Essay Quiz
1. How does the term fluid mosaic describe the structure of the plasma membrane?
Let’s find out first what it is plasma membrane and its function. The plasma membrane is the boundary between the cell and its environment. It regulates what enters and exits the cell. Plasma membrane plays a vital role in protecting the integrity of the interior of the cell by allowing only selected substances into the cell and keeping other substances out. It also serves as a base of attachment for the cytoskeleton in some organisms and the cell wall in others. Thus the cell membrane supports the cell and helps in maintaining the shape of the cell. The cell membrane is primarily composed of proteins and lipids. While lipids help to give membranes their
…show more content…
Proteins and phospholipids make up most of the membrane structure. According to Bailey (2016) Phospholipids form a lipid bilayer in which their hydrophilic head areas spontaneously arrange to face the aqueous cytosol and the extracellular fluid, while their hydrophobic tail areas face away from the cytosol and extracellular fluid. The lipid bilayer is semi-permeable, allowing only certain molecules to diffuse across the membrane to enter or exit the cell. On the other hand, membrane proteins are free to move within the lipid bilayer as a result of its fluidity. Although this is true for most proteins, they can also be confined to certain areas of the bilayer with enzymes. Membrane proteins perform various functions, and this diversity is reflected in the significantly different types of proteins associated with the lipid bilayer (Spark Notes, …show more content…
Endocytosis is a general term for the process whereby very large particles of material are wrapped with plasma membrane and moved into the cell in the form of vesicles or vacuoles. None of the trapped material actually moves through the membrane, but remains on the other side of the original membrane, even while the vacuole is inside the cell. Exocytosis is the export of large quantities of material from the cell. Vesicles containing the material to be exported fuse with the plasma membrane, dumping the contents into the environment around the cell (Simon, 2015, pg.
The beet Lab experiment was tested to examine bio-membranes and the amount of betacyanin extracted from the beets. The betacyanin is a reddish color because it transmits wavelengths in red color and absorbs most other colors. The membrane is composed of a phospholipid bilayer with proteins embedded in it. The phospholipid bilayer forms a barrier that is impermeable to many substances like large hydrophilic molecules. The cells of beets are red and have large vacuoles that play a big role for the reddish pigment. This experiment aimed to answer the question, “How do cell membranes work?” The hypothesis we aim to test is: Cell membranes work as a fluid mosaic bilayer of phospholipids with many embedded proteins. We predicted that the 50% Acetone will break down the most betacyanin. Our hypothesis was proven wrong by our data collected. We could test our predictions by doing the experiment multiple times and compare the
This cell membrane plays an important part in Diffusion. Cell membrane and Diffusion Diffusion is the movement of the molecules of gas or liquids from a higher concentrated region to a lower concentration through the partially permeable cell membrane along a concentraion gradient. This explanation is in the diagram shown below: [IMAGE] Turgor When a plant cell is placed in a dilute solution or a less concentrated solution then the water particles pass through the partially permeable membrane and fill the cell up with water. The cell then becomes Turgor or hard. An example of this is a strong well-watered plant.
Homeostasis is essential to the cell’s survival. The cell membrane is responsible for homeostasis. The membrane has a selective permeability which means what moves in and out of the cell is regulated. Amino acids, sugars, oxygen, sodium, and potassium are examples of substances that enter the cell. Waste products and carbon dioxide are removed from the cell.
The direction of osmosis depends on the relative concentration of the solutes on the two sides. In osmosis, water can travel in three different ways. If the molecules outside the cell are lower than the concentration in the cytosol, the solution is said to be hypotonic to the cytosol, in this process, water diffuses into the cell until equilibrium is established. If the molecules outside the cell are higher than the concentration in the cytosol, the solution is said to be hypertonic to the cytosol, in this process, water diffuses out of the cell until equilibrium exists. If the molecules outside and inside the cell are equal, the solution is said to be isotonic to the cytosol, in this process, water diffuses into and out of the cell at equal rates, causing no net movement of water. In osmosis the cell is selectively permeable, meaning that it only allows certain substances to be transferred into and out of the cell. In osmosis, the proteins only on the surface are called peripheral proteins, which form carbohydrate chains whose purpose is used like antennae for communication. Embedded in the peripheral proteins are integral
Endoplasmic Reticulum, Golgi Apparatus, and Lysosomes. (2013). In Scitable Nature Education. Retrieved December 09, 2013, from http://www.nature.com/scitable/topicpage/endoplasmic-reticulum-golgi-apparatus-and-lysosomes-14053361
In 1871 Hugo de Vries cell membrane permeability for ammonia and glycerol, this was leading upto the first successful X-ray study by Bernal and Crowfoot in 1934 of the globular protein pepsin, however even though it shows water covering the protein surface, it doesn’t show it in high resolution. Many years has past with more testing and experiments but it wasn’t until 1925 when E, Gorter and F, Grendel proposed the phospholipid layers in the cell membrane which resulted in them doing first bilayer structure experiment test, obtaining this by measuring the size of water surface that phospholipids taken from red blood cell can cover, the area in which it covered was nearly twice as much as the total area of red blood cells used to extract the phospholipids, as a result this ended up being a lucky find in bilayer structure and with more accurate measuring and due to the presence of proteins within the membrane the ratio of the two surfaces wouldn’t of been 2:1, although this original finding was not able to be duplicated as stimulated membrane research, it steered it in the right direction. In 1985 M. Diesenhofer, R.Huber and H. Michel show the structure of the membrane protein in high resolution, showing alpha helical transmembrane segments.
