Biology Chapter on Eukaryotic Cells

BY451: Introduction to Microorganisms and Plants

• Course code: BY451
• Module lecturer: Dr lan Cooper
• Teaching team member: Dr Maureen Berg

Today's Learning Objectives

• Understand fundamental properties of life
• Understand processes for life evolving on Earth
• Understand the concept of SET
• Know the differences between Prokaryotes and Eukaryotes
• Understand the timeframe for life diversification on Earth
• Understand taxonomic hierarchy
• Grasp binomial nomenclature
• Learn how to use dichotomous keys

All Living Organisms Have

• Cellular Organization
• Metabolism
• Homeostasis
• Growth and Development
• Reproduction (Heredity)
• Responsiveness/Interactions
• Evolution

Hierarchical Organization of Organisms

• All organisms are made of one or more cells
• There is a hierarchy of cell organization (atoms, molecules, macromolecules, cells, tissues, organs, organ systems, organisms, populations, communities, biosphere)

Fundamental Properties of Life

• Organic Composition
• Metabolism: Obtaining and using energy. Includes anabolism (building complex molecules) and catabolism (breaking down complex molecules).
• Growth and Reproduction
• Ability to Respond
• Ability to Evolve and Adapt
• Homeostasis: Maintaining stable internal conditions (e.g., temperature, fluid balance) within limits.

Reproduction and Heredity

• Reproduction is crucial for species continuation.
• Heredity involves passing traits from parents to offspring via genes (DNA, mutations).
• Evolution results in population changes over time, leading to diverse life forms.
• Traits are passed on genetically.
• Overproduction of offspring and variation are key drivers of evolution.
• Changing survival pressures drive adaptation and evolution.

Summary of Fundamental Properties of Life

• Cellular organization: Living things are made of cells.
• Metabolism: Organisms break down substances and build new ones.
• Homeostasis: Organisms maintain stable internal conditions.
• Growth and development: Organisms increase in size and complexity.
• Reproduction/Heredity: Organisms create new individuals.
• Responsiveness/Interactions: Organisms react to their environment.
• Evolution: Organisms change over time.

View of Most Scientists Regarding the Origin of Life

• The universe began with the Big Bang
• Earth is 4.55 billion years old
• Life arose on Earth spontaneously
• Earliest life forms were bacteria (3.5 billion years ago)
• Genetic drift and natural selection led to changes in populations
• Millions of species have evolved over billions of years
• All life is cellular

Life: Geological Time Scale

Lots of Fossil Evidence for Life, but How Did Life Evolve?

• Primitive Earth's chemicals combined to form organic molecules.
• Organic molecules formed primitive cells (proto-cells).
• Primitive cells evolved into true cells.

Evidence That Organic Molecules Could Form Spontaneously

• Miller-Urey experiments demonstrated the formation of organic compounds (e.g., amino acids) from inorganic gases and electricity.

Process from Inorganic Compounds to Building Blocks of Life for Polymers

• The origins of organic molecules
• Formation of organic polymers
• Discovery of alkaline vents and the similarity with the "proton pump"
• The origin of RNA replication and work with the RNA world

Chemical Evolution

• Ongoing debate about the actual path of chemical evolution (e.g., which came first: RNA or proteins).
• RNA world hypothesis suggests that self-replicating RNA molecules were early forms of life.
• Protein world hypothesis suggests that proteins, crucial for metabolism, were paramount.
• Peptide-nucleic acid world hypothesis proposes an intermediate stage between RNA and protein.
• Organic molecules from space (e.g., meteorites containing organic molecules like amino acids) may have contributed to the development of life.

Current Suggestion of the Timeline

A flow chart showing the proposed timeline of the evolution of life.

Comparison of Two Possible Views for the Path to Protocellular Structures

• The "biopolymer first" theory suggests self-replicating RNA or proteins came first
• The "lipid world" theory proposes that lipid-like molecules spontaneously assembled first, and led to the capability for dynamic self-organization and compositional inheritance.

Example of How Life Could Have Evolved in Alkaline Hydrothermal Vents

• Prebiotic synthesis may have occurred in alkaline hydrothermal vents
• Key aspect: chemical reactions might occur at hydrothermal vents

Early Cellular Life Evolved Into More Complex Life Forms

Achaea

• Defined as extreme-condition prokaryotes.
• Lack peptidoglycan in cell walls.
• Diverse metabolisms, including methane production and oxidizing.
• Thought to have diverged from bacteria ~2 billion years ago.

