What are proteins?
Proteins are one of the four main groups of macromolecules found in all living organisms, formed through condensation reactions between amino acids, creating peptide bonds.
What are the two main classes of protein sources?
First-class proteins (animal origin, containing all essential amino acids) and second-class proteins (plant sources).
What are first-class proteins? Give examples.
First-class proteins contain all essential amino acids and are mainly of animal origin. Examples include lean meat, fish, eggs, milk, and cheese.
What are second-class proteins? Give examples.
Second-class proteins are derived from plant sources. Examples include vegetables, legumes like beans and soya beans, and groundnuts.
Name three examples of proteins and their functions.
Keratin (found in skin, hair, and nails), Insulin (a hormone that regulates blood sugar), and Haemoglobin (carries oxygen in red blood cells).
What are the building blocks of proteins?
Amino acids.
What two functional groups does every amino acid contain?
An amino group (-NH₂) and a carboxyl group (-COOH).
How are amino acids linked together in a protein?
They are connected via peptide bonds, which are amide linkages.
What is formed during the creation of a peptide bond?
A molecule of water is eliminated between the carboxyl group of one amino acid and the amino group of another.
What is the primary structure of a protein?
The specific sequence in which atoms are covalently bonded to form chains and cross-links, unique to each protein.
What is a polypeptide?
A long chain formed by linking many amino acids together through peptide bonds.
What is the general solubility of proteins in water?
Most proteins are insoluble in water, though some like insulin and pepsin are soluble, and others may form colloidal solutions.
What happens to a protein solution like egg white when heated above 50°C?
It undergoes coagulation or precipitation, a process called denaturation.
What is hydrolysis of proteins?
The process of breaking peptide bonds in proteins, usually by boiling with acids, alkalis, or enzymes, to break them down into individual amino acids.
How do you perform the Biuret test for proteins?
Add sodium hydroxide (NaOH) solution to the sample, followed by a few drops of copper(II) sulfate (CuSO₄) solution.
What is the result of a positive Biuret test?
A violet or purple coloration.
Describe Millon's Test for proteins.
Add Millon's reagent to the protein solution and heat. A white precipitate forms that turns brick-red, indicating the presence of protein.
Describe the Trioxonitrate(V) Acid test for proteins.
Treat the protein solution with concentrated nitric acid (HNO₃). A white precipitate forms and turns intense yellow upon heating.
What are three uses of proteins?
1. Haemoglobin transports oxygen. 2. Hormones regulate biological processes. 3. Enzymes catalyze biological reactions.
What are enzymes?
Enzymes are organic catalysts that facilitate metabolic reactions in living organisms. They are protein molecules secreted by living cells.
What are hydrolases?
Enzymes involved in hydrolysis reactions, such as those aiding in digestion.
What is a key property of enzymes regarding their action?
They act specifically on their target substrates.
What is the optimal temperature range for most enzymes?
Between 33°C and 40°C.
What happens to enzymes at temperatures above their optimal range?
They become denatured and lose their function.
How does pH affect enzyme activity?
Enzymes are pH-sensitive and work best within specific pH ranges.
What is the first step in how an enzyme works?
The enzyme binds with the substrate to form an enzyme-substrate complex.
What is the second step in how an enzyme works?
Within the enzyme-substrate complex, the substrate reacts to form an enzyme-product complex.
What is the final step in how an enzyme works?
The enzyme-product complex separates into the final product and the unchanged enzyme, which is ready for another cycle.
What is casein and what is it used for?
Casein is a milk protein used to make artificial wool and silk.
What is the name of the protein that is a key component of elastic fibers?
Elastin.
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