In life, it is critical to understand what substances can permeate the cell membrane. This is important because the substances that are able to permeate the cell membrane can be necessary for the cell to function. Likewise, it is important to have a semi-permeable membrane in the cell due to the fact that it can help guard against harmful items that want to enter the cell. In addition, it is critical to understand how water moves through the cell through osmosis because if solute concentration is unregulated, net osmosis can occur outside or inside the cell, causing issues such as plasmolysis and cytolysis. The plasma membrane of a cell can be modeled various ways, but dialysis tubing is especially helpful to model what substances will diffuse or be transported out of a cell membrane. The experiment seeks to expose what substances would be permeable to the cell membrane through the use of dialysis tubing, starch, glucose, salt, and various solute indicators. However, before analyzing which of the solutes (starch, glucose, and salt) is likely to pass through the membrane, it is critical to understand how the dialysis tubing compares to the cell membrane.
The cell plasma membrane, a bilayer structure composed mainly of phospholipids, is characterized by its fluidity. Membrane fluidity, as well as being affected by lipid and protein composition and temperature (Purdy et al. 2005), is regulated by its cholesterol concentration (Harby 2001, McLaurin 2002). Cholesterol is a special type of lipid, known as a steroid, formed by a polar OH headgroup and a single hydrocarbon tail (Wikipedia 2005, Diwan 2005). Like its fellow membrane lipids, cholesterol arranges itself in the same direction; its polar head is lined up with the polar headgroups of the phospholipid molecules (Spurger 2002). The stiffening and decreasing permeability of the bilayer that results from including cholesterol occurs due to its placement; the short, rigid molecules fit neatly into the gaps between phospholipids left due to the bends in their hydrocarbon tails (Alberts et al. 2004). Increased fluidity of the bilayer is a result of these bends or kinks affecting how closely the phospholipids can pack together (Alberts et al. 2004). Consequently, adding cholesterol molecules into the gaps between them disrupts the close packing of the phospholipids, resulting in the decreased membrane fluidity (Yehuda et al. 2002).
its original shape and shape. Within the phospholipid bi-layer there are proteins, and these. proteins are made up of polypeptide chains which are joined together. by hydrogen, hydrophobic and peptide bonds. Once the temperature has increased above 40°C the molecules vibrate so energetically that these bonds break easily and therefore create holes within the cell wall.
The cell membrane is a structure that controls what enters and leaves the cell. In a basketball stadium, the security guards are like the cell membrane. They can say who comes in if they don’t cause any problems and are following the rules and they can reject them and make them leave if they have something they aren’t supposed to or they are doing something wrong. This is how security guards are like a plant cell’s cell membrane because the security guards control what enters and leaves the stadium like the membrane controls what enters and leaves the cell.
to construct and or maintain the cell membrane. In a microscopic view of the cell membrane we can
The cytoskeleton is a highly dynamic intracellular platform constituted by a three-dimensional network of proteins responsible for key cellular roles as structure and shape, cell growth and development, and offering to the cell with "motility" that being the ability of the entire cell to move and for material to be moved within the cell in a regulated fashion (vesicle trafficking)’, (intechopen 2017). The cytoskeleton is made of microtubules, filaments, and fibres - they give the cytoplasm physical support. Michael Kent, (2000) describes the cytoskeleton as the ‘internal framework’, this is because it shapes the cell and provides support to cellular extensions – such as microvilli. In some cells it is used in intracellular transport. Since the shape of the cell is constantly changing, the microtubules will also change, they will readjust and reassemble to fit the needs of the cell.
There are many functions lipids have. One of the main functions lipids are structural components in the cell. Lipids make up approximately 50% of the mass of most cell membranes. The lipids that are found in the cell membrane are called phospholipid. Phospholipid are the predominant lipids of cell membrane. Phospholipids aggregate or self-assemble when mixed with water, but in a different manner than the soaps and detergents. Because of the two pendant alkyl chains in phospholipids and the unusual mixed charges in their head groups, micelle formation is unfavorable relative to a bilayer structure.
Synaptic vesicles exist in different types, either tethered to the cytoskeleton in a reserve pool, or free in the cytoplasm (Purves, et al., 2001). Some of the free vesicles make their way to the plasma membrane and dock, as a series of priming reactions prepares the vesicular and plasma membrane for fusion (Lodish, Berk, Zipursky, Matsudaira, Baltimore, & Darnell, 2000).
If we examine the detailed structures of many transmembrane proteins, we see that they often have three different domains, two hydrophilic and one hydrophobic .(fig 1&2) A hydrophilic domain (consisting of hydrophilic amino acids) at the N-terminus pokes out in the extracellular medium, a hydrophobic domain in the middle of the amino acid chain, often only 20-30 amino acids long, is threaded through the plasma membrane, and a hydrophilic domain at the C-terminus protrudes into the cytoplasm. The transmembrane domain, because it is made of amino acids having hydrophobic side chains, exists comfortably in the hydrophobic inner layers of the plasma membrane. Because these transmembrane domains anchor many proteins in the lipid bilayer, these proteins are not free-floating and cannot be isolated and purified biochemically without first dissolving away the lipid bilayer with detergents. (Indeed, much of the washing we do in our lives is necessitated by the need to solubilize proteins that are embedded in lipid membranes using detergents!)