Chemistry 9 Lesson 53: Protein

1. Theoretical Summary

1.1. Natural state

1.2. Composition and molecular structure

a) Composition

Mainly carbon, hydrogen, oxygen, nitrogen and a small amount of S, P, metals…

b) Molecular structure

Proteins are made up of amino acids, each amino acid molecule forming a “link” in the protein molecule.

1.3. Nature

a) Hydrolysis reaction

Protein + Water \(\xrightarrow[Axit/Bazo]{t^{0}}\) Amino acid mixture

b) Decomposition by heat

In hair, the main component is protein, so when heated strongly and without water, protein is decomposed creating volatile substances and has a burning smell.

c) Coagulation

⇒ Some proteins are soluble in water, forming colloidal solutions, when heating or adding chemicals to these solutions, protein precipitation often occurs. This is called protein coagulation.

1.4. Application

• The main application of Protein is for food.
• In addition, there are applications in the textile industry (wool, silk), leather, fine arts (horn, ivory).

2. Illustrated exercise

2.1. Form 1: Determine the molecular formula

When analyzing substance X separated from the product of protein hydrolysis, it was found that the molar mass of X was 75 grams/mol.

Burning 1.5 grams of X found to produce 1.76 grams of CO₂, 0.9 grams H₂O and 0.28 grams N₂.

a) Determine the molecular formula of X.

b) Write down the structural formula of X.

Solution guide

a) The mass of substances produced when 1 mole X is burned is:

mCO₂ = 1.76/1.5 x 75 = 88g → in 1 mole there is mC = 88/44 x 12 = 24g

mH₂O = 0.9×75/1.5 = 45g → mH = 45/18 x 2 = 5g

In 1 mole of X there is mN = 0.28/1.5 x 75 = 14g

Let the formula for X be C_xH_yO_zWOMEN_t

We have: 12x + y + 16z + 14t = 75

So: 12x = 24 → x = 2

y = 5

14t = 14 → t = 1

Substituting the values ​​of X, y, t in we get: 16z = 32 → z = 2.

So the formula for X is C₂H₅O₂N.

2.2. Form 2: Explaining the actual phenomenon

Explain the following phenomena:

a) When cooking crab soup, crab bricks emerge.

b) When washing clothes woven from silk or wool, they should not be washed with highly alkaline soap but should be washed with neutral soap.

Solution guide

a) Because when heated, the water-soluble proteins coagulate.

b) Silk, wool, and wool are composed of proteins. When washed with highly alkaline soaps, they are easily hydrolyzed, making clothes quickly damaged.

3. Practice

3.1. Essay exercises

Question 1: In the following foods and foods: rice, candy, peanut oil, eggs, which type?

a) contains the most fat?

b) contains the most sugar?

c) contains the most powder?

d) contains the most protein?

Verse 2: There are two pieces of silk that look alike: One is woven from silk thread and the other is woven from cotton yarn. Show a simple way to tell them apart.

Question 3:

a) Compare the similarities and differences in composition, molecular structure of amino acetic acid (H₂N – ONLY₂ – COOH) with acetic acid.

b) Two molecules of aminoacetic acid join together by splitting – OH of the -COOH group and -H of the -NH group₂. Write the chemical equation that occurs.

3.2. Multiple choice exercises

Question 1: Choose the correct comment:

A. Proteins have large molecular weight and simple structure.

B. Proteins have a large molecular weight and are made up of many identical amino acid molecules.

C. Protein has a very large molecular weight and an extremely complex structure made up of many amino acids.

D. Protein has a large molecular weight made up of many aminoacetic acid molecules.

Verse 2: In the molecular composition of proteins, in addition to the elements C, H, and O, there must be elements

A. sulfur.

B. iron.

C. chlorine.

D. nitrogen.

Question 3: To distinguish silk woven fabrics and cotton woven fabrics. We can

A. Heat to carry out the coagulation reaction.

B. burning and smelling if there is a burning smell is silk fabric.

C. use litmus.

D. use hydrolysis.

4. Conclusion

After the lesson, you should know the following:

• Concept, molecular structure (made up of many amino acids) and molecular weight of proteins
• Chemical properties: Hydrolysis reactions are catalyzed by acids, bases or enzymes, coagulated under the effect of chemicals or heat, easily hydrolyzed when heated strongly.