Bacteria

• Second major group of prokaryotes.
• Strong cell walls.
• Simpler gene structure.
• Includes many modern prokaryotes.
• Includes photosynthetic bacteria (cyanobacteria).

Prokaryotes vs. Eukaryotes

• Prokaryotes are single-celled organisms without membrane-bound organelles.
• Eukaryotes contain a nucleus and membrane-bound organelles.
• Eukaryotes likely arose through endosymbiosis (a mutually beneficial relationship) where one cell lived inside another.

Energy-Producing Bacteria and Endosymbiotic Relationship

• Certain bacteria were engulfed by larger cells, leading to a symbiotic relationship giving rise to organelles like mitochondria and chloroplasts.

Evidence of Endosymbiosis

• Organelles (like mitochondria and chloroplasts) have their own DNA and reproduce independently.
• Organelles are composed of a peptidoglycan cell wall.
• Organelle ribosomes are similar to those in bacteria.

Great Oxidation Event

• A period in Earth's history where the atmosphere transitioned from oxygen-poor to oxygen-rich.
• Photosynthesis is a key driver in this event.

Earth is Very Old, Providing Plenty of Time For Evolution to Occur

• Geological time gives ample time for evolution
• Continental drift fostered the diversity of life forms over time.

Promotion of Biodiversity

• Earth's age and geological processes have contributed to biodiversity

The Diversity of Life

• Display of diverse life forms.

Finding Order in Diversity

• Biologists have identified and named about 1.7 million species.
• Many more species remain to be discovered.
• Organising, naming, and classifying species based on shared characteristics is useful

Approaches to Classifying Organisms

• Historical approaches to classifying organisms, including taxonomic levels.
• The concept of Domains (Bacteria, Archaea, Eukarya) as a more contemporary approach.

Evolutionary Trees of Life (Tree of Life)

• How different organisms relate to each other based on rRNA sequencing and evolutionary relationships.

Hierarchical Classification

• "Did King Philip Come Over For Gumbo Sunday?" (memorizing taxonomic order)
• Taxon: the named taxonomic group at different levels
• Panthera pardus. Example of a species name (Genus species)

Linnaeus's System of Classification

• Species (basic unit; organisms that can reproduce)
• Genus (group of similar species)
• Family (group of similar genera)
• Order (group of similar families)
• Class (group of similar orders)
• Phylum (group of similar classes)

Systematics, Taxonomy, and Phylogenetics

• Taxonomy: naming and classifying organisms
• Systematics: classifying organisms according to their evolutionary relationships
• Phylogenetics: reconstructing evolutionary relationships among organisms

Binomial Nomenclature

• Standard naming system using two parts (Genus species).
• Developed by Carolus Linnaeus, used to prevent confusion using common names.
• Genus name is capitalized, species is lowercase and italicized.

Dichotomous Keys

• A tool for identifying organisms based on contrasting characteristics.
• Couplets: pairs of statements with choices (yes/no) to guide through the key identifying the organism.

Using a Dichotomous Key

• Follow steps in the key for identification of organism.

Identification Solution

• Result of using a dichotomous key for identification of organism.

Quiz 4: Identifying Organisms using Taxonomic Keys - Summary Questions

• What are some of the benefits/purposes of dichotomous keys?
• The two part naming system for classifying species is binomial nomenclature.
• In a dichotomous key, what's the first step to take?

Additional Information: Geological Timeframes

• Geological eras (eons), their sequences, and subdivisions.
• Understanding the relationship between epochs, periods, and eras.

Life: Geological Time

Hadean Eon

• Conditions on early Earth (molten rock, lack of oxygen).
• Formation of the Solar System, Earth and Moon.

Archaean Eon

• Early Earth's crust
• Possible traces of life's origin.

Proterozoic Eon

• Evolution of life
• First signs of oxygen in the atmosphere

Phanerozoic Eon

• Age of visible life
• Diversification of life forms including animals.

Test your knowledge on the origin and classification of eukaryotic cells. This quiz covers key concepts such as the Endosymbiont Theory, genetic variation, and the hierarchical system of classification. Perfect for biology students looking to deepen their understanding of cell biology.