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Cell Membrane: The process of protein synthesis

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The cell membrane

The cell membrane is a thin semi-permeable membrane that surrounds the cytoplasm of the cell. Its function is to act a barrier that separate’s a cell from its surrounding environment which protects the integrity by allowing certain substances into the cell, while keeping other substances out. Also, the cell membrane helps to support the cell, its shape and the outer boundary of a cell which is called the plasma membrane. The plasma membrane is composed of four different types of molecules such as, phospholipids, cholesterol, proteins and carbohydrates.

The fluid mosaic model describes the structure of the cell membrane as being flexible and is certainly not a solid. Firstly, phospholipids are a major component’s of a cell membrane as they make up the basic structure. A single phospholipids molecule has two different ends, the head and the tail. Phospholipids create a lipid bilayer in which the head contains a phosphate group which is hydrophilic. This means that it is attracted to water molecules. The hydrophilic head can rearrange to face the aqueous cytosol and the extracellular fluid. Whereas the tail end is made up of two strings of hydrogen and carbon atoms called fatty acid chains. The chains are called hydrophobic which means they do not like water molecules, for example, when vegetable oil is poured in to water, the vegetable oil does not mix with the water. Therefore the hydrophobic tail face away from the cytosol and extracellular fluid. The phospholipid of a cell membrane are arranged in a double layer called the lipid bilayer and the hydrophilic phosphate heads are always arranged so that they are near water. The water fluid is found inside and outside the cell and the hydrophobic tails of membrane phospholipids are organized in a way that keeps them away from water.

Cholesterol is another lipid component of animal cell membranes and is an extremely important component of cell membranes. The cholesterol molecules are made up of four rings of hydrogen and carbon atoms, also they are hydrophobic and are found among the hydrophobic tails in the lipid bilayer. The cholesterol molecules are also dispersed between the membrane phospholipids this is because it helps to keep the cell membrane from becoming stuff by preventing phospholipids from being too closely together. Cholesterol molecules are important for maintaining the consistency of the cell membrane and they strengthen the membrane by preventing some small molecules from crossing it. Also, the cholesterol molecules keep the phospholipids tails from coming into contact and solidifying which ensures the cell membrane stays fluid and flexible.

Furthermore, some plasma membrane proteins are in the lipid bilayer which are called integral proteins and other proteins are called peripheral proteins, and they are outside of the lipid bilayer. The peripheral proteins are found on either side of the lipid bilayer. Membrane proteins can function as enzymes that can speed up chemical reactions, act as receptors for specific molecules, or transport materials across the cell membrane. Carbohydrates, or sugar, are sometimes found attached to proteins or lipids on the outside of the cell membrane, for example, glycolipids are located on the cell membranes surfaces and have a carbohydrates sugar chain attached to them. They help the cell to recognize other cell of the body. Together, these carbohydrates form the glycocalyx. The glycocalyx of a cell has many functions including that it provides cushioning and protection for the plasma membrane and it is important in cell recognition. Based on the structure and types of carbohydrates in the glycocalyx, the body can recognize cells and determine if they should be there or not.

The cell membrane contains two proteins, peripheral membrane proteins and integral membrane proteins. The peripheral membrane proteins are exterior to and connected membrane by interactions with other proteins. The integral membrane proteins are inserted into the membrane and most can pass through membrane. The proteins in the cell membrane have a number of different functions including that structural proteins help to give the cell support and shape. The cell membrane receptor proteins help cells communicate with the environment using hormones, neurotransmitter, and other signalling molecules. Transport proteins, such as globular proteins that transport molecules across the cell membranes by facilitated diffusion. Also, glycoproteins have a carbohydrate chain attached to them. They are in the cell membrane and help cells to communicate and molecules transport across the membrane.

The bacteria flagellum

The flagellum are long, thin, whip-like structures that is attached to a bacterial cell that allows bacterial movement. A bacterial cell is typically between 0.1 micrometres and 50 micrometres in diameter, but on average around 2 micrometres. However, the flagellum can be several times longer than the cell also some bacteria can have a single flagellum, while others may have many flagella surrounding the entire cell. The flagellum is rotated by a motor apparatus in the plasma membrane which allows the cell to swim in fluid environments. Also, the long portion of the flagellum, known as the filament which is composed of a protein called flagellin. These proteins form long chains that give the flagellum a helical shape. The flagellum also becomes wider and forms the hook, which attaches the long filament to the cell at the motor. The motor is a series of protein rings that span the cell membrane, anchoring the flagellum to the cell and therefore providing movement to the flagellum.

The mitochondria

The survival of cells requires energy to perform different functions, therefore the mitochondria are important as these organelles supply all the necessary energy of the cell. The energy of a cell is from the enzymatic oxidation of chemical compounds in the mitochondria and so the mitochondria is referred to as the ‘power houses’ of a cell. The biochemical processes of a cell are known as cellular respiration. Many of the reactions involved in cellular respiration happen in the mitochondria. Therefore, the mitochondria are the working organelles that keep the cell full of energy. The mitochondria are a membrane bound cellular structure and is found in most eukaryotic cells which are small organelles floating free through the cell. These organelles generate most of the energy of a cell in the form of adenosine triphosphate and it is used as a source of chemical energy. Also, of a cell believes it if not getting enough energy to survive, more mitochondria can be created. The mitochondria can grow larger or combine with other mitochondria based on the needs of a cell.

The mitochondria are a rod-shaped structure found in both animal and plant cells which are shaped perfectly to maximize their productivity. They are made of two membranes which means it is a double membrane bound organelle. The outer membrane covers the organelle and contains it like a skin. The inner membrane folds over many times and creates layered structures called cristae. Although the membranes are made up of phospholipids and proteins and the fluid contained in the mitochondria is called the matrix. The folding of the inner membrane increases the surface area inside the organelle and since many chemical reactions act on the inner membrane, the increased surface area creates more space for reactions to occur.

The functions of the mitochondria are specific on the cell type in which they are present. Firstly, the most important function of the mitochondria is to produce energy. The simpler molecules of nutrition are sent to the mitochondria to be processed and to produce charged molecules. The charged molecules in combination with oxygen produce ATP molecules and this process is known as oxidative phosphorylation. Also, the mitochondria help the cells to maintain the correct concentration of calcium ions within the compartments of the cell. The mitochondria also help in building certain parts of blood and hormones, for example, testosterone and oestrogen. Finally, the mitochondria are important in the process of apoptosis which is abnormal death of cells due to the dysfunction of mitochondria that can affect the function of organs.

The rough endoplasmic reticulum

The rough endoplasmic reticulum (RER) is extremely important in the synthesis and packaging of proteins. The ribosomes that are attached to the membrane of the endoplasmic reticulum (ER), therefore making it ‘rough’. The rough endoplasmic reticulum is also attached to the nuclear envelope that surrounds the nucleus. The movement of molecules through both membranes are allowed by the direct connection between the perinuclear space of the lumen of the endoplasmic reticulum.

The process of protein synthesis begins when mRNA moves from the nucleus to a ribosome on the surface of rough endoplasmic reticulum. The ribosomes build the amino acid chain also the chain is pushed into the cisternal space of the rough endoplasmic reticulum. When the proteins are complete, they collect and the rough endoplasmic pinches off a vesicle.

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