Full Answer
When did the first cells evolve?
As organic molecules evolved before cells, the molecules must have evolved about 4.5 billion years ago. The earliest cells may have been just nucleic acid inside a lipid membrane. Did DNA or RNA evolve first? Some scientists believe RNA evolved first.
Are present-day cells descended from one primordial ancestor?
In spite of these differences, the same basic molecular mechanisms govern the lives of both prokaryotes and eukaryotes, indicating that all present-day cells are descended from a single primordial ancestor. How did this first cell develop? And how did the complexity and diversity exhibited by present-day cells evolve? NCBI
How did the earliest cells make their own food?
The earliest cells were probably autotrophs - that is, they made their own food through photosynthesis. False - heterotrophs (got their food from other organic molecules) A digital clock uses DNA sequences to estimate how long ago related species diverged from a common ancestor.
What killed off the first cells on Earth?
The oxygen catastrophe killed off many early cells. The earliest cells were probably autotrophs - that is, they made their own food through photosynthesis. A digital clock uses DNA sequences to estimate how long ago related species diverged from a common ancestor.
What is the earliest form of cellular life?
ProkaryotesProkaryotes were the earliest life forms, simple creatures that fed on carbon compounds that were accumulating in Earth's early oceans. Slowly, other organisms evolved that used the Sun's energy, along with compounds such as sulfides, to generate their own energy.
How did cellular life originate?
The central hypothesis on the origin of the cell is that organic molecules self-assembled to form the first protocell some 4 billion years ago (Fig. 2).
What is the common ancestor of all life?
It is known as Luca, the Last Universal Common Ancestor, and is estimated to have lived some four billion years ago, when Earth was a mere 560 million years old.
What is common to all cellular life?
All cells process energy and nutrients. All cells use changes in its DNA to adapt to its environment. All cells contain a cytoplasm surrounded by a plasma membrane, DNA in the form of chromosomes and ribosomes.
What are the 7 theories of the origin of life?
Although science still seems unsure, here are some of the many different scientific theories on the origin of life on Earth.It started with an electric spark.Molecules of life met on clay.Life began at deep-sea vents.Life had a chilly start.The answer lies in understanding DNA formation.Life had simple beginnings.More items...•
What is cellular life?
2:3016:23Introduction to cellular life - YouTubeYouTubeStart of suggested clipEnd of suggested clipSo life on earth is cellular. And so that is one of the characteristics of life on earth all livingMoreSo life on earth is cellular. And so that is one of the characteristics of life on earth all living things are cellular they're either one cell or made of many cells stuck.
What is our oldest ancestor?
Australopithecus afarensisanamensis is the oldest unequivocal hominin, with some fossils dating from as far back as 4.2 million years ago. For years it has occupied a key position in the family tree as the lineal ancestor of Australopithecus afarensis, which is widely viewed as the ancestor of our own genus, Homo.
What is the most recent common ancestor of humans?
The exact origin of modern humans has long been a topic of debate. Modern humans originated in Africa within the past 200,000 years and evolved from their most likely recent common ancestor, Homo erectus. Modern humans (Homo sapiens), the species? that we are, means 'wise man' in Latin.
What are some examples of common ancestry?
Some examples, include the appearance of hind limbs in whales as evidence of a terrestrial ancestor, teeth exhibited by chickens, additional toes observed in modern horse species, and the back flippers of bottlenose dolphins.
What was the first genetic material?
RNAExperiments in the 1960s showed that messenger RNA has the ability to store genetic information, while transfer and ribosomal RNA have the ability to translate genetic information into proteins.
Is bacteria a cellular life form?
bacteria, singular bacterium, any of a group of microscopic single-celled organisms that live in enormous numbers in almost every environment on Earth, from deep-sea vents to deep below Earth's surface to the digestive tracts of humans.
Which is a basic characteristic of all living cells quizlet?
What characteristics do all living things share? Living things are made up of basic units called cells, are based on a universal genetic code, obtain and use materials and energy, grow and develop, reproduce, respond to their environment, maintain a stable internal environment, and change over time.
What is Luca and what is a plausible explanation for the origin of cellular life?
What is LUCA, and what is a plausible explanation for the origin of cellular life? LUCA is the hypothetical "last universal common ancestor" of all extant life on Earth and is believed to have existed 3.8-3.7 billion years ago.
How was the cell discovered?
Initially discovered by Robert Hooke in 1665, the cell has a rich and interesting history that has ultimately given way to many of today's scientific advancements.
When was the origin of photosynthesis?
