Defining Life and Its Origins (Ch.1) Learning Objectives

Understand why it is difficult to define life

Defining life is challenging because life exists on a continuum, and characteristics of living entities can vary. Life exhibits diverse forms, and the definition must encompass all living organisms, including those with unique characteristics.

List and describe the seven properties of life as discussed in this chapter

Order: Living organisms exhibit organized structures.

Regulation: Organisms maintain internal stability.

Growth and Development: Organisms undergo growth and controlled development.

Energy Utilization: Living entities acquire and use energy.

Response to the Environment: Organisms respond to stimuli.

Reproduction: Living organisms produce offspring

Evolutionary Adaptation: Populations evolve over time.

Explain why viruses are not considered to be true living organisms

Viruses lack cellular structures and cannot carry out metabolic processes independently. They require a host cell to replicate and are considered obligate intracellular parasites.

List the three key attributes common to all modern cells

Plasma Membrane: Separates the cell from the environment.

Genetic Material (DNA or RNA): Carries hereditary information.

Cytoplasm: Cellular fluid containing organelles.

Explain the general steps that must have occurred from abiotic chemical origins to result in a living cell that displays the three key attributes of a modern cell

Abiotic synthesis, polymer formation, protobiont development, RNA emergence, self-replication, metabolic pathways, evolutionary selection, transition to DNA, cellular complexity.

Describe the Oparin-Haldane reducing atmosphere hypothesis on the origin of life and explain how the Miller-Urey experiment supported this hypothesis

The hypothesis suggests that life originated in a reducing atmosphere. The Miller-Urey experiment simulated early Earth conditions, producing amino acids, supporting the idea that life's building blocks could form abiotically.

Describe the "information system" of the cell, including the roles of DNA and RNA in this system

encompasses the genetic material and processes involved in storing, replicating, and utilizing genetic information. The flow of genetic information from DNA to RNA to proteins is fundamental to the operation of the cell and the expression of its genetic code.

- DNA stores genetic information, and RNA transcribes and translates this information to synthesize proteins.

Compare and contrast RNA and DNA as information storage molecules

Both carry genetic information, but RNA is usually single-stranded, contains ribose, and has uracil, while DNA is double-stranded, contains deoxyribose, and has thymine.

Describe a potential scenario of the evolution of proteins and DNA, based on the development of life in an 'RNA world'

In an 'RNA world,' RNA served both as genetic material and a catalyst (ribozymes). Proteins and DNA evolved later, with proteins assuming catalytic roles.

Describe how ribozymes are thought to have been significant in the origins of life

Ribozymes, RNA molecules with catalytic activity, could have played a role in early cellular processes, serving as both information carriers and catalysts.

Describe the characteristics of an alkaline hydrothermal vent and explain how it may have led to the First Cells

Alkaline vent: high pH, mineral-rich, hydrogen, methane.

Role in first cells: chemical energy, mineral catalysis, protocell formation.

Describe, at a general level, metabolism

Metabolism encompasses all chemical reactions occurring in an organism, involving the synthesis and breakdown of molecules to obtain and utilize energy.

Distinguish between the forward citric acid cycle and the reverse citric acid cycle

the forward citric acid cycle is primarily catabolic, breaking down acetyl-CoA to generate energy, while the reverse citric acid cycle operates in anabolic processes, fixing carbon dioxide and participating in the synthesis of complex molecules. The reverse cycle is often found in certain bacteria, archaea, and in pathways involved in anabolic metabolism in eukaryotic cells.

Describe the function of the citric acid cycle in oxidative mode and in reductive mode

Oxidative Mode: Extracts energy by breaking down acetyl-CoA, producing NADH and FADH₂ for ATP generation.

- produces ATP

Reductive Mode: Functions in anabolic processes, using CO₂ fixation and reductive reactions to build complex molecules, with NADPH as a product.

- consumes ATP

Describe how the First Cell may have been created and explain the significance of the cell membrane in the evolution of life

The first cell is thought to have arisen by the enclosure of self-replicating RNA and associated molecules in a membrane composed of phospholipids

List the seven common biological attributes of all current life forms on Earth

the ability to respire, grow, excrete, reproduce, metabolize, move, and be responsive to the environment.

Explain how the attributes of all life forms currently on Earth relate to the hypothesis of a last common universal ancestor (LUCA)

The universal genetic code is arguably the most robust evidence for the existence of LUCA. Virtually every organism, from the tiniest bacteria to the largest mammals, uses the same genetic code. This means that the triplet sequences of nucleotides in DNA, called codons, code for the same amino acids almost universally.

Describe, at a general level, how oxygenic photosynthesis differs from non-oxygenic photosynthesis

Oxygenic photosynthesis requires the presence of oxygen; non-oxygenic photosynthesis does not.

Oxygenic photosynthesis produces oxygen, while non-oxygenic photosynthesis does not.

Describe the types of organisms that carried out the earliest forms of photosynthesis

eukaryotic photosynthesis originated from endosymbiosis of cyanobacterial-like organisms, which ultimately became chloroplasts (Margulis, 1992). So the evolutionary origin of photosynthesis is to be found in the bacterial domain.

Describe the impact of oxygenic photosynthesis on the evolution of life

Oxygenic photosynthesis led to the accumulation of oxygen, changing the Earth's atmosphere and influencing the evolution of aerobic organisms.

Describe the endosymbiotic theory of the origin and evolution of mitochondria and chloroplasts

Endosymbiotic theory proposes that mitochondria and chloroplasts originated from free-living bacteria engulfed by ancestral eukaryotic cells

Describe the lines of evidence that support the endosymbiotic theory of the origin and evolution of mitochondria and chloroplasts

Bacteria, a prokaryote, has circular DNA, as do mitochondria and chloroplasts. This provides support for the Endosymbiotic Theory, which states that the mitochondria and chloroplast in eukaryotic cells were once aerobic (needs oxygen to survive) bacteria (prokaryote) that were ingested by a large anaerobic (does not need oxygen to survive) bacteria (prokaryote).

Describe horizontal gene transfer as it would have occurred after the endosymbiosis leading to mitochondria and chloroplasts

After endosymbiosis, genes from the engulfed bacteria may have transferred to the host nucleus, contributing to genetic diversity.