From DNA to protein

 

What is a protein?

Proteins are the building blocks for ever organism and make up bones, teeth, hair, muscle, enzymes, antibodies etc. Proteins are used in the body for structure, function and regulation. These large, complex molecules are made up of long chains of smaller units called amino acids. There are around 20 different types of amino acids that can be used to make a protein, with the order of amino acids determining the proteins structure and function.

How are proteins made?

DNA, or deoxyribonucleic acid, is found in all known living things and act like a set of biological instructions. These instructions are stored as a type of code that is made up of units called bases. There are four different bases found in DNA and these are named adenine (A), guanine (G), cytosine(C) and thymine(T). Each base unit is linked to a sugar molecule and a phosphate molecule, which allows a string of bases to form. Just as a sequence of letters can be used to form words, and words be used to form sentences, so too can the sequences of bases on the string be used to produce the proteins that make up each organism. The sequence of bases that produces a protein is known as a gene. In order for a gene to be expressed, or a protein be made, a two-step process is required.

Why are two steps required to make a protein?

DNA is stored in every single cell (apart from red blood cells) and is kept in the nucleus, the core of each cell, to prevent it from being damaged. Proteins are made in a thick solution, called the cytoplasm, which is outside of, and surrounds, the nucleus. Two stages, known as transcription and translation, are needed in order to get the information held in the DNA out of the nucleus and converted into a protein in the cytoplasm.

What is transcription?

This is the first step in decoding DNA’s code. In the cell’s nucleus, a copy of the code is made in order to transport it out of the nucleus and in to the cytoplasm. To initiate this process, the DNA molecule unwinds and separates.  An enzyme (RNA polymerases) travels along the unwound DNA and builds a new complementary version of the code, called RNA (ribonucleic acid). RNA is similar to DNA apart from A) it is single stranded, B) the sugar molecule has different chemical properties (RNA is made up of ribose instead of deoxyribose), C) It uses the base uracil instead of thymine and D) because RNA is single stranded, it does not form a helix. The particular type of RNA that is made is called messenger RNA (or mRNA) because it carries the information, or message, from the DNA in the nucleus into the cytoplasm.

What is translation?

This step occurs in the cytoplasm of the cell where the mRNA interacts with a ribosome. This is a structure that translates the base sequences of the mRNA into amino acids, the building blocks of a protein. Three bases in a row create a unit called a codon. One codon creates one amino acid. Another type of RNA, known as transfer RNA (tRNA), helps to construct the protein, one amino acid at a time until the ribosome comes across a specific codon which tells it to stop.

How is protein production regulated?

Each cell turns expresses only a small number of its genes, while the others remain switched off. The way in which these genes are turned on and off is called gene regulation. Gene regulation ensures that each cell looks and acts appropriately according to its function, for example, the proteins produced by liver cells and muscle cells will be specific to their role.  Gene regulation usually occurs during transcription, although it can occur at any point of gene expression.

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