3.4 billion years oldOrigin. Available evidence from geobiological studies of Archean (>2500 Ma) sedimentary rocks indicates that life existed 3500 Ma. Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old, consistent with recent studies of photosynthesis.
Is there non cellular life?
Viruses, virions, and viroids are all examples of non-cellular life. Viruses are parasites that infect plants, animals, fungi, and bacteria. They consist of genetic material and a protective protein coat. Viruses are dormant without a host.
What is the scenario of precellular evolution?
A scenario of precellular evolution is presented that involves cohesion of the genomes of the emerging cellular life forms from primordial pools of small genetic elements that eventually segregated into hosts and parasites.
Is all life on Earth cellular?
All life on earth can be naturally classified into cellular life forms and virus-like selfish elements, the latter being fully dependent on the former for their reproduction.
How long ago did cells evolve?
Nevertheless, synthesis of theoretical, computational and experimental approaches from diverse disciplines seems to be instrumental in progressively narrowing down the space of open possibilities which conceivably is the best one can hope for when it comes to events that took place about 4 billion years ago, and perhaps only once in the observable universe.
How many genes are in a prokaryotic cell?
Attempts to reconstruct the gene set for a minimal cell by combining comparative genomic data on gene conservation and biological considerations yield estimates of about 250–300 genes (Gil et al. 2004; Koonin 2003; Mushegian 1999; Mushegian and Koonin 1996 ). Numerous intracellular parasitic bacteria with gene repertoires of this size and even smaller indeed have been isolated (McCutcheon and Moran 2012; Moran et al. 2008 ). Some of the smallest bacteria in this category, with less than 200 genes, have lost genes for certain components of the translation system and might be on their way to becoming organelles (Nakabachi et al. 2006; Sloan et al. 2014 ). Endosymbiotic organelles, most notably mitochondria and chloroplasts, arguably represent the penultimate stage of cellular degradation (Gray 1999, 2012; Gray et al. 2001; Lang et al. 1999 ). These organelles retain their own genomes, albeit with very few genes, their own internal translation systems and their own membranes, although substantially modified from the ancestral bacterial membranes. In particular, the organelle membranes are equipped with protein import systems that deliver into the organelle the protein products of former endosymbiont genes that have been transferred to the nuclear genome of the host. Thus, the organelles remain cell-like reproducers but most of their protein-coding capacity has been relegated to the genome of a distinct reproducer, the host cell. The ultimate stage of cellular degradation are derivatives of the mitochondria, such as hydrogenosomes and mitosome that have lost genomes and translation systems but retain the membrane (Embley 2006; van der Giezen 2009 ). All the proteins required for the function of these organelles are encoded in the nucleus, synthesized by the cytoplasmic translation system and transported into the organelle. Thus, in this case, the membrane seems to be the only remaining entity that maintains the cell-like status of the organelles.
What are the key components of the DNA replication machinery?
The richness of the reconstructed gene repertoire of the LUCA would imply that this ancestral life form possessed the same level of organization as modern bacteria and archaea if not for two glaring holes in its reconstructed gene set: (i) the key components of the DNA replication machinery, namely the polymerases that are responsible for the initiation (primases) and elongation of DNA replication, and for gap-filling after primer removal, and the principal DNA helicases, and (ii) most of the enzymes of lipid biosynthesis. These essential proteins fail to make it into the reconstructed gene repertoire of LUCA because the respective processes in bacteria, on the one hand, and archaea, on the other hand, are catalyzed by distinct, unrelated enzymes and, in the case of membrane phospholipids, yield chemically distinct membranes (the archaeal membrane phospholipids are isoprenoid ethers of glycerol 1-phosphate whereas bacterial lipids are fatty acid esthers of glycerol 3-phosphate, i.e., the lipids in the two domains differ not only in their chemical composition but also in chirality) (Edgell and Doolittle 1997; Leipe et al. 1999; Lombard et al. 2012; Martin and Russell 2003; Mushegian and Koonin 1996; Pereto et al. 2004 ).
What is the difference between cellular and selfish?
In contrast, simple selfish elements are replicators that can complete their life cycles within the host cell starting from genomic RNA or DNA alone . The origin of the cellular organization is the central and perhaps the hardest problem of evolutionary biology. I argue that the origin of cells can be understood only in conjunction with the origin and evolution of selfish genetic elements. A scenario of precellular evolution is presented that involves cohesion of the genomes of the emerging cellular life forms from primordial pools of small genetic elements that eventually segregated into hosts and parasites. I further present a model of the coevolution of primordial membranes and membrane proteins, discuss protocellular and non-cellular models of early evolution, and examine the habitats on the primordial earth that could have been conducive to precellular evolution and the origin of cells.
