Cell Membrane Structure Phospholipid Bilayer

Cell Membrane Structure Phospholipid Bilayer A cell is the basic unit of life, and the cell membrane is an important structure present in all cells, irrespective of whether they are plant cells or animal cells. This structure is a vital component of any cell and it has a variety of important functions. Cell membrane functions include maintaining the boundaries of the cells, thus supporting the contents of the cell, maintaining proper cell to cell contact, regulating the entry and exit of molecules in and out of the cell, etc. Thus, to understand how the cell membrane manages to carry out this procedure, one needs to understand the cell membrane structure. Given below are the various components that comprise the structure of the cell membrane according to the Fluid Mosaic model. The first layer of cell membrane consists of a phosphid bilayer. The phosphate molecules are arranged in such a way that the hydrophilic heads are on the outside, while the hydrophobic fatty acid tails are on the inside, facing each other. The tails of the molecule are said to be hydrophobic and that is why they points inwardly towards each other. This specific arrangement of the lipid bilayer is for the purpose of preventing the entry of polar solutes, like amino acids, proteins, carbohydrates, etc. Thus, the phosphate lipid bilayer is one of the main factors responsible for regulating the entry and exit of molecules in and out of the cell. Integral Membrane Proteins Integral membrane proteins are those proteins that are a part of the cell membrane structure. They are present between consecutive molecules of phopholipids. These fibrous proteins present may span the entire length of the cell membrane. These molecules have important functions, as they serve as receptors for the cell. Some of the proteins of the cell membrane may also enter the cell. Sometimes, a part of the protein molecule is inside and some of it is outside. These kind of protein molecules act as carriers for active transport of substances in and out of the cell. Some of these protein molecules form pores and thus, allow fatty acids and other lipid insoluble in water molecules to pass through. Furthermore, other integral proteins serve as channel proteins as well to aid in selective transport of ions in and out of the cell. Such molecules are visible with the help of an electron microscopy. Other Elements Certain other elements may also be present along the length of the cell membrane, depending on the location and needs of the cell. These structures include globular proteins, which are peripherally placed and are only at times associated with the cell. These protein molecules may even be enzymes or glycoproteins. In such cases, either the cell will have special functions, or the location of the cell may require it to perform certain specific functions. When speaking of plant cell vs animal cell, there is one important structure that is additionally present most of the time in animal cells. These molecules are cholesterol molecules, which aid the phospholipids in making the membrane impermeable to water soluble substances. These cholesterol molecules also stabilize the membrane and provide the cell with a cushion effect, which prevents it from suffering any major injuries due to trauma and impact forces. Cell Membrane Function Cell membrane is the outer covering of a cell, which keep the ingredients of a cell intact. Apart from that, there are various other functions, that are carried out by this structure. Read on It is a common fact that cells are the fundamental building blocks of life. These structures form the basic structural and functional unit of any living thing. While some organisms, like, bacteria are single-celled, most other living things are multicellular. In case of multicellular organisms like humans (an adult human has around 100 trillion cells in the body), there are various types of cells, which are assigned different functions. Each cell is made of intricate structures, which forms an interconnected network, which strives to carry out the function of that cell. As the nature of the function of the cells differ, the functions of various parts of the cells too differ. Let us take a look at the various parts of a cell, especially, the cell membrane and cell membrane function. Cell Membrane and Other Parts of a Cell Basically there are two types of cells eukaryotic and prokaryotic. While plants, animals, fungi, protozoans, etc. possess eukaryotic cells, prokaryotic cells are found in bacteria only. The difference between the two types of cells lie in the fact that prokaryotic cells do not have nucleus (and/or some other organelles) and are comparatively smaller, as compared to eukaryotic ones. As far as eukaryotic cells are concerned, the basic structure includes parts like