The Truth about Science and Religion. Fraser Fleming

Чтение книги онлайн.

СКАЧАТЬ sorting process imparts information through selecting for what is important. Evolutionary models often trace the sorting mechanism to the environment, an ecological niche in biology or crystals capable of absorbing biological molecules, for example. Complex biological environments allow information to flow between organisms, such as changes to an animal’s coloring to blend into the environment. In this sense biological evolution is a natural process that distills information from the environment and captures the information in the genetic code. More difficult to understand is the generation of information from simple environmental features, such as crystals, which are regular and repetitious but have minimal information content. In the beginning of earth’s development there were no obvious sources of complex information. The search is for a natural process capable of amplifying minimal information inherent in minerals into complex genetic information.

      The difficulty inherent in disentangling the origin of information is illustrated in spark discharge experiments. Mixtures of amino acids are generated that differ in a very subtle spatial orientation. The spatial complexity stems from an unusual peculiarity of carbon: the orientation of the four bonds allows two molecules to be assembled together with exactly the same connectivity but different arrangements in space. Each carbon center is like a hand with projecting fingers, thumb, and forearm attachments. The carbon center can have a “left” and “right” handedness, each of which naturally interlocks only with another left or right. In biological systems, the carbons of each amino acid is comprised of only one “hand.” Proteins have very specific, and usually very long, sequences all with the same geometric sequence—all “lefties” in a sense. The resulting sequence imparts very specific molecular complexity, particularly near the active site of enzymes where changing just one amino acid out of hundreds can render the enzyme inactive. Spark discharge experiments generate an equal mixture of two mirror-image amino acids that are very difficult to separate because their physical and chemical properties, like melting and boiling points, are identical. Randomly incorporating amino acids of each mirror image series from a mixture also containing natural and non-natural amino acids generated in discharge experiments is not likely to lead to a functional protein.

      For the chemical synthesis of proteins, all of the amino acids must have the same handedness in a very specific order. As an analogy, if a house (protein) were to be built from an array of a hundred Lego blocks comprised of twenty different colors (amino acids) then the chance of assembling only a red house would be one in 20100! The chance of randomly assembling a functional protein is roughly the same as finding one grain of sand in a desert many times the size of the Sahara.

      One estimate for the probability of assembling a functional enzyme through random chance puts the odds at one chance in 1020. Getting the sequence right is vital because proteins serve extremely diverse biological functions. Some proteins act as enzymes, some act as ropes that anchor bone and tendons together, while others form rubber-like soft tissue that surrounds the major arteries. Random chance seems unlikely to explain the complexity required for assembling the large, “handed,” three-dimensional structures so prevalent in nature. Is this the hand of God?

      Assembling a functional protein requires positioning the amino acids in a specific sequence that encodes information. Enzymes contain very specific sequences of amino acids that create three dimensional “biological machines” where the sequence codes information specific to each type of enzyme. The information cannot come from some underlying attraction between amino acids because otherwise only one amino acid sequence would result. The amino acid sequence is flexible, allowing different sequences to code for different three-dimensional structures having different functions. The information coded into a protein vastly exceeds the information content of the laws governing molecular attraction. The term “specified complexity” tries to capture the meaning within a piece of information, specified in the sense of requiring a description for a specific function and complex in being unlikely to occur through chance. In this sense quartz is complex because the molecules pack into the crystal lattice in a very specific orientation, but there is minimal specificity. DNA has a very specific nucleotide order and is complex in being unlikely to have arisen by chance; other chance nucleotide orderings are possible but would not be specified. The laws of molecular attraction lead to regular repeating structures with minimal information, as found in beautiful crystals like Pyrite or fool’s gold. Crystals contain one instruction repeated millions of times whereas proteins and DNA contain many different instructions depending on the one sequence specified out of the millions of possibilities.

      Information is fundamental to the nature of the universe. As the universe expands there are increasing numbers of states that can potentially be adopted and so the potential for increasing information. Intelligent agents are able to distinguish whether potential states are random or contain information encoded through abstract symbolism. The ability to perform abstract thinking is the link between information and intelligence which forms the basis for mathematics, computing, and all forms of communication.

      People’s experience is that information comes from intelligent beings. The “Search for Extra-Terrestrial Intelligence” (SETI) involves searching for radio signals with specific patterns that convey information. Life’s existence is predicated on a vast amount of information whose source remains unknown. For some, such as SETI staff, the inability to find other sentient beings simply spurs the search on to different corners of the universe. For religious believers, God is the source of the intelligence in the universe. Each individual makes a free choice, informed by experience and logic, in deciding where the universe’s information comes from.

      Replication

      The distinction between molecules and living organisms is the information contained in the minimum number of instructions for replication. How the first proteins formed is an unsolved issue in origin-of-life research. Proteins have the remarkable ability to assemble themselves into very specific three-dimensional shapes with exactly the right groups positioned to execute their catalytic function. A protein’s shape not only defines the enzymatic active site but is also changed by interactions with other cell components. Ligand binding changes the protein sufficiently to prevent enzymatic activity and effectively functions as a molecular switch, turning an enzyme on and off. The dual functionality of proteins to manipulate the cell’s atomic building blocks and to provide a feedback mechanism signaling the needs of the cell has been called the second secret of life.

      The same replication and feedback loops plague the formation of the first functional RNA and DNA. Polynucleotide strands require linking together one specific geometrically complex sugar with one of four nucleotide bases. Mechanisms continue to be discovered for condensing the monomeric units into the polymers required in functional DNA, with some remarkable consequences. For example, clay particles can provide active surfaces that not only facilitate the monomer condensation but also protect nucleic acids from degradation by a variety of energy sources. Small RNA sequences chosen to be partially self-complementary can self-assemble with a high preference for one monomeric “hand,” providing some encouragement for the origin of RNA sequences having the same sense of handedness.

      The same information requirement reoccurs in many of the biomolecules required in cells. Proteins, DNA, fats, and a myriad of cell components are built from smaller components, requiring assembly in very specific sequences for normal cell function. If DNA is the software storing the cell’s information then proteins are the hardware that perform the cell’s functions. Some RNA can catalyze the formation of proteins but the amino acids are not specified during this process in the same way in which cells read DNA and select amino acids for protein synthesis. The fundamental problem lies in achieving replication; DNA codes for RNA that directs protein synthesis that, in addition to acting as the catalytic cell workers, ultimately result in the assembly of DNA.

      The Beginning of Life

      Exactly what separates living and non-living organisms? Defining the transition from organic molecules to life is enormously difficult because living organisms exhibit such remarkable diversity of complexity. Is a virus “alive”? Is an egg alive immediately after the sperm penetrates СКАЧАТЬ