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Unformatted text preview: Clicker Question I presented a physico-chemical scenario for physicothe origin of life. How plausible is it to you that it took place without any need for a Creator? A) Very plausible. I know that the universe started as a fluctuation and then followed the necessary laws of chemistry and physics. B) I am not sure, but leaning toward A. C) Sometimes I think it is plausible, other times I think it is unlikely. D) I am not sure, but leaning toward E. E) Very unlikely. I know that such a scenario is impossible without a Creator. Where are we? Last time I covered: A physico-chemical explanation for the origin of physicolife This time I am going to discuss: The structure and function of the organelles in the cell. How the organelles of the cell function in the cellular processes that underlie life. The Cell The Basic (Physico-Chemical and Biological) Unit of Life This is the golden age of biology. A single cell from a Cornellian woman can be worth between $7,500 and $75,000. Here is a recent advertisement in the Sun. Life in the United States On July 4, 1776, the thirteen colonies of the United States unanimously declared: "When in the Course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with another, and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation." separation." "We hold these truths to be self-evident, that all selfmen are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Life, Happiness. --That to secure these rights, --That Governments are instituted among Men, deriving their just powers from the consent of the governed, --That whenever any Form of --That Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, it, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness." Happiness." 1 The Seneca Falls Declaration The work of Thomas Jefferson was improved by Elizabeth Cady Stanton when she wrote The Seneca Falls Declaration, which was adopted at the Seneca Falls Convention, fifty miles north of here in 1848. She rewrote the second paragraph to include women: "We hold these truths to be self-evident: that self- I Have a Dream (Martin Luther King, August 28, 1963 ) "When the architects of our republic wrote the magnificent words of the Constitution and the Declaration of Independence, they were signing a promissory note to which every American was to fall heir. This note was a promise that all men, yes, black men as well as white men, would be guaranteed the unalienable rights of life, liberty, and the pursuit of happiness." happiness." all men and women are created equal; that they are endowed by their Creator with certain inalienable rights; that among these are life, liberty, and the pursuit of happiness...." happiness... Life in the United States Life in the United States Is it possible that we can understand the laws of nature in such a way that we can ensure safer and happier lives? Perhaps. These three great works emphasize that when our government's idea of life is no longer consistent with the government' Laws of Nature, we have the right to change it. The right to question authority has been the most important aspect of the so-called scientific method, first written down by somethod, Francis Bacon. Richard Feynman, a physicist who dabbled in genetics, believed that the greatest value of science is the "freedom to doubt". doubt" Taken together, these great documents emphasize the unalienable right to life for all men and women and suggest that one should use the Laws of Nature and Nature's God to ensure safe and happy Nature' lives. Cells, Like Other Living Beings move by internal forces transform one kind of energy into other forms of energy synthesize large organic molecules that cause them to grow generate electricity respond appropriately to the environment reproduce with near perfect fidelity 2 Who likes cells? The Discovery of Cells Robert Hooke (1665) looked at cork, which was just beginning to be used to seal wine bottles. The cork was composed of tiny empty compartments, which he called cells, since they looked like the empty cells in which monks lived. Cells as the Basic Unit of Life Plant Cells as the Basic Unit of Life Revolutions cells typically have easily-visible easilyextracellular matrices while animal cells have nearly invisible thinner ones. to the near-invisibility of animal cells, nearmany scientists believed that only plants and not animals were composed of cells. Dutrochet (1824) was an exception. His careful microscopic observations led him to conclude that all living organisms are composed of cells, and that the cell is the fundamental unit of life. in scientific thinking usually do not occur until a new generation of scientists are born who are ready to think differently. Due The mid 1800s was a time when scientists were looking for the unity among