What is life? A Nobel Prize-winning scientist answers | Paul Nurse Full Interview

Key Concepts

Cell, gene, evolution by natural selection, chemistry of life (biochemistry, enzymes, proteins), information management, DNA (deoxyribonucleic acid), cell cycle, heredity, bounded physical entities, chemical and informational machine.

The Fundamental Question: What Is Life?

The video explores the fundamental question of biology: what distinguishes living things from non-living things. Paul Nurse emphasizes that a simple definition of life is elusive, drawing inspiration from Erwin Schrödinger's book "What Is Life?". He approaches the question by examining five core ideas in biology: the cell, the gene, evolution by natural selection, life as chemistry, and life as information.

The Cell: Life's Atom

The cell is presented as the simplest, unambiguous unit of life. It's not just a structural unit but also a functional one, capable of growth, division, and reproduction. Single-celled organisms exhibit all characteristics of life in a simplified form. The cell is likened to the atom in physics, a fundamental building block. All living organisms are either single cells or composed of cells working together. The speaker recalls his first encounter with cells under a microscope, inspired by his teacher Mr. Neal, mirroring Robert Hooke's discovery of cells in 1665, documented in "Micrographia."

Cell Reproduction and the Ancient Connection Between Yeast and Humans

Cell reproduction, the division of one cell into two, is a fundamental characteristic of life. The speaker's research focused on understanding how cells control their reproduction, using yeast as a model system. Yeast cells, like human cells, are eukaryotes, meaning their DNA is enclosed in a nucleus. The discovery that the same molecules control cell division in yeast and humans revealed an ancient, conserved process dating back 1.5 billion years. This was demonstrated by the interchangeability of human and yeast genes controlling cell division. Yeast is also valuable for genetic studies, allowing for easy crossing of strains and mutation experiments to understand the cell cycle (the process from cell birth to division). Mutants that grow but cannot divide were used to identify cell division cycle (CDC) genes.

Genes, DNA, and Evolution

The video traces the understanding of genes from Gregor Mendel's 19th-century experiments with pea plants, which revealed particulate inheritance. Mendel's work, initially ignored, was later rediscovered and became the foundation of genetics. Genes are made of DNA, as demonstrated by Avery's experiments with pneumococcus bacteria. The structure of DNA, a double helix, was elucidated by Watson and Crick, building on X-ray diffraction images from Rosalind Franklin and Maurice Wilkins. DNA's structure allows for information storage (via the sequence of bases A, G, C, T) and precise copying, which is the basis of heredity. DNA replication occurs during the S phase of the cell cycle, ensuring each daughter cell receives a complete and accurate copy of the genome.

Evolution by Natural Selection

Evolution by natural selection, proposed by Charles Darwin, explains the diversity of life. Darwin's observations during his voyage on the Beagle led him to propose that organisms with advantageous traits are more likely to survive and reproduce, leading to gradual changes in populations over time. This process allows for design without a designer. The speaker uses the example of single-celled organisms with different colored coats to illustrate how a mutation conferring an advantage (e.g., resistance to predation) can lead to the prevalence of that trait in the population. Evolution implies that all living things are related by descent. The speaker recounts a personal experience with gorillas in Uganda, highlighting the deep connection between humans and other life forms. This relatedness implies a responsibility to be stewards of all life on Earth.

Life Equals Chemistry Plus Information

Understanding life requires considering both chemistry and information. Life involves complex chemistry, with thousands of reactions occurring simultaneously in cells, catalyzed by enzymes (proteins). Proteins are chains of amino acids, and their structure and function are determined by the sequence of bases in DNA. The compartmentalization of cells allows for different chemical reactions to occur in close proximity. Life also relies on information management. The speaker uses the example of a butterfly sensing its environment to illustrate how organisms capture, process, and respond to information. DNA is a digital information storage device, and the transfer of information from DNA to proteins is essential for cellular function. Control systems, such as negative feedback loops, maintain homeostasis by regulating gene expression based on the concentration of specific substances. Understanding life requires combining knowledge of chemistry with an understanding of information flow and processing. The speaker uses the term "wetware" to describe how information is managed in living systems through molecular communication and dynamic rewiring of connections.

Principles of Life

The video concludes by summarizing the core principles of life:

1. Bounded physical entities: Living things are self-contained and separate from their environment.
2. Chemical and informational machine: Living things function as complex chemical systems that process and manage information.
3. Hereditary system with variability: Living things have a system of heredity (DNA) that allows for variation and adaptation.
4. Evolution by natural selection: Living things evolve over time through natural selection, acquiring purpose and becoming better adapted to their environment.

These principles emphasize the interconnectedness of the core ideas and provide a framework for understanding the fundamental nature of life.