Polypeptides and proteins 50-51

Question 1

Explain what peptides are made from and how the peptide is made.

Answer 1

Amino acids join together by peptide linkages to form peptides. When two amino acids join together, a dipeptide is formed with the elimination of a water molecule. This is a condensation reaction.

Question 2

What is a ‘peptide linkage’ or ‘peptide bond’?

Answer 2

The name used for the amine bond in proteins and polypeptides.

Question 3

Write out the reaction for the formation of a dipeptide between glycine and alanine.

Answer 3

Question 4

What are one of the characteristics of the glycine and alanine reaction?

Answer 4

It is possible to form a diffirent dipeptide from the same two amino acids. Either carboxyl group of glycine or alanine can react with the amino group of other amino acid.

Question 5

What are proteins?

Answer 5

Proteins are simply long polypeptides, generally with more than 50 amino acids.

Question 6

Describe the acid hydrolysis of polypeptides and proteins.

• conditions
• reagents

Answer 6

Can be hydrolysed using aqueous acid. A water molecule is needed to break each peptide link to form a mixture of the amino acids that made up the protein.

During acid hdyrolysis, the amino acids formed are positively charged because of the presence of the H* ions from the acid.

Traditionally the protein or polypeptide is heated under reflux with 6mol dm^-3 for 24 hours.

Question 7

Write the acid hydrolysis of a dipeptide.

Answer 7

Question 8

Describe the alkaline hydrolysis of polypeptides and proteins.

• Reagents
• Conditions

Answer 8

A solution of alkali, in the form of aqueous sodium hydroxide, is used at just above 100*C. The polypeptide is broken down into amino acids in the form of their sodium salts.

Question 9

Write out the alkaline hydrolysis of a general polypeptide chain.

Answer 9

Answer is figure 5 on page 51