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How Organelles Work Together to Make and Secrete the Protein Insulin

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Human Biology Unit 1 Assignment The human body is made up of 100 trillion cells. All cells have the same basic structure (see figure 1) however some cells are specialised to suit a specific purpose. An example of this is the pancreatic beta cells found in the islets of Langerhans. These cells are specialised to synthesise the protein insulin that is involved in the metabolism of glucose in the cells. (Layden, 2010) Figure 1 – Picture to show basic structure of a cell. (Farrabee, M J. 2007) But how is insulin made? The production of insulin starts in the nucleus which is the cellular organelle where the DNA (deoxyribonucleic acid) is found.

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They form a series of multiple linear molecules which are then folded in the nucleolus in to chromosomes as a gene. Genes are sections of DNA which contain instructions on how to make proteins and in this case insulin. The DNA molecule however is too large to get through the nuclear pores of the membrane so by the process of transcription a section of the instruction is copied in to RNA (ribonucleic acid).

The RNA then takes the section of the instruction and leaves the nucleus and joins with a ribosome where it can be used to synthesise the protein. Hickman and Thain 2004) Ribosomes are either free in the cytoplasm or are attached to the ER. Each ribosome has one conformational groove to fit the growing polypeptide chain and another for the messenger RNA. It has a gap between both of its sub units to permit the entry of transfer RNA. The tRNA is then bonded to an amino acid from the amino acid pool. The amino acid pool is composed by amino acids that the body has broken down and put in to the bloodstream via facilitated diffusion. Figure 2- Passive Transport, Diffusion & Osmosis (Coli, E. 2007)

Diffusion is the process that is used in oxygen entering a cell, and carbon dioxide leaving. These molecules will move from where they are at a high concentration to where they are at a lower concentration they diffuse down a concentration gradient. The blood system in humans continually brings more oxygen to the cell and takes carbon dioxide away. This maintains a high concentration gradient. Since the movement is always down the concentration gradient, it requires no energy. The small molecules pass from one side of the membrane to the other by moving between the lipid molecules.

Osmosis is the diffusion of water molecules across a partially permeable membrane, from an area of high water potential a higher concentration of water molecules to an area of low water potential a lower concentration of water molecules. (S-cool, 2013) Facilitated diffusion is a type of passive transport that allows substances to cross membranes down a concentration gradient with the assistance of special transport proteins. Through the use of ion channel proteins and carrier proteins that are embedded in the cell membrane these substances can be transported in to the cell.

Ion channel proteins allow specific ions to pass through the protein channel. The ion channels are regulated by the cell and are either open or closed to control the passage of substances in to the cell. Carrier proteins bind to specific molecules, change shape and then deposit the molecules across the membrane. Once this complete the proteins return to their original position. (Bailey, 2013) ‘The ribosome then translates the mRNA in to a single chain precursor called preproinsulin; thereafter the removal of its signal peptide during insertion in to the endoplasmic reticulum generates proinsulin. ’ (Barret, Brooks, Boitano, Barman, 2009)

Figure 3 – Pre/Pro Insulin Diagram. (Noske, A. 2010) Figure 4 – Rough & Smooth ER’s, Golgi and Vesicles. Proinsulin consists of three parts: an amino- terminal B chain, a carboxy-terminal A chain and a connecting peptide in the middle known as a C peptide. In the endoplasmic reticulum, the proinsulin is exposed to several specific endopeptidases which excise the C peptide; this forms the mature form of insulin. The Insulin and free C peptide are packed in the Golgi bodies into secretory granules which accumulate in the cytoplasm and when needed the insulin is secreted to the portal vein via exocytosis. Mandal, no Date) The rough ER is an extensive organelle composed of a greatly convoluted but flattened sealed sac. Studded on its outer surface are ribosomes. It is involved in the production, folding, quality control and despatch of proteins. (BSCB, 2013) The smooth ER is a separate sealed interconnecting network. It is associated in the; metabolism and production of lipids, steroid and hormone manufacturing, the transport of intracellular products and detoxification. (BSCB, 2013) A vesicle is bubble like membranous structure that stores and transports cellular products and digests metabolic waste in a cell. Biology Online, 2008) The golgi complex is a structure composed of flattened sacs known as cisternae. It is involved in the modification and packaging of proteins, the manufacturing of lysosomes and transport of products via vesicles. (Bailey, R, 2013) (Bailey, R. 2012) Exocytosis is the process of how hormones, digestive enzymes and lipids are released from the cell. Vesicles containing the product pinch off from the sacs of the golgi apparatus and move towards the plasma membrane. The vesicles then fuse with the plasma membrane and release the product outside the cell. CGP, 2009) The cell membrane surrounds all living cells, and is the cell’s most important organelle. It controls how substances can move in and out of the cell and allows cell communication and recognition. Membranes are composed of phospholipids proteins and carbohydrates arranged in a fluid mosaic structure shown below: Figure 5 – Structure Of The Cell Membrane (Biology Mad, 2004) Table to show cell membrane properties and how they help Cell Membrane Properties| How They Help| The membrane is a good barrier against most water soluble molecules| Phospholipids are the major component of the membrane bilayer.

