MSc General Chemistry: Proteins

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Questions and Answers

What percentage of the cell's dry weight is composed of proteins?

Two-thirds (correct)

One-quarter

One-third

Three-quarters

What is the role of prothrombin and fibrinogen in the body?

Maintaining skin and bone structure

Helping in blood clotting (correct)

Defending the body against diseases

Regulating body temperature

What is the building unit of protein?

Nucleic acids

Fats

Carbohydrates

Amino acids (correct)

What happens to proteins when they are treated with acids or bases?

They are decomposed into their constituent amino acids Signup and view all the answers

What is the primary structure of a protein?

The sequence of amino acids in the peptide chain Signup and view all the answers

What is the quaternary structure of a protein?

The arrangement of folded structures to form a functional protein Signup and view all the answers

Which of the following elements are found in proteins?

All of the above Signup and view all the answers

What is the function of camaglobulin?

Defending the body against diseases Signup and view all the answers

What type of amino acids are essential for the Xanthoprotic reagent experiment?

Aromatic amino acids Signup and view all the answers

What is the aim of the experiment using ninhydrin?

To detect the presence of proteins and amino acids Signup and view all the answers

What is the color of the nitro compounds formed when the amino acid is heated with Concentrated nitric acid?

Yellow Signup and view all the answers

What is added to the test tube containing the protein in the Xanthoprotic reagent experiment?

Drops of nitric acid solution Signup and view all the answers

What is the pH range in which ninhydrin is a strong oxidizing substance?

pH 4-8 Signup and view all the answers

What is the basis of the experiment 'Precipitation of proteins by acids'?

Amphoteric property of proteins Signup and view all the answers

What is the purpose of adding sodium hydroxide solution in the Biuret reagent experiment?

To add a strong base to the reaction Signup and view all the answers

What is the resulting compound formed in the Biuret reagent reaction?

A complex of Cu+2 and four nitrogen atoms Signup and view all the answers

What is the result of adding an acid that carries an amount of negative charges to a protein?

Protein carries a positive charge Signup and view all the answers

What happens when more acid is added to the albumin in the 'Precipitation of proteins by acids' experiment?

Protein is precipitated Signup and view all the answers

What is the purpose of adding copper sulphate in the Biuret reagent experiment?

To form a complex with the peptides Signup and view all the answers

What is the color formed when a protein reacts with the Biuret reagent?

Violet Signup and view all the answers

Which of the following amino acids do not provide detection with the Biuret reagent?

Histidine, serine, and threonine Signup and view all the answers

What is the name of the complex formed in the Biuret reagent reaction?

Copper coordination complex Signup and view all the answers

Study Notes

Proteins

Proteins are the most important and complex vital compounds in cells, making up two-thirds of a cell's dry weight.
They have multiple functions, including:
- Playing a major role in all vital activities
- Being involved in the structure of membranes, muscles, and tissue
- Helping to defend the body through camaglobulin
- Helping in blood clotting through prothrombin and fibrinogen
Proteins are composed of elements such as sulfur, hydrogen, nitrogen, phosphate, iron, zinc, carbon, oxygen, and copper.

Amino Acids

Amino acids are carboxylic acids with an amino group attached to an alpha carbon atom.
Amino acids differ depending on the group R.
Proteins are decomposed into their constituent amino acids when treated with acids or bases.
Amino acids are linked to each other by a peptide bond.

Structural System of Protein Molecules

The structural system of protein molecules has four levels:
Primary Structure
- Sequence of amino acids in the peptide chain
- Can be open, circular, or branched
Secondary Structure
- Consists of helical structures and bent plate structures
Tertiary Structure
- Spherical or oval shape resulting from bending of the spiral structure
Quaternary Structure
- Regularly folded or single folded structures combining to form a quaternary structure

Detection of Proteins and Amino Acids

Ninhydrin Reagent
- Detects proteins and amino acids
- Reaction depends on the amine group (NH2) and the carboxyl group (COOH)
- Resulting color is blue
Biuret Reagent
- Detects proteins based on the presence of two or more peptide bonds (C-NH4)
- Results in a violet color
Xanthoprotic Reagent
- Detects amino acids containing an aromatic ring
- Reaction involves nitration of the benzene ring
- Results in yellow or orange color
Precipitation of Proteins by Acids
- Based on the property of protein as an amphoteric acid
- Acids with negative charges neutralize the positive charges carried by the protein, forming salts that are deposited at the bottom.