the diverse phenomena that had been recently discovered. and Schwann promoted the idea that although there is a magnificent diversity among all living things, the thing that unites them all is that they are all composed of cells and that the cell is the basic unit of life. Henri Schleiden 3 Cells are not Empty and Come in All Shapes and Sizes 4 Cells are not Hollow Spaces With a good microscope, like you have in the BIO G 110 lab, you can see that cells are not hollow places. Let's look at an Let' Elodea cell. Elodea lives in Fall Creek in the summer, in the BIO G 110 lab in Stimson and perhaps in your fish tank right now. Look at how much movement goes on in the cell. It is like watching life itself. Cytoplasmic Streaming in Elodea 5 Chloroplasts The two clearly inorganic molecules and with the energy of sunlight convert them into carbohydrates and release oxygen. chloroplasts take carbon dioxide and water, Photosynthesis The carbohydrates provide the food for the rest of the cell. They provide the carbon skeletons necessary for making all the other chemicals in the cell. CO2 + H2O + Light energy C(H2O) + O2 carbon dioxide inorganic carbohydrate organic We can pinpoint the chloroplast as the location where the conversion of nonliving to living matter takes place in a process known as photosynthesis. Autotrophic vs. Heterotrophic Only green plant cells have chloroplasts. However, when we consider all the cells in the roots and stems of trees, we realize that the majority of plant cells, just like all animal cells are heterotrophic and must get their food from the autotrophic green plant cells. Plasma Membrane The plasma membrane is the frontier of the cell and can be visualized with the electron microscope. The lipids in the plasma membrane provide the major barrier to the movement of waterwatersoluble nutrients and other polar molecules like, sugar, ATP and proteins. Lipids Carbons that lack two hydrogen atoms form double bonds. The presence of double bonds affects the shape of the lipid. Saturation depends on the number of double bonds in the fatty acyl chain: 0: Saturated 1: monounsaturated 2-3: polyunsaturated 6 Unsaturated Fatty Acyls are Kinky The greater the number of double bonds, the kinkier is the lipid. Unsaturated fatty acyls are kinkier than saturated fatty acyls. acyls. Effect of Double Bonds Unsaturated double bonds cause the fatty acyl to kink. This causes the lipids to pack loosely at a given temperature which makes the membrane less solid and more liquid. In order to function at a given temperature, the plasma membrane cannot be too solid or too liquid. For each organism, there are good combinations of fatty acyls that allow the plasma membrane to be a liquid-crystal at its liquidnatural temperature. Lipids Lipids formed from saturated fatty acids are liquid crystals at higher temperatures (in warm blooded animals and in tropical plants). Think of butter and palm oil. Omega ()-fatty acids ( Omega Due to kinks, lipids formed from polyunsaturated fatty acids are liquid crystals at low temperatures (temperate plants). Think of soybean and canola oil as well as fats from fish living in cold water. ()-fatty acids are polyunsaturated ( fatty acids that make up some of the lipids in the membrane. Our bodies can not synthesize -6 and -3 fatty acids, making linoleic and linolenic acids, respectively, essential nutrients. -3 fatty acids have their first double bond between carbons 3 and 4. -6 fatty acids have their first double bond between carbons 6 and 7. (count carbon farthest from carboxylic acid group as 1). Olive oil, which comes from olives grown in Mediterranean climates have monounsaturated fatty acids and form liquid crystals at intermediate temperatures. Plasma Membrane Embedded in the lipid barrier is the machinery (i.e. proteins) to move things into and out of the cell. The plasma membrane has proteins that generate electricity to help move charged molecules into and out of the cell. These proteins can be considered to be enzymes that catalyze transport and electrical reactions. transport ions across membranes in the kidney to stabilize the blood transmit electrical impulses in the brain that allow thinking 7 Osmosis: Solute-induced movement Soluteof water Osmosis Water (like everything else) moves passively from high concentration to low concentration. When one places sugar in water, the concentration of the water itself in the solution decreases. If a solution of water is separated from a solution of sugar water by a differentially permeable membrane, there will be a net movement of water from the pure water to the sugar solution. This net movement is called osmosis. The plasma membrane is differentially permeable. That is, it is permeable to the small water molecules but not to the larger sugar molecules. Osmosis: Evidence of a Plasma Membrane When one places Elodea cells in a solution of sugar, water rushes out of the cells faster than the sugar molecules can move in and the cells shrink. can infer that there is a differentially permeable membrane that surrounds the cells. We The differentially permeable membrane is NOT the easily visible extracellular matrix that surrounds the cells but the nearly invisible plasma membrane. Plant and Animal Cells Plant cells, which have a thick extracellular matrix to protect them, swell when placed in pure water. Animal cells, which do not have a thick extracellular matrix lyse (pop) when placed in pure water. 