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BIOL 1090
Marc Coppolino

BIOLOGY 1090 Textbook Notes Chapter 1.1 – 1.3, 1.4 The Discovery of Cells  We do not know when humans first discovered microscopes but that is the only way we can see cells as they are SO small.  Robert Hook (1600s) observed the empty sell walls of dead plant tissue in a piece of cork… he called it cells as they reminded him of the monks living in cells of a monastery.  Leeuwenhoek was the first to examine a drop of pond water under a microscope and observe the teeming microscopic “animalcules”. He was also the first to describe various forms of bacteria.  Leeuwenhoek was criticized at first but once Hook confirmed his statements, he became a celebrity  In 1838, Mathias Schleiden concluded that, despite the differences in the structure of various tissues, plants were made of cells and that the plant embryo arose from a single cell.  In 1839, Theodor Schwann published a comprehensive report on the cellular basis of animal life. Schwann concluded that the cells of plants and animals are similar structures and proposed these two tenets of cell theory: -All organisms are composed of one or more cells - The cell is the structural unit of life  Schleiden and Schwann’s ideas on the origin of cells proved to be less insightful as they both agreed that cells could arise from noncellular material.  It tool a while for other biologists to be recognized and taken seriously when they discovered and declared that cells did not arise in this manner any more than organisms arose by spontaneous generation.  By 1855, Rudolf Virchow, made a convincing case for the third tenet of the cell theory: - Cells can arise only by division from a preexisting cell Basic Properties of Cells  Cells in the body generally die from their own hand – victims of an internal program that causes the cell that are no longer needed or cells that pose a risk of becoming cancerous to eliminate themselves.  First culture of human cells was begun by George and Martha Gey of Johns Hopkin’s University in 1951. Cells were obtained from malignant tumor (names HeLa cells after the donor, Henrietta Lacks).  Because they are so much simpler to study than cells situated in the body, cells grown in-vitro (in a culture OUTSIDE the body) have become an essential tool of cell and molecular biologists.  Cells are highly complex and organized – Many parts that must be in their proper place, little tolerance for errors in the nature and interaction of the parts, and the lots of regulation or control that must be exerted to maintain the system is required.  DNA duplication, for example, occurs with an error rate of less than one mistake every ten million nucleotides incorporated –and most of these are quickly corrected by an elaborate repair mechanism that recognizes the defect  Though humans are very different anatomically, their specific types of cells are very similar in organization and function  Cells Posses a Genetic Program and the Means to Use it – Organisms are built according to information encoded in a collection of genes  The human genetic program is so large that it can fill millions of pages with text however, it is condensed into a set of chromosomes that occupies the space of a cell nucleus – hundred of times smaller than the dot on this i  Genes are storage lockers for information – they constitute the blueprints for constructing cellular structures, the directions for running cellular activities, and the program for making more of themselves  Molecular structure of genes allows for change in genetic information (mutations) that lead to variations among individuals, which forms the basis of biological evolution  Cells Are Capable of Producing More of Themselves – Cells reproduce by division, a “mother” cell divides into two “daughter” cells  Prior to division, the genetic material is duplicated and each daughter cells receives and complete and equal share of genetic material. In most cases, the sizes of both cells are relatively the same except for the human egg (ovule) cell... The Oocyte. In this case, one cell recives nearly all the cytoplasm even though it only receives half the genetic material (remember that sex cells are different than body cells).  Cells Acquire and Utilize Energy – The energy of light (from the sun) is trapped by light-absorbing pigments present in the membranes of photosynthetic cells.  Light energy is converted by photosynthesis into chemical energy that is stored in energy-rich carbohydrates, such as sucrose or starch. For most animal cells, energy arrives prepackaged, often in the form of sugar glucose.  In humans, glucose is released by the liver, into the blood where it circulates through the body delivering chemical energy to all the cells.  