Biology a light microscope) showed that cells

Biology Module 1: Assignment 1 Biochemistry of the Cell Structure and function of Cell Membrane  This paper will explore the discovery of cells with explanations on structure and function of cell membrane in eukaryotic cells and prokaryotic cells.   The development and production of glass lenses in the 17th Century started the process of cell discovery.  These lenses were powerful enough to make out details to invisible to the naked eye.  Robert Hooke examined a piece of cork and in 1665 reported to the Royal Society of London that the cork was composed of a mass of minute chambers.  He named these chambers ‘cells’, as they resembled the simple rooms occupied by monks in a monastery.  After this discovery Hooke paired up with Dutch contemporary Antoni Van Leeuwenhoek and together they observed living cells for the first time a world teeming with motile microscopic organisms.   The process of cell biology was a long process which many individuals all contributed to.  Botanist Matthias Schleiden and Zoologist Theodor Schwann’s publications were among the pivotal journals published in 1839. Their documented results of systematic investigation of plant and animal tissues (using a light microscope) showed that cells were the universal building blocks for all living tissues.  From their work other 19th century microscopists led the discovery that all cells are formed by the growth and division of existing cells.   Essential Cell Biology. (1998) Moving through the nineteenth century electron and scanning electron microscopes were developed leading to greater magnification and resolving power.  Transmission electron microscopes which were also designed in the 1930s, use a high voltage beam passed through a very thin sample.  This allows the resolution of the internal structure of the cell.  “In 1925 Dutch Physiologists Gorter and Grendel approached the discovery of our present model of the plasma membrane structure as a lipid bi-layer with the polar hydrophilic heads facing outwards towards the aqueous environment and the hydrophobic tails facing inwards away from the aqueous surroundings on both sides of the membrane.  In 1935 physiologists Davson and biologist Danielli refined the Gorter-Grendel model adding to the phospholipids bi-layer a proteins mono-layer.” SEBIOLOGY. (2017). PLASMA MEMBRANE   From these technologies (electron microscope) Danelli and Davson came up with their model of the plasma membrane. Figure 1 a  They suggested that the plasma membrane was built of lipids and worked with artificial membranes coated with protein with polar pores. The lipid described in the model was phospholipid.  They have 2 fatty tails, Hydrophobic (do not mix with water) and the other is hydrophilic phosphate head which is polar (does mix with water).    However, the biggest problem with this model stems from previous research into cell theory, in terms of growth and division of existing cells.  The 1st model had no spaces for pores for transport or diffusion in this model and also it did not contain vital carbohydrates for cell recognition.  Davson-Danielli proposed a new model (Figure 1a) in the 1950’s which also was flawed in terms of accuracy and didn’t match the evidence from research.   In 1972 a 3rd model was proposed by Singer and Nicolson, there was evidence to support this model which was named the fluid mosaic model. The cell membrane acts as a boundary between the cell and its environment. Controls what goes in and what goes out depending on what the cell is dispositioned to perform. The cell membrane is composed almost entirely of phospholipids and proteins.  Singer and Nicholson suggested that the cell membrane had a fluid structure because the phosolipid part is capable of movement and the protein part floats within it.  The idea of the structure of a cell is called a fluid mosaic model.  See figure 1b of a fluid mosaic model.   Figure 1b (2017)  The proteins have 2 parts to their molecules, a hydrophobic part which is buried in the ‘tails’ of the lipid layer and a hydrophilic phosphate head which is involved in a variety of activities.    There are thousands of different proteins associated with cell membranes.  Some of them move freely and other are fixed in one place.  Some extend right across the lipid bilayer (integral proteins) whilst others only penetrate part of the way or remain outside of the lipid layer (peripheral proteins).   Churchman, J. and Pedder, K. (2002). Biology. Integral proteins (or transmembrane protein) of the plasma membrane are synthesized in the rough endoplasmic reticulum (RER) and sent to the Golgi apparatus.  The Golgi takes proteins produced in the RER & Lipids (made in the smooth endoplasmic reticulum) and alters them into the correct functional shape (in the form of newly formed vesicles) then sends them to wherever they are required in the cell.  They can also be sent to the cell/plasma membrane to be exported out of the cell.  These transmembrane proteins can pass straight through the membrane and have extracellular and intracellular domain. There are many functions which depend on the plasma membrane.  It is vital for transport in and out of the cell.  Cell membranes also contain cholesterol in the phospholipid bilayer.  In some membranes there are only a few cholesterol molecules, but in others there are as many cholesterols as phospholipids.  Cholesterol makes the bilayer stronger, more flexible but less fluid, less permeable to water-soluble substances such as ions and monosaccharides. Carbohydrate groups (chains) are present only on the outer surface of the plasma membrane and are attached to proteins, forming glycoproteins, or lipids, forming glycolipids.    Figure 1c (2017). ACTIVE TRANSPORT: Transport may occur by diffusion and osmosis across the membrane. It can also occur when a vesicle (from the Golgi apparatus) attaches to the cell membrane from the inside and then opens to form a pocket, expelling its contents to the outside. This may be called exocytosis. The cell membrane may also envelope something on the outside and surround it, taking it into the cell. This may be called endocytosis.  Endocytosis and exocytosis are processes that move large materials in or out of the cell, by forming vesicles to allow passage through the cell membrane.  Both processes require the expenditure of energy which is considered an active process.  If the substance taken into the cell is liquid, the intake is referred to as pinocytosis.  If the substance taken into the cell is particulate matter, the intake is referred to as phagocytosis. Diffusion requires no energy (passive), it is the movement of a gas or liquid substance from an area of high concentration to low.  In Figure 1c, Oxygen is moving through the plasma membrane from high concentration to low concentration.   Facilitated diffusion is another form, in figure 1c diffusion through aqueous channel movement of (Na+) Enzyme and the movement of Glucose (C6H12O6).  Again, this form of diffusion requires no energy, there are two types of proteins that permit facilitated diffusion:  Carrier proteins and channel proteins.  Carrier proteins bind to the ions on one side and change shape and release particle on the other side of the membrane.  Channel proteins are water filled pores and allow the polar particles to pass through.   Osmosis is also a passive form of transport requiring no energy, (not indicated in figure 1c) another vital form of diffusion.  It is the net movement of water molecules from a less concentrated solution to a more concentrated solution across a partially or semi-permeable membrane.  Allowing small solvent molecules of water to pass but prevents the movement of larger solute molecules.   Active transport requires energy.  It is the process of moving molecules against the concentration gradient.  For example, the sodium-potassium pump which exists in the cell membrane figure 1d.    Figure 1d   It moves sodium ions out of the cell to the extracellular fluid and moves potassium ions into the cell opposite their concentration gradients.   Cellular energy is required and generally, comes from ATP.  The discovery of the cell membrane and its functions give insight to how all cells grow and divide. The complexity of the cell membrane was only discovered along with breakthrough technology that could examine various stages of cell development and behaviours.  The chemical reactions required for cells to perform, start within the cell membrane. The plasma membrane is vital to support of both eukaryotic cells and prokaryotic cells.  This area of exploration leads through to biochemistry and connecting the reactions that happen in every element of the cell including the intricate cell membrane.  By researching this area of the cell, scientists have been able to break down the chemical elements of each of these functions. Leading cytology into biochemistry connecting the intricacies of the cell membrane with evidence and research.  This is vital in understanding how everything from nutrition, genetics through to diseases effect animal and plant cells.    Word Count 1461