BIOL 215 Lecture 1

Characteristics of Living Things

• There are 9 main characteristics of living things:   * Organization of structures   * Evolution of populations   * Having DNA   * Ability of reproduction   * Growth/Development   * Response to Environment   * Metabolism   * Maintaining homeostasis   * Contains one or more cells
• A considerable debate is if viruses are living organisms are not → the consensus has become chiefly that they are not   * This is because they don’t always possess DNA genomes and cannot reproduce on their own   * The only characteristics of life they possess are the evolution of populations and organization of structures
• Viruses are very relevant to COVID-19   * COVID-19 stands for Coronavirus Disease 2019   * $SARS-CoV-2$: Severe Acute Respiratory Syndrome Coronavirus 2, the virus that causes COVID-19

History of Cell Biology

1. $Zacharias Jansen$ invented the first microscope in the late 1500s.
2. $Robert Hooke$ published Micrographia and coined the term “cell” to describe the compartments he saw in cork slices in 1665.
3. $Antonie van Leeuwenhoek$ improved lens quality and observed living cells in the late 1600s.
4. The compound microscope was invented and lens quality improved in the 1830s.
5. $Robert Brown$ found the nucleus in 1831.
6. $Theodor Schwann$ and $Matthias Schleiden$ put forth their cell theory in $1838$

       1. Their cell theory had three tenets:

             1. The cell is a unit of structure, function, and organization in all living things       2. The cell is both a distinct entity and a building in making organisms       3. Cells form by free cell formation, similar to how crystals form

7. $Rudolf Virchow$ revised the third tenet of the cell theory to say that all cells come from pre-existing cells in 1855
8. The Miller-Urey experiment performed by $Stanley Miller$ and $Harold Urey$ suggested organic compounds can be formed in abiotic conditions in 1953.

Early Life and the Miller-Urey Experiment

Early Earth and the Evolution of the First Cells

• The four steps that led to the evolution of the first cells in order were:   * Abiotic synthesis of simple organic compounds   * Abiotic synthesis of organic macromolecular polymers   * Evolution of an information storage molecule capable of replication   * Formation of a membrane surrounding the information storage molecule
• The atmosphere of early earth was much different than it is today   * The atmosphere of early earth was made of mostly reduced gases like Hydrogen gas (H2), Methane (CH4), Ammonia (NH3), and Water Vapor (gaseous H2O)   * The current composition of the atmosphere is 78% Nitrogen gas (N2), 21% Oxygen gas (O2), 0.9% Argon (Ar), and 0.1% other gases     * These other gases include Carbon Dioxide (CO2), Water Vapor (H2O), Neon (Ne), Helium (He), and Ozone (O3)

The Miller-Urey Experiment

• This experiment tested the hypothesis that lightning energy powered the formation of simple organic compounds from reduced atmospheric gases.
• They tried to replicate early earth conditions by exposing a mixture of gases that was like the types and proportions of gases found in early earth to electric discharge.
• After conducting the experiment, they found the simple amino acids alanine and glycine after a week of exposing the gases to electric discharge.   * These results suggested organic compounds can be made in abiotic conditions

The Modern Cell Theory

• The modern cell theory still has 3 tenets:   * The cell is a building block of all living things.   * Cells can exist as a singular entity or function as a unit in making organisms.   * All cells come from pre-existing cells.

Classification of Life

• All life can be classified into one of three $domains$:   * $Eukarya$- all the eukaryotes   * $Archaea$- prokaryotic organisms including extremophiles   * $Bacteria$- prokaryotic organisms
• These three domains of life were made by biologists $Carl Woese$ and $George Fox$
• Organisms were reclassified into these three domains based on similarities in rRNA gene sequences   * rRNA gene sequences were used because:     * all living things have rRNA because all living things have ribosomes     * these gene sequences do not evolve rapidly     * in vitro replication of these sequences through PCR is easy
• After analyzing rRNA gene sequences, Woese and Fox found out about three main things   * There are 2 separate groups of prokaryotes: bacteria and archaea   * Eukaryotes and archaea are more closely related to each other than either is to bacteria   * Protists should not be in one kingdom     * $Protists$: any eukaryotes that aren’t animals, fungi, or plants     * Some protists aren’t even closely related to each other

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