Once in the cell, the glucose is dissembled in such a way that its energy content can be stored in a readily available form (usually ATP) that is later put to use in running all of the cell’s myriad energy-requiring activities  Much of cells energy is used in breaking down and rebuilding its organelles and macromolecules (called “turnover”)  Cells Carry Out a Variety of Chemical Reactions: Virtually all chemical changes that take place in cells require enzymes – molecules that greatly increase the rate at which a chemical reaction occurs. The sum total of the chemical reactions in a cell represents that cell’s metabolism  Cells Engage in Mechanical Activities: There are many things going on within a cell at the same time; the breaking down and building of organelles, materials being transported from place to place and even the cell itself, moving from one site to another… These types of activities are based on dynamic, mechanical changes within the cell, many of which are initiated by changes in the shape of the “motor” proteins.  Motor proteins are just one of many types of molecular “machines’ employed by cells to carry out mechanical activities.  Cells are Able to Respond to Stimuli: Some cells respond in obvious ways: Single-celled protists move away from an object in its path or moves towards a source of nutrients  Cells within a multicellular plant or animal respond to stimuli less obviously. Most cells are covered in receptors that interact with substances in the environment in highly specific ways.  Cells are Capable of Self-Regulation – Importance of cell’s regulatory mechanisms become most evident when they break down. Ex., failure of a cell to correct a mistake when it duplicates the DNA may result in a debilitating mutation, or a breakdown in a cell’s growth-control safeguards can transform the cell into a cancer cell with the capability of destroying the entire organism  The information for “product design” resides in the nucleic acids, and the “construction workers” are primarily, proteins.  These two macromolecules are the main factors that sets the chemistry of cells from nonliving things  Each step is a spontaneous process which automatically triggers the next  Cells Evolve – Presumed that cells evolved from some precellular life form, which in turn evolved from non living organic materials…  Bacteria cell living in the human intestinal tract and the cell which is a part of the tract itself are extremely different yet both have evolved from a common ancestral cell that lived more than three billion years ago. Two Fundamentally Different Classes of Cells  Prokaryotic and Eukaryotic  Distinguished by size, and the type of internal structures (organelles), they contain  Prokaryotics are structurally simpler and include bacteria  Eukaryotics are structurally more complex and include protists, fungi, plants and animals  Evidence of prokaryotic life on rocks about 2.7 billion years old… not only do these rocks contain fossilized microbes, they also contain complex organic molecules that are characteristic of particular types of prokaryotic organisms, including cyanobacteria  Unlikely that such molecules could have synthesized abiotically, that is, without the involvement of living cells.  Cyanobacteria almost certainly appeared about 2.4 billion years ago as that is when the atmosphere became infused with molecular oxygen, which is a by- product of the photosynthetic activity of these prokaryotes.  Eukaryotic appeared rather suddenly about 600 million years ago but there is considerable evidence that simpler eukaryotic organisms were present on Earth more than one billion years go  Characteristics that Distinguish Prokaryotic and Eukaryotic Cells – Eukaryotic cells almost certainly evolved from prokaryotic ancestors. Due to this, both types of cells share an identical genetic language, a common set of metabolic pathways, and many common structural features… fro ex., both cells are bound by plasma membranes of similar construction that serve as a selectively permeable barrier between the living and nonliving worlds. Both types may also be surrounded by a rigid, nonliving cell wall that protects the delicate life form within… though cell walls of eukaryotes and prokaryotes have similar function, their chemical composition is very different  Both contain a nuclear region, which houses the cell’s genetic material, surrounded by cytoplasm.  The genetic material in a prokaryotic cell is present in a nucleotide: a poorly demarcated region of the cell that lacks a boundary membrane to separate it from the surrounding cytoplasm  In contrast, eukaryotic cells have a nucleus: a region bounded by a complex membranous structure called the nuclear envelope.  Prokaryotic cells contain relatively small amounts of DNA; the DNA content of bacteria ranges from about 600,000 base pairs to nearly eight million and encodes about 500 and several thousand proteins  Both prokaryotic and eukaryotic cells have DNA-containing chromosomes. Eukaryotic cells possess a number of separate chromosomes, each containing a single linear molecule of DNA whereas nearly all prokaryotes contain a single, circular chromosome. Furthermore, the chromosomal DNA of eukaryotes, unlike prokaryotes, is tightly associated with proteins to form a complex nucleoprotein known as chromatin.  