The Biological Sciences - Molecular Biology (1981)

foreign [Music] [Music] approximately 4 billion years ago a newly formed planet revolves around its Sun an average yellow star water covers most of the planet's surface the atmosphere a swirling cloud of gaseous compounds methane hydrogen ammonia no oxygen at least no free oxygen is present in the primordial atmosphere energy pours into the system ultraviolet radiation from the Sun and electrical discharges in the atmosphere provide the energy for chemical reactions at this point in time the sea is a chemical broth the scene is set life is just off stage waiting for its cue to enter but first the molecules of Life must have a chance to form molecules which have the potential to control life's chemistry molecules with the potential for reproduction understanding how molecules control biological processes is what the science of molecular biology is trying to accomplish and with great success But ultimately molecular biologists would like to develop a framework of theory which describes how the molecular bases of Life got started back in the days of primordial soup our picture of Prebiotic Earth is based on evidence and on assumptions one important assumption is that the Earth and other planets all formed from the same cloud of dust and gas some 4.6 billion years ago since then life has changed our planet however the outer planets may have retained some of their original atmospheric composition as Voyager space probes analyzed Jupiter Saturn and their moons were they time traveling to the Earth of 4 billion years ago if so our hypothesis about the early Earth is a good one for the data indicate atmospheres containing hydrogen methane ammonia and water in the form of ice biologists have carried out many kinds of experiments to probe what may have happened in Earth's early environment a Pioneer in this work Dr Stanley Miller devised a reaction vessel simulating conditions thought to exist before life appeared on our planet he put in raw materials hydrogen methane ammonia and water an electric spark simulated lightning on a very small scale and the experiment was allowed to run for several days his results were stunning all sorts of organic compounds were created including compounds that have been thought to occur only in living organisms compounds such as amino acids sugars fatty acids the building blocks of life through these simulation experiments we can imagine how organic molecules may have formed spontaneously on primitive Earth but these are only building blocks small chemical units that in living things are assembled into long chains macromolecules once building block molecules accumulated in the primordial soup how were they coupled together to form proteins and other macromolecules one theory is that a common readily available substance promoted this process a substance which must have been abundant on primitive Earth clay [Music] is composed of microscopic mineral crystals which can act as catalysts to promote chemical reactions in theory building block molecules could be attracted to the charged surfaces of clay crystals under these conditions a crystal might act as a template for assembling macromolecules thank you [Music] watching crystals form we can imagine their special role as organizers of macromolecules there is great repetition and exactness in crystal structure did the first chains of macromolecules roll off a crystal assembly line [Music] there is another aspect of the clay Theory microscopic layers of clay have tremendous surface area all clay particles in one spoonful could be spread out it is estimated that their combined surface areas would exceed that of a football field think of the possibilities for synthesis of macromolecules on the shallow sea floors of ancient Earth there was a lot of space and plenty of time for synthesis [Music] foreign however to carry out any kind of life functions macromolecules must be contained so that they can associate and interact today the simplest cells are surrounded by membranes and it seems likely that thin envelopes of some sort were vital in the early development of life [Music] these slowly growing bodies are not alive they are simple membranes made from fatty acids a kind of building block molecule created under primitive Earth conditions like the membranes of living cells they concentrate molecules by allowing certain substances to enter while keeping others out [Music] if such membrane structures developed in the primordial soup they would have concentrated macromolecules an important step leading to life [Music] so the stage is set building blocks are rising spontaneously macromolecules synthesized on crystal templates concentration and Association these are preliminary steps but to be alive a collection of macromolecules must be able to acquire and utilize energy in living organisms Every Act involves energy transactions energy is used to produce new substances for Locomotion for getting materials into cells for Behavior life has an insatiable appetite for energy one of the landmark discoveries of molecular biology was that living things from microbes to mammals use the same kind of energy-rich molecules to drive their life processes molecules called ATP adenosine triphosphate ATP can be visualized as an adenosine unit with three phosphate molecules attached by high energy bonds the bond which holds the end phosphate is most easily broken giving up energy in a Cell ATP circulates donating its energy to chemical reactions early life forms may have extracted energy from atp-like molecules formed in the primordial soup but life is greedy reproducing competing in time the supply would have run out what then did early microorganisms develop the chemical Machinery to trap solar energy and use it to make energy-rich molecules like ATP this process called photosynthesis is the basis for life today from single-celled organisms to the complex cells of green plants photosynthesis transforms light energy into chemical energy for living [Music] within cells chemical processes are controlled by genes information molecules that can be duplicated and passed on to new generations of cells one of the ultimate goals of molecular biology is to understand this control system beginning with information molecules located in the cell nucleus [Music] the glistening precipitate forming in the test tube is pure DNA the master information molecule this DNA is extracted from nuclei taken from calf thymus gland here is all of the genetic information for a prize cow in principle DNA works like a tape recording that contains information for building macromolecules like tape DNA can be copied with high Precision assuring that future Generations will get the correct genetic instructions for example instructions on how a single fertilized egg should develop to become an active human being much of the coded information on DNA directs the synthesis of protein molecules not only familiar proteins like muscles tendons and hair but also the enzymes that catalyze chemical reactions associated with living [Music] enzymes do their work quietly carrying out digestion building new products or breaking down harmful ones for example when a scratch is disinfected with hydrogen peroxide an enzyme called catalase goes to work catalase deactivates hydrogen peroxide the enzyme chemically recognizes hydrogen peroxide breaking it down into harmless products water and oxygen the froth of bubbles is oxygen being given off in the reaction looking at the action of catalase consider that each of the thousands of reactions accompanying life is catalyzed by its own enzymatic protein and somewhere on information molecules within our cells are the instructions for each of these enzymes but what is the connection how does an information molecule like DNA code for a protein consider hemoglobin a red oxygen carrying protein found in blood cells painstaking work by biochemists has produced an accurate picture of this large molecule like all proteins hemoglobin is made up of a specific sequence of amino acids valine histidine leucine and so on for a total of almost 600 amino acid units making up a hemoglobin molecule translating this coded information into a protein requires intricate cellular machinery but before the process can begin a cell must have a supply of amino acids protein building blocks where do they come from [Music] part of the answer lies within chloroplasts the round green energy trapping bodies found in plant cells chloroplasts have the ability to synthesize amino acids from raw materials when an animal eats a plant it picks up plant proteins long chains of amino acids ready for reprocessing into animal protein [Music] protozoans illustrate this process at the cellular level [Music] here a paramecium is feeding on bacteria funneling them into food vacuoles where digestion occurs [Music] contained in a vacuole bacteria are broken down to their building blocks fats to fatty acids starches to simple sugars proteins amino acids and so on all of these digested products are absorbed into the cell and are either used for energy or recycled into new macromolecules foreign [Music] s must have obtained building blocks directly from their environment Scavenging molecules from the primordial soup as the soup became depleted some organisms may have developed the means of making their own building blocks just as bacteria and plants do today information molecules are the key to this primordial scenario but how they began programming proteins at other macromolecules remains a fascinating mystery at the heart of molecular biology perhaps in the not too distant future a team of molecular biologists will synthesize a genetic control system under primordial conditions and recreate some of the events which may have led to the first tiny cells [Music] foreign foreign [Music]