Cell Biology: Life Functions

[Music] in the biology laboratory we can easily cultivate a culture of yeast a simple plant taking a sample of this yeast we prepare it for viewing under the microscope through timlapse photography the yeast cells are seen to grow and reproduce these cells are alive now here are time-lapse films of sulfur crystals they too appear to move and grow but are they alive no what then distinguishes non-living things from living organisms the answer lies in the chemistry of individual cells for in the cell chemical reactions and interactions take place and give rise to certain processes known as life functions thus the cell represented by this mod model is the basic unit of life although scientists have much to learn about the nature of life itself they know a good deal about the organel the structures of the cell and the chemical and physical life processes that take place within them one important physical characteristic of any cell is that it is made up of molecules whether it is a plant cell such as this yeast or an animal cells such as these human cells the molecules within cells are in constant motion we'll demonstrate how the molecules tend to become evenly distributed as they move the dye in this bottle is highly concentrated that is the dye molecules are close together a few drops are added to the flask of water we see in time-lapse photography that the Dy moves from a region of Greater density where it is concentrated to a region of lesser density this process diffusion occurs among the molecules within the cell let's now demonstrate the diffusion of molecules into the cell in this Beaker we have a dyed solution of sugar water this Beaker contains plain water thus there is less density or concentration of water molecules in this Beaker because of the dye and sugar molecules than there is in the beaker of plain water covering this thisal tube is a very thin membrane this membrane is roughly similar to that which surrounds and gives shape to a cell it is a differentially permeable membrane which means that some molecules will pass through its pores and others will not this particular membrane is permeable to water molecules but not to dye and sugar molecules which are larger we place the tube and attached membrane into this Beaker which has a high concentration of water molecules and pour the dyed sugar solution into the tube we marked the level of the sugar solution in the tube sometime later the dyed sugar solution has become lighter this indicates that water molecules are diffusing into the tube that is water molecules are passing from a region of higher concentration through the membrane to a region of lower concentration also the level of liquid in the tube has risen indicating that diffusion is taking place against the force of gravity the diffusion of water molecules through a differentially permeable membrane is called osmosis the force generated by osmosis shown in the rising level in the tube is called osmotic pressure what is the function of the two physical processes diffusion and osmosis in the cell it is this through diffusion and osmosis and a third process known as active transport in which the cell actively draws certain molecules through its membrane the nutrients necessary to life functions are obtained and the wastes expelled every cell whether part of a complex tissue or a single celled protoo is surrounded by a film of water the water contains molecules of certain chemical compounds or nutrients these nutrients essential to the cell's life functions often enter and reach the various organel of the cell through the physical processes of diffusion and osmosis within the organel chemical processes initiate life functions including active transport movement growth and reproduction all of these functions require energy how do molecules inside the cell chemically interact to yield energy to begin with we know that the protoplasm of the cell consists mainly in addition to water of molecules of nutrients here are molecular models of a typical fat carbohydrate and proteum this model shows only some of the atoms of a typical protein molecule proteans are the basic building blocks of cell structures protein molecules are composed of atoms of carbon hydrogen oxygen and nitrogen here is the chemical formula for this part of a particular protein molecule here is a schematic drawing of the same part of a protein molecule this geometric figure represents two smaller molecules linked together in the cell protein molecules may be split in a process requiring a molecule of water the component molecules thus formed are called amino acids each has its own formula this process is called hydrolysis and releases energy the reverse process may also occur amino acids can join to produce a protein molecule this process requires energy and splits off a molecule of water in this way proteins are put together or synthesized in the Cell from molecules of amino acids let's remember that every protein is an extremely large molecule often synthesized from hundreds of amino acids some proteins enable red blood cells to carry oxygen a function related to respiration other proteins help muscle cells contract a function related to movement and still others form skin and hair cells a function related to growth energy for the cell to perform other life functions of continued growth and reproduction is yielded mainly from a second group of chemical compounds carbohydrates this is a model of a very common carbohydrate called Mose carbohydrate molecules are made up of atoms of carbon hydrogen and oxygen the exact number of each in this molecule is shown in the formula for malose here is a schematic drawing of maltose this carbohydrate molecule is composed of smaller molecules called called simple sugars in the cell simple sugars may be joined together to produce large carbohydrate molecules or carbohydrates may be split apart to form the smaller molecules of simple sugars this splitting apart process releases energy and utilizes a molecule of water when simple sugars join to produce a large carbohydrate molecule the process requires energy and splits off a molecule of water carbohydrates are utilized in the living cell to yield immediate energy reproduction seen here highly speeded up is one life function requiring immediate energy to carry on life functions cells May utilize a reserve store of energy supplied by a third group of compounds fats fat molecules are extremely large this model shows one of the typical fat or lipid