Magnesium is required as a co-factor for thermostable DNA polymerase. Taq polymerase is a magnesium-dependent enzyme and determining the optimum concentration to use is critical to the success of the PCR reaction.[3] Some of the components of the 1. Alpha Helix
• rod like
• CO & NH of the main chain are hydrogen bonded together, allowing the main chain to be buried
• n+4 H bonding scheme
• all alpha carbons are H bonded and in line with each other
• R groups are on the outside & backbone on the inside
• always right handed (clockwise)
• can be a single chain (usually less than 45 Angstroms)
• Residues that are 1 & 2 residues apart are on opposite sides, while residues that are 3 & 4 residues apart are on the same side; this allows small steric hindrance
• 1.5 Angstroms rise (from one alpha carbon to the second)
• 100 degree rotation
• 3.6 residues per turn
• Ramachandran diagrams (1) Right handed: can only occur between -60, -60; little hindrance (2) Left handed: +60, +60; large hindrance

2. Beta Sheet
• sheet like
• Beta sheets are formed by linking 2 or more Beta strands by H bonds
• side chain of adjacent residues point in opposite directions
• only trans peptide bonds give R groups on opposite sides
• cannot exist as a single Beta strand; must be 2 or more
• in proteins, 4-5 strands make up a beta sheet; it is possible to be made of more than 10
• 3.5 Angstroms rise between residues
• 7 Angstroms between R groups
• Arrow in