Polypeptide synthesis- transcription and translation
Proteins are made up of polypeptides. Every organism needs to make their own proteins. The biochemical machinery in the cytoplasm of each cell has the capacity to make every protein from just 20 amino acids. The proteins it manufactures depend upon the instructions that are given by the DNA in the cell's nucleus. The process is that DNA provides the instructions in the form of a long sequence of ...view middle of the document...
The pre-mRNA is spliced to form mRNA. The mRNA is used as a template to which complementary tRNA molecules attach to and the amino acids they carry are linked to form a polypeptide, this is translation.
Transcription is the process of making pre-mRNA using part of the DNA as a template. The enzyme DNA helicase acts on a specific region of the DNA molecule to break the hydrogen bonds between the bases, causing the two strands to seperate and expose the nucleotide bases in that region. This causes the specific region called cistron to unwind. One of the strands is used as a template to make an mRNA copy.The enzyme RNA polymerase moves along one of the two DNA strands, known as the template strand causing the nucleotides on this strand to join with the individual complementary nucleotides from the pool which is present in the nucleus. Specific base pairing occurs so guanine joins with cytosine, cytosine joins with guanine, thymine joins to adenine and adenine joins with uracil. Only around 12 base pairs lon the DNA are exposed every time. When the RNA polymerase reaches a particular sequence of bases on the DNA that it recognises as a stop triplet code it detaches and the production of pre-mRNA is complete.