of biological molecules in evolution.

Organic Compounds Overview

Introduction to Organic Compounds (3.1-3.3)

• Importance of Carbon: Carbon's versatility in forming covalent bonds makes it central to the structure of organic compounds, which typically include hydrogen atoms.

• Organic Compounds Types:

  • Carbohydrates (3.4-3.7): Serve as energy sources and structural materials.

  • Lipids (3.8-3.11): Diverse hydrophobic molecules.

  • Proteins (3.12-3.14): Essential for numerous bodily functions.

  • Nucleic Acids (3.15-3.16): Store and transmit genetic information.

Properties of Carbon

• Carbon's Bonding Capacity: Each carbon can form four covalent bonds, allowing for diverse molecular structures (straight, branched, or ring).

• Isomers: Molecules with the same formula but different structures showcase the complexity of carbon-based life.

• Hydrocarbons: Basic organic compounds composed solely of carbon and hydrogen, foundational in biological processes.

Key Chemical Groups (3.2)

• Functional Groups: Influence molecular properties and reactivity. Key functional groups include hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), amino (-NH2), phosphate (-PO4), and methyl (-CH3).

• Hydrophilic vs. Hydrophobic: Most functional groups are hydrophilic, while methyl groups are hydrophobic and non-reactive.

Macromolecules and Polymers

Construction and Breakdown of Polymers (3.3)

• Polymers: Large molecules made from smaller units (monomers) linked through dehydration reactions (removal of water).

• Hydrolysis: The reverse process that involves breaking polymers into monomers using water, essential in digestion.

• Enzymatic Role: Enzymes facilitate both dehydration and hydrolysis reactions.

• Macromolecule Diversity: The variety of arrangements in monomer sequences leads to unique polymers across different biological functions.

Carbohydrates (3.4 - 3.7)

Monosaccharides and Disaccharides

• Monosaccharides: Simplest carbohydrates (e.g., glucose and fructose) with a formula of (CH2O)n. They serve as energy sources and can bond to form disaccharides like sucrose (glucose + fructose) or lactose (glucose + galactose).

• Health Implications of Sugar: The average American consumes excessive sugar, contributing to health issues such as obesity and cardiovascular diseases.

Polysaccharides

• Types and Functions:

  • Starch: Energy storage in plants; humans can digest it.

  • Glycogen: Energy storage in animals.

  • Cellulose: Structural component of plant cell walls; not digestible by humans, classified as dietary fiber.

  • Chitin: Structural polysaccharide in fungi and exoskeletons of arthropods.

Lipids (3.8 - 3.11)

• Characteristics: Lipids are hydrophobic, differing from other macromolecules since they are not huge polymers but share various structures and functions (fats, phospholipids, and steroids).

• Fats: Composed of glycerol and fatty acids; can be saturated (solid at room temperature) or unsaturated (liquid/oil due to double bonds).

• Health Risks of Trans Fats: Formed during hydrogenation; linked to cardiovascular diseases. Regulatory measures have been taken to reduce trans fat usage in food.

Proteins (3.12 - 3.14)

Protein Structure and Function

• Diversity of Proteins: Made from 20 different amino acids, proteins have unique shapes that determine their function, such as enzymes, structural, transport, and communication roles.

• Levels of Structure:

  • Primary Structure: Sequence of amino acids.

  • Secondary Structure: Coiling or folding patterns stabilized by hydrogen bonds.

  • Tertiary Structure: Overall 3D shape formed by interactions in the R groups.

  • Quaternary Structure: Association of multiple polypeptides.

Denaturation and Diseases

• Denaturation leads to loss of function, often due to environmental factors like temperature or pH changes, relevant in diseases caused by misfolded proteins.

Nucleic Acids (3.15 - 3.16)

Structure of Nucleic Acids

• Monomers: Nucleotides composed of a sugar, a phosphate group, and a nitrogenous base.

• DNA vs RNA: DNA is double-stranded (contains thymine), while RNA is usually single-stranded (contains uracil).

• Gene Expression: Involves the processes of transcription (DNA to RNA) and translation (RNA to protein), central to cellular function and inheritance.

Evolution of Lactase Persistence

• Discusses the genetic mutations associated with lactose tolerance across different populations, highlighting convergent evolution as adaptive responses to dietary changes.