Lecture 2 (BES 108, OITE)

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Questions and Answers

What was the first step in the sequence of stages leading to the origin of life on Earth?

Abiotic synthesis of small organic molecules (correct)

Origin of self-replicating molecules

Packaging of molecules into protocells

Joining of small molecules into macromolecules

What was a likely composition of Earth's early atmosphere?

Water vapor and nitrogen compounds (correct)

Carbon monoxide and ozone

Methane and sulfur dioxide

High levels of oxygen and argon

What contributed to the formation of larger bodies in the solar system about 4.6 billion years ago?

The solidification of solar radiation

The collision and sticking together of particles (correct)

The retreat of the oceans back into the atmosphere

The cooling of Earth over millions of years

Why did water seas not form on Earth until about 4.2 to 3.9 billion years ago?

Oceans were vaporized due to intense heat from bombardment (C) Signup and view all the answers

What process may have allowed for the packaging of molecules into protocells?

Droplet formation with membranes (A) Signup and view all the answers

Which of the following gases was not likely present in the early atmosphere of Earth?

Ozone (B) Signup and view all the answers

What significant event marked the end of the massive bombardment of Earth?

Setting the stage for the origin of life (A) Signup and view all the answers

Which of the following best describes 'self-replicating molecules'?

Molecules that enabled inheritance (B) Signup and view all the answers

What significant environmental change occurred due to the reaction of hydrogen with oxygen?

It produced oceans that reduced the atmospheric hydrogen. (D) Signup and view all the answers

What hypothesis did A.I. Oparin and J.B.S. Haldane propose regarding the early atmosphere?

Organic compounds formed from simpler molecules in a reducing environment. (A) Signup and view all the answers

What was the aim of the Miller-Urey experiments conducted in 1953?

To demonstrate the abiotic synthesis of organic molecules in a reducing atmosphere. (D) Signup and view all the answers

According to the hypotheses about the early oceans, what metaphor was used to describe them?

A primordial soup. (A) Signup and view all the answers

Which location is speculated to be a potential site for the synthesis of organic compounds?

Near volcanoes and deep-sea vents. (A) Signup and view all the answers

What natural phenomenon is suggested to have provided energy for the synthesis of organic compounds in early Earth environments?

Lightning and UV radiation. (C) Signup and view all the answers

What unique condition exists around deep-sea alkaline vents that could assist in organic molecule synthesis?

A significant pH gradient. (C) Signup and view all the answers

What might have led to the formation of ribozymes capable of self-replication?

Natural selection on the molecular level (B) Signup and view all the answers

Amino acids and other organic molecules have been found in which source, indicating their possible extraterrestrial origin?

Meteorites. (A) Signup and view all the answers

What was likely the primary function of early RNA molecules in protocells?

Storing and replicating genetic information (C) Signup and view all the answers

What advantage did DNA provide over RNA as genetic material?

It was genetically more stable and replicated more accurately. (C) Signup and view all the answers

What does the fossil record primarily document?

Changes in the history of life on Earth. (A) Signup and view all the answers

Which factor does the fossil record bias in favor of?

Species that existed for a long time and were widespread. (C) Signup and view all the answers

What is one reason why the fossil record is considered incomplete?

Many organisms did not die in conditions suitable for fossilization. (D) Signup and view all the answers

How is the geologic record established according to the study of fossils?

By studying the strata of sedimentary rocks. (A) Signup and view all the answers

What is one characteristic of strata in sedimentary rocks in terms of fossil preservation?

They are the richest source of fossils. (A) Signup and view all the answers

What is a protocell?

A theoretical model resembling an early form of life (B) Signup and view all the answers

How do montmorillonite clay particles contribute to protocell formation?

By concentrating organic molecules on their surfaces (A) Signup and view all the answers

Which of the following is NOT a characteristic of protocells?

They have complex organelles like mitochondria (B) Signup and view all the answers

What are ribozymes?

RNA molecules that can catalyze reactions (D) Signup and view all the answers

Which statement accurately describes the formation of RNA monomers?

They can spontaneously arise from simple molecules (A) Signup and view all the answers

What role do vesicles play in the context of protocells?

They can exhibit simple reproduction and metabolism (C) Signup and view all the answers

What is the main reason conditions on early Earth facilitated RNA polymerization?

Catalytic surfaces provided by minerals (B) Signup and view all the answers

Which molecule was likely the first genetic material, according to the content?

RNA (B) Signup and view all the answers

What does radiometric dating specifically measure to determine the age of fossils?

The ratio of carbon-14 to carbon-12 (C) Signup and view all the answers

How long is the half-life of Carbon-14?

5,730 years (D) Signup and view all the answers

What element does Carbon-14 decay into?

Nitrogen-14 (B) Signup and view all the answers

What are the surrounding layers of sedimentary rocks used for in dating older fossils?

Estimating sediment ages (A) Signup and view all the answers

Which type of cells are believed to have contributed to later increases in atmospheric O2?

Eukaryotic cells containing chloroplasts (B) Signup and view all the answers

What major event is referred to as the 'oxygen revolution'?

The rise of photosynthetic prokaryotes leading to increased oxygen (D) Signup and view all the answers

What is a characteristic of half-lives of isotopes used in radiometric dating?

They are constant for each isotope (C) Signup and view all the answers

Which group of organisms was likely extinct due to the oxygen revolution?

Anaerobic prokaryotic groups (A) Signup and view all the answers

Study Notes

Lecture 2: Organisms in Their Environment

Lecture was given on January 10, 2025, in BES 108D.
The lecturer was Dr. Benazir Alam.
The topic was the history of life on Earth, focusing on prokaryotes (bacteria and archaea).