The molecules automatically arrange themselves in to a bilayer- the hydrophilic heads face out towards the water on either side of the membrane, and the hydrophobic tails face inwards. This hydrophobic centre makes it difficult for water soluble substances such as sodium ions and glucose to get through. | The membrane controls what enters and leaves| Proteins in the membrane allow the passage of large or charged water soluble substances that would otherwise find it difficult to cross the membrane. | The membrane allows cell communication| Membranes contain receptor proteins.

These allow the cell to detect chemicals released from other cells. The chemicals signal to the cell to respond in some way. Eg. The hormone insulin binds to receptors in the membranes of the liver cells, and this tells the liver cells to absorb glucose. Communication is vital for the body to function properly. | The membrane allows cell recognition | This relates to white blood cells. Glycoproteins and glycolipids tell white blood cells that the cells are either your own or not. So if they are not they can attack cells they don’t recognise. | The membrane is fluid| The phospholipids in the plasma membrane are constantly moving around.

The more un-saturated fatty acids there are in the phospholipid bilayer, the more fluid it becomes. Cholesterol molecules fit in between the phospholipids of the bilayer, binding there hydrophilic tails causing them to pack more closely together. So the more cholesterol molecules there are the less fluid the membrane becomes. Cholesterol is important as it makes the cell membrane more rigid and prevents it from breaking up. | (Biologymad, 2004) All the processes which are not passive described in the production and manufacturing of insulin require energy. The mitochondria are where aerobic respiration takes place.

Aerobic respiration needs oxygen and produces carbon dioxide and water. The chemical reactions of aerobic respiration take place in the central matrix of the cell and on the inner membrane of the mitochondria. Respiration produces a chemical called adenosine triphosphate (ATP) which is the chemical energy that all cells use. (Biology Online, 2008) Cells use ATP to fuel any process that requires energy such as movement this is important in the production of insulin as motor molecules in particular kinesin use microfilaments and microtubules in the cytoskeleton to move along. Bibliography Main Essay :- About Biology. (2013).

The Golgi Complex. Availible at: http://biology. about. com/od/cellanatomy/ss/golgi-complex. htm Bailey, R. (2013) Diffusion and Passive Transport. Available at: http://biology. about. com/od/cellularprocesses/ss/diffusion_2. htm (Accessed 5th March 2013). Figure 4 – Bailey, R. (2012) About. Com Website. Available at: http://biology. about. com/od/cellanatomy/ss/mitochondria. htm (Accessed 5th March 2013). Barret, K. Brooks, H. Boitano, S. Barman S. Ganong 23rd Edition. (2009) Review Of Medical Physiology. Available at:http://www. scribd. com/doc/57882272/Review-of- Medical-Physiology-Ganong-23rd-Ed (Accessed 5th March 2013).

Figure 5 – Biology Mad, (2004). The Cell Membrane. Available at: http://www. biologymad. com/cells/cellmembrane. htm (Accessed 5th March 2013. Biology Online. (2008). Vesicles. Availible at: http://www. biology-online. org/dictionary/Vesicle (Accessed 5th March 2013) BSCB, (2013). Smooth & Rough ER. Availible at: http://www. bscb. org/? url=softcell/er (Accessed 5th March 2013). Figure 2 – Coli, E. (2007) Passive Transport. Availible at: http://eschecoli. blogspot. co. uk/2007/08/facilitated-diffusion. html (Accessed 5th March 2013) Coordination Group Publications Ltd. (2009) AS & A2 BIOLOGY.

Page 19. Figure 1 – Farabee, M J. (2007) Cellular Organisation. Available at: http://www2. estrellamountain. edu/faculty/farabee/biobk/BioBookCELL2. html (Accessed: 5th March 2013). Hickman, M. And Thain, M. (2004). The penguin dictionary of biology, London: Penguin books. Page 622. Layden, B. (2010) G-Protein-Coupled Receptors, Pancreatic Islets, and Diabetes. Available at: http://www. nature. com/scitable/topicpage/g-protein-coupled-receptors-pancreatic-islets-and-14257267 (Accessed: 5th March 2013). Mandal, A, (no date). Insulin, what is insulin? Available at: http://www. news-medical. et/health/Insulin-Synthesis. asp (Accessed 5th March 2013). Figure 3 Noske, Andrew. (2010). Location and function of beta cells within the islets of Langerhans. Available at: http://www. andrewnoske. com/student/uq_phdthesis. php (Accessed 5th March 2013). Figure 2 – Pearson Education Inc. (2010) Eukaryotic Cell Components. Available at:http://www. uic. edu/classes/bios/bios100/lectures/cells. htm (Accessed 5th March 2013). S-cool, (2013). Movement And Diffusion. Available at: http://www. s-cool. co. uk/a-level/biology/cells-and-organelles/revise-it/movement (Accessed 5th March 2013).

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