What are the two classes of cells that define the cellular state and cleanly separate cells from virus-like entities?
The two classes of such complexes that define the cellular state and cleanly separate cells from virus-like entities are (i) membrane embedded energy transformation and molecular transport systems and (ii) translation system that makes all the proteins required for the cell function. A fundamental and striking feature of cells is that formation of a cell de novo has never been observed. According to the famous dictum of Rudolf Virchow, Omnis cellula e cellula, i.e. new cells are generated exclusively from old ones, by various forms of division or budding (Virchow 1858 ). Using the definitions of Szathmary and Maynard Smith (Szathmary and Maynard Smith 1997 ), cells are reproducers rather than replicators, i.e. cellular reproduction is not reducible to genome replication, in contrast to the reproduction of many simple selfish elements. Indeed, all the advances of synthetic biology notwithstanding, we are far from being able to generate a cell using genomic DNA alone, whereas for example positive-strand RNA viruses or plasmids can be reproduced indefinitely starting from pure RNA or DNA.
Why are lipids not viable in primordial cells?
A pure lipid bilayer is not a viable solution for the membrane of a primordial cellular life form because it would effectively prevent exchange of all ions and complex molecules between the inside of a vesicle and the environment. Because of the hydrophobic barrier, ions can penetrate the lipid bilayer only with the help of specialized membrane proteins, such as channels or translocases. The membrane-embedded portions of these proteins consist almost entirely of hydrophobic amino acids, and the proteins themselves are water-insoluble. Hence a chicken and egg problem: channels and translocases could not evolve without membranes, whereas membranes without channels and translocators could not support the first life forms. Given the dependence between the conductivity of lipid bilayers and the length of the acyl tails (Paula et al. 1996 ), it has been proposed that primordial membranes might have been built of lipids with short hydrophobic tails and so were thinner than modern ones, with a lower hydrophobic barrier that allowed ions to spontaneously cross the membrane (Deamer 1997, 2008 ). This mechanism, however, would not work for large molecules such as proteins or polynucleotides, the transport of which is thought to have been important during the early steps of cellular evolution, for proto-cell division and/or for the functioning of primordial virus-like particles (see also below).
Is Luca a modern cell?
The “uniformitarian assumption”, namely, that LUCA was a more or less regular, modern-type cell, akin to the extant bacteria and archaea, often seems to be adopted in accounts of early evolution without much critical evaluation (Forterre et al. 1992; Forterre and Philippe 1999 ); (Forterre et al. 2005 ). To account for the lack of conservation of key elements of the DNA replication and membrane biogenesis machineries, the uniformitarian hypotheses of LUCA would invoke one of the two scenarios:
What are biological cells?
Contemporary biological cells are highly sophisticated dynamic compartment systems which separate an internal volume from the external medium through a boundary, which controls, in complex ways, the exchange of matter and energy between the cell's interior and the environment. Since such compartmentalization is a fundamental principle of all forms of life, scenarios have been elaborated about the emergence of prebiological compartments on early Earth, in particular about their likely structural characteristics and dynamic features. Chemical systems that consist of potentially prebiological compartments and chemical reaction networks have been designed to model pre-cellular systems. These systems are often referred to as " protocells ". Past and current protocell model systems are presented and compared. Since the prebiotic formation of cell-like compartments is directly linked to the prebiotic availability of compartment building blocks, a few aspects on the likely chemical inventory on the early Earth are also summarized.
Why are molecular data and methods important to evolutionary analysis?
Molecular data and methods have become centrally important to evolutionary analysis, largely because they have enabled global phylogenetic reconstructions of the relationships between organisms in the tree of life. Often, however, molecular stories conflict dramatically with morphology-based histories of lineages. The evolutionary origin of animal groups provides one such case. In other instances, different molecular analyses have so far proved irreconcilable. The ancient and major divergence of eukaryotes from prokaryotic ancestors is an example of this sort of problem. Efforts to overcome these conflicts highlight the role models play in phylogenetic reconstruction. One crucial model is the molecular clock; another is that of 'simple-to-complex' modification. I will examine animal and eukaryote evolution against a backdrop of increasing methodological sophistication in molecular phylogeny, and conclude with some reflections on the nature of historical science in the molecular era of phylogeny.
What are the two types of cell envelopes in bacteria?