8 The Nucleus While looking at the epidermal cells of an orchid, Robert Brown serendipitously noticed a big round structure in the middle of each cell. He named it the nucleus, but only mentioned it in passing, because he was really interested in studying pollination in orchids. Elodea Nucleus Nucleus After the introduction of carmine dyes, one could see that the nucleus split up into little bodies that could be colored by the dyes and were thus called chromosomes (colored bodies). Nature seemed to take great pains to ensure the perpetuation and accurate distribution of the chromosomes during cell division. hereditary material of the cell. This made it likely that the chromosomes contained the We now know that the hereditary information in the chromosomes is stored in the sequence of DNA. Nuclear Division: Mitosis E. B. Wilson (1925) wrote, "To our limited intelligence, it would seem a simple task to divide a nucleus into equal parts. The cell, manifestly, entertains a very different opinion. Nothing could be more unlike our expectation than the astonishing sight that is step by step unfolded to our view by the actual performance. The nucleus is cut in two in such a manner that every portion of its net-like netinner structure is divided with exact equality between the two daughter-nuclei, and the cell daughterperforms this spectacular feat with an air of complete and intelligent assurance." assurance." 9 "The net-like framework is spun out into long netthreads or chromosomes; these are divided lengthwise into exactly similar halves; they shorten, thicken, separate and pass to opposite poles; and from the two groups formed, are built up two daughter-nuclei, while the cell-body divides daughtercellbetween them. Such a process seems in some respects to contradict all physical principles; but its meaning has now become perfectly plain. In a general way it means...that the nucleus is not means... composed of a single homogeneous substance, but is made up of different and self-perpetuating selfcomponents; and it means that these components are strung out in linear alignment in the threads so that they may be divided, or distributed in particular manner, by doubling of the thread." thread." The Movement of the Chromosomes Requires the Generation of Force The generation of force is performed by enzymes (e.g. myosin) that act as mechanochemical force transducers. Mechanochemical force transducers transform the chemical energy of ATP into the kinetic energy of motion. Nucleus: The Hereditary Organelle Friedrich Miescher (1868) began to isolate the hereditary material from the nuclei of pus cells. He called this substance nuclein. nuclein. He found that it differed chemically from proteins, lipids and carbohydrates in that it contained a lot of phosphorus. Later the purified nuclein was named, nucleic acid and still later, DNA. DNA: The Genetic Material The nucleus also contains a nucleolus. The nucleolus is where the ribosomes are made. Once the ribosomes move into the cytoplasm, they serve as the site of protein synthesis. The synthesis. ribosomes are the place where the hereditary information coded by the DNA is, indirectly through an RNA intermediate, translated into the amino acid sequence that gives a protein its characteristics. Most of these proteins will be enzymes. 10 The Endomembrane System (Golgi, ER and vacuole) Golgi, While the nucleus contained the hereditary information, it was clear that many vital processes toke place in the cytoplasm outside the nucleus. More organelles were eventually discovered in the cytoplasm. Camillo Golgi stained owl cells with silver, which like photographic paper, blackened when the silver became reduced, and he found an internal system of membranes what came to be known as the Golgi reticulum. 