Cell Biology - The Cytoplasm (1988)

one hundred years ago improved microscopes opened a new world to investigation the  internal world of the cell [Music] seen for the first time within cells  were tiny bodies called organelles but was there more to be seen the problem  was that smaller structures would also be smaller than the shortest wavelengths  of light and so could not be seen this limit imposed by light literally left  biologists in the dark when it came to observing the inner workings of cells particularly in  the region of the cell called the cytoplasm cytoplasm is that part of a cell within the  plasma membrane but not including its nucleus this is the cytoplasm cytoplasm is made up  of a watery fluid the cytosol containing the cell's supply of dissolved material suspended  in the cytosol are the cytoplasmic organelles the internal structure of even large organelles  remained a mystery until an Imaging system was developed that used an Illuminating source  with much shorter wavelengths than light the electron microscope gave biologists their  first detailed look at the inner structure of cytoplasmic organelles discovering the function  of these bodies continues to be a major goal of cell biologists their investigations  often Begin by first breaking up cells they can then isolate batches of  a particular kind of organelle by taking advantage of small differences in  density between the various cell parts once isolated an organelle's function can  be explored using a variety of techniques [Music] this approach showed that major life functions  like cellular respiration digestion and protein synthesis are each associated with a  particular kind of cytoplasmic organelle many of the processes going on in the organelles  of a cell involve the formation or breakdown of macromolecules giant molecules made  from smaller molecular building blocks for example simple sugars are the building  blocks that make up polysaccharides fatty acids are the building blocks of fats  amino acids are the building blocks of proteins nucleotides are the building blocks that bond  together to form the nucleic acids RNA and DNA the cells of animals differ from  plant cells in one important way their method of acquiring their building block  molecules animals pick up most of their building blocks from the original manufacturers  plants in an animal's intestine the plant's macromolecules are broken down into  their building blocks during digestion these smaller molecules are absorbed into the animal's  bloodstream and carried to its cells [Music] however simple animals often  carry out a more direct kind of digestion digestion within individual cells when this primitive animal Hydra swallows  its prey the prey undergoes preliminary breakdown in hydra's sac-like digestive  cavity releasing bits and pieces of food that are then engulfed and adjusted  by individual cells lining the gut this kind of digestion digestion within cells  is best seen in organisms that are made of but a single cell this one forticella gulps in  bacteria which are then broken down to their building blocks entirely within the cell cytoplasm  during this process the bacteria are encased in a pocket formed by a piece of plasma membrane that  pinches off and circulates around the cell [Music] these food-filled membrane bubbles or  food vacuoles contain digestive enzymes the enzymes actively break down the bacteria's  macromolecules into their building blocks [Music] special dyes can provide a clue to the  conditions necessary for this breakdown to occur this indicator die turns  deep red in acid Solutions and Amber in neutral Solutions when the dye  is applied to living cells it concentrates in food vacuoles the deep red color of  newly formed vacuoles shows that they're acidic important because digestive enzymes work  most efficiently under acid conditions [Music] the digestive enzymes come from small  dense particles that occur in the cytoplasm these organelles called lysosomes are particularly  abundant in cells that ingest their meals [Music] a lysosome is basically a sack of powerful  digestive enzymes that can be dumped into a food vacuole its membranes also contain  protein pumps that pump hydrogen ions into the vacuole making them acidic and  so assuring effective digestion [Music] foreign s are only one of many kinds of  proteins manufactured in the cytoplasm these enzymes like other proteins are assembled  on Tiny organelles called ribosomes that dot the membranes surrounding the nucleus this region of  the cytoplasm is called the endoplasmic reticulum it is the cell's major site of protein assembly  once manufactured digestive enzymes travel to the Golgi apparatus where they are packaged in sacs  of membrane and enter the cytosol as lysosomes lysosomes are key players in our body's  defense system here a human white blood cell pursues a harmful bacterium eventually the  bacterium will be engulfed and broken down into its component molecules by a swarm of  lysosomes within the white blood cell [Music] lysosomes also help to recycle a cell's worn  or damaged parts as a worn out organelle is digested in the lysosome its building  block molecules are returned to the cytosol many of these building blocks whether acquired  from the digestion of food molecules or by recycling of worn out parts are used  to supply the cell with energy [Music] oh extracting this energy from building blocks  takes place in mitochondria structures that occur by the hundreds and thousands in  the cells of plants animals and protists a mitochondrion is composed of two layers  of membrane the inner membrane is folded extending into the organelle's central cavity  increasing surface area for chemical reactions in three dimensions the organelle looks  like this the Cutaway shows the two layers in living cells mitochondria can be seen  concentrating in areas where energy needs are greatest in vorticella they line  up along the spring-like stalk ready to power the contraction that may  snap the cell out of danger [Music] in muscle cells the mitochondria  lie close to the contractile fibers plant cells are loaded with  mitochondria that extract energy from sugars and fatty  acids made by photosynthesis to release the energy contained in food molecules  a mitochondrion must also take in oxygen in this process called aerobic respiration the  Key Energy events occur on the knobby lining of the inner membrane here the energy released from  sugars and fatty acids is used in the formation of ATP the universal energy carrier an ATP molecule  holds this energy in a powerful chemical bond the reaction is reversible so that  the ATP can donate energy to drive reactions anywhere in the cell and then  be recharged at another mitochondrion while mitochondria are found in all types  of nucleated cells chloroplasts life's primary energy Transformers are only found in  plants and green protists within a chloroplast the electron microscope shows stacks of inner  membranes organized like arrays of solar cells layers of chlorophyll molecules capture the  light that drives photosynthesis in a plant much of the energy gained through photosynthesis  is used to split water into hydrogen and oxygen the hydrogen is used in a complex chain of  reactions that produce carbohydrates and fats the oxygen is given off as a waste gas  adding oxygen to our atmospheric Reservoir while carbohydrates and fats provide all cells  with energy proteins are the macromolecules that form much of a cell's structure and as  we saw proteins called enzymes control the thousands of chemical reactions that go on each  second in the cytoplasm of every living cell we have also seen that proteins are  assembled from amino acid building blocks the amino acid sequence for each protein is stored  on string-like molecules of DNA in the nucleus along the DNA molecule each amino acid  is represented by a code word or codon consisting of three nucleotides the code is  copied onto a closely related nucleic acid RNA this messenger RNA migrates out of pores in  the membrane surrounding the nucleus moving toward the endoplasmic reticulum where it  connects with one of the many ribosomes here Transfer RNA also from the nucleus identifies  individual amino acids which are assembled in strict accordance with the sequence of codons  carried on the messenger RNA instruction tape the chain grows creating the protein macromolecule  that will eventually play its role in cell chemistry the completed proteins move to the  Golgi apparatus where some are packaged into lysosomes and others released directly into the  cytosol some like hormonal proteins are exported into the bloodstream providing communication  between cells in different parts of the body [Music] foreign so in its overall function  the cytoplasm resembles a factory it breaks down complex materials  into their building block molecules which can be reassembled into new  macromolecules or used for energy and while we know the basic outline of how  the cytoplasm carries out these processes there is still much to be learned about its  control systems and how it segregates and transports the many different kinds of molecules  essential for the life of a cell [Music] thank you [Music] foreign [Music]