Curiously, two distinct types of cell envelope exist in bacteria: monoderm (Gram-positive) with a single membrane, and diderm (Gram-negative) with two membranes. When and how the transition between monoderm and diderm bacteria occurred is one of the greatest questions in evolutionary biology, and incites intense debate. Fortunately, we have ideal model organisms that can help better understand this transition: Negativicutes and Halanaerobiales. These two distinct and diverse clades of bacteria represent an evolutionary enigma; they belong phylogenetically to the classical monoderm Firmicutes, yet possess outer membranes (OM) with lipopolysaccharides (LPS) similar to classic diderm bacteria. The three goals of this Doctoral work are to: 1. Describe the outer membranes of diderm Firmicutes, 2. Elucidate the evolutionary history of these envelopes, 3. Find a mechanism of transition between diderm and monoderm Firmicutes.
What are the major evolutionary transitions?
Major evolutionary transitions include the origin of prokaryotic and then eukaryotic cells, multicellular organisms and eusocial animals. All or nearly all cellular life forms are hosts to diverse selfish genetic elements with various levels of autonomy including plasmids, transposons and viruses. I present evidence that, at least up to and including the origin of multicellularity, evolutionary transitions are driven by the coevolution of hosts with these genetic parasites along with sharing of ‘public goods’. Selfish elements drive evolutionary transitions at two distinct levels. First, mathematical modelling of evolutionary processes, such as evolution of primitive replicator populations or unicellular organisms, indicates that only increasing organizational complexity, e.g. emergence of multicellular aggregates, can prevent the collapse of the host–parasite system under the pressure of parasites. Second, comparative genomic analysis reveals numerous cases of recruitment of genes with essential functions in cellular life forms, including those that enable evolutionary transitions. This article is part of the themed issue ‘The major synthetic evolutionary transitions’.
What are the features of the genetic code?
First, nucleic acids are highly complicated polymers requiring numerous enzymes for biosynthesis. Secondly, proteins have a simple backbone with a set of 20 different amino acid side chains synthesized by a highly complicated ribosomal process in which mRNA sequences are read in triplets. Apparently, both nucleic acid and protein syntheses have extensive evolutionary histories. Supporting these processes is a complex metabolism and at the hub of metabolism are the carboxylic acid cycles. This paper advances the hypothesis that the earliest predecessor of the nucleic acids was a β-linked polyester made from malic acid, a highly conserved metabolite in the carboxylic acid cycles. In the β-linked polyester, the side chains are carboxylic acid groups capable of forming interstrand double hydrogen bonds. Evolution of the nucleic acids involved changes to the backbone and side chain of poly (β-d-malic acid). Conversion of the side chain carboxylic acid into a carboxamide or a longer side chain bearing a carboxamide group, allowed information polymers to form amide pairs between polyester chains. Aminoacylation of the hydroxyl groups of malic acid and its derivatives with simple amino acids such as glycine and alanine allowed coupling of polyester synthesis and protein synthesis. Use of polypeptides containing glycine and l-alanine for activation of two different monomers with either glycine or l-alanine allowed simple coded autocatalytic synthesis of polyesters and polypeptides and established the first genetic code. A primitive cell capable of supporting electron transport, thioester synthesis, reduction reactions, and synthesis of polyesters and polypeptides is proposed. The cell consists of an iron-sulfide particle enclosed by tholin, a heterogeneous organic material that is produced by Miller-Urey type experiments that simulate conditions on the early Earth. As the synthesis of nucleic acids evolved from β-linked polyesters, the singlet coding system for replication evolved into a four nucleotide/four amino acid process (AMP = aspartic acid, GMP = glycine, UMP = valine, CMP = alanine) and then into the triplet ribosomal process that permitted multiple copies of protein to be synthesized independent of replication. This hypothesis reconciles the "genetics first" and "metabolism first" approaches to the origin of life and explains why there are four bases in the genetic alphabet.
What is the importance of repeating sequences in evolution?