11 The Endomembrane System (Golgi, ER and vacuole) Golgi, The Golgi reticulum is part of a membranous secretory system that transports membranes that enclose carbohydrates or proteins through the cell. The Golgi apparatus is a polarized organelle, in which one side is associated with the membrane system known as the endoplasmic reticulum and the other side is associated with the plasma membrane/extracellular matrix and the membrane/extracellular vacuolar system. The Endomembrane System (Golgi, ER and vacuole) Golgi, RER). RER). Some parts of the endoplasmic reticulum have ribosomes, ribosomes, which give the ER a rough appearance (rough ER or The ribosomes on the RER take the information from the genes in the nucleus, in the form of messenger RNA, which they use as a template to synthesize the proteins that will travel through the endomembrane system. The part of the ER that does not contain ribosomes is known as the smooth ER. It specializes in synthesizing membrane lipids. Together, the rough and smooth ER make the proteins and lipids necessary to form all the other membranes. The Endomembrane System (Golgi, ER and vacuole) Golgi, On the other side of the Golgi apparatus, the membranes also elaborate. Vesicles are pinched off from some of these membranes and they fuse with the plasma membrane to make more plasma membrane so that the cell can grow or renew old plasma membrane that has aged. The contents of the vesicles are secreted: some secretory products form the extracellular matrix, others act as hormones (e.g. insulin) or digestive enzymes. The endocrine and exocrine gland cells are rich in endomembranes. endomembranes. 12 The Endomembrane System (Golgi, ER and vacuole) Golgi, The Endomembrane System (Golgi, ER and vacuole) Golgi, In Vesicles are also pinched off from the Golgi apparatus that give rise to the vacuolar compartment. The vacuole is a prominent organelle in plant cells and often takes up 60-95% of the volume of the cell. This is 60wonderful for plants because they can grow tall and capture sunlight, water and carbon dioxide to make food without going through the energetic expense of filling the volume with protein. The watery cell sap is separated from the protoplasm by a membrane known as the vacuolar membrane and is thus a good site for the storage of nutrients taken up from the environment and for toxic chemicals that protect the plant from herbivores. These chemicals are often used as pharmaceuticals. animal cells (as well as in many heterotrophic plant cells), the vacuole is primarily concerned with digestion and acts like a lysosome to dissolve food. The lysosome digests the old parts of the cell and recycles the building blocks to be reused. In protozoa, the food is brought into the cell through the invagination of the plasma membrane, in a process known as endocytosis. The contents of the endocytotic vesicles are digested after they fuse with the vacuole. The Vacuole of Plants May be very visible in flowers at a distance. The may contain anthocyanins whose color depends on pH (acidity). Anthocyanin Colors and pH Color pH cherry red 1-2 cerise 3 plum 4 royal purple 5 blue purple 6 blue 7 blue green 8 emerald green 9-10 grass green 10-11 lime green 12-13 yellow 14 13 Movement Through the Cytoplasm The cytoplasm, through which all the vesicles move, is filled with lots of enzymes lined up in strands. This allows the efficient movement of metabolites through certain pathways. Together all these strands make the microtrabecular lattice which acts as a viscous (thick) fluid through which the vesicles must move. Movement Through the Cytoplasm Due to the viscous nature of the cytoplasm, the vesicles require motors to pull them through it. Some of these motors use the actin microfilament/myosin system, which also moves the chloroplasts in Elodea, and is highly elaborated Elodea, in muscle cells. Others use the microtubule/dynein or microtubule/dynein microtubule/kinesin system. The microtubule microtubule/kinesin system typically moves the chromosomes to the poles during mitosis. Microtubules and microfilaments run throughout the cell in order to bring the vesicles to their proper destination. The Microtubular System Can Move Whole Cells The microtubular system is highly elaborated in cilia and flagella, two words for the same structure. Cilia and flagella are found along the respiratory tract and in sperm. Sensory cells, including light-sensitive cells lightin our eyes, are modified cilia. 14 Mitochondria The motors that move the vesicles through the cell require ATP to run. Indeed, almost every biosynthetic process requires ATP. The ATP is synthesized in the mitochondria. It was hard to see the mitochondria until they could be stained with dyes used by the newly-developed fabric dye newlyindustry. The mitochondria reduced the dye and the dye became colorless. Due to the mitochondria's ability to reduce dyes, it was mitochondria' guessed that they were the site in the cell that reduced the oxygen that was so necessary for life. The mitochondria are the organelles that use molecular oxygen to burn food. 15 Mitochondria: Burning Food Burning Respiration food means to remove the hydrogen atoms (protons and electrons) that are attached to the carbon atoms of foodstuffs so that H2O is made and CO2 is left. Mitochondria