Protein synthesis:
Within DNA molecules are genes. These contain genetic coding - the instructions necessary for the production of proteins. Proteins play many critical roles in the body - from controlling the rate of chemical reactions, to making up many structural components of the body, thus their synthesis is one of the most important metabolic processes. They are made up of hundreds, and sometimes even thousands of smaller units known as amino acids. These are attached to each other in long chains and there are 20 different types which can be arranged in many different ways to create a protein. A sequence of three nitrogenous bases is code for a particular amino acid. These are then joined together to make proteins.
However, protein synthesis is a complicated and highly controlled process which is made up of two parts: transcription and translation. Transcription occurs in the nucleus and begins with splitting of the double helix by an enzyme known as helicase. This thus creates two single stranded molecules, and the strand is now referred to as RNA (ribonucleic acid). RNA differs from DNA in the way that it consists of only a single strand of sugars and phosphates, and the nitrogenous bases occur singularly, and not in pairs. A protein known as RNA polymerase then "reads" the RNA and creates a copy of it, which is referred to as Messenger RNA or mRNA. mRNA differs from RNA, as the code encrypted on it is the complement to that on the RNA. Also, all the Thymine (T) bases are replaced with Uracil (U). For example, if the RNA code was CAG TGG CAA TGC, then the mRNA code would be GUC ACC GUU ACG.
The mRNA is then transferred out of the nucleus to the cytoplasm. The codons (set of three nitrogenous bases), are then "read" by Transfer RNA (tRNA), which interprets the mRNA. Attached to each tRNA is a ribosome, which receives the translated genetic code, and generates the corresponding amino acid. Several of these amino acids are then joined together to create a protein. The polypeptide chain begins its creation when the tRNA encounters a "start" codon, and the chain ends when tRNA encounters a "stop" codon. The protein created can then be used for various metabolic activities.
The whole process of gene transcription and translation to synthesise proteins is referred to as gene expression. One ribosome is able to create a protein containing 400 amino acids in just 20 seconds, and each messenger RNA may be attached to 10 or 20 ribosomes. There also may be as many as 300 000 identical mRNA in a cell, which means that a cell may produce as much as 150 000 protein molecules a second.
However, protein synthesis is a complicated and highly controlled process which is made up of two parts: transcription and translation. Transcription occurs in the nucleus and begins with splitting of the double helix by an enzyme known as helicase. This thus creates two single stranded molecules, and the strand is now referred to as RNA (ribonucleic acid). RNA differs from DNA in the way that it consists of only a single strand of sugars and phosphates, and the nitrogenous bases occur singularly, and not in pairs. A protein known as RNA polymerase then "reads" the RNA and creates a copy of it, which is referred to as Messenger RNA or mRNA. mRNA differs from RNA, as the code encrypted on it is the complement to that on the RNA. Also, all the Thymine (T) bases are replaced with Uracil (U). For example, if the RNA code was CAG TGG CAA TGC, then the mRNA code would be GUC ACC GUU ACG.
The mRNA is then transferred out of the nucleus to the cytoplasm. The codons (set of three nitrogenous bases), are then "read" by Transfer RNA (tRNA), which interprets the mRNA. Attached to each tRNA is a ribosome, which receives the translated genetic code, and generates the corresponding amino acid. Several of these amino acids are then joined together to create a protein. The polypeptide chain begins its creation when the tRNA encounters a "start" codon, and the chain ends when tRNA encounters a "stop" codon. The protein created can then be used for various metabolic activities.
The whole process of gene transcription and translation to synthesise proteins is referred to as gene expression. One ribosome is able to create a protein containing 400 amino acids in just 20 seconds, and each messenger RNA may be attached to 10 or 20 ribosomes. There also may be as many as 300 000 identical mRNA in a cell, which means that a cell may produce as much as 150 000 protein molecules a second.