Repeating sequences generated from RNA gene fusions/ligations dominate ancient life, indicating central importance of building structural complexity in evolving biological systems. A simple and coherent story of life on earth is told from tracking repeating motifs that generate α/β proteins, 2-double-Ψ-β-barrel (DPBB) type RNA polymerases (RNAPs), general transcription factors (GTFs) and promoters. A general rule that emerges is that biological complexity that arises through generation of repeats is often bounded by solubility and closure (i.e. to form a pseudo-dimer or a barrel). Because the first DNA genomes were replicated by DNA template-dependent RNA synthesis followed by RNA template-dependent DNA synthesis via reverse transcriptase, the first DNA replication origins were initially 2-DPBB type RNAP promoters. A simplifying model for evolution of promoters/replication origins via repetition of core promoter elements is proposed. The model can explain why Pribnow boxes in bacterial transcription (i.e. (-12)TATAATG (-6)) so closely resemble TATA boxes (i.e. (-31)TATAAAAG (-24)) in archaeal/eukaryotic transcription. The evolution of anchor DNA sequences in bacterial (i.e. (-35)TTGACA (-30)) and archaeal (BREup; BRE for TFB recognition element) promoters is potentially explained. The evolution of BREdown elements of archaeal promoters is potentially explained.
When were bacteriophages discovered?
About one century ago bacteriophages, viruses that infect bacteria, were discovered and reported in the scientific literature. This review aims at a comprehensive survey of bacteriophage discovery, research and applications since the 1920s and its impact on molecular biology, biotechnology, health, ecology and economy. Phage therapy has been proven a valuable asset since the early 1920s to deal with pathogenic bacterial infections. It has been practiced ever since, especially in the former Soviet Union and in Eastern Europe. The Western world remained skeptical and resorted to the widespread use of antibiotics since the 1940s. Now that antibiotic resistance among pathogenic bacteria has spread alarmingly and few really novel antibiotic compounds are in the pipeline, renewed attention is being directed to the use of phages as antibacterial agents in medicine. Because of this renewed interest in phage therapy in the Western world, novel applications with phages are being pursued in the human health, environmental and the agri‐food sectors. This review will focus on 1) the history of early phage use and its successes and problems, 2) the study of phages as important tools in the development of molecular biology and biotechnology, 3) current developments in phage research including the use of phage endolysins for use in antibacterial treatment, 4) phage production systems including undesirable phage contamination of industrial fermentation processes based on bacteria, 5) recent applications in phage therapy and in phage based control, and 6) the roles of phages in nature and in the human gut.
What is the first cell?
The first cell is presumed to have arisen by the enclosure of self-replicating RNAin a membrane composed of phospholipids( Figure 1.4). As discussed in detail in the next chapter, phospholipidsare the basic components of all present-day biological membranes, including the plasma membranes of both prokaryotic and eukaryotic cells. The key characteristic of the phospholipids that form membranes is that they are amphipathicmolecules, meaning that one portion of the molecule is soluble in water and another portion is not. Phospholipids have long, water-insoluble (hydrophobic) hydrocarbon chains joined to water-soluble (hydrophilic) head groups that contain phosphate. When placed in water, phospholipids spontaneously aggregate into a bilayer with their phosphate-containing head groups on the outside in contact with water and their hydrocarbon tails in the interior in contact with each other. Such a phospholipid bilayerforms a stable barrier between two aqueous compartments—for example, separating the interior of the cell from its external environment.
How long ago did life start?
The First Cell. It appears that life first emerged at least 3.8 billion years ago, approximately 750 million years after Earth was formed (Figure 1.1). How life originated and how the first cell came into being are matters of speculation, since these events cannot be reproduced in the laboratory.
What is the nucleus of an eukaryotic cell?
Like prokaryotic cells, all eukaryotic cellsare surrounded by plasma membranes and contain ribosomes. However, eukaryotic cells are much more complex and contain a nucleus, a variety of cytoplasmic organelles, and a cytoskeleton(Figure 1.7). The largest and most prominent organelle of eukaryotic cells is the nucleus, with a diameter of approximately 5 μm. The nucleus contains the genetic information of the cell, which in eukaryotes is organized as linear rather than circular DNAmolecules. The nucleus is the site of DNA replication and of RNAsynthesis; the translationof RNA into proteinstakes place on ribosomes in the cytoplasm.
What is the largest organelle in eukaryotes?
The largest and most prominent organelle of eukaryotic cells is the nucleus, with a diameter of approximately 5 μm. The nucleus contains the genetic information of the cell, which in eukaryotes is organized as linear rather than circular DNAmolecules.
How did photosynthesis help the cell?
The development of photosynthesisis generally thought to have been the next major evolutionary step, which allowed the cell to harness energy from sunlight and provided independence from the utilization of preformed organic molecules. The first photosynthetic bacteria, which evolved more than 3 billion years ago, probably utilized H2S to convert CO2to organic molecules—a pathway of photosynthesisstill used by some bacteria. The use of H2O as a donor of electrons and hydrogen for the conversion of CO2to organic compounds evolved later and had the important consequence of changing Earth's atmosphere. The use of H2O in photosynthetic reactions produces the by-product free O2; this mechanism is thought to have been responsible for making O2abundant in Earth's atmosphere.
