Ch.3 - Protein Structure and Function

Freeman - Biological Science 8th Edition

Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook

Freeman 8th Edition

Ch.3 - Protein Structure and Function

Problem 7

Chapter 3, Problem 7

Why are proteins not considered to be a good candidate for the first living molecule?
a. Their catalytic capability is not sufficient for most biological reactions.
b. Their amino acid monomers were not likely present in the prebiotic soup.
c. They cannot serve as a template for replication.
d. They could not have polymerized from amino acid monomers under early Earth conditions.

Verified step by step guidance

Understand the role of proteins in biological systems: Proteins are essential macromolecules that perform a wide range of functions, including catalysis of biochemical reactions, structural support, and transport of molecules.

Consider the requirements for the first living molecule: The first living molecule would need to have the ability to store information, replicate, and catalyze reactions.

Evaluate the ability of proteins to serve as a template for replication: Proteins are composed of amino acids linked by peptide bonds, but they do not have the ability to store genetic information or serve as a template for replication like nucleic acids (DNA or RNA) do.

Assess the presence of amino acids in the prebiotic environment: While amino acids are the building blocks of proteins, their availability and the conditions required for polymerization into proteins under prebiotic conditions are uncertain.

Analyze the catalytic capabilities of proteins: Although proteins can act as enzymes to catalyze reactions, the first living molecule would need to have a broader range of capabilities, including self-replication, which proteins alone cannot achieve.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Catalytic Capability of Proteins

Proteins are known for their role as enzymes, catalyzing a wide range of biological reactions. However, the catalytic capability of proteins alone is not sufficient for the origin of life, as they require a pre-existing system to synthesize and fold them into functional structures. This limitation suggests that proteins may not have been the first self-replicating molecules necessary for life.

Amino Acid Availability in Prebiotic Soup

The prebiotic soup theory posits that early Earth had a mixture of organic compounds from which life originated. However, the specific amino acids required to form proteins may not have been abundantly available or in the right conditions to spontaneously form complex proteins, making them unlikely candidates for the first living molecules.

Template for Replication

For a molecule to be considered a candidate for the first living molecule, it must have the ability to replicate itself. Proteins lack the ability to serve as templates for replication, as they do not have a straightforward mechanism to encode and transfer genetic information, unlike nucleic acids such as RNA, which can both store information and catalyze reactions.

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Related Practice

Textbook Question

Make a concept map that relates the four levels of protein structure and shows how they can contribute to the formation of hemoglobin. Your map should include the following boxed terms: Primary structure, Secondary structure, Tertiary structure, Quaternary structure, Amino acid sequence, R-groups, αα-helices, and ββ-pleated sheets.

Textbook Question

Based on what you know of the peptide bonds that link together amino acid residues, why would proline's side chain reduce the flexibility of the backbone?

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Textbook Question

If a cell were to use only 10 of the 20 possible amino acids, how much effect would you expect this to have on protein diversity? Calculate and compare the number of different sequences that can be generated by randomly assembling either 10 or 20 amino acids into peptides that are five residues long.

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Textbook Question

Explain how molecular chaperones facilitate protein folding in many different polypeptides, each with their own specific shape.

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Textbook Question

Which of the following correctly describe an active site? Select True or False for each statement.

T/F It is the location in an enzyme where substrates bind.

T/F It is the place where a molecule or ion binds to an inactive enzyme to induce a shape change to make it active.

T/F It is the portion of an enzyme where chaperones bind to help enzymes fold.

T/F It is the site on an enzyme where catalysis occurs.

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Textbook Question

Predict the effect on protein function if each polypeptide adopted only a single, inflexible shape based on its primary structure.

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