Question

In 1952, the Miller-Urey experiment showed that an electrical discharge in a gas-phase mixture of ammonia, hydrogen, methane, and water produced five amino acids. When the experiment was conducted, evidence indicated that this mixture was representative of the Hadean (early Earth) atmosphere. The experiment was repeated in the presence of jets of hot steam, simulating Hadean volcanic eruptions and producing an even larger variety of amino acids. A. Consider the following criticisms of the “organic soup” model and justify the selection of data that other experiments might provide regarding the origin of life on Earth. • Biopolymers on Earth have a left-hand symmetry at the carbon adjacent to the carboxylic acid carbon, and these experiments produced mixtures of both leftand right-hand symmetries. • No peptide bonds between amino acids were mobserved. • Early Earth’s atmospheric oxygen concentration is known to have been very low, implying the absence of an ozone layer to filter high-energy ultraviolet (uv) radiation. • Ammonia decomposes when it absorbs high-energy uv radiation, but diatomic nitrogen does not. Models of the abiotic synthesis of biomolecules suffer from a “chicken and egg” dilemma. Proteins are needed to synthesize DNA and RNA, and DNA and RNA are needed to synthesize proteins. Which molecules came first? B. In light of the following observations, evaluate the hypothesis that nucleotides arose from a prebiotic mixture. • Nuclei acids are not found in experiments like those of Miller and Urey. • Purines and pyrimidines decompose at high temperature, and Earth was bombarded by meteors and comets during the Hadean eon. • Bonds in the purine and pyrimidine rings of nucleic acids are broken by high-energy uv radiation. • Carl Sagan and colleagues synthesized ATP from a mixture of adenosine, ribose, and phosphate when exposed to uv radiation. • Ribose has never been synthesized in experiments like those conducted by Miller and Urey. • Ribose has a left/right symmetry, and the righthanded form occurs in Earth organisms. Continuing with the analogy, if neither the chicken nor the egg came first, then both must have arisen together. Some regard simultaneous innovations in both catalysis and information storage and retrieval as too improbable. In samples of meteorites, both amino acids and nucleic acids have been found. The amino acids are mixtures of left- and right-handed symmetries, although some have shown a significant bias toward the left-handed form (J. Elisa et al., ACS Central Science, 2016). The arrival from space of the seeds of biomolecules is called panspermia. Carl Sagan (1966) and Francis Crick (1973), one of the first to describe the structure of DNA, regarded panspermia as the only plausible origin of life on Earth. In fact, their belief was in directed panspermia, the intentional seeding by intelligent aliens. C. Describe the questions that must be addressed for panspermia to be a scientific hypothesis about the origin of life on Earth and describe the reasons for the directed panspermia revision of this hypothesis. To avoid the conflicting chicken-and-egg claims that “protein catalyst was first” and “DNA information storage was first,” two alternatives have emerged regarding the origin of life on Earth. Consider two simple ideas: 1) water blocks uv radiation, and cracks in the ocean floor (hot vents) provide a temperature difference that generates a source of entropy; and 2) ribosomes are composed of RNA. D. Describe one of the following as a hypothesis concerning the origin of life on Earth: • Reactions among molecules in the vicinity of hot vents became organized in space and time, eventually developing structures that foreshadow the proton gradient upon which metabolism is based. This alternative is the basis for what is referred to as the metabolism-first hypothesis. • The catalytic properties of the ribosome reflect the self-catalytic polymerization of nucleotides with sequential structures conserved in modern DNA, the catalytic properties conserved in proteins, and the catalytic properties of the ribosome whose core structure is RNA. This alternative is the basis for what is referred to as the RNA-first hypothesis.

Name: Problem 73, Chapter 18: Biology for AP Courses
Uploaded: 2021-04-23T15:57:44-08:00
Duration: 14 min 5 s
Channel: Eric Goldman

