Amino Acids and Essential Nutrition

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Questions and Answers

What is a characteristic of amino acids at physiologic pH?

The carboxyl group is dissociated and the amino group is protonated (correct)

The carboxyl group is protonated

The carboxyl group is neutral and the amino group is neutral

The amino group is dissociated

Which of the following amino acids are not synthesized by the human body?

Gly, Ala, Ser, Pro

Cys, Tyr, Asn, Gln, Asp, Glu

Hydroxyproline, hydroxylysine, γ-carboxyglutamate

Val, Leu, Ile, Phe, Met, Thr, Lys, Arg, Trp (correct)

What is the functional group that is bonded to the α-carbon atom in an amino acid?

R-group (side chain) (correct)

Hydroxyl group

Carboxyl group

Amino group

What is the result of peptide bond formation in proteins?

The carboxyl and amino groups are combined and are not available for chemical reaction Signup and view all the answers

Which of the following amino acids have a secondary amino group?

Pro Signup and view all the answers

What is the term for amino acids that require nutritionally essential amino acids for their synthesis?

Semiessential amino acids Signup and view all the answers

What is the primary function of the selenocysteine insertion element in the untranslated region of the mRNA?

It facilitates the incorporation of selenocysteine into the growing polypeptide during translation. Signup and view all the answers

What is the term used to describe the 21st protein L-α-amino acid?

The 21st amino acid Signup and view all the answers

What is the result of the post-translational modification of peptidyl proline and peptidyl lysine?

The conversion to 4-hydroxyproline and 5-hydroxylysine. Signup and view all the answers

What is the characteristic of nutritionally nonessential amino acids?

They are synthesized in the body and are sufficient to satisfy the normal requirement. Signup and view all the answers

How many L-α-amino acids are encoded by nucleotide triplets called codons?

20 Signup and view all the answers

What is the role of tRNASec in the incorporation of selenocysteine into proteins?

It enables the incorporation of selenocysteine into the growing polypeptide during translation. Signup and view all the answers

What is the unique feature of proline's side chain and α-amino N?

A rigid, five-membered ring structure Signup and view all the answers

What type of amino acid is proline frequently referred to as?

An imino acid Signup and view all the answers

What is the consequence of the substitution of polar glutamate by nonpolar valine in the β subunit of hemoglobin?

Sickle cell disease Signup and view all the answers

What is the primary function of a buffer in biological systems?

To maintain a stable pH Signup and view all the answers

What is the purpose of amino acid titration?

To determine the concentration of an amino acid in a solution Signup and view all the answers

What is the indicator of the stoichiometric equivalence point in amino acid titration?

A specific pH value Signup and view all the answers

Why is proline often found in collagen, a fibrous protein?

Because of its unique geometry, which contributes to the formation of fibrous structures Signup and view all the answers

What is the composition of a typical buffer solution?

A weak acid and its conjugate base Signup and view all the answers

Study Notes

Amino Acids

Nutritionally essential amino acids are those that cannot be synthesized by the body and must be obtained through the diet.
Examples of essential amino acids: Val, Leu, Ile, Phe, Met, Thr, Lys, Arg, His, Trp
Semiessential amino acids require nutritionally essential amino acids for their synthesis.

Non-Essential Amino Acids

Non-essential amino acids can be synthesized by the body and are not required in the diet.
Examples of non-essential amino acids: Gly, Ala, Ser, Pro, Cys, Tyr, Asn, Gln, Asp, Glu

Structure of Amino Acids

Amino acids have a carboxyl group, a primary amino group, and a distinctive side chain (R-group) bonded to the α-carbon atom.
At physiologic pH, the carboxyl group is dissociated, forming the negatively charged carboxylate ion (–COO–), and the amino group is protonated (–NH3+).
In proteins, the carboxyl and amino groups are combined through peptide linkage and are not available for chemical reaction except for hydrogen bond formation.

The Genetic Code

The genetic code specifies 20 L-α-amino acids encoded by nucleotide triplets called codons.
Some proteins contain additional amino acids that arise by post-translational modification of an amino acid already present in a peptide.

Selenocysteine

Selenocysteine is the 21st protein L-α-amino acid, found in proteins from every domain of life.
Selenocysteine is not the product of a post-translational modification, but is inserted directly into a growing polypeptide during translation.
Selenocysteine is specified by a large and complex genetic element that utilizes the UGA anticodon that normally signals STOP.

Proline

Proline differs from other amino acids in that its side chain and α-amino N form a rigid, five-membered ring structure.
Proline has a secondary (rather than a primary) amino group and is often referred to as an imino acid.
The unique geometry of proline contributes to the formation of the fibrous structure of collagen and often interrupts the α-helices found in globular proteins.

Sickle Cell Disease

Sickle cell disease is an inherited blood disorder marked by defective hemoglobin.
It inhibits the ability of hemoglobin in red blood cells to carry oxygen.
The disease results from the substitution of polar glutamate by nonpolar valine at the sixth position in the β subunit of hemoglobin.

Buffers

A buffer is a solution that resists changes in pH when small amounts of acid or base are added to it.
Buffers are typically composed of a weak acid and its conjugate base (or a weak base and its conjugate acid) in roughly equal amounts.
Buffers are crucial in various biological, chemical, and laboratory applications where maintaining a stable pH is essential.

Titration

Amino acid titration refers to the process of determining the concentration of amino acids in a solution by gradually adding a titrant solution of known concentration until a specific endpoint is reached.
During the titration, the pH of the amino acid solution is monitored, and changes in pH occur as the titrant is added.
At the endpoint, the pH reaches a certain value, indicating that the stoichiometric equivalence point has been reached.

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Description

This quiz covers the basics of amino acids, including nutritionally essential and semiessential amino acids, and their synthesis pathways.