18 Questions
What is the reason why these compounds are sometimes called alpha amino acids?
because the amine functional group is located on the first carbon
What determines the identity of an amino acid?
the side chain itself
What is the characteristic of the most polar side chains?
they are largely in their ionized form at physiological pH
What is the advantage of using one-letter abbreviations over three-letter abbreviations?
they are more commonly used by biochemists
What is a characteristic of hydrogen bonds?
they occur when a hydrogen atom is directly bonded to an oxygen or nitrogen atom
How are the amino acids grouped in Figure 12.44?
according to their relative polarities
What is the characteristic of enantiomers?
They have identical chemical and physical properties, except for how they interact with polarized light and other chiral species.
What type of species is a zwitterion?
Electrically neutral with separated positive and negative ionic charges
What is the result of the intramolecular acid-base reaction between the amino group and the carboxyl group of an amino acid?
Formation of a zwitterion
What is the property of amino acids that enables proteins to differentiate between two enantiomeric isomers?
Their chirality
What is the characteristic of naturally occurring amino acids?
They belong to the L-family
What type of reaction occurs between the amino group and the carboxyl group of an amino acid?
An acid-base reaction
What is the main difference in properties between enantiomers?
Their interaction with other chiral molecules and plane-polarized light
Why can our bodies only use one of the handed isomers of a chiral molecule?
Because our bodies can only recognize the correct-handed isomer
What is a stereocenter in a molecule?
A carbon with four different groups
What is the effect of introducing the wrong-handed isomer of a chiral molecule into the body?
It has a disastrous effect
Which of the following belongs to the left-handed family?
Amino acids
What happens when the wrong-handed isomer of a chiral molecule is introduced into the body?
The body ignores it
Study Notes
Amino Acids
- Amino acids are also called alpha amino acids because the amine functional group is located on the first carbon out from the main functional group (the carboxylic acid).
- Each amino acid has a unique side chain that gives the amino acid its characteristic physical and chemical properties.
Side Chains
- The identity of an amino acid is determined by the side chain.
- Amino acid side chains can be grouped according to the main functional group in the side chain.
- Side chains can be polar or non-polar, with hydrocarbon groups being the least polar and acidic and basic side chains being the most polar.
Stereochemistry of Amino Acids
- Naturally occurring amino acids belong to the L-family, meaning the amino group is on the left when drawn as a Fischer projection.
- All amino acids (except glycine) are chiral, making proteins also chiral.
- The inherent handedness of proteins enables them to differentiate between two enantiomeric isomers.
Acid–Base Properties of Amino Acids
- Amino acids have both an acidic functional group and a basic functional group.
- The basic amino group takes a proton from the acidic carboxyl group, resulting in the formation of a zwitterion.
- A zwitterion is a species that is electrically neutral but has separated positive and negative ionic charges.
Optical Activity and Chirality
- Enantiomers have identical chemical and physical properties, except for how they interact with other chiral molecules and plane-polarized light.
- Chiral molecules interact differently with other chiral molecules, and the wrong-handed isomer of a chiral molecule can have significant effects.
Understand the stereochemistry of naturally occurring amino acids, their chirality, and how proteins differentiate between enantiomeric isomers. Learn about the L-family of amino acids and their Fischer projections.
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