In 1952, the Miller-Urey experiment showed that an electrical discharge in a gas-phase mixture of ammonia, hydrogen, methane, and water produced five amino acids.
When the experiment was conducted, evidence indicated that this mixture was representative of the Hadean (early Earth) atmosphere. The experiment was repeated in the presence of jets of hot steam, simulating Hadean volcanic eruptions and producing an even larger variety of amino acids.
A. Consider the following criticisms of the “organic soup” model and justify the selection of data that other experiments might provide regarding the origin of life on Earth.
• Biopolymers on Earth have a left-hand symmetry at the carbon adjacent to the carboxylic acid carbon, and these experiments produced mixtures of both leftand right-hand symmetries.
• No peptide bonds between amino acids were mobserved.
• Early Earth’s atmospheric oxygen concentration is known to have been very low, implying the absence of an ozone layer to filter high-energy ultraviolet (uv) radiation.
• Ammonia decomposes when it absorbs high-energy uv radiation, but diatomic nitrogen does not.
Models of the abiotic synthesis of biomolecules suffer from a “chicken and egg” dilemma. Proteins are needed to synthesize DNA and RNA, and DNA and RNA are needed to synthesize proteins. Which molecules came first?
B. In light of the following observations, evaluate the hypothesis that nucleotides arose from a prebiotic mixture.
• Nuclei acids are not found in experiments like those of Miller and Urey.
• Purines and pyrimidines decompose at high temperature, and Earth was bombarded by meteors and comets during the Hadean eon.
• Bonds in the purine and pyrimidine rings of nucleic acids are broken by high-energy uv radiation.
• Carl Sagan and colleagues synthesized ATP from a mixture of adenosine, ribose, and phosphate when exposed to uv radiation.
• Ribose has never been synthesized in experiments like those conducted by Miller and Urey.
• Ribose has a left/right symmetry, and the righthanded form occurs in Earth organisms.
Continuing with the analogy, if neither the chicken nor the egg came first, then both must have arisen together. Some regard simultaneous innovations in both catalysis and information storage and retrieval as too improbable. In samples of meteorites, both amino acids and nucleic acids have been found. The amino acids are mixtures of left- and right-handed symmetries, although some have shown a significant bias toward the left-handed form (J. Elisa et al., ACS Central Science, 2016). The arrival from space of the seeds of biomolecules is called panspermia. Carl Sagan (1966) and Francis Crick (1973), one of the first to describe the structure of DNA, regarded panspermia as the only plausible origin of life on Earth. In fact, their belief was in directed panspermia, the intentional seeding by intelligent aliens.
C. Describe the questions that must be addressed for panspermia to be a scientific hypothesis about the origin of life on Earth and describe the reasons for the directed panspermia revision of this hypothesis. To avoid the conflicting chicken-and-egg claims that “protein catalyst was first” and “DNA information storage was first,” two alternatives have emerged regarding the origin of life on Earth. Consider two simple ideas: 1) water blocks uv radiation, and cracks in the ocean floor (hot vents) provide a temperature difference that generates a source of entropy; and 2) ribosomes are composed of RNA.
D. Describe one of the following as a hypothesis concerning the origin of life on Earth:
• Reactions among molecules in the vicinity of hot vents became organized in space and time, eventually developing structures that foreshadow the proton gradient upon which metabolism is based. This alternative is the basis for what is referred to as the metabolism-first hypothesis.
• The catalytic properties of the ribosome reflect the self-catalytic polymerization of nucleotides with sequential structures conserved in modern DNA, the catalytic properties conserved in proteins, and the catalytic properties of the ribosome whose core structure is RNA. This alternative is the basis for what is referred to as the RNA-first hypothesis.

