Tin is a malleable silvery-white metal which takes a high polish. It possesses a highly crystalline structure and is moderately ductile. When a bar of tin is bent, the crystals break, producing a characteristic 'tin cry'. Two or three allotropic forms of tin exist. Gray or a tin has a cubic structure. Upon warming, at 13.2Â°C gray tin changes to white or b tin, which has a tetragonal structure. This transition from the a to the b form is termed the tin pest. A g form may exist between 161Â°C and the melting point.
The particular order of the bases arranged along the sugar-phosphate backbone is called the DNA sequence; the sequence specifies the exact genetic instructions required to create a particular organism with its own unique traits. Each strand of the DNA molecule is held together at its base by a weak bond.
Helicase, made of six proteins arranged in a ring shape, unwinds the DNA double helix into two individual strands. Single-strand binding proteins, or SSBs, are tetramers that coat the single-stranded DNA.This prevents the DNA strands from reannealing to form double-stranded DNA.Primase is an RNA polymerase that synthesizes the short RNA primers needed to start the strand replication process. DNA polymerase is a hand-shaped enzyme that strings nucleotides together to form a DNA strand.his prevents the DNA strands from reannealing to form double-stranded DNA. Primase is an RNA polymerase that synthesizes the short RNA primers needed to start the strand replication process. DNA polymerase is a hand-shaped enzyme that strings nucleotides together to form a DNA strand.