39. Final Protein in its Tertiary
Structure
Start
Codon
Codon
Codon
Codon
Stop
Codon
40. Summary
The first stage of protein synthesis, DNA transcription, occurs in the
nucleus of the cell where the DNA is stored. It begins when RNA polymerase
unwinds a DNA molecule that is in a double helix structure. The enzyme
starts at the beginning of a gene and binds onto it. It then travels the whole
way down the molecule from the promoter region to the termination
sequence and unwinds molecule. When the DNA is unwound, one of the two
separate strands that were separated is used as a template that RNA
polymerase attaches complementary nucleotides to. However, in RNA,
adenine is paired with uracil instead of thymine such as it does in DNA. When
the matching is complete the product is a mRNA molecule known as
messenger RNA. This molecule then detaches from the template strand and
exits the nucleus through the nuclear pore, therefore entering the cytoplasm.
The original DNA molecule then returns to its starting double-helix formation.
The next step of the process is DNA translation which occurs in the
cytoplasm. In this step, mRNA molecules meet the ribosomes which are
organelles that make proteins. From there, the ribosomes read the mRNA
strand, starting at the start codon and ending at the stop codon, like a book
and convert it into a sequence of amino acids. This is done by the ribosome
41. Summary
moving down the mRNA strand and tRNA molecules attaching to the
molecule and then falling off. Each tRNA contains an anticodon and an amino
acid. The anticodon binds to the codon for only a temporary period. A
peptide bond connects the amino acids every time a tRNA molecule falls off
the mRNA strand as the ribosome travels down it. This creates an amino acid
chain once that ribosome reaches the stop codon and the last tRNA molecule
falls off of the strand. This amino acids chain folds upon itself to give it its
final three dimensional structure. This final shape will ultimately determine
the function of the newly formed protein. This then completes the process of
protein synthesis.