Biology for AP Courses

Julianne Zedalis,…

Chapter 18, Problem 73

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04/23/2021

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In 1952, the Miller-Urey experiment showed that an electrical discharge in a gas-phase mixture of ammonia, hydrogen, methane, and water produced five amino acids. When the experiment was conducted, evidence indicated that this mixture was representative of the Hadean (early Earth) atmosphere. The experiment was repeated in the presence of jets of hot steam, simulating Hadean volcanic eruptions and producing an even larger variety of amino acids. A. Consider the following criticisms of the “organic soup” model and justify the selection of data that other experiments might provide regarding the origin of life on Earth. • Biopolymers on Earth have a left-hand symmetry at the carbon adjacent to the carboxylic acid carbon, and these experiments produced mixtures of both leftand right-hand symmetries. • No peptide bonds between amino acids were mobserved. • Early Earth’s atmospheric oxygen concentration is known to have been very low, implying the absence of an ozone layer to filter high-energy ultraviolet (uv) radiation. • Ammonia decomposes when it absorbs high-energy uv radiation, but diatomic nitrogen does not. Models of the abiotic synthesis of biomolecules suffer from a “chicken and egg” dilemma. Proteins are needed to synthesize DNA and RNA, and DNA and RNA are needed to synthesize proteins. Which molecules came first? B. In light of the following observations, evaluate the hypothesis that nucleotides arose from a prebiotic mixture. • Nuclei acids are not found in experiments like those of Miller and Urey. • Purines and pyrimidines decompose at high temperature, and Earth was bombarded by meteors and comets during the Hadean eon. • Bonds in the purine and pyrimidine rings of nucleic acids are broken by high-energy uv radiation. • Carl Sagan and colleagues synthesized ATP from a mixture of adenosine, ribose, and phosphate when exposed to uv radiation. • Ribose has never been synthesized in experiments like those conducted by Miller and Urey. • Ribose has a left/right symmetry, and the righthanded form occurs in Earth organisms. Continuing with the analogy, if neither the chicken nor the egg came first, then both must have arisen together. Some regard simultaneous innovations in both catalysis and information storage and retrieval as too improbable. In samples of meteorites, both amino acids and nucleic acids have been found. The amino acids are mixtures of left- and right-handed symmetries, although some have shown a significant bias toward the left-handed form (J. Elisa et al., ACS Central Science, 2016). The arrival from space of the seeds of biomolecules is called panspermia. Carl Sagan (1966) and Francis Crick (1973), one of the first to describe the structure of DNA, regarded panspermia as the only plausible origin of life on Earth. In fact, their belief was in directed panspermia, the intentional seeding by intelligent aliens. C. Describe the questions that must be addressed for panspermia to be a scientific hypothesis about the origin of life on Earth and describe the reasons for the directed panspermia revision of this hypothesis. To avoid the conflicting chicken-and-egg claims that “protein catalyst was first” and “DNA information storage was first,” two alternatives have emerged regarding the origin of life on Earth. Consider two simple ideas: 1) water blocks uv radiation, and cracks in the ocean floor (hot vents) provide a temperature difference that generates a source of entropy; and 2) ribosomes are composed of RNA. D. Describe one of the following as a hypothesis concerning the origin of life on Earth: • Reactions among molecules in the vicinity of hot vents became organized in space and time, eventually developing structures that foreshadow the proton gradient upon which metabolism is based. This alternative is the basis for what is referred to as the metabolism-first hypothesis. • The catalytic properties of the ribosome reflect the self-catalytic polymerization of nucleotides with sequential structures conserved in modern DNA, the catalytic properties conserved in proteins, and the catalytic properties of the ribosome whose core structure is RNA. This alternative is the basis for what is referred to as the RNA-first hypothesis.

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Key Concepts

RNA-first Hypothesis

The RNA-first hypothesis argues that RNA, with its dual role as both an information carrier and a catalyst for chemical reactions, was the initial critical molecule in the emergence of life. This concept suggests that RNA not only stored genetic information but also catalyzed its own synthesis and other biochemical processes, eventually leading to the evolution of DNA and proteins.

Metabolism-first Hypothesis

The metabolism-first hypothesis posits that metabolic networks and energy-utilizing chemical cycles arose before the appearance of genetic molecules like RNA or DNA. According to this view, the establishment of energy gradients and organized chemical reactions provided a framework upon which life could emerge, eventually leading to the evolution of more complex informational molecules.

Chicken and Egg Dilemma in Origins of Life

The chicken and egg dilemma in origins of life encapsulates the interdependent relationship between proteins (which act as catalysts) and nucleic acids (which store genetic information). It highlights the challenge of determining which of these critical components appeared first, or whether both emerged simultaneously through a series of interrelated chemical and evolutionary processes.

Directed Panspermia

Directed panspermia is a variant of the panspermia hypothesis which proposes that life on Earth was intentionally seeded by an advanced extraterrestrial civilization. This concept introduces the possibility that life’s origin might involve not only natural processes but also purposeful intervention by intelligent beings.

Abiotic Synthesis

Abiotic synthesis refers to the production of organic molecules from inorganic precursors without the intervention of biological processes. This concept is central to studies on the origin of life and explores how key building blocks such as amino acids and nucleotides might have been formed under the conditions present on early Earth or delivered from outer space.

Prebiotic Chemistry

Prebiotic chemistry studies the chemical processes and reactions that preceded the emergence of life on Earth. It focuses on the formation and evolution of simple organic molecules into more complex structures that could give rise to life, considering factors such as environmental conditions, energy sources, and the role of various chemical catalysts.

Chirality in Biomolecules

Chirality in biomolecules refers to the molecular handedness, meaning that molecules like amino acids and sugars can exist in left- or right-handed forms. In biological systems, there is a pronounced bias (homochirality), which is critical because the specific orientation of these molecules can greatly influence biochemical interactions and the functioning of enzymes and cellular structures.

Miller-Urey Experiment

The Miller-Urey experiment was a pioneering laboratory study designed to simulate the conditions of early Earth’s atmosphere and demonstrate that organic compounds, specifically amino acids, could be generated by chemical reactions using simple gases and energy sources. This experiment has been foundational in supporting the concept of a chemical origin for life.

