What is scientifically the most probable explanation for the emergence of life on Earth?
I’m not keyed into current thinking but last i read we suspect that a mixture of physical and chemical processes (lightning, volcanic activity etc) created a mixiture of simple organic compounds in the lakes and seas - amino acids, sugars, nucleotides etc. This mix could build up over billions of years - in the absence of life, nothing is trying to “eat” these compounds. Various templating mechanisms - fibrous clay layers, undersea volcanic vault chimneys etc - eventually support the creation of self replicating molecules but since a) there can’t be any fossils of such tiny and prmitive atructures and b) whatever came next ate them, we’ll never know which particular mechanism was involved.Once self-replication exists, variation and natural selection drive the evolution of more efficient self-replicators. We believe at some point, all life on earth was RNA based. RNA can act as an information store AND an enzyme all on its own but it is rather unstable compared to DNA. DNA, on the other hand, doesn’t work an an enzyme, but if RNA life lead to RNA & protein life, DNA can then step in and out-do RNA life due to its greater stability.Now press fast forward for a few more billion years…
Can or Could RNA self replicate?
RNA should in theory be able to self replicate without the help of proteins however this is not seen in nature. There are RNA molecules catalyse chemical reactions, a role usually carried out only by protein enzymes, these are called ribozymes. Ribozymes can facilitate the creation of both peptide bonds in proteins, and the bonds between phosphate and ribose in RNA.This means that under the right conditions some RNA sequences could both store information and implement the information. RNA is considered an attractive candidate as a primordial catalysis in the origin of life. There are some plant parasites called viroids.Viroids are small, circular, noncoding(they do not code for protein) RNAs that infect plants. They replicate in the nucleus or chloroplast and then traffic from cell to cell and from organ to organ to establish systemic infection. Viroids directly interact with host cellular enzymes. Their replication mechanism involves RNA polymerase II, an enzyme normally associated with synthesis of messenger RNA from DNA, which under the influence of the viroid instead catalyses "rolling circle" synthesis of new RNA using the viroid's RNA as template. Parts of the long RNA strand produced then fold into ribozymes that cleave the RNA into viroid genome unit length strands.
Why is DNA better than RNA as a genetic material?
Genetic material (RNA or DNA) of an organism carries information of the structure, shape and function of each and every cell of that organism, and carries the same information for generations. Hence the more stable the genetic material, the less are chances in incorporation of mutations in genome. With evolution the lesser stable genetic material (RNA) got replaced by the more stable ones (DNA).RNA is unstable because of the presence of Uracil instead of Thymine. RNA has ribose sugar and DNA has deoxy-ribose sugar in their monomers, the presence of one free -OH group at 2nd Carbon in ribose sugar makes it more prone to oxidation. The smaller grooves in DNA make it less prone to enzyme degradation and the larger grooves in RNA makes it more prone to enzymes attack. The other reasons why RNA was eliminated as genetic material during the course of evolution is because of the high chances of mutations that occur during replication. DNA has less chances of mutation , because the coding parts (exons, 2% of human genome) and interrupted by non coding parts (introns, 98% of human genome), hence in case of a mutation , there are high chances that they occur in non-coding region. One more advantage of DNA is the proof reading during the replication process, which ensures that no mutations are inserted.Due to high stability of DNA over RNA, it was chosen as genetic material of evolved species.
How was the first cell formed?
The generally accepted version of Abiogenesis (the formation of living from non-living materials) is that what formed first were self-replicating molecules, possibly RNA or something similar which can act as both a template for themselves and also an enzyme to catalyse self-replication. Different replicator would have competed with each other for raw materials to create duplicates of themselves with the fastest and most accurate replicators dominating over slower or less accurate rivals. It seems likely that such replicators also became ("evolved into") enzymes capable of breaking down rival replicators. This digestion would have provided further raw materials for the successful molecules at the expense of the less successful. Present while all this was going on were naturally occurring oils produced during similar chemical process taking place at the time. Oils naturally form hollow balls (called "liposomes"). If one of these self-replicating molecules became encapsulated inside a liposome, it would be protected from attack by rival replicating molecules. This, in effect is the first cell. EDIT: @ Simon. The bible is not a text book. It is a collection of Bronze Age myths and legends written by Bronze Age scribes. It provides no explanation of cells at all for the very good reason that Bronze Age people had no idea they even existed (apparently god forgot to tell them when they were writing the bible). There is no justification for ever saying "I have a gap in my knowledge or understanding and the only possible way of filling it is to invent a supernatural being"
Every other code that we have ever known to exist has a creator, what about DNA?