molecules carbon hydrogen and oxygen atoms make up fat molecules the chemical formula for this particular fat shows the large number of atoms combined in a fat molecule like other nutrient molecules fats are also composed of smaller molecules these are fatty acids and glycerol in the cell these molecules may be joined together or they may be split apart splitting apart releases energy and utilizes three molecules of water combining requires energy and splits off three molecules of water through this process a fat molecule is formed let's review briefly in the living cell we've seen that molecules of fats carbohydrates and proteins may be split apart by chemical reaction with water this process is hydrolysis and it releases energy the splitting a part of nutrient molecules hydrolysis provides only a very small fraction of the overall energy requirements of the cell much more energy for life functions is released when the nutrient molecules are broken down through the process of oxidation the substances in the cell responsible for oxidation are compounds called enzymes hundreds of different enzymes are present in a living cell a particular reaction in oxidizing a nutrient molecule is initiated or hastened by a particular enzyme an enzyme is simply one kind of very large protein molecule the characteristics of a given cell depend upon the type of enzymes present the key to the formation of any enzyme lies in the nucleus in thread-like structures the chromosomes in these living cells the dark chromosomes are easily seen within the chromosomes is a complex chemical substance known as deoxyribonucleic acid usually abbreviated DNA DNA molecules are made up of four different types of smaller molecules called nucleotides the arrangement of the nucleotide molecules in DNA determines the particular kinds of enzymes that will be formed this is a two-stage process first DNA acts as a kind of pattern for the formation of another substance also composed of nucleotides this is a nucleotide of ribonucleic acid abbreviated as RNA DNA nucleotides will attract some of the RNA nucleotides which are chemically different and are also four in number however some of the RNA nucleotides will be rejected when the proper RNA na components are attracted a completed RNA molecule patterned after the DNA molecule is formed this RNA molecule is then released from the DNA molecule and passed out from the cell nucleus into the outer region of the cell the cytoplasm it is in the cytoplasm that the second stage of enzyme formation takes place this stage begins with RNA one particular amino acid molecule is attracted to a group of three nucleotides in the RNA molecule additional amino acid molecules link together to form the large protein molecule called an enzyme when we realize the thousands of combinations of nucleotides that can form RNA we can understand how RNA may serve as a pattern to form thousands of different enzymes in the living cell the production of enzymes is much more complex than we have indicated and several kinds of RNA molecules are involved in enzyme production one group of enzymes found in the mitochondria these organel is particularly important in the release of energy in this photomicrograph arrows indicate the mitochondria in which these enzymes are produced we know that energy is used for physical life functions but chemical functions such as the formation of nucleic acids and enzymes themselves also require energy the key source of this energy is the compound whose molecule we have modeled here ATP or adenosine triphosphate this is the formula for ATP the tremendous energy of ATP is located in three groups of atoms each group containing a phosphorus atom these are called phosphate groups in this schematic drawing the three phosphate groups are located here in the living cell a great deal of energy is released as the outermost of the phosphate groups is split off from the molecule this is how most of the energy for the cell's life functions is derived the resulting molecule is called adenosine diphosphate or ADP ATP can be synthesized from ADP by the replacement of the third phosphate group but this requires energy this energy is obtained by the oxidation of the simple sugar glucose glucose is found in abundant amounts in most cells in its simplest sense oxidation is burning when when paper made up largely of glucose is oxidized as demonstrated here oxygen is consumed while carbon dioxide and large amounts of energy are yielded in the laboratory this energy takes the form of heat oxidation of glucose in the cell releases large amounts of chemical energy rather than heat energy particular enzymes oxidize the glucose molecule in slow stages in this process the hydrogen atoms of the molecule are passed from one enzyme to another with chemical energy released at each step enough chemical energy is released by this process it is thought to synthesize from 38 molecules of ADP 38 molecules of ATP thus ATP is continually replenished this replenishment is based on the oxy iation of glucose molecules by enzymes so it is these enzymes located as we saw in the mitochondria which initiate the chemical cycle of energy transformations that keeps the cell alive that life depends on a chain of reactions which we have been tracing throughout this film the reactions begin with a physical process when nutrients enter the cell through osmosis and are dispersed through diffusion with nutrient molecules in the cell certain chemical reactions take place hydrolysis and oxidation are chemical reactions which release energy for the living cell to carry out its life functions these reactions we saw are initiated by a group of compounds the enzymes enzyme formation is under the control of the nucleic acid RNA RNA in turn is produced under the control of another nucleic acid DNA energy for the formation of these and other chemical compounds is obtained from the compound ATP the cell Storehouse of energy as energy is released in the cell a second compound ADP is formed the slow oxidation of glucose a carbohydrate releases enough energy to synthesize from ADP new stores of ATP these are some of the more important chemical reactions which take place simultaneously in the cell reactions which yield tremendous amounts of energy which are utilized by the cell for movement digestion excretion growth and reproduction so the unique ability of the cell to combine physical and chemical processes into the release and utilization of energy forms the basis of its life functions [Music]