Panspermia

Panspermia is the hypothesis that life, or the elements necessary for life, exists throughout the Universe and can be distributed by space dust, meteoroids, asteroids, and comets. This idea suggests that the seeds of life may have been delivered to Earth from extraterrestrial sources, providing an alternative to the entirely Earth-based origins of life.

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Transcript

00:01 For this question, we're looking at this organic soup model to try and explain the origins of life.

00:07 So what this organic soup is about is we know that the atmosphere in that prehistoric earth consisted of different molecules, ammonia, hydrogen, water, and methane.

00:23 And from these molecules, in the presence of some sort of electric or energy source, you're able to convert.

00:30 These into amino acids and make up proteins.

00:34 And we know that proteins are the base substance required to make life.

00:40 So here they're proposing that the presence of these molecules allowed for the random formation of life over a long period of time.

00:48 However, there are several complications that have to be addressed in this matter.

00:53 So for a, we're looking at the problems with these proteins themselves.

00:57 The first thing we have to consider is the presence of biopolymers in different forms.

01:05 So amino acids can settle in either a left -handed form or a right -handed form.

01:11 So either l or d.

01:13 The thing is, we only witness l being used in life.

01:19 There are rare forms of d amino acids being found in certain organisms, but we primarily look at the l form.

01:27 So the issue with this is if these molecules are going to randomly assemble together to make those amino acids, we should have an equal distribution of about 50 % to 50 % of these l to d forms.

01:43 So it isn't very consistent that we're going to see primarily 100 % in the l form with only rare contributions of the d form, if we originally started from this 50 to 50.

01:56 Based on this theory, life should compose of an equal distribution of these l and d forms.

02:04 So that's the first issue to address.

02:07 The second issue to address is the presence of peptide bonds.

02:13 So during this experiment where these scientists combined these gaseous molecules and the presence of energy and electricity, these amino acids were not bound together.

02:24 So here, we only have the presence of amino acids, and no presence of proteins.

02:31 And we know that amino acids are not sufficient enough to give rise to the complex proteins we see in life.

02:38 So without these peptide bonds being formed, it's hard to make the conclusion that we're able to make life from the formation of these amino acids if they are not able to bond together to make proper proteins.

02:52 For the third part, we're considering the process of uv radiation, affecting the molecule of ammonia.

03:01 So uv radiation is going to break down ammonia, so it can no longer be combined into the amino acids required for proteins.

03:09 So that's the first issue.

03:11 What we do know, though, is that we can use the gaseous molecule of nitrogen in order to form them, but this requires the work of certain proteins in order to convert it into ammonia to make that proper form.

03:25 However, you can't have proteins unless you have them originally formed from these gaseous molecules.

03:32 So you can't have proteins without ammonia, but you can't have ammonia without nitrogen being converted into these protein molecules.

03:42 So that creates that chicken and the egg model that they are explaining, that you can't have one without the other.

03:49 So it's hard to determine whether we had ammonia come first, it's going to make protein.

03:55 And those proteins are able to convert nitrogen into that ammonia source.

04:01 Or whether we start with our ammonia source, we have some sort of proteins existent that are able to convert that gastrous nitrogen into ammonia.

04:12 So it's hard based on the presence and requirement of this protein in the absence of that ammonia molecule.

04:21 For part b of this organic soup theory, they're asking us about the complication of nucleotides inside of this factor.

04:30 So during this experiment, we don't have the presence of any nucleotides being formed.

04:35 And we know that nucleotides are responsible for dna and rna, which are required to assemble those proteins.

04:44 And without either of these two structures, you can't really have a reliable source of life.

04:51 So that's the first issue that those nucleotides aren't even present.

04:55 The second issue is that the temperature is also incompatible with those nucleotides.

05:01 So the temperature of earth back in those prehistoric times was too high to support the accumulation of nucleotides to form dna and rna.

05:12 So again, you're not going to be able to create that consistent form of proteins in that environment.

05:19 For the third part, the uv radiation is also a concern for the formation of nucleotides.

05:26 We know that there was little oxygen in the atmosphere at those times, and uv radiation has the capabilities to break apart dna and rna molecules.

05:36 So again, you're going to have complications forming those reliable structures or coding sequences to make proteins.

05:45 For the fourth part in ongoing, we know that we can make atp inside of uv radiation, and we know that atp is required for making energy needed to sustain life.

05:57 So that at least is viable option...

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