The cytoplasm of the two types of cells is also very different  Cytoplasm of eukaryote filled with great diversity of structures… Even yeast (which is the simplest eukaryote) is much more complex than the average prokaryote (bacteria) even though the two have a similar number of genes  Eukaryotes contain an array of membrane-bound organelles and also include a mitochondria, an organelle where chemical energy is made available to fuel cellular activities; an endoplasmic reticulum, an organelle where many of the cell’s proteins and lipids are manufactured; a Golgi complex, an organelle where materials are sorted, modified and transported to specific cellular destinations; and a variety of simple membrane bound vesicles of varying dimension  Plant cells contain additional structures like chloroplasts (sites of photosynthesis) and often a single large vacuole (can occupy most of the volume of a cell  In contrast, the cytoplasm of prokaryotic cells is essentially devoid of membranous structures however the complex photosynthetic membranes of cyanobacteria are a major exception on this generalization  As prokaryotic cells are relatively small, necessary movement of materials can occur through simple diffusion however, a system of interconnecting channels and vesicles is necessary for eukaryotes.  Cytoskeleton (involved in cell contractility, movement, and support) of prokaryotes is much simpler than eukaryotes (until recently it was believed that prokaryotes didn’t even have cytoskeletons)  Both possess ribosomes – nonmembranous particles that function as “workbenches” on which the proteins are manufactured. Prokaryotes just have smaller ones and contain fewer components  Eukaryotes divide by a complex process called mitosis whereas in prokaryotes, there is no compaction of the chromosome and no mitotic spindle. The DNA is duplicated, and the two copies are separated accurately by the growth of an intervening cell membrane  For the most part, prokaryotes are nonsexual organisms but even though true sexual reproduction is lacking, some are capable of conjugtion, in which a piece of the DNA is passed from one cell to another  However, the recipient almost never receives a whole chromosome from the donor, and the condition in which the recipient cell contains both its own and its partner’s DNA is fleeting.  Cell soon reverts back to possession of a single chromosome  Though prokaryotes are not as efficient as eukaryotes at exchanging DNA, they are better than eukaryotes at picking up and incorporating foreign DNA from their environment  Movement of prokaryotic cell may be accomplished by a thin protein filament, called flagellum, which protrudes from the cell and rotates  Rotations can exceed 1000 times per second, exert pressure against the surrounding fluid, propelling the cell through the medium  Certain eukaryotes also have flagella but its much more complex and they generate movement by a different mechanism Viruses  Diseases such as AIDS, influenza, polio, cold sores, measles, and a few types of cancer are all caused by viruses  All viruses are obligatory intracellular parasites; that is, they cannot reproduce unless present within a host cell.  Depending on the type of virus, the host can be a plant, animal, or bacteria cell.  Outside the host, the virus exists as a particle called virion, which is little more than a macromolecular package  Virion contains small amount of genetic material that, depending on the virus, can be single-stranded or double-stranded, RNA or DNA  Some viruses have as few as three or four different genes but others may have as many as several hundred  The genetic material of the virion is surrounded by a protein capsule or capsid.  Viruses are not considered to be organisms or considered alive as they cannot reproduce, metabolize, or carry out any other various activities associated with life on their own  Viral capsids are generally made up of a specific number of subunits  The advantage to that is being an economy of genetic information  If a viral coat is made of many copies of a single protein, as is that of TMV, or a few proteins, as are the coats of many other viruses, the virus needs only one or a few genes to code for its protein container  Many viruses have a capsid whose subunits are organized into a polyhedron, that is, a structure having planar faces  Particularly common polyhedral shape is the 20-sided icosahedron… ex., adenovirus, which causes respiratory infections in mammals, has a icosahedral capsid.  In many animal viruses such as HIV, the capsid is surrounded by a lipid- containing outer envelope that is derived from the modified plasma membrane of the host cell as the virus buds from the host surface  Bacterial viruses, or bacteriophages, are among the most comp
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