What is the next step in evolution?
The next step in evolution was the formation of macromolecules. The monomeric building blocks of macromolecules have been demonstrated to polymerize spontaneously under plausible prebiotic conditions. Heating dry mixtures of amino acids, for example, results in their polymerization to form polypeptides. But the critical characteristic of the macromolecule from which life evolved must have been the ability to replicate itself. Only a macromolecule capable of directing the synthesis of new copies of itself would have been capable of reproduction and further evolution.
What is the 2nd edition of The Cell?
The Cell: A Molecular Approach. 2nd edition.
How did the parasitic elements evolve?
The genes they parasitized began to evolve different types of genetic information and other barriers to protect themselves from the genetic freeloaders, which ultimately evolved into cells.
Where did viruses come from?
The predominant theories for the origin of viruses propose that they emerged either from a type of degenerate cell that had lost the ability to replicate on its own or from genes that had escaped their cellular confines.
Why do giant viruses go undetected?
Giant, Yet Undetected. Abergel and Claverie suspected that giant viruses abound in the natural world but go undetected because of their size. They took samples of amoebae-filled water from nearly every locale they visited.
How many genes are in the pandora virus?
With a staggeringly high number of genes, approximately 2,500, pandoravirus seemed to herald an entirely new class of viral life. "More than 90 percent of its genes did not resemble anything else found on Earth," Abergel said. "We were opening Pandora's box, and we had no idea what might be inside."
What does it mean when a virus is old?
It means that a giant virus or one of its ancestors existed before other types of life and may have played a major role in shaping life as we know it. This could mean that viruses are one of the dominant evolutionary forces on this planet and that each organism has a deep, viral past. ( Read "Small, Small World" in National Geographic magazine .)
What are the three domains of life?
He and others are accumulating evidence that viruslike elements spurred several of the most important stages in the emergence of life: the evolution of DNA, the formation of the first cells, and life's split into three domains—Archaea, bacteria, and eukaryotes.
When were giant viruses first described?
Giant viruses, first described in 2003, began to change that line of thinking for some scientists. These novel entities represented an entirely new kind of virus. Indeed, the first specimen—isolated from an amoeba living in a cooling tower in England—was so odd that it took scientists years to understand what they had.
What were the first cells?
The earliest cells were probably autotrophs - that is, they made their own food through photosynthesis.
When did life first appear?
Life first appeared about 4 billion years ago, but photosynthesis did not appear until 3 billion years ago.
Why was oxygen toxic to early cells?
Oxygen was toxic to most early cells because they had evolved in its absence. As a result, many of them died out. Place the following in the order in which they evolved: eukaryotic cell, prokaryotic cell, photosynthesis, organic molecules. organic molecules - prokaryotic cell - photosynthesis - eukaryotic cell.
How long ago did organic molecules evolve?
As organic molecules evolved before cells, the molecules must have evolved about 4.5 billion years ago.
What is the history of life on Earth based on?
Much of what we know about the history of life on Earth is based on the fossil record.
Which formed first, the oceans or the atmosphere?
In the early Earth, the oceans formed first, followed by the atmosphere.
Do fossils need to be dated?
In order for fossils to provide useful information, they must be dated.
Comparative Genomics, Ancestral Gene Repertoires, and Luca
on The Origin of Cell Membranes
- As pointed out above, the second major area of non-homology between archaea and bacteria involves the lipid chemistry and the enzymes of lipid biosynthesis. The glycerol moieties of archaeal and bacterial phospholipids are of the opposite chiralities, and the hydrophobic chains differ as well, being based on fatty acids in bacteria and on isoprenoids in archaea. In addition, i…
Coevolution of Membranes and Membrane Proteins
- A common solution to chicken and egg paradoxes is coevolution of the egg and the chicken. With regard to the evolution of cell membranes, this idea implies coevolution of the membranes and membrane proteins. Multiple lines of evidence indicate that the universal membrane ATPases (ATP synthases) evolved from simple membrane pores that recruited helicases and other protei…
The Habitats of Pre-Cellular Life Forms and The Origin of Cells
- Compartmentalization is obviously essential for the evolution of ensembles of replicators, even if only as means for concentrating the required monomers and thus enabling their polymerization (Meyer et al. 2012). It is well recognized that molecular crowding, i.e. high intracellular concentrations of the abundant macromolecular complexes, such as r...