DNA, ribosomes, vesicle, endoplasmic reticulum (both rough and smooth), Golgi apparatus, cytoskeleton, mitochondria, vacuole, centrioles, lysosome, cytoplasm, plasma membrane and cell wall. While plant cells have a large vacuole and a definite cell wall, animal cells lack cell wall but some may have very small vacuoles. Animal cells do not have chloroplasts too. This article is about cell membrane, which is also known as plasma membrane or plasmalemma. Scroll down for information about cell membrane function. Read more on: Similarities Between Eukaryotic and Prokaryotic Cells Plant Cell vs Animal Cell Plant Cell Organelles What is a Cell Membrane? Cell membrane or plasma membrane is one of the vital parts of a cell that encloses and protects the constituents of a cell. It separates the interior of a cell from outside environment. It is like a covering that encloses the different organelles of the cell and the fluid that harbors these organelles. To be precise, cell membrane physically separates the contents of the cell from the outside environment, but, in plants, fungi and some bacteria, there is a cell wall that surrounds the cell membrane. However, the cell wall acts as a solid mechanical support only. The actual function of cell membrane is the same in both cases and it is not much altered by the mere presence of a cell wall. The cell membrane is made of two layers of phospholipids and each phospholipid molecule has a head and a tail region. The head region is called hydrophilic (attraction towards water molecules) and the tail ends are known as hydrophobic (repels water molecules). Both layers of phospholipids are arrange d so that the head regions form the outer and inner surface of the cell membrane and the tail ends come close in the center of the cell membrane. Other than phospholipids, cell membrane contains lots of protein molecules, which are embedded in the phospholipid layer. All these constituents of the cell membrane work jointly to carry out its function. The following paragraph deals with cell membrane function. Read more on cell nucleus: structure and functions and cytoplasm function in a cell. What is the Function of the Cell Membrane? As mentioned above, one of the basic functions of a cell membrane is to act like a protective outer covering for the cell. Apart from this, there are many other important cell membrane functions, that are vital for the functioning of the cell. The following are some of the cell membrane functions. Cell membrane anchors the cytoskeleton (a cellular skeleton made of protein and contained in the cytoplasm) and gives shape to the cell. Cell membrane is responsible for attaching the cell to the extracellular matrix (non living material that is found outside the cells), so that the cells group together to form tissues. Another important cell membrane function is the transportation of materials needed for the functioning of the cell organelles. Cell membrane is semi permeable and controls the in and out movements of substances. Such movement of substances may be either at the expense of cellular energy or passive, without using cellular energy. The protein molecules in the cell membrane receive signals from other cells or the outside environment and convert the signals to messages, that are passed to the organelles inside the cell. In some cells, the protein molecules in the cell membrane group together to form enzymes, which carry out metabolic reactions near the inner surface of the cell membrane. Read more on how do enzymes work. The proteins in the cell membrane also help very small molecules to get themselves transported through the cell membrane, provided, the molecules are traveling from a region with lots of molecules to a region with less number of molecules. Biological Membranes and the Cell Surface http://www.uic.edu/classes/bios/bios100/f06pm/plasmamemb.jpg Membrane Functions Form specialized compartments by selective permeability Unique environment Creation of concentration gradients pH and charge (electrical, ionic) differences Asymmetric protein distribution Cell-Cell recognition Site for receptor molecule biding for cell signaling Receptor binds ligand (such as a hormone) Induces intracellular reactions Controls and regulates reaction sequences Product of one enzyme is the substrate for the next enzyme Can line up the enzymes in the proper sequence Membrane Structure According to the Fluid Mosaic Model of Singer and Nicolson http://www.uic.edu/classes/bios/bios100/f06pm/fmm.jpg The membrane is a fluid mosaic of phospholipids and proteins Two main categories of membrane proteins integral and peripheral Peripheral proteins bound to the surface of the membrane Integral proteins permeate the surface of the membrane Membrane regions differ in protein configuration and concentration Outside vs. inside different peripheral proteins Proteins