Question

Amino acids are the building blocks of proteins. The simplest amino acid is glycine \(\left(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{COOH}\right) .\) Draw a Lewis structure for glycine. \((\)Hint : The central atoms in the skeletal structure are nitrogen bonded to carbon, which is bonded to another carbon. The two oxygen atoms are bonded directly to the rightmost carbon atom.)

Short answer

The Lewis structure for glycine has nitrogen bonded to a carbon, which is bonded to another carbon that has one double bonded oxygen and one single bonded oxygen with a lone pair and a negative charge.

Step-by-step solution

Identify the Central Atoms

According to the skeletal structure hint, nitrogen (N) is bonded to a carbon (C), which is in turn bonded to another carbon. The rightmost carbon will have the two oxygen atoms bonded to it.

Distribute Electrons to Terminal Atoms

Place the hydrogen atoms (H) around the nitrogen and the leftmost carbon. Each hydrogen will form a single bond with its respective central atom. The two oxygen atoms will also form bonds with the rightmost carbon. One oxygen will form a double bond to complete its octet, and the other will form a single bond and will also have a lone pair to complete its octet.

Complete the Octets of the Central Atoms

Complete the octet of the nitrogen atom by adding a lone pair of electrons. Ensure that each carbon atom also has a complete octet by adding the necessary bonds and lone pairs.

Check the Formal Charges

Calculate the formal charges for each atom to make sure the most stable structure is achieved. A formal charge of zero or as close to zero as possible for each atom is preferred.

Draw the Lewis Structure

Based on the steps above, draw the Lewis structure with the nitrogen (N) bonded to the first carbon (C), which is bonded to the second carbon (C), which in turn has one oxygen (O) with a double bond and another oxygen (O) with a single bond and a negative charge, and where the hydrogen (H) atoms are singly bonded to the nitrogen and the first carbon.

Key concepts

Amino Acids

Amino acids are organic compounds that serve as the fundamental building blocks of proteins, which play crucial roles in biological processes. Each amino acid consists of a central carbon atom, known as the \( \alpha \) carbon, bonded to an amino group (\( -NH_2 \)), a carboxyl group (\( -COOH \)), a hydrogen atom, and a distinctive side chain or R group that determines the properties of the amino acid.

The simplest amino acid, glycine, is unique because its R group is a single hydrogen atom, making it the only amino acid without a chiral center. Its simple structure allows us to explore various biochemical principles, such as the formation and properties of peptides and proteins. Peptides are short chains of amino acids linked by peptide bonds, while proteins are longer chains that fold into specific three-dimensional structures essential for their function.

Protein Building Blocks

Proteins are composed of long chains of amino acids that fold into specific three-dimensional structures resulting in a vast array of functions including catalysis of biochemical reactions (enzymes), signal transduction (receptors), and support (structural proteins).

The sequence in which amino acids are arranged determines the protein's structure and function. This sequence is encoded in the organism's genetic material (DNA/RNA) and is translated during protein synthesis.

As the building blocks of proteins, the chemical properties of amino acids influence the final protein structure. Glycine, being non-polar and small, can add flexibility to protein chains and fit into tight spaces within proteins' structures. The study of amino acids, such as glycine, and their roles in protein structure and function is fundamental in biochemistry and molecular biology.

Electron Distribution

The concept of electron distribution is crucial in understanding chemical bonding and molecular structure. Electrons are distributed around an atom in such a way that the configuration tends towards the most stable, or ground, state possible, usually reflected by the 'octet rule'.

In drawing the Lewis structure for glycine, electrons are distributed amongst the atoms to fulfill their octet, or duet in the case of hydrogen, ensuring that the molecule is represented as accurately as possible. The structure demonstrates electron sharing through bonds—single or double—as well as electron pairs that do not participate in bonding, known as lone pairs. In the case of glycine, the rightmost carbon forms both a double bond with one oxygen atom and a single bond with another oxygen atom, illustrating the distribution of electrons to satisfy the octet rule.

Formal Charge Calculation

Formal charge calculation is a method used to determine the charge of an atom within a molecule based on the assumption that electrons in chemical bonds are shared equally between atoms. This helps in predicting the most stable Lewis structure for a molecule.

To calculate the formal charge on an atom, one can use the following formula: \[ Formal\ Charge = (Valence\ Electrons) - (Non-bonding\ Electrons) - \frac{1}{2}(Bonding\ Electrons) \] By applying this formula to each atom in glycine, we ensure that we have the most stable structure where the formal charges of the atoms are as close to zero as possible. For example, the oxygen atom double-bonded to the rightmost carbon in glycine has a formal charge of zero because it shares four bonding electrons and has four non-bonding electrons, aligning with its six valence electrons.