Insulin Is Synthesized By Beta Cells Biology Essay

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Insulin is produced in the pancreas when blood sugar levels are too high so it can bring it down again to an optimum level. This is called maintaining homeostasis or an internal equilibrium. Insulin does this by transporting the extra glucose to be stored as fat cells, muscle reserves and in the liver which is called glucose homeostasis. For example, when you eat a carbohydrate the body will release insulin to stop your blood sugar level from raisin too high. When this insulin is released, it will cause the liver to store glucose as glycogen which is a stored form of carbohydrate energy (like the energy reserves in your muscles). Because of the increase in insulin sensitivity the body's ability to uptake amino acids is also increased.

If the liver already has lots of glycogen and is full, extra glucose will be stored as fat cells. What opposes this is the glucagon hormone which is also produced in the pancreas, this hormone regulates blood sugar level. This is only released when blood sugar levels are too low to stimulate an increase in blood sugar levels by glucose. This is done by using the glycogen stored in the liver then it will stimulate muscle breakdown to in order to get more glucose. This opposes insulin so they work together in this complex operation. (Eating low Glycemic Index foods will stop your body from releasing too much insulin to absorb what you just ate).

Insulin is synthesized by β (Beta) cells. These are in the islets of Langerhans area within the pancreas which forms the endocrine gland by spherical clusters of hormone producing cells. These cells are categorized into: α ( alpha) cells, β (beta) cells, δ (delta) cells and PP (F) cells. Alpha cells secrete glucagon which as previously mentioned regulates blood sugar levels in conjunction with insulin which are what beta cells are. δ (delta) cells secrete Somatostatin which inhibits the secretion of hormones. PP (F) cells secrete a pancreatic polypeptide hormone.

To the right is a beta cell that synthesizes insulin. There are Secretory Vesicles, the Golgi Apparatus, a Nucleus, a Rough Endoplasmic Reticulum and Mitochondria in this cell which are all involved in the production of insulin.

The Golgi Apparatus processes the insulin in its amino acid chain forming the final protein molecule (explained more specifically later), this is then later stored in the vesicles. These vesicles store the insulin until the glucose levels elevate too high causing potassium brings the cells surface (membrane) closer and its calcium channels open. When the calcium ions enter it causes depolarization resulting in the vesicles moving closer to the cell membrane and releasing the stored insulin.

The nucleus controls the functions of the cell with its DNA (Deoxyribose Nucleic Acid). As I explain protein synthesis it is important to understand DNA. DNA is made up of nucleotides twisted into a double helix. There are ten cross-links of nucleotides for ever complete turn of the double helix spiral.

The ladder of the spiral is made up of Nucleotide pairs facing inwards toward each other. The Nucleotides consist of a sugar and a phosphate bonded together in one nitrogen base. There are four standard nitrogen bases. Purine bases are Adeine (A) Guanine (G). Pyrimidine bases are Cytosine (C) and Thymine (T). As well as a base a nucleotide is made of a sugar and a phosphate group. The base pairing is controlled by the hydrogen bonds (covalent bonds) for example C and G require 3 bonds when A and T require 2. This means that the molecular structure is organized so the G's (Guanine-Purine base) and C's (Cytosine-Pyrimidine base) can only be together and the T's (Thymine-Purine base) and A's (Adeine-Pryimidine base) can only be together. Either side of the helix is a sugar (deoxyribose) then a phosphate then a sugar then a phosphate and so on. Between the sugars lies the base pair explained above.

The sequence and number of bases is what makes DNA unique

This genetic information is needed to control the functions of the cell by governing the synthesis of proteins by amino acid chains. Also, it controls genetic inheritance from cell to cell by Mitosis and passes on genetic information from generation to generation by Miosis. Proteins are built from amino acids which start off like building blocks with 20 amino acids in nature that are starting points. When the protein is assembled by the cell, the amino acids need to bond together in a specific order. Depending on the forces in the acids, the chain will bend and twist to a specific shape. This is done every time an acid 'link' is added as it will repel and attract something a little more eventually causing the chain to form the shape required. The average protein has 200 amino acids. The DNA governs the order of the chain from start to finish, resulting in the correct protein required.

Although each cell in the body has the genetic instructions from the DNA to make all proteins it will only make the proteins for its specific function. In beta cells, that function is insulin production.

DNA is found in all eukaryotic cells including humans, animals, plants and fungi. DNA is also found in prokaryotic cells like bacteria where the DNA has no membrane bound nucleus. For this reason, in humans, the DNA can never leave the eukaryotic cell's nucleus. Fortunately, DNA is the only molecule (and the largest molecule) in the human body that can self replicate. It does this copying through a process called transcription. As briefly mentioned the DNA copies itself into RNA which is transported to the Ribosome through translation. The protein synthesis which is governed by the information in the RNA takes place in the ribosome.

The DNA carries the information for the amino acid sequence. So Firstly, the DNA has to split into two by transcription. Transcription is


As the DNA is split into two strands, only one strand can go into the protein. Nucleotides connect individually in the process explained through base pairs to the strand that is left and forms a double helix of messenger RNA. So you have DNA on one side and a complete RNA on the other side. Once all this has happened, it splits apart and the two strands of DNA recombine. There is now a messenger RNA in the nucleus. As the DNA cannot leave the nucleus and the messenger RNA can (hence messenger) the messenger RNA leaves the nucleus and attaches onto a ribosome in the cytoplasm of the cell.

Each 3 bases in the RNA has a code for one amino acid. "Transfer" RNA molecules bring amino acids in to where they are (in the ribosome). The amino acids then join in the right order to form the right chain (A protein molecule specifically in this case, Insulin). The exact process of how the amino acids form the chain has previously been explained. But basically it is the specific order the amino acids are in that will form the protein.