only exposed to one surface Proteins extend completely through exposed to both surfaces Membrane lipid layer fluid Proteins move laterally along membrane Membrane Lipids Phospholipids most abundant Phosphate may have additional polar groups such as choline, ethanolamine, serine, inositol These increase hydrophilicity Cholesterol a steroid Can comprise up to 50% of animal plasma membrane Hydrophilic OH groups toward surface Smaller than a phospholipid and less amphipathic (having both polar and non-polar regions of the molecule) Other molecules include ceramides and sphingolipds amino alcohols with fatty acid chains These lipids distributed asymmetrically Bilayer Formation Membrane components are Amphipathic (having both polar and non-polar regions of the molecule) Spontaneously form bilayers Hydrophilic portions face water sides Hydrophobic core Never have a free end due to cohesion Spontaneously reseal Fuse Liposome Circular bilayer surrounding water compartment Can form naturally or artificially Can be used to deliver drugs and DNA to cells Membrane Fluidity Membrane is Fluid Lipids have rapid lateral movement Lipids flip-flop extremely slowly Lipids asymmetrically distributed in membrane Different lipids in each side of bilayer Fluidity depends on lipid composition Saturated fatty acids All C-C bonds are single bonds Straight chain allows maximum interaction of fatty acid tails Make membrane less fliuid Solid at room temperature Bad Fats that clog arteries (animal fats) Unsaturated fatty acids Some C=C bond (double bonds) Bent chain keeping tails apart Make membrane more fluid Polyunsaturated fats have multiple double bonds and bends Liquid at room temperature Good Fats which do not clog arteries (vegetable fats) Cholesterol Reduces membrane fluidity by reducing phospholipid movement Hinders solidification at low (room) temperatures How Cells Regulate Membrane Fluidity Desaturate fatty acids Produce more unsaturated fatty acids Change tail length (the longer the tail, the less fluid the membrane) Membrane Carbohydrates Glycolipids and Glycoproteins Face away from cytoplasm (on outside of cell) Attached to protein or lipid Blood antigens Determine blood type bound to lipids (glycolipids) Glycoproteins Protein Receptors Provide specificity for cell-cell or cell-protein interactions (see below) Membrane Proteins Peripheral Proteins completely on membrane surface ionic and H-bond interactions with hydrophilic lipid and protein groups can be removed with high salt or alkaline Integral Proteins Possess hydrophobic domains which are anchored to hydrophobic lipids alpha helix more complex structure An Example Asymetry of Intestinal Epithelial Cell Membranes Apical surface selectively absorbs materials Contains specific transport proteins Lateral surface interacts with neighboring cells Contains junction proteins to allow cellular communication Basal surface sticks to extracellular matrix and exchanges with blood Contains proteins for anchoring The Extracellular Matrix (ECM) and Plant Cell Walls In animal cells, the ECM is a mish-mash of proteins (usually collagen) and gel-forming polysaccharides The ECM is connected to the cytoskeletin via Integrins and Fibronectins Plant Primary Cell Walls for a rigid cross-linked network of cellulose fibers and pectin a fiber composite Fiber composites resist tension and compression Plant Secondary Cell Walls are further strengthened w/ Lignin Secondary Cell Walls is basically what comprises wood Cell to Cell Attachments Tight Junctions and Desmosomes Tight Junctions are specialized proteins in the plasma membranes of adjacent animal cells they stitch together adjacent cells form a watertight cell Desmosomes are specialized connection protein complexes in animal cells they rivet cells together they are attached to the intermediate fibers of adjacent cells Cell Gaps Plasmodesmata Gap Junctions In plant cells, Plasmodesmata are gaps in the cell wall create direct connections between adjacent cells May contain proteins which regulate cell to cell exchange form a continuous cytoplasmic connection between cells called the symplast In animal cells, Gap Junctions are holes lined with specialized proteins allow cell-cell communication (this is what coordinates your heartbeat) Cell Communication In multi-cellular organism, cells can communicate via chemical messenger Three Stages of Cellular Communication Reception A chemical message (ligand) binds to a protein on the cell surfaceÂÂ   Transduction The binding of the signal molecule alters the receptor protein in some way. The signal usually starts a cascade of reactions known as a signal transduction pathway Response The transduction pathway finally triggers a response The responses can vary from turning on a gene, activating an enzyme, rearranging the cytoskeleton There is usually an amplification of the signal (one hormone can elicit the response of over 108 molecules No matter where they are located, signal receptors have several general characteristics signal receptors are specific to cell types (i.e. you wont find insulin receptors on bone cells) receptors are dynamic the number of receptors on a cell surface is variable the ability of a molecule to bind to the receptor is not fixed (i.e. it may decline w/ intense stimulation) receptors can be blocked Two Methods of Cell-Cell Communication Steroid Hormones can enter directly into a cell bind to receptors in the cytosol hormone-receptor complex binds to DNA, inducing change testosterone, estrogen, progesterone are examples of steroid hormones Signal Transduction conversion of signals from one form to another Very complicated pathways all are different! G Protein receptors G-proteins are called as such because they have GTP bound to them Receptors have inactive G-proteins associated with them When the signal binds to the receptor, the G-protein changes shape and becomes active (into the on configuration) The active G-protein binds to an enzyme which produces a secondary message Frequently, second messengers activate other messengers, creating a cascade G-protein signal transduction sequences are extremely common in animal systems embryonic development human vision and smell over 60% of all medications used today exert their effects by influencing G-protein pathways Tyrosine-Kinase Receptors Another Example of a Signal Transduction Pathway Tyrosine-Kinase Receptors often have a structure similar to the diagram below: http://www.uic.edu/classes/bios/bios100/f06pm/tyro-kin02.jpg Part of the receptor on the cytoplasmic side serves as an enzyme which catalyzes the transfer of phosphate groups from ATP to the amino acid Tyrosine on a substrate protein The activation of a Tyrosine-Kinase Receptor occurs as follows: Two signal molecule binds to two nearby Tyrosine-Kinase Receptors, causing them to aggregate, forming a dimer The formation of a dimer activated the Tyrosine-Kinase portion of each polypeptide The activated Tyrosine-Kinases phosphorylate the Tyrosine residues on the protein The activated receptor protein is now recognized by specific relay proteins They bind to the phosphorylated tyrosines, which cause, you guessed it, a conformation change. The activated relay protein can then trigger a cellular response One activated Tyrosine-Kinase dimer can activate over ten different relay proteins, each which triggers a different response The ability of one ligand binding event to elicit so many response pathways is a key difference between these receptors and G-protein-linked receptors (that, and the absence of G- proteins of course) Abnormal Tyrosine-Kinases that aggregate without the binding of a ligand have been linked with some forms of cancer Signal Transduction Shutdown Most signal-transduction/hormone systems are designed to shut down rapidly Enzymes called phosphatases remove the phosphate groups from secondary messengers in the cascade This will shut down the signal transduction pathway at least until another signal is received

Analysis of “Time Talks, with an Accent” by Robert Levine

In the article, â€Å"Time Talks, with an Accent', author Robert Levine explores a cross cultural contrasts in the idea of time, called ‘social time'. He discovers that this concept includes the components of waiting, rushing; being early or late; as well as the past, present and future. He chose to be a professor of social psychology so that he could manage his own time. While teaching in Brazil, he discovers the concept of amanha, which signifies that everything that can be postponed, should be.He observes that not one clock in the city of Niteroi is accurate and students arriving to his class are casual about when class began and ended, which contrasts with how Americans relate to time. Levine has numerous mishaps with amanha during his stay. When he consults his department chair about the issue, she arrives late for their appointment. His students come and go to appointments without reason. Levine then tries to use what he has learned about amanha when his landlord runs la te. Levine runs an errand and misses the appointment and angers the landlord for keeping him waiting.Levine concludes that the understanding of time concepts are a part of larger, cultural values. He outlines the work of Edward Hall, a social anthropologist whose work focused on what he called the †the silent language† (30) of time, which is unspoken, yet easily learned by children. Understanding this silent language is vital for the success of a foreigner living abroad. Since his time in Brazil, Levine has focused on the concept of punctuality and its effects on the health of people and society. He has found great diversity in the concept of time, among cultures and within countries.

