Amino Acids and Proteins

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Questions and Answers

What is the role of the R group in an amino acid?

Determines the sequence of the amino acid chain

Causes the polypeptide to fold into a biologically active shape

Gives each amino acid its identity (correct)

Forms the amide bond

How many amino acids are needed to form a dipeptide?

2 (correct)

Which type of bond joins amino acids together to form peptides and proteins?

Peptide bond (correct)

Ionic bond

Covalent bond

Hydrogen bond

What happens when the number of amino acids in a polypeptide chain exceeds 40?

It is considered a protein Signup and view all the answers

Which type of amino acids are the building blocks of proteins in the body?

L-isomers Signup and view all the answers

What are proteins made up of?

Chains of polypeptides Signup and view all the answers

What is the main purpose of the Biuret test?

To test for the presence of proteins and peptide bonds Signup and view all the answers

What is the minimum number of peptide bonds required for a positive Biuret test?

2 Signup and view all the answers

What is the reverse process of hydrolysis?

Condensation Signup and view all the answers

What is the purpose of the Ninhydrin test?

To test for the presence of α-amino acids in proteins Signup and view all the answers

What is the general test for carbohydrates?

Molisch's test Signup and view all the answers

Why do antibiotics not always produce a predictable result in the Biuret test?

Antibiotics contain additives that interfere with the test Signup and view all the answers

Which test is used to detect the presence of aromatic amino acids?

Xanthoproteic Test Signup and view all the answers

Which amino acid is egg albumin lacking?

Both b and c Signup and view all the answers

What is the purpose of the Millon's Test?

To detect the presence of phenolic compounds and tyrosine Signup and view all the answers

Which test result indicates the presence of tryptophan?

Violet-ring at the junction Signup and view all the answers

Which amino acid is considered stable in phenylalanine and does not react with the reagent in the Xanthoproteic Test?

Phenylalanine Signup and view all the answers

Which test is used to detect the presence of sulfhydryl-containing amino acids?

Lead Sulfide Test Signup and view all the answers

Study Notes

Peptide Bonds and Amino Acids

Peptide bonds are formed through a condensation reaction, combining simple compounds to create a complex compound and releasing water.
Amino acids are joined together, releasing water, to form polypeptides.
Formation of polypeptides involves removing oxygen from the precedent amino acid and two hydrogens from the subsequent amino acid, then placing the groups next to each other.

Protein Tests

Biuret Test: general test for proteins, indicating the presence of amide/peptide bonds, resulting in a purple/violet solution.
Dipeptide and amino acid will have a negative test, while tripeptide, tetrapeptide, and pentapeptide will have a positive test.
40 amino acids or more are considered a protein.

Amino Acid Tests

Ninhydrin Test: tests for the presence of α-amino acid in proteins, resulting in a blue-violet/purple-blue solution.
Alanine is an amino acid and will have a positive test.
Egg albumin contains 18 amino acids, except glutamine and asparagine.

Aromatic Amino Acids

Xanthoproteic Test: tests for the presence of aromatic amino acids, resulting in a yellow/orange-yellow solution.
Egg albumin contains all aromatic amino acids, including tyrosine and tryptophan.
Phenylalanine is an aromatic amino acid but does not react with the reagent, resulting in a negative test.

Phenol and Tyrosine

Millon’s Test: tests for phenolic compounds and detects the presence of tyrosine, the only amino acid containing a phenol group, resulting in a pink/red/brick-red precipitate.

Tryptophan

Hopkins-Cole Test: tests for the presence of tryptophan, the only amino acid containing an indole group, resulting in a violet-ring at the junction.

Sulfhydryl-Containing Amino Acids

Lead Sulfide Test: tests for the presence of sulfhydryl-containing amino acids.

Amino Acid Structure

Amino acids are organic compounds containing an amino group and a carboxyl group.
The 20 common amino acids used to build proteins are mostly α-amino acids.
The sequence of the amino acid chain causes the polypeptide to fold into a shape that is biologically active.
The amino acid sequences of proteins are encoded in the genes.

Protein Classification

2-39 amino acids are considered polypeptides.
Exceeding 40 amino acids, it will be called a protein.
Alpha amino acid: 19 out of 20 amino acids are alpha amino acids.
Not an alpha amino acid is an Imino acid; proline.

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Description

Test your knowledge about amino acids, the building blocks of proteins, and how they are essential for biological activity. Explore the concept of polypeptides and how the amino acid sequences in genes encode for proteins.