20 Amino Acids Quiz: Structure and Properties

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Questions and Answers

Which type of amino acid has a chiral carbon?

Both L and D amino acids (correct)

Only D amino acids

Only L amino acids

Neither L nor D amino acids

Which amino acid does not have a chiral carbon?

Valine

Alanine

Glycine (correct)

Lysine

At what pH does the COOH group of an amino acid get ionized into COO- and H+?

pH 9

pH 7

pH 2 (correct)

pH 10

At what pH does the amino group of an amino acid get deprotonated into NH2 and H+?

pH 9 Signup and view all the answers

What is the net charge of COOH and NH2 groups in an amino acid at low pH?

+1 Signup and view all the answers

Which species are present in an amino acid at high pH?

NH2 and COO- Signup and view all the answers

What is the pKa value for the COOH group of an amino acid?

~2 Signup and view all the answers

At what pH is the NH3+ form of the amino group observed?

<9 Signup and view all the answers

How many of the 20 amino acids have readily ionisable side chains?

7 Signup and view all the answers

Which type of bond gets formed between the carboxyl group of one amino acid and the amino group of the other amino acid?

Peptide bond Signup and view all the answers

What is the primary structure of a protein?

Amino acid sequence in the polypeptide chain Signup and view all the answers

Which amino acid is not found in alpha-helices due to its side chain that prevents it from forming hydrogen bonds?

Proline Signup and view all the answers

What stabilizes the tertiary structure of proteins?

Multiple weak bonds Signup and view all the answers

What is the simplest form of quaternary structure in proteins?

Dimer Signup and view all the answers

Which element can be included in a protein's 3D structure as a prosthetic group?

Metal ions Signup and view all the answers

What can denature a protein and result in the loss of its function?

Extreme pH Signup and view all the answers

What is the part of a polypeptide chain that folds independently into a compact structure?

Domain Signup and view all the answers

What type of bond can form between cysteines in different polypeptide chains?

Disulphide bond Signup and view all the answers

What determines the function of a protein?

Amino acid sequence Signup and view all the answers

Proteins always fold into the lowest energy conformation

True Signup and view all the answers

The primary structure of a protein is the sequence of amino acids in the polypeptide chain, which is always the same for all proteins

False Signup and view all the answers

Cystine is the only amino acid with an SH group that can form disulphide bonds

False Signup and view all the answers

The side chains of amino acids in beta-sheets stick out above and below the sheet

True Signup and view all the answers

Renaturation of denatured proteins is always possible

False Signup and view all the answers

Study Notes

Structure of Amino Acids

A central carbon atom is bonded to an amino group, a carboxyl group, a hydrogen atom, and a R group (variable side chain)
All amino acids except glycine have a chiral carbon, with 4 different chemical groups attached, allowing for L and D isomers
Only L amino acids are found in proteins

Glycine

Glycine is the only amino acid without a chiral carbon, due to having only 3 different groups attached
The R group in glycine is a hydrogen atom

Amino Acid Properties

Different amino acids can vary in size, shape, charge, polarity, and chemical reactivity
Key features of amino acids to know include their size, polarity, and unique characteristics

Amino Acids in Solution

Amino acids in solution tend to exist as zwitterions, with both COOH and NH2 groups ionized
The nature of the species present depends on the pH
At low pH, both COOH and NH3 get protonated, resulting in a net charge of +1
At high pH, both COOH and NH3 get deprotonated, resulting in a net charge of -1

pKa and Ionisation State

pKa is the pH at which the concentrations of protonated and unprotonated forms are equal
The ionisation state of amino acids varies with pH
pKa for COOH is around 2, with COOH present at pH below 2 and COO- present at pH above 2
pKa for the amino group is between 9-10, with NH3+ present at pH below 9 and NH2 present at pH above 10

Ionisable Side Chains

7 of the 20 amino acids have readily ionisable side chains

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Description

Test your knowledge of amino acid structure and properties with this quiz. Learn about the central carbon, amino group, carboxyl group, chiral carbon, R group, isomers, and the unique properties of glycine. Explore the variations in different amino acids and their significance in proteins.