Ethical Problems associated to Information Technology Essay

Information technology has been continuously booming with new technological products that create a more diverse information environment. There have been dramatic changes associated with the IT, and these changes create ethical problems and upheavals that usually have something to do with ethics. True, there has been technological development in the arena—one that occurs â€Å"when either the technological paradigm is elaborated in terms of improved concepts, theories, and methods, or in instances of the paradigm are improved† (Moor, 2008, p. 27), such as in terms of efficiency, effectiveness, and safety. This creates an enormous social impact, and it has led to a technological revolution that considerably takes time and is difficult to predict. Information technology has gone over the introduction stage and the permeation stage. We are on the power stage wherein the technology is readily available, affecting people directly and indirectly. This creates an impact that is superbly enormous; yet, there are always the ethical problems that springs forth in the arena. Ethical problems that surround the self-identity, anonymity, and privacy of a person are always attached when it comes to IT. The technological revolution has a large-scale effect that transforms the society, while affecting the manner in which the society functions (Moor, 2008, p. 29). It is evident that open technological revolutions in open societies still need some enhancements, so that the ethical problems would be controlled and maximized. Main Body There are a number of important issues that surround the technological paradigm of IT, especially in relation to ethics. Some of these are in the form of self-identity, anonymity, as well as privacy. There are also other unethical issues (e. g. , cheating, hacking, wardriving) that are attached to the technological paradigm of IT. Ethical problems in self-identity The self-identity is being constructed according to how the individual interacts with the society and with himself or herself. In the social landscape of modernity, there are numerous major changes in the external social environment that affects the individual during this social transformation. In the age of the IT, people get to have the capacity to reconstruct the universe through the everyday realities and circumstances that take place in their specific worlds. It is a continuous state of affairs that largely creates the self-identity and the personal feelings attached to this paradigm. This new sense of identity are being formed with the intrusion of the IT in a person’s life, and people get to have personal relationship even with people who are unknown to them—people who suddenly pop out in their computer’s screens, with names that may or may not be factual. Personal relationships help form the self-identity, offering opportunities for self-expression and the self-renewal. According to Giddens (1991), The modern world is a ‘runaway world’: not only is the pace of social change much faster than in any prior system, so also is its scope, and the profoundness with which it affects pre-existing social practices and modes of behavior. (Giddens, 1991, p. 16) With this, it is apparent that the IT becomes an active component in the continuous transformation of a person’s identity, as it creates and affects the social practices and the modes of a person’s behavior. Thus, problems that affect the personal life of the individual could affect not only the self-identity, but the social practices and the environment as a whole. Ethical problems in terms of anonymity and privacy, for example, can lead to an identity that is blemished because of unethical conduct. Despite the fact that people always carry discursive interpretations of their behavior, this practical consciousness drives the person into creating or destroying the ontological security of human activity in a culture. As an effect, people tend to write comments anonymously while hiding their true identities. Ethical problems in anonymity According to the article that Richard Perez-Pena (2010) wrote entitled ‘News Sites Rethink Anonymous Online Comments’, it says that Internet users usually make use of the digital disguise, revealing their power and their sentiments without acknowledging their true identities to the viewers. This constitutes a sort of freedom for the digital users, and this is most typical in news sites, wherein the viewers are allowed to post comments without indicating their true identities, keeping their privacy in a world that is being presented in public. As indicated in the article, â€Å"Anyone could weigh in and remain anonymous† (Perez-Pena, 2010, p. 1), and this leads to the question on whether or not viewers of Internet sites should be allowed to remain anonymous when dictating their comments and suggestions. This is a very significant ethical problem associated to IT, since it has been ethically accepted that any type of idea or sentiment should be associated to the respectful person who has formed the idea. According to Arianna Huffington, founder of The Huffington Post, Anonymity is just the way things are done. It’s an accepted part of the Internet, but there’s no question that people hide behind anonymity to make vile or controversial comments. (Perez-Pena, 2010, p. 1) It has, therefore, been advised that viewers should indicate their factual names, especially when making a significant commentary about the society. They should use their real names, and this may be done by requiring people to register first before posting their commentaries. Ethical problems in privacy According to the article that Scott Rosenberg (2010) wrote entitled ‘Online Comments Need Moderation, Not Real Names’, there is also the statement that defines how newspaper website managers have been reacting in terms of anonymity and privacy keeping. As stated, â€Å"If only they could make people sign their real names, surely the atmosphere would improve† (Rosenberg, 2010, p. 1). Online conversation spaces make media outlets turn the common software on and then leave