Learning Resource 03. The Learning Resource goal is to use the Internet and become independent of the textbook. It is a project in progress...   Ch. x
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  Giardia lamblia. (Source: Mader. Biology, ed. 10.)  Cellular Level of Organization ---  We have now advanced to the cellular level of organization. The inventor of the microscope Antoni van Leeuwenhoek (1632 - 1723; figure to the right) may have been the first person to see living cells, and reported seeing the parasite Giardia lamblia in his feces (see figure on top of page). Giardia is a unicellular organism -- made of one cell, while humans are multicellular organisms -- made of trillions of cells. In this chapter we will discuss cells, the fundamental building blocks of organisms.  Biological Organization In biology scientists works with scientific theories. While a non-scientist may define a "theory" as a speculation, a "scientific theory" is NOT a speculation, but rather a "concept supported by a broad range of observations, experiments, and data". Examples of such scientific theories are the atomic theory, the theory of evolution and the cell theory.The cell theory is one of the major theories of biology, which states that organisms are made up of cells; cells are capable of self-reproduction and come only from preexisting cells.  Cell Theory stipulations All living organisms are composed of cells. CELL THEORY. Viruses are not composed of cells and therefore not considered living. A microscope us usually needed to see the cells, because cells are normally small. Some cells can be seen with the human eye, e.g., a frog's egg about 1 mm in diameter. Chicken eggs, or the larger ostrich eggs, are examples of large cells. Once a chicken egg or an ostrich egg is incubated and the metabolic activity begins, the egg divides repeatedly without growth. Eventually a small bird hatch from the original size egg. Cell Size. Cells are small in order to have an adequate amount of surface area to volume to allow adequate nutrition to enter and to rid itself of wastes. If cells were large they would not have enough surface area to exchange nutrients and wastes. As mentioned above a chicken egg is several centimeters in diameter, but the egg is mot actively metabolizing. Once a chicken egg is incubated and the metabolic activity begins, the egg divides repeatedly without growth.
 Lower limits on cell size -- DNA.
The cells must have enough DNA -- to provide enough instructions to carry out necessary functions.
Upper limits on cell size -- metabolic requirements (surface to volume area problems).
The cells must have enough surface area to be able to obtain oxygen and nutrients, and get rid of carbon dioxide and other waste products. If the cell is too large this becomes difficult due to surface to volume area problems (to small surface area).-- transportation problems across the cell membrane -- diffusion problems inside the cell • Because of these limitations, multicellular organisms consist of many small cells. Same problems to solve -- transportation across the cell membrane, and diffusion. Many are located far from the surface and the surrounding environment. These organisms have solved this by having distribution systems supplying nutrients etc., and removing waste.
 Prokaryotic cells --- There are two major groups of prokaryotic cells, the Bacteria and the Archaea. These groups form two of the three classification domains. Prokaryotic cells are much smaller than the type of cell we have in our body. They lack nucleus, and other membrane bound organelles. The DNA is located in a region called a nucleoid, not enclosed by a nuclear membrane. Evolutionary tree showing the domains and kingdoms  Eukaryotic cells --- Eukaryotic cells are much larger than prokaryotic cells, and have organelles with specific functions. The figure below compares prokaryotic cells with eukaryotic cells. According to the endosymbiotic theory the mitochondrion and the chloroplast may have arisen when a eukaryotic cell took up bacteria and algae. This is supported by observations that mitochondria have bacteria-like structure, contain their own DNA, and function fairly independent inside our cells. All other membranous organelles are in constant communication with help of transport vesicles (see the endomembrane system). What is implied by what we have learned about the mitochondria and the chloroplasts is the endosymbiotic theory, that the ancestors, of what today is mitochondria and chloroplasts, existed as independent prokaryotic organisms ("bacteria") that at some point started living in a symbiotic relationship with and inside of a large eukaryotic cells.