How about the code that makes every bag of potato chips act the same way - the big unbroken chips are always on the top, and the crumbs are down at the bottom?No code actually involved. it just turns out that whenever a large and a small chip are edge-to-edge, it’s easier for the smaller chip to slide under the big one than vice versa.Similarly, there’s good lab evidence that DNA can just happen due to the way chemistry and physics works. DNA and RNA are made up of nucleic acids, and we already *know* that those can be created by chance by filling up a container with stuff like methane and CO2 and feeding it some energy. The Miller-Urey experiment showed that back in 1952.https://en.wikipedia.org/wiki/Mi...(Note that RNA self-replicators almost certainly came first, because RNA can self-replicate, while DNA can only replicate by making an RNA mirror image of itself, then making a DNA mirror of the RNA mirror string…)Other things we know about nucleic acids are that if there’s a bunch of them floating in a liquid, they’ll randomly collide, and sometimes bond together and form a chain. And when the chain gets long enough, things start to happen…A big advance came earlier this year, when Philipp Holliger of the MRC Laboratory of Molecular Biology in Cambridge, UK, and colleagues unveiled an RNA enzyme called tC19Z. It reliably copies RNA sequences up to 95 letters long, almost half as long as itself (Science, vol 332, p 209). To do this, tC19Z clamps onto the end of an RNA, attaches the correct nucleotide, then moves forward a step and adds another. “It still blows my mind that you can do something so complex with such a simple molecule,” Holliger says.https://www.newscientist.com/art...Yes, this sort of molecule happening by chance is unlikely - you’re more likely to get struck by lightning on the same day you win $750 million in the Powerball lottery than have it happen in a test tube you’re cooking in your spare bedroom.What people don’t realize is that if you have a test tube the size of the Pacific Ocean, and you cook it for several hundred million years, eventually even very unlikely things will happen by chance….
Can you disprove this creationist statement? (Not claiming evolution is false)
Scientists write answers with references. Who claimed/calculated it?“Probability of just one DNA arranging itself”… One DNA? DNA of two different people are very close, but not similar. What specific DNA arrangement are we talking about? Genes are mutating and changing constantly. There’s no fixed DNA formation.Imagine you have four chemicals in your hand. You know that mixing these four chemicals in a certain ratio will give you Chemical X! But you do not know the ratio. Yet, you have billions of test tubes, and millions of hands to pour the chemicals simultaneously. How long will it take before you figure out the actual ratio?The DNA had its chances. A human body has close to one hundred trillion bacteria living in it (more than your body cells). Imagine how many bacteria were present when the whole world contained only unicellular organisms (mostly bacteria). Now, the genetic codes of each essential gene were tried and tested in each one of them. Nature (evolution) had time and resources to make errors. It had only four base pairs to work with. Yet, evolution of multi-cellular organisms from single cellular organisms took nearly 2 billion years. Because most of the genes regarding essential biochemical pathways had to be fixed.Genetic information is complicated, but not as complicated as some people claim it to be. They just like the awe of the things they do not understand.FINALLY, why use inches? Why not nanometers? You’ll get closer to the previous value! If you are still using inches, grow up. Metric system is in place. And they use parsecs.
According to the RNA world hypothesis, there was an RNA molecule that could self-replicate. How does that work?
DNA can replicate under some conditions, but it can’t act as a enzyme. DNA requires another molecule to act as an enzyme. The double strand structure of DNA limits the shape that the molecule can take, so it can’t catalyze chemical reactions.The enzymes that enable DNA to replicate in extant organisms are proteins, so they are made of amino acids. So DNA couldn’t replicate unless there were amino acids around. RNA could replicate, even if there were no amino acids around.Both RNA and DNA are made of a simple sugar and nucleic acides bound together. Enzymes in extant organisms are made of amino acids. So if DNA codes for proteins, and proteins catalyze the replication of DNA, then it seems that the two must have emerged at the same time.RNA can replicate and act as an enzyme. One RNA molecule can act as the enzyme that enables another RNA molecule to replicate. The single strand structure of RNA enables it to take on a wide variety of shapes, so it can catalyze chemical reactions.One model for biogenesis hypothesizes that the first living things (proto-organisms?) used RNA instead of DNA to pass on hereditary information. This is called the ‘RNA world’ model. This proto-organism had no enzymes made of protein. The proto-organism used enzymes made of RNA.The RNA organisms evolved into DNA organisms in this model. Complex organisms made almost completely from RNA evolved to make protein and DNA to better replicate themselves. The remaining RNA organisms went extinct.The RNA remains in modern organisms as a way of translating the DNA code in a protein code. However, the concept of translating is rather subjective. Maybe it is more accurate to say that the RNA molecule builds a cell that makes more RNA molecules. The DNA and the proteins are basically the means by which an RNA molecule replicates itself. Maybe in the past, the RNA made RNA more directly without DNA or protein.My own take is that the RNA-world doesn’t completely explain abiogenesis. It seems to me that the RNA organisms would at best be one small step in evolution.There are a lot of models out there that hypothesize a ‘metabolism first’ world. ‘Metabolism first models’ hypothesize that minerals were used to catalyze the synthesis of proteins before there was DNA or RNA. These organisms evolved make protein-based enzymes that made DNA and RNA.So maybe the RNA world is unnecessary step toward DNA based organisms. Or maybe RNA is an intermediate step to DNA.