Origin of Life & Evolution of Cells PDF

Introduction to Cell and its functions Unit-II ORIGIN OF LIFE and EVOLUTION OF CELLS Origins of life on earth.. How are fossil ages determined? What is life? Gro...

Introduction to Cell and its functions Unit-II ORIGIN OF LIFE and EVOLUTION OF CELLS Origins of life on earth.. How are fossil ages determined? What is life? Growth/ Reproduct ion Organisati on Heredity Characteri stics of Life Metabolis m and Response homeosta sis Evolution, adaptatio n Origin of life? Theories of the origin of life PANSPERMIA Given by Richer in 1865; also known as cosmozoic theory. Life formation did not take place on earth. It took place somewhere else in the space or on any other planet and ‘seeds of life’ were carried to the earth. Biological entities can be carried via asteroids, meteorites and comets. Lithopanspermia: rocks from one solar system to another Ballistic panspermia: rocks from one planet to another Directed panspermia: intentional, from the Earth to other planets via humans or extraterrestrial beings.  ABIOGENESIS Generation of all life from non-living matter decaying and rotting matter like straw, mud, etc. Very similar to the concept of spontaneous generation. Francesco Redi, Lazzaro Spallanzani and Louis Pasteur disproved these theories.  Oparin and Haldane Theory of Chemical Evolution Earth’s early atmosphere was a reducing environment, in which organic compounds could have formed from simpler molecules. The energy for this synthesis could have come from lightning and UV radiation. Haldane suggested that the early oceans were a solution of organic molecules, a “primitive soup” from which life arose.  Miller Urey experiment Tested the Oparin-Haldane hypothesis by creating laboratory conditions comparable to those that scientists at the time thought existed on early Earth. This experiment was found to produce many organic compounds including amino acids. Other theories.. Another hypothesis is that organic compounds were first produced in deep-sea hydrothermal vents, areas on the seafloor where heated water and minerals gush from Earth’s interior into the ocean, releasing Hydrogen rich molecules. There are also beliefs of “chilly start” theory of origin of life suggesting that life could have evolved from layers of deep ice https://www.sci.news/biology/life-hydrothermal-vents-07772.html https://www.discovermagazine.com/planet-earth/did-life-evolve-in-ice  Polymerised organic compounds It was found that solutions of amino acids or RNA nucleotides onto hot sand, clay, or rock, have produced polymers of these molecules. Adenine formed by condensation of HCN, sugars have been synthesized by condensation of HCHO catalysed by clays, alumina or divalent cations. Polymerised complexes of amino acids called proteinoids were then hypothesized to be formed. Catalytic proteins were formed. Primitive atmosphere Simple Complex Simple organic inorganic organic compounds compounds molecules Hydrogen, Simple Proteins, oxygen, carbon, sugars, nucleic acids, sulphur, purines, amino acids, phosphorous, pyrimidin polysaccharid nitrogen formed es, amino es NH3, HCN, H2O acids Coacervates: Biological evolution begins Self assembly: complex macromolecules organized into membrane bound droplets (coacervates and microspheres) in a colloidal system and developed selective permeability to store compounds, use energy, exchange material and increase in size. Elementary anerobic metabolism began using existing organic compounds. Heterotrophs evolved into autotrophs which performed chemosynthesis.  Protocells Amphipathic membranes developed, later enclosing RNAs which further evolved to form genetic material. Mechanisms of reproduction of molecules, natural selection and inheritance were later established RNA world hypothesis The first genetic material was most likely RNA, not DNA. RNA plays a central role in protein synthesis, but it can also function as a catalyst. Such RNA catalysts are called ribozymes. It is proposed that these ribozymes carried out initial replication of RNA from nucleotides. Early entities formed by the transfer of these RNAs to daughter cells formed protocells. Cognogeny & Evolution of prokaryotes Earth’s first organisms were single-celled prokaryotes that lived in the ocean. Stromatolites are layered rocks that form when certain prokaryotes bind thin films of sediment together (bacterial With gradual increase in the number of heterotrophs as they fossils) consumed nutrients of the ocean, there became a declination in organic nutrients. So they began to search other alternatives for obtaining food. Membranes Inheritance, energy Simple use Organic coacervates/ Heterotrophic compounds in Microspheres/ prokaryotes primordial soup Protocells  Origin of photosynthetic prokaryotes Some prokaryotes developed chlorophyll and like compounds to utilize the sun’s energy. Oxygenic photosynthesis first evolved—in photosynthetic prokaryotes similar to today’s cyanobacteria. This “oxygen revolution” had an enormous impact on life. In some of its chemical forms, oxygen attacks chemical bonds and can inhibit enzymes and damage cells. Some species survived in habitats that remained anaerobic, but most organisms adapted to becoming the eukaryotic cell.  Horizontal gene transfer There have been substantial movements of genes between organisms in the different domains. These took place through horizontal gene transfer a process in which genes are transferred from one genome to an unrelated genome through mechanisms such as exchange of transposable elements and plasmids, viral infection in between and within members of prokaryotes, archae and to some extent- eukaryotes. Lateral gene transfer is a powerful evolutionary force, allowing the The transfer of a gene encoding a unique metabolic enzyme from a species of Pasteurella bacteria to the protozoan parasite Trichomonas vaginalis is suspected to have facilitated the latter organism’s  Origin of the eukaryotic cell: Endosymbiosis Current evidence indicates that the eukaryotes originated by endosymbiosis when a prokaryotic cell engulfed a small cell that would evolve into the mitochondrion. Later, plastid forming cells were engulfed in a similar manner to give rise to a photosynthetic eukaryotic cell that could utilize atmospheric O2. The serial endosymbiosis hypothesis supposes that mitochondria evolved before plastids through a sequence of endosymbiotic events. Exhaustion of Chlorophyll Atmospheric oxygen nutrients Endosymbiosis Chemoautotrop Photoautotroph and eukaryotic hs prokaryotes ic prokaryotes cell Origin of multicellularity Some* single celled eukaryotes gave rise to multicellular forms, whose descendants include a variety of algae, plants, fungi, and animals. Transition to multicellularity involves structural and functional differentiation of cells. Causes? Cooperation offers selective advantage in ecology Small red algae fossils have been the earliest fossils of eukaryotic cells found. Many present-day animal phyla appeared early in the Cambrian period. This phenomenon is referred to as the Cambrian explosion. This was followed by animal and plant species colonizing the land, establishing complex Tissue differentiation mechanisms of evolution, Diversificatio adaptation, gene Multicellulari Conquest of n and exchange, organism ty land adaptation interactions, changes in body forms and development and the rise Biomolecules of the cell