Protein Structure and Function

Questions and Answers

Which of the following statements is true about the peptide bond?

It is a covalent bond between the R-group of one amino acid and the amino group of another.

It is a bond between the α-carbon of one amino acid and the carboxyl group of another. (correct)

It is an ionic bond between the amino group of one amino acid and the carboxyl group of another.

It is a hydrogen bond between the nitrogen and oxygen atoms of two amino acids.

What is the main function of the R-group in an amino acid?

It is involved in the denaturation of proteins.

It is responsible for the formation of the peptide bond.

It defines the properties and function of the amino acid. (correct)

It determines the pH of the amino acid.

What is the result of defects in amino acid metabolism?

Proteins are more readily folded and have a more stable tertiary structure.

Proteins are more stable and less prone to denaturation.

Defects in amino acid metabolism may lead to disease. (correct)

Proteins are more resistant to changes in pH and temperature.

What is the role of the α-carbon in an amino acid?

It is attached to the amino and carboxyl groups. Signup and view all the answers

What is the state of the amino and carboxyl groups at physiological pH?

They are both ionised. Signup and view all the answers

What is the number of universal structural amino acids that are encoded in DNA?

20 Signup and view all the answers

What is the role of the peptide bond in protein structure?

It forms the primary structure of proteins. Signup and view all the answers

What is the result of the nitrogen and oxygen atoms of the peptide bond interacting with other peptide units?

The formation of hydrogen bonds. Signup and view all the answers

What is the result of a defective phenylalanine hydroxylase enzyme in Phenylketonuria?

Reduced production of tyrosine and hormones derived from it Signup and view all the answers

What is the function of the partial charges on the peptide bond?

To form hydrogen bonds that are key for protein structure Signup and view all the answers

What is the unique feature of selenocysteine?

It is encoded by a subset of STOP codons Signup and view all the answers

What is the role of hydroxyproline in collagen?

It allows the formation of a specific triple helix structure Signup and view all the answers

What is the result of a defective tyrosinase enzyme in Albinism?

Reduced production of melanin Signup and view all the answers

What is the purpose of amino acid polymerization?

To form polypeptides (proteins) Signup and view all the answers

What is the characteristic of the peptide bond?

It has features of a double bond Signup and view all the answers

What is the function of homocysteine?

It is necessary for the synthesis of cysteine Signup and view all the answers

Study Notes

Amino Acids

Amino acids have an amino group and carboxylic group attached to the same carbon (α- carbon)
There are 20 universal structural amino acids that are encoded in DNA
Each amino acid has a different R-group attached to the α- carbon, which defines its properties and function
At physiological pH, the amino and carboxyl group are ionized

Classification of Amino Acids

Some amino acids are essential for the human diet due to the lack of enzymes to synthesize them de novo
Other amino acids exist in cells that are not universally encoded in DNA, such as:
- Hydroxyproline: formed by hydroxylation of proline, important component of collagen
- Selenocysteine: contains Se instead of S, reduced pKa useful for enzymes in anti-oxidant activity
- Homocysteine: contains an extra methyl group compared to cysteine, needed to synthesize cysteine

Peptide Bond Formation

Amino acids polymerize to form polypeptides (proteins) via the formation of the peptide bond between the alpha amino and alpha carboxylic groups of adjacent amino acids
The formation and hydrolysis of peptide bonds require enzymes
The peptide bond is very strong and has some features of a double bond:
- It is shorter than the standard C-N bond length
- There is no rotation
- The R-groups are in the trans configuration
- There is a partial negative charge on the oxygen atom and partial positive charge on the nitrogen atom

Importance of Peptide Bond

The partial charges on the peptide bond are important in the formation of hydrogen bonds that are key for protein structure
Defects in metabolism result in a number of clinical conditions, such as:
- Phenylketonuria (PKU): defective phenylalanine hydroxylase
- Albinism: defective tyrosinase

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Description

This quiz covers the structure and function of proteins, including amino acid recognition, peptide bonds, and alpha helices. Learn about the importance of amino acid side chains and hydrogen bonds in protein formation.