use the energy in the C-H bonds to Csynthesize ATP. ATP is a readily usable energy source that is used to move things across membranes, to synthesize DNA, RNA and protein, and to run the motor proteins. O2 + C(H2O) H20 + CO2 + chemical energy carbohydrate organic inorganic Endosymbiotic Theory The mitochondria (and chloroplasts) have their own genetic systems (e.g. DNA and ribosomes). ribosomes). mitochondria and chloroplasts may have arisen from the endocytotic uptake of prokaryotes. in these cases, after the engulfment, the endocytotic vesicles did not fuse with the lysosome and the prokaryotes within were not digested. The However, 16 Endosymbiotic Theory are Rhodospirillium and Prochloron, two Prochloron, prokaryotes that may have given rise to the mitochondrion and chloroplast, respectively. Their Here It is usually thought that prokaryotes do not have internal membranes and that this limits their size. I just showed you two prokaryotes that do have internal membranes. In fact, there is a bacterium known as Epuloposcium that is larger than most eukaryotic cells. Epuloposcium follows the law of nature that says that in order to take up nutrients, expel wastes and perform biochemical reactions, the surface to volume ratio in a cell must be high. It does not follow the convenient law of classification that states that prokaryotes must be small because the surface layer is the only membrane in prokaryotes. Convenient vs Natural Laws internal membranes look like the cristae of mitochondria and the thylakoids of chloroplasts. Endosymbiotic Theory So each eukaryotic cell is a symbiosis between two or three genetic individuals. These individuals compete for many of the same substrates, yet work together and cooperate for the common good. Symbiotic Relationships and Classification Loose symbiotic relationships between cells continue today. Paramecium bursaria is an association between an alga, and a protist. I have been growing these Paramecium bursaria cells on inorganic medium and they have been living autotrophically since 1999. These plant-like animals and or animal-like plants certainly do not fit clearly into any non web-like classification scheme. In fact, all living creatures may be related in a web-like fashion due to virus-induced gene transfer between organisms. 17 The Lives of a Cell question of my identity, and, more than that, my human dignity. I did not mind it when I first learned of my descent from lower forms of life. I had in mind...ape-men...I had never bargained on descent mind...apefrom single cells without nuclei. I could even make my peace with that, if it were all, but there is the additional humiliation that I have not, in a real sense, descended at all. I have brought them all along with me, or perhaps they have brought me...If I concentrate, I can imagine that I feel them; they do not quite squirm, but there is, from time to time, a kind of tingle. I cannot help thinking that if only I knew more about them, and how they maintain our synchrony, I would have a new way to explain music." music." Lewis Thomas (1974) wrote in his delightful book, The Lives of a Cell, "Finally, there is the whole Cell, The Lives of a Cell "There is something intrinsically good-natured goodabout all symbiotic relations, necessarily, but this one, which is probably the most ancient and most firmly established of all, seems especially equable...If you are looking for something like natural law to take the place of the `social Darwinism' of a century ago, you would have a Darwinism' hard time drawing lessons from the sense of life alluded to by my chloroplasts and mitochondria, but there it is." is." Organ Specialization Mirrors Cell Specialization The organs of the human body are composed of cells that contain the organelles we just discussed. Muscle cells have highly developed actin networks. Brain cells have highly developed plasma membranes to manipulate the ion concentrations required to think thoughts. The cells of the kidney have highly developed plasma membranes to regulate the ion concentration of the blood. The liver cells have many mitochondria to supply the ATP needed to perform many biochemical syntheses. The secretory cells of the endocrine and exocrine glands have highly developed endomembrane systems. Plant cells have many chloroplasts necessary to make food. The Structure of a Given Cell is Related to Its Function Throughout the semester we will be discussing the structure and function of organs made up of specialized cells that allow digestion, movement, reproduction and thinking possible. 18 ...
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This note was uploaded on 02/15/2008 for the course BIO G 110 taught by Professor Wayne,r. during the Spring '07 term at Cornell University (Engineering School).

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