I finally discovered why the plant needed me so much. It turns out that after plants turn carbon dioxide into glucose by photosynthesis, they sometimes change the glucose that was just created. At first, it seemed kind of silly to me that they would go through such a hassle to make glucose to not keep it. These molecules called amino acids told me that I would soon be like them. They get together and have huge parties where they make proteins. It sounded like an adventure so I was excited to become an amino acid. The plant made me a part of serine which was great except for the fact that I was told I was nonessential. I wonder if I'll find out what that means!
Amino acids are the building blocks of proteins and are vital to experiencing a normal, functioning life. Amino acids are made and then destroyed constantly, according to the bodies' needs. They are considered small biochemical molecules with a molecular mass of 135 g. There are actually only twenty amino acids even though more have been discovered. These magic 20 are important because all other amino acids can be created from them through the processes of hydroxylation (adding OH-) and phosphorylation (adding PO43-). In plants, photosynthesis plays a vital role in amino acid synthesis. This is due to the fact that plants use the intermediates of carbohydrate metabolism to create all amino acids. Therefore, bacteria, yeasts, molds, and plants are unique because they are able to produce all needed amino acids by themselves.
In general form, all amino acids look like this:
The COOH section is termed the carboxyl group while the NH2 is considered the amine group. The "R" is representative of any side chain that may be present in an amino acid. The chemical composition of the R group is the only aspect that separates one amino acid from the next. Although all amino acids can be synthesized in the plant, the difficulty level varies greatly. Let's look at a specific amino acid, serine, to become familiar with the process of amino acid synthesis.
Serine synthesis begins with glucose and involves four reactions before producing serine. Although the reactions that follow are for bacteria and molds, plants act in much the same manner. However, little is known about the nature of enzymes in amino acid synthesis for plants. The process begins with glucose which forms 3-phosphoglycerate. This molecule is then oxidated to yield 3-phosphohydroxypyruvate. This substance is transaminated with glutamate to form 3-phosphoserine. Transamination means that the amino group of glutamate is moved to other carbon chains. Then, 3-phosphoserine is hydrolyzed by serine phosphatase (an enzyme) resulting in serine. Serine is formed by the following reactions:
This molecule has a net charge of +1. As the pH increases and the acidity
decreases, the amino acid reaches an isoionic point or pl. Due to the
absence of many amino acids or perhaps the gain of more basity (depending on how
you approach it), COOH is ionized into COO- causing alanine to look like this:
The net charge is now 0 and the amino acid is in a dipolar state at
physiological pH. However, if the pH continued to increase, then the
solution would become very basic causing the amino acid to donate a proton (H+) to
neutralize the surrounding basity. Therefore, the molecule would have a net charge of -1
and look like:
These pKa' values, the values at which the amino acid dissociates, are extremely important in biochemistry. Most often there are two pKa' values, when the net charge goes from +1 to 0 and when it changes from 0 to -1. However, an amino acid can have three pKa' values if its side chain can be dissociated. These values are important because not only do they add to the general knowledge of amino acid activity, they are utilized in buffer systems.
There are two interesting features of amino acid synthesis. One is that the supply of amino acids is guaranteed due to the fact that the reactions are irreversible because of the vast energy loss. For instance, during amino acid synthesis, ATP is either converted to ADP or AMP:
ATP-->ADP + Pi
ATP-->AMP + PPi
Another tool that amino acid synthesis uses to ensure successful creation of amino acids is the reduction reaction. In bacteria, NADH is used as a reductant, but plants eventually evolved into the use of NADPH as a reductant.