them as it is, as if the discussions would â€Å"magically take care of themselves† (Rosenberg, 2010, p. 1). The problem, however, is that the commenters should not be faceless and should carry identities that are open for the other viewers. This problem is in the identity system, with the Web having no identity system that would ethically reconnect the idea to the person who has declared it. As stated in the article, The Web has no identity system, and though the FBI can track you down if the provocation is dire enough, and if you get editors mad enough they can track you down, too, most media companies aren’t going to waste the time and money. (Rosenberg, 2010, p. 1) Ethical privacy problems can also be in the form of ‘hacking’ or â€Å"using unauthorized access to an information system† (Floridi, 2008, p. 43). This indulges privacy and confidentiality. Conclusion There are other ethical problems associated with the IT of the modern social world, such as using the new technology in order to cheat one’s taxes, or deviating the user from his or her true name or identity. It can also be in the form of wardriving wherein people try to connect wirelessly to other people’s networks (Moor, 2008, p. 33). All these unethical conducts can create an enormous social impact that leads to technological revolution that can contract IT in its power stage. With proper management, it can develop the IT into something that is more powerful and enormous, without the ethical problems that have large-scale effects on the society. It is evident, therefore, that open societies through the IT still need some enhancements, so that the ethical problems would be controlled and maximized. References Floridi, L. (2008). Information ethics: its nature and scope. In Eds. Jeroen van den Hoven and John Weckert’s Information technology and moral philosophy. New York, NY: Cambridge University Press. Giddens, A. (1991). Modernity and self-identity: self and society in the late modern age. Stanford, CA: Stanford University Press. Moor, J. (2008). Why we need better ethics for emerging technologies. In Eds. Jeroen van den Hoven and John Weckert’s Information technology and moral philosophy. New York, NY: Cambridge University Press. Perez-Pena, R. (2010, April 11). News sites rethink anonymous online comments. Retrieved May 7, 2010, from The New York Times Company database: http://www. nytimes. com/2010/04/12/technology/12comments. html. Rosenberg, S. (2010, April 13). Online comments need moderation, not real names. Retrieved May 7, 2010, from Salon Media Group, Inc. database: http://www. salon. com/news/feature/2010/04/13/newspaper_online_comments_moderation_open2010.

Review on Paynes Ive got the Light of Freedom - Free Essay Example

Sample details Pages: 2 Words: 508 Downloads: 4 Date added: 2018/12/18 Category History Essay Type Book review Level High school Tags: Development Essay Did you like this example? The book Ive Got the Light of Freedom by Charles M. Paynes is a very educative book with a lot of information since it a book with the contents on organizing, something which is necessary to every individuals regarding the normal activities. We realize that this book highlights the families organizations that are enhanced togetherness during that movement at that time[footnoteRef:1]. Payne bases his argument his manner of describing the struggles that the African American went through while they were fighting for their civil rights during the 20th century. [1: Payne, Charles M. Ive got the light of freedom: The organizing tradition and the Mississippi freedom struggle. Univ of California Press, 2007. The book is an important focus on an analysis how the freedom movement was carried out from a different dimensions as well as the efforts against how the African American people were oppressed. It brings out clearly how factors like strategic organization and the organizing dy namics between the whites and the blacks seems to be the main themes and factors for success. The fact that this was during a movement on fights for civil rights then, we see how the organizations brought into being by the Ella baker/septima school which clearly shows the importance of being organized to an extend of developing leadership[footnoteRef:2]. This is something very encouraging since leadership to them implies that someone is responsible for them to come up together in order to develop strategies as well as personal leadership. Paynes brings it clearly to show how such strategies are of much value not only in such an activity that sees the struggle for freedom by the millions of people but also its value in our day to day activities. [2: Payne, Charles M. Ive got the light of freedom: The organizing tradition and the Mississippi freedom struggle. Univ of California Press, 2007. From Paynes book, the theme of change tends to be clear from his argument as brought about i nformation on so many aspects[footnoteRef:3]. We find out he brings out some of the downfalls also known to be a snowball effect, of the success of the various activism at that time. These struggles as seen through the various activists are what results to their use of knowledge at the same time some of the organizations such as SNCC got advantage on this information through guidance. It is through this that through such information and guidance, organizations easily pick up well and with much energy that results to greater growths. Everyone develops and are in transformation towards better leadership. This has greatly been recommended by Paynes who has seen tactics for progress that brings change where change seems to be the main theme. [3: Payne, Charles M. Ive got the light of freedom: The organizing tradition and the Mississippi freedom struggle. Univ of California Press, 2007.] Critique tends to be based around on what clearly the book doesnt come out very well. The history of such a movement especially in 1963 we realize that a lot of information during this time wasnt brought out very clear. Don’t waste time! Our writers will create an original "Review on Paynes Ive got the Light of Freedom" essay for you Create order