Stereochemistry and Classification of Amino Acids

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Questions and Answers

Which amino acid can form disulfide bonds due to its sulfhydryl group?

Lysine

Cysteine (correct)

Alanine

Arginine

At physiological pH (7.4), which form of an amino acid predominantly exists?

Cationic form

Zwitterionic form (correct)

Anionic form

Protonated form

Which of the following amino acids does NOT have an ionizable side chain?

Alanine (correct)

Lysine

Aspartic Acid

Histidine

Which amino acids have three acid-base groups due to their ionizable side chains?

Lysine, Arginine, Histidine Signup and view all the answers

What happens to the charge of an amino acid when the pH changes?

It changes based on the ionization of functional groups. Signup and view all the answers

Which category do amino acids with side chains that are non-polar belong to?

Non-polar amino acids Signup and view all the answers

Which amino acids absorb UV light?

Tyrosine, Tryptophan, and Phenylalanine Signup and view all the answers

Who was a leader in the field of bioinformatics that developed the single letter code for amino acids?

Dr. Margaret Dayhoff Signup and view all the answers

Which of the following amino acids has a unique first letter in its name?

Serine Signup and view all the answers

Which letter corresponds to the amino acid Asparagine in the single letter code?

N Signup and view all the answers

Which of these amino acids was assigned the letter 'E' in the single letter code?

Glutamic acid Signup and view all the answers

Which amino acid is known for having a phonetically suggestive name and corresponds to the code 'F'?

Phenylalanine Signup and view all the answers

What property do all amino acids share concerning light absorption?

They all absorb light in the infrared region Signup and view all the answers

What is one consequence of chirality in drug effectiveness?

Only one enantiomer is usually therapeutically active. Signup and view all the answers

What is a typical result when amino acids are synthesized in the lab?

A racemic mixture of both enantiomers is obtained. Signup and view all the answers

How does chirality influence enzyme reactions?

Enzymes typically interact with one enantiomer. Signup and view all the answers

Which of the following statements about chiral pesticides is true?

Enantiomers of chiral pesticides can have different environmental impacts. Signup and view all the answers

What is the typical configuration of amino acids found in proteins?

L-configuration amino acids. Signup and view all the answers

How do chiral compounds affect sensory properties like taste and smell?

Different enantiomers can have distinct tastes and smells. Signup and view all the answers

What role does chirality play in the optical properties of molecules?

Chiral molecules can rotate plane-polarized light. Signup and view all the answers

Which of the following statements is true regarding the chirality of amino acids?

Chirality is generally not emphasized in drawing amino acids. Signup and view all the answers

Study Notes

Stereochemistry of Amino Acids

Chirality affects many properties and behaviors of molecules.
One enantiomer of a chiral molecule is usually more active than the other.
Enzymes are chiral and interact with only one enantiomer of a substrate.
The effectiveness of pesticides and herbicides can differ between enantiomers.
The smell and taste of chiral compounds can differ between enantiomers.
Chiral molecules can affect the optical properties of materials.
In biochemistry, the chirality of amino acids is not usually a critical point.
Amino acids in proteins are usually of the L configuration.
Some bacteria peptides have D amino acids, making them resistant to enzymatic attack.
Biosynthetic processes produce pure stereoisomers.

Classification of Amino Acids

The R group (side chain) determines the amino acid's characteristics.
Amino acids are categorized into:
- Non-polar (hydrophobic)
- Polar (hydrophilic), uncharged
- Polar (hydrophilic), charged (positive or negative)

Spectroscopic Properties of Amino Acids

All amino acids absorb light in the infrared region.
Tyrosine, Tryptophan, and Phenylalanine absorb UV light.
Phenylalanine absorbs UV light to a lesser degree than the other two.

Single-Letter Code for Amino Acids

Developed by Dr. Margaret Dayhoff to shorten protein sequence files for computers.
Six amino acids have unique first letters, making the code simple:
- Cysteine (Cys): C
- Histidine (His): H
- Isoleucine (Ile): I
- Methionine (Met): M
- Serine (Ser): S
- Valine (Val): V
Other amino acids with the same first letter were assigned based on frequency in proteins.
Some single-letter codes are phonetically suggestive.

Modified Amino Acids

20 amino acids are encoded in DNA and incorporated directly into proteins.
Some amino acids can be chemically modified after being assembled into proteins.
The cysteine sulfhydryl group (–SH) allows for disulfide bond formation.

Ionizable Groups in Amino Acids

Amino acids can ionize, meaning their charge can change with pH.
Amino acids are weak acids, possessing at least two acid-base groups:
- -carboxyl group
- -amino group
Some amino acids have ionizable side chains (R groups) and three acid-base groups:
- Lysine
- Arginine
- Histidine
- Glutamic Acid
- Aspartic Acid
- Cysteine
- Tyrosine
At physiological pH (7.4), amino acids exist in their zwitterionic form.
The charge of an amino acid changes with pH.
Alanine lacks an ionizable side chain, so its charge is determined by the amino and carboxyl groups.

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Description

Explore the fascinating world of amino acids by understanding their stereochemistry and classification. This quiz delves into concepts like chirality, enzyme interaction with enantiomers, and the various categories of amino acids based on their side chains. Test your knowledge on how these features influence biological processes and characteristics.