Fundamental Properties of Life and Biomolecules: Introduction to Cells CHP 2

Introduction to Biology

What Is Biology?

Biology is the scientific study of life, encompassing the structure, function, growth, origin, evolution, and distribution of living organisms. It seeks to understand how life works at all levels, from molecules to ecosystems.

Definitions of Life

Scientists and philosophers have proposed several definitions of life, focusing on its self-sustaining, replicating, and evolving nature:

• Self-sustained chemical system capable of undergoing Darwinian evolution (Joyce 1995, NASA definition)

• Self-replicating, evolving system based on organic chemistry (Page 2001)

• Vital quality distinguishing living from non-living (medical definition)

Fundamental Properties of Life

Core Characteristics

All living things share several essential properties:

• Membrane delimited: Surrounded by a selectively permeable membrane

• Cellular organization: Composed of one or more cells

• Information storage and transmission: Genetic instructions stored and followed

• Energy storage and use: Ability to store and utilize energy

• Self-replication: Capable of reproducing

• Response to environment: Regulates internal functions and adapts to external changes

• Evolution: Changes in heritable traits over generations

Biomolecules Supporting Life

Four main classes of biomolecules facilitate these properties:

• Lipids: Form membranes, store energy

• Carbohydrates: Provide energy, structural support

• Nucleic Acids: Store and transmit genetic information

• Proteins: Catalyze reactions, provide structure, regulate functions

Biomolecules and Their Functions

Lipids: Membrane Formation

Lipids are hydrophobic molecules that form the selectively permeable barriers of cells, enabling compartmentalization and protection.

• Phospholipids: Major component of cell membranes, with hydrophilic heads and hydrophobic tails

• Function: Create a boundary, regulate transport, and maintain cellular integrity

Nucleic Acids: Information Storage and Transmission

Nucleic acids, such as DNA and RNA, are polymers of nucleotides that store and transmit genetic information essential for life.

• DNA: Stores genetic instructions

• RNA: Transmits instructions and facilitates protein synthesis

Carbohydrates: Energy Storage and Structure

Carbohydrates are organic molecules composed of monosaccharides, which serve as energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose)

• Polysaccharides: Complex carbohydrates (e.g., starch, cellulose)

Proteins: Function and Response

Proteins are polymers of amino acids that perform a wide range of functions, including catalysis, structure, signaling, and response to environmental changes.

• Enzymes: Catalyze biochemical reactions

• Structural proteins: Provide support and shape

• Regulatory proteins: Control cellular processes

Energy in Biological Systems

ATP: Cellular Energy Currency

Cells convert energy from sunlight or organic compounds into ATP, a nucleotide that powers cellular work.

• ATP (Adenosine Triphosphate): Stores and releases energy for cellular processes

• Energy sources: Sunlight (photosynthesis), organic compounds (cellular respiration)

Evolution: Change Over Generations

Definition and Importance

Evolution is the change in heritable characteristics of biological populations over successive generations, driven by mechanisms such as mutation, selection, and genetic drift.

• Heritable traits: Passed from parent to offspring

• Population change: Leads to adaptation and diversity

Cells: The Fundamental Unit of Life

Cell Theory and Essential Features

Cells are the smallest units that exhibit all properties of life. All organisms are composed of one or more cells, which carry out essential functions.

• Cell theory: All living things are made of cells; cells are the basic unit of life; all cells arise from pre-existing cells

• Types of cells: Prokaryotic and eukaryotic

Prokaryotic Cells: Archaea and Bacteria

Prokaryotic cells lack a nucleus and membrane-bound organelles. They are typically small, with circular DNA and rapid replication.

• No nucleus: DNA is free in the cytoplasm

• Small size: 0.1–5 microns

• Fast replication: Efficient reproduction

Eukaryotic Cells: Membrane-Bound Nucleus and Organelles

Eukaryotic cells possess a nucleus and various membrane-bound organelles, allowing compartmentalization and specialization of functions.

• Nucleus: Contains genetic material

• Organelles: Specialized structures (e.g., mitochondria, endoplasmic reticulum)

Summary Table: Biomolecules and Properties of Life

Biomolecule	Main Function	Property of Life Supported
Lipids	Membrane formation, energy storage	Membrane delimited, energy use
Carbohydrates	Energy source, structure	Energy storage and use
Nucleic Acids	Information storage and transmission	Instruction storage, replication, evolution
Proteins	Catalysis, structure, regulation	Function control, response, replication

Class Recap/Objectives

• Practice designing controlled experiments

• Understand varying definitions of "living"

• Set up course definition of life

• Introduce biomolecules and their roles

• Recognize cells as the units of life

• Compare types of cells: prokaryotic vs. eukaryotic