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Origins of Life: Unraveling the Biology of Existence ( BI100)

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Course
BI100

Institution
Wilfrid Laurier University (WLU )

Notes include: Flowcharts, images and summaries, first year biology ( BI100). Dive into the summary of biology and explore the defining characteristics of life, the debate on the classification of viruses, and the evolutionary milestones that shaped our understanding of existence. These notes i...

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Defining Life and its origins

**Living vs. Non-Living**

- Frog in pond tracking insect: Illustrates the distinction between living and non-living entities.
- Perception: Frog is alive, water is not: Common intuitive understanding of living organisms and inanimate matter.
- Question: Is water alive? Raises the intriguing possibility of water being alive due to shared atomic composition.
- Atoms are the same in living and non-living entities: Highlights the identical nature of atoms in living cells, water, and rocks.
- Living cells follow chemistry and physics laws: Emphasizes that the fundamental laws governing living cells are the same as those governing non-living entities.
- Need to define what distinguishes living from non-living: Sets the stage for discussing the criteria that differentiate life from non-life.

**NASA's Definition of Life**

- NASA's working definition: "self-sustaining system capable of Darwinian evolution": Defines life as self-sustaining and capable of undergoing Darwinian evolution,
which involves natural selection.
- Issue with NASA definition: Exceptions like sterile mules: Acknowledges limitations in the definition as certain clearly living entities, such as sterile mules, cannot
reproduce.

**Life-Like Qualities in Non-Living Entities**

- Some non-living things exhibit life-like qualities: Acknowledges that certain inanimate entities possess characteristics typically associated with life.
- Examples: Fire (reproduction and growth), mineral crystals (order): Provides specific examples of non-living entities demonstrating life-like traits, such as fire's
ability to reproduce and grow and mineral crystals maintaining ordered structures.
- Order maintenance as a key property of life (Erwin Schrödinger, 1945): Discusses Erwin Schrödinger's idea that maintaining order is a fundamental property of life.

**Recent Research and Exceptions**

- Recent research on light-driven self-organizing behaviors in "living crystals": Highlights contemporary research where light energy drives self-organizing behaviors
in particles referred to as "living crystals."
- Mention of computer viruses: reproduction and evolution: Notes that computer viruses can exhibit attributes of life, including the ability to reproduce and evolve.
These attributes will be further explored.

- **Viruses and Their Classification as Life:**
- Historical debate on whether viruses should be considered life.
- Lack of independent metabolism, respiration, or photosynthesis in viruses.
- Commonalities with life: contain nucleic acid, replicate, evolve through natural selection.
- Dependency on invading living cells (bacteria or humans) for their lifecycle.
- Lack of essential protein-making factories (ribosomes and key enzymes).
- Some categorize viruses as "not life" due to their parasitic nature.
- Comparison to Rickettsia, a bacterium considered alive despite host cell dependency.

- **Complexity of Viruses:**
- Introduction of mimivirus in 1992, initially thought to be a bacterium.
- Mimivirus is exceptionally large, observable with conventional light microscopy.
- Genome size of 1.2 million base pairs, larger than most viruses and some bacteria.
- Genome encodes over 900 proteins, including novel functions not seen in viruses.
- Presence of proteins related to protein synthesis and metabolism, characteristics of life.
- Despite its complexity, mimivirus still relies on host cell ribosomes for protein synthesis.
- Mimivirus's classification as life is still debated, as its dependence on host cell processes blurs the distinction.

Seven Characteristics Shared by All Cellular Life Forms

**Seven Characteristics of Life:**

1. **Display Order (a):**
- All life forms exhibit a highly organized structure.
- Cells are the fundamental units that demonstrate this order.

Chapter 1 Page 1

, 2. **Harness and Utilize Energy (b):**
- Life acquires energy from the environment and uses it to maintain order.
- Like a hummingbird, organisms require energy for their functions.

3. **Reproduce (c):**
- All living organisms have the ability to create offspring of their own kind.
- Bacteria division is an example of this reproductive capability.

4. **Respond to Stimuli (d):**
- Organisms can adapt their structure, function, and behavior in response to environmental changes.
- For instance, plants can adjust stomata size to regulate gas exchange.

5. **Exhibit Homeostasis (e):**
- Life can maintain a relatively stable internal environment.
- Humans sweat to dissipate heat and regulate body temperature.

6. **Grow and Develop (f):**
- Organisms increase in size or cell number.
- Many life forms undergo changes and development over time.

7. **Evolve (g):**
- Populations of organisms change across generations to better suit their environment.
- Adaptation, as seen in the snowy owl, is a result of evolutionary processes.

• One of the tenets of cell theory states that cells arise only from the growth and division of preexisting cells.
• , has probably been true for a few billion years, yet there must have been a time when this was not the case.
• There must have been a time when no cells existed, when there was no life.
• It is thought that, over the course of millions of years, cells with the characteristics of life arose out of a mixture of molecules that existed on early Earth.

Earth was formed about 4.6 billion years ago, at the same time as the rest of the planets in the solar system. The age of our planet has been arrived
at using the technique of radiometric dating, which looks at specific isotopic ratios in rocks and knowledge of their rate of decay. The decay of
uranium to lead, in particular, has been used to age Earth. To give us some sense of just how long 4.6 billion years is, as well as the relative timing
of some major events in the history of life on Earth, Figure 1.5 condenses the entire history of Earth into a unit of time that we are more familiar
with: 1 year. With 4.6 billion years condensed into a single year, each day represents an interval of 12.6 million years!

Using our condensed version of the history of Earth, we set the date of the formation of Earth as January 1 at 12:00 a.m. We will discuss this in detail later but, based on
chemical evidence, life may have started as early as 4 billion years ago. This translates to mid-March in our one-year calendar. The first clear fossil evidence of prokaryotic
cells occurs in late March, or about 3.5 billion years ago. Fossil evidence of eukaryotes has been dated to about 2 billion years ago, which is not until early July using our 1-
year analogy. Perhaps surprisingly, animals do not make an appearance until mid-October (about 525 million years ago) and land plants until the following month.

Biologically Important Molecules Can Be Synthesized outside Living Cells

- **Essential Macromolecules:**
- All organisms are composed of nucleic acids, proteins, lipids, and polysaccharides.
- These macromolecules are continually synthesized within cells through various metabolic processes.
- The origin of these molecules, necessary for life, is termed abiotic synthesis.

- **Early Earth's Atmosphere (4 billion years ago):**
- Earth was significantly different from today.
- Atmosphere included abundant water vapor, hydrogen, carbon dioxide, ammonia, and methane.
- Remarkably, there was little to no oxygen in the early atmosphere.
- Oparin and Haldane proposed that essential organic molecules could form in this environment, known as the
Oparin-Haldane hypothesis.

Chapter 1 Page 2

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