Topic 1: Prokaryotes: Bacteria and Archaea (Chapter 25)

Early Earth conditions made the origin of life possible.
Abiotic synthesis of small organic molecules (e.g., amino acids, nitrogenous bases).
Joining of these molecules into macromolecules (e.g., proteins, nucleic acids).
Encapsulation of molecules into protocells with membranes maintaining internal chemistry.
Origin of self-replicating molecules allowing inheritance.

Synthesis of Organic Compounds on Early Earth

The solar system formed 4.6 billion years ago, and early Earth was bombarded by asteroids and comets.
This bombardment vaporized water, preventing oceans from forming until 4.2-3.9 billion years ago.
Early Earth's atmosphere had little oxygen and contained water vapor and volcanic gases (e.g., nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide).
As Earth cooled, water vapor condensed into oceans, and hydrogen escaped into space.

Further Synthesis of Organic Compounds on Early Earth

In the 1920s, Oparin and Haldane hypothesized the early atmosphere was a reducing environment, ideal for organic molecule formation.
They theorized that organic compounds formed from simpler molecules using energy from lightning and UV radiation.
Haldane suggested the presence of a "primitive soup" in early oceans from which life arose.
Miller and Urey's 1953 lab experiments demonstrated abiotic synthesis of organic molecules in a reducing atmosphere is possible.
Early organic compounds may have been synthesized near volcanoes or deep-sea vents.
Miller-Urey-type experiments showed organic molecule formation with various possible atmospheres.

Early Earth's Organic Compounds & Volcanic Eruptions

1953 Miller-Urey experiment compared to 2008 reanalysis shows variations in the mass of amino acids synthesized in simulated volcanic eruptions.

Organic Compounds and Deep-Sea Vents

Some deep-sea alkaline vents release water with high pH (9-11) and warm temperatures (40-90°C).
This environment could be suitable for abiotic organic molecule synthesis and the origin of the first cells.
A pH gradient would have existed between the vent interior and the surrounding ocean water, providing potential energy for organic compound synthesis.

Abiotic Synthesis of Macromolecules

Amino acids and other organic molecules may be present in meteorites.
RNA monomers might have been produced spontaneously from simple molecules.
Scientists have produced polymers of organic molecules using heat, clay or rock as catalysts and without enzymes or ribosomes.
Minerals in clay and rock can provide catalytic surfaces for the polymerization of small molecules into larger chains (like proteins and RNA).

Protocells

A protocell is a theoretical model of an early life form, resembling a cell but lacking complex structures.
Protocells can be thought of as a transitional step from non-living chemistry to living organisms.
Protocells might have been fluid-filled vesicles with a membrane-like structure that spontaneously formed from lipids in water.
Adding clay may increase the rate of vesicle formation.
Vesicles exhibit simple reproduction and metabolism while maintaining an internal environment separate from their surroundings.

Role of Montmorillonite Clay

Montmorillonite clay, common in early Earth, is composed of silicate layers.
Clay provides surfaces for concentrating organic molecules, increasing the chance of reactions to form vesicles.
The presence of clay enhances the rate of vesicle self-assembly.

Self-Replicating RNA

RNA, not DNA, was likely the first genetic material.
RNA plays a role in protein synthesis and can act as an enzyme-like catalyst (ribozyme).
Ribozymes catalyze various reactions, such as making complementary RNA copies using nucleotide building blocks, potentially signifying a self-replication process.
Natural selection in early organic molecules might have produced stable, self-replicating ribozymes, defining a possible "RNA world".
Small RNA molecules, capable of replicating and storing genetic information about protocells, played a vital role.
Early protocells carrying RNA might have limited function.
RNA could provide a template for the emergence of DNA.
DNA's greater stability and better replication could have led to its dominance.

Transition from RNA to DNA

Accurate replication was favored as genomes grew in size.
The development of DNA marked a pivotal point that paved the way for the proliferation and evolution of new life forms.

The Fossil Record

The fossil record shows changes in the history of life.
Sedimentary rocks, which form layers called strata, are a primary source of fossils.
Fossils offer an incomplete record due to limitations in preservation and discoveries.
The record is biased toward organisms that lived for long periods, were widespread, and had hard parts.

How Rocks and Fossils are Dated

Sedimentary strata provide relative ages of fossils.
Dating relies on radiometric dating techniques analyzing the decay of radioactive isotopes to determine the absolute ages of fossils.
Each radioisotope has a characteristic decay rate or half-life, unaffected by environmental factors.
Radiocarbon dating can accurately date organic material up to 75,000 years.

Radiometric Dating

Living organisms contain various isotopes (e.g., carbon-12, carbon-14), with carbon-14 being radioactive.
After death, the uptake of carbon-14 stops, allowing its decay.
Measuring the ratio of carbon-14 to carbon-12 can estimate the fossil's age.
Dating older fossils uses surrounding rock strata's age markers.

The Geologic Record

The geologic record shows the evolution of life's diversity across geologic time.
Early geological time periods are documented in the fossil record.
The timeline includes the appearance of prokaryotes, eukaryotes, multicellular organisms, and specific geologic events, such as the Cambrian explosion.

Oxygen Revolution

Early rise in atmospheric oxygen levels was largely due to oxygenic photosynthetic prokaryotes.
Later increases in atmospheric oxygen might be attributed to the evolution of eukaryotic cells containing chloroplasts.
The "oxygen revolution" around 2.7-2.4 billion years ago led to the extinction of many anaerobic groups, causing some surviving organisms to adapt through cellular respiration.

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Explore the vital role of prokaryotes in the history of life on Earth in this quiz based on Lecture 2. Delve into the conditions that facilitated the origin of life, the synthesis of organic compounds, and the evolution of early cellular structures. Perfect for students interested in biology and environmental science!