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Secondary structure—this is the structure component related to the protein’s three-dimensional shape. There are two major protein structures. The alpha helix is a coiled string structure mad by hydrogen bonding in the protein’s polypeptide chain. The beta pleated sheet is a folded or pleated structure made by hydrogen bonding lined up so that there are parts of the chain lying side-byside with one another.
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The tertiary structure of the protein molecule is also three-dimensional but it is determined by specific interactions of the R side chains. The R group can be hydrophobic or hydrophilic, which determines how the peptide is folded. Hydrophobic groups will fold themselves to keep these groups away from water. There can be hydrogen bonding, ionic bonding, and disulfide bridges between R groups that specifically determine the peptide’s shape. Van der Waals forces also help the polypeptide have a particular shape.
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The quaternary structure is the structure made of the protein by the interaction of more than one peptide unit. It is the type of structure formed by molecules like hemoglobin, which actually consists of two pairs of globular subunit chains.
PROTEIN SYNTHESIS Protein synthesis is actually a drawn-out process that starts with the DNA blueprint in the nucleus of the cell. The basic function of DNA is to encode for proteins that are made in the ribosomes of the cell. DNA in the cell only codes for proteins; it does not code for other cellular structures. The genome of the cell is the full complement of DNA for the cell, while the proteome is the entirety of the proteins made by the cell. Genes are discrete sections of DNA that encode for specific proteins. There are about 20,000 genes in the human genome. Most of the DNA, however, is not made into genes and is considered noncoding DNA. Proteins are made from amino acids and are made by “reading” the DNA in the genome. Remember that, for DNA, there are four different bases (adenine, thymine, guanine, and cytosine). In order for there to be enough sections of DNA to encode for all the possible twenty amino acids plus sections for starting and stopping protein synthesis, the DNA 87
