Stereoisomers, Chirality, and Biochemistry

Enantiomers and Racemic Mixtures

Enantiomers are molecules that are mirror images of each other.
They possess identical physical properties such as boiling points and forces of attraction.
A racemic mixture is an equal mixture of enantiomers.
Pharmaceuticals often contain racemic mixtures when a specific enantiomer cannot be isolated.
Side effects of medications can arise from the presence of unwanted enantiomers in a racemic mixture.

Individual responses to medications vary due to differences in biochemical pathways.
A medication's effect depends on how it interacts with an individual's neurons and neural response.
Pharmacists can provide information about potential side effects of medications.
Drug commercials list all possible side effects, even rare ones, because they occurred in at least one person.

Diastereomers are geometric isomers, including cis and trans isomers.
A chiral molecule must have an sp^3 hybridized tetrahedral structure, usually with carbon as the central atom.
The central carbon atom in a chiral molecule is bonded to four different groups.
Amino acids are examples of chiral molecules.

To identify chiral centers, find carbons with four bonds.
Ensure that all four groups attached to the carbon are different from each other.
Carbons in a benzene ring are sp^2 hybridized and not chiral.
If a carbon has a double bond, it is sp^2 hybridized and not chiral.
Consider implicit hydrogen atoms when determining the four bonds around a carbon.
If any two groups attached to a carbon are identical, the carbon is not chiral.

Hybridization involves the mixing of atomic orbitals (e.g., one s and three p orbitals to form sp^3 hybrids).
An AX4E0 molecule has four bonded atoms and no lone pairs.
For a carbon to be chiral, it must be directly bonded to four different groups.

Biochemistry involves memorization of many steps and names of intermediaries in cycles like the Krebs cycle.

Seven key elements from the periodic table are central to biochemistry:
- Carbon (C)
- Nitrogen (N)
- Oxygen (O)
- Phosphorus (P)
- Sodium (Na)
- Sulfur (S)
- Potassium (K)
The backbone of DNA is phosphorus.
Carbon is the main chain in large biological molecules, and how it folds determines its structure (e.g., alpha helix).

Proteins are large molecules composed of amino acids.
The exact order of amino acids is the primary structure.
DNA and transfer RNA use codons (three-letter sequences) to code for specific amino acids.
Transfer RNA reads DNA, sends information to messenger RNA in ribosomes, and codes for amino acids.
There are 20 amino acids.

As a protein is built, intermolecular forces cause it to fold and curl.
Hydrophobic regions of the protein avoid water, while hydrophilic regions are attracted to water, influencing the folding.
The secondary structure arises from the folding and manipulation of shape due to these interactions.
The overall shape of the protein is its tertiary structure, which determines its function.
Form follows function; the tertiary structure dictates the protein's role.
Hemoglobin, found in red blood cells, carries oxygen through the blood.

Proteins are built from 20 amino acids, some of which must be obtained through diet.
Deficiencies in particular amino acids can cause symptoms.
Zwitterions are ionic forms of amino acids that aid in building and folding proteins.

The primary structure is the exact sequence of amino acids, often listed by their first letter.
The secondary structure includes alpha helices and beta sheets, formed by folding.
The tertiary structure is the overall 3D shape, often resembling a lock and key to fit specific locations.

Some proteins act as enzymes, which are catalysts that speed up chemical reactions.