Protein Synthesis is the process whereby DNA (deoxyribonucleic acid)
codes for the production of essential proteins, such as enzymes and
hormones. Proteins are long chains of molecules called amino acids.
Different proteins are made by using different sequences and varying
numbers of amino acids. The smallest protein consists of fifty amino
acids and the largest is about three thousand amino acids long.
Protein synthesis occurs on ribosomes in the cytoplasm of a cell but
is controlled by DNA located in the nucleus.
Protein synthesis is a two-part process that involves a second type of
nucleic acid along with DNA. This second type of nucleic acid is RNA,
ribonucleic acid. RNA differs from DNA in three main respects.
First, the sugar units in RNA are ribose as compared to DNA's
deoxyribose. Because of this difference, RNA does not bind to the
nucleotide base Thymine (T), instead, RNA contains the nucleotide base
Uracil (U) in place of T. (RNA also contains the other three bases:
Adenine (A), Cytosine (C) and Guanine (G). Secondly, RNA, unlike DNA
is a single stranded molecule and is therefore not bonded to a
The third difference between RNA and DNA is that there are three
different types of RNA, mRNA (messenger RNA), tRNA (transfer RNA) and
rRNA (ribosome RNA). mRNA carries the genetic code (instructions how
to assemble the protein) from the DNA in the nucleus to ribosomes in
the cytoplasm. tRNA picks up and transfers amino acids from cytoplasm
to the mRNA on the ribosomes and is shaped similar to a cloverleaf.
rRNA forms a structural part of ribosome that helps join the amino
acids together form a protein.
DNA is a giant twisted molecule made up of many nucleotides linked
together resembling a double helix. It provides a base triplet, a
sequence of three bases on one of the strands of DNA, that code for
one amino acid. The sequence of base triplets on DNA molecules
determines the order of the amino acids on the protein chain.
In the first phase of transcription, the first process of protein
synthesis that occurs in the nucleolus, a portion of a DNA molecule
unwinds and serves as a template. Free nucleotides floating in the
nucleoplasm pair up with their complimentary bases on the DNA strand.
(Except that uracil replaces thymine). The nucleotides form
sugar-phosphate bonds with each other and become an mRNA strand but
they do not form bonds with the DNA strand. The sequence of three
exposed bases on mRNA, that are complimentary to the base...