| ^Basics | |
| ------------- | |
| ^Before Cells | |
| ------------- | |
| >Nucleic Acids | |
| ------------- | |
| *Amino Acids | |
| ------------- | |
| >Lipids | |
| ------------- | |
| >Sugars | |
| ------------- | |
| >Properties of Water |
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Amino Acids
Amino acids are the subunits of proteins. Each protein is formed by a chain of amino acids linked together through peptide bonds. The chain of amino acids takes on different shapes to form different proteins. The various shapes allow proteins to take on different characteristics in cells. Each amino acid is composed of
a constant (always remain the same) group and a variable amine group as shown below:
There are 20 common amino acids that are responsible for forming proteins. They can be classified into 4 main families based on their chemical characteristics: acidic, basic, uncharged polar, and nonpolar.
How Proteins are Made From DNA
Now that you know what amino acids and proteins are, you might ask what the relationship is between DNA and amino acids and proteins. While they seem to be unrelated entities, DNA actually plays a crucial role in protein production. When a cell wants to manufacture a certain protein, it has to go find the recipe for that protein. The recipe is stored in the form of DNA. Combinations of three nucleotides correspond to different amino acids. For example, CCT codes for proline and CGT codes for arginine. This way, during protein synthesis, DNA turns into the instruction for making a protein. For the details of protein synthesis, please visit Protein Synthesis page.
Amino Acid Codon Table. This is commonly used to identify the DNA sequence for each amino acid.
Proteins
Proteins consist of strands of amino acids folded into a specific shape. The different protein structures can be classified by four levels of folding, each successive one being constructed from the preceding one.
| Primary Structure - The very basic strand of amino acids is the called the primary structure. |  |
| Secondary Structure - The hydrogen-bond interaction among strands of amino acids gives rise to the first level of folding, alpha-helices and beta-sheets. |  |
| Tertiary - Interaction between alpha-helices and beta-sheets comprise the second level of folding, protein domains. These protein domains are then strung together through third level folding to form small globular proteins. The combination of second and third level folding yields tertiary structure. |  |
| Quaternary Structure - In order to achieve enhanced function, small globular proteins often come together to form protein aggregates. This fourth level of protein structure is called the quaternary structure. A famous example of quaternary structure is hemoglobin. |  |