 Comparison of prokaryotic cells and eukaryotic cells  Endosymbiotic Theory  The Endosymbiotic Theory  Generalized Cells All (Eukaryotic) cells have:1. Plasma membrane (Cell membrane). 2. Cytoplasm 3. DNA 4. Organelles  Generalized Animal Cell  Generalized Plant Cell  Organelles There are two kinds of organelles, non- membranous and membranous.NON-MEMBRANOUS ORGANELLES. RIBOSOMES. Site of the protein synthesis. Two kinds, free in the cytoplasm, or attached to one of the membranous organelles -- the endoplasmic reticulum.MEMBRANOUS ORGANELLES. NUCLEUS. The nucleus is bounded by a so called nuclear envelope with pores. These pores are passageways between the inside of the nucleus and the outside cytoplasm. The nucleus is the location of DNA and contains one or several nucleoli, a region where rRNA is produced to be used in ribosomes. Ribosomes function in protein synthesis -- some occur in the cytoplasm while others are attached to the Rough Endoplasmic Reticulum.Generalized Animal Cell 
ENDOPLASMIC RETICULUM, GOLGI APPARATUS, LYSOSOMES, TRANSPORT VEHICLES (Vacuoles). These organelles make up the endomembrane system functions as a protein and lipid transport system, and includes several organelles -- the endoplasmic reticulum (both the rough ER and the smooth ER), the Golgi apparatus (named after the person discovering it, Nobel prize winner Camillo Golgi (see picture to the right), sometimes also called Golgi body or Golgi complex), the lysosomes (in animal cells) and transport vesicles. New proteins and lipids are modified in the endoplasmic reticulum, "packed" into transport vesicles (made from the ER membrane), and moved to different places, especially to the Golgi apparatus. In the Golgi apparatus further modification takes place. When needed, again they are "packed" into transport vesicles and moved, sometimes a transport vesicle fuses with the plasma membrane and the proteins or lipids are released, "secreted", for use outside the cell. Some proteins are "packed" into organelles called lysosomes, which carry out intracellular digestion (inside the cell). Damage to the lysosome membrane can trigger release of the contained enzymes, destroying other parts of the cell. When these enzymes are released they can trigger a chain reaction, causing tissue necrosis. This can be caused by, e.g., pesticides, snake bites (e.g., Fer-de-lance (classification)), or spider bites (Brown recluse spider (classification)). (Look at figure to the right and you will never forget lysosomes...)Brown Recluse bite Watch the video below, and you will never forget the Golgi Apparatus. CENTRAL VACUOLE. Some vesicles and vacuoles do not communicate with the endomembrane system and is therefore not part of it, for example, the large central vacuole (in plant cells), which functions in storage and breakdown of molecules.
Generalized Animal Cell Generalized Plant Cell PEROXISOMES. Peroxisomes are membrane bound vesicles containing enzymes transported into the vesicle from the cytoplasm. The vesicles have many functions but are especially important for lipid digestion. The enzyme action in peroxisomes results in the production of hydrogen peroxide, which is toxic -- which can be harmful and/or contribute to the ageing process (see below). The hydrogen peroxide is broken down to water and oxygen by the enzyme catalase also contained in the peroxizomes. When you put hydrogen peroxide on a wound, the bubbles you see is the oxygen formed from the action of catalase. Studies show that low levels of catalase may play a role in the graying process of human hair. The body produces hydrogen peroxide naturally and catalase breaks it down. If there is not enough catalase, hydrogen peroxide cannot be broken down, which causes the hydrogen peroxide to bleach the hair from the inside out.
 Gray hair from studying? Click on the picture! Can Gray Hair Be Reversed? (ABC News) (The video can not be embedded. Click on the link to navigate to YouTube. CHLOROPLASTS, MITOCHONDRIA. Energy transformers. We (our cells) require energy to stay alive. This is why we eat food. This energy originally came from the sun -- was captured by chloroplasts in plant cells producing carbohydrates ("sugar") in the process called "photosynthesis" (which we will discuss later in the semester). Carbohydrates (or molecules derived from carbohydrates) are used by mitochondria to produce ATP (energy), in a process called "cellular respiration" (which we also will discuss later in the semester). CYTOSKELETON and CENTRIOLES, Cilia and Flagella. The cytoskeleton is for cell structural support -- contains actin filaments, intermediate filaments, and microtubules. These structures maintain the shape of the cell and allow it and organelles to move. The centriole is not present in plant cells, and functions in cell division of animal like cells. CELL MEMBRANE, CELL WALL. Barriers that separates the cell from the outside environment. Some cells have both, some cells only the cell membrane. The cell membrane is semi-permeable, and will let certain things through. The cell wall is not present in animal cells, and is for protection of the cells that have the structure.Generalized Animal Cell Generalized Plant Cell • 4.13 Organelles (Compartmentalization of Eukaryotic cells)
 - - - Parts of a cell (Khan Academy You Tube) - - -COMMENT ON THE YOUTUBE: "Wow, just a few minutes in and it's so much more clear. I like that you use color, awesome video! I hope this helps on my test." If you have problems understanding the concept "organelles" and the "endomembrane system", here is an excellent YouTube video from Khan Academy, which will help you understand. Although, while discussing the various organelles, the video connects it to the function of the protein synthesis, which is beyond what is required for this class AT THIS MOMENT in the semester. After you have read about the protein synthesis later in the semester, you may want to watch this video AGAIN. It is 21 minutes long; I don't recommend that you try to view it from home unless you are connected via broadband. It takes too long to download via telephone modem. View it at STC instead... Sometimes YouTube videos disappear. Hopefully it will not happen often, but if it does there is nothing that can be done about it...ACTIVITY: Cell Structures: Organelles Label the structures of the animal cell.  Source: http://images.slideplayer.com/9/2497996/slides/slide_60.jpg. Used for educational purposes. Prokaryotic cells do not have the structures inside called organelles. The only kind of organelle present in bacteria is the ribosome -- which are of a different kind than the ribosome in our cells. (This is one way antibiotic works -- destroying the bacterial ribosome, but leaving our ribosome unharmed.) Eukaryotic cells, on the other hand, contain several types of organelles, but not all eukaryotic cells contain every organelle.
(Source: Mader, S.S. 2010. Biology. Ed. 10. ) |
