Colloidal Systems and Dialysis

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Questions and Answers

What is the dispersed phase in a colloidal system?

Proteins and nucleic acids

Macromolecular solids and liquids (correct)

Insoluble materials

Stable foam

Colloids can be filtered by ordinary filters.

False

List three types of membranes used for dialysis.

Cellulose-based membrane: PES, PAN, and PVDF
Regenerated cellulose-based membrane
Composite membrane

Dialysis is a process in which solvent molecules, other small molecules, and hydrated ions pass through a ______________.

membrane Signup and view all the answers

Match the following amino acids with their categories:

Neutral AA = Glycine, Serine, Proline Acidic AA = Aspargine, Aspartic Acid, Glutamic Acid Basic AA = Lysine, Arginine, Histidine Signup and view all the answers

What is the specific sulfhydryl group containing amino acid that reacts with nitroprusside to yield a purple colored compound?

Cysteine Signup and view all the answers

What is the process known as when proteins precipitate due to the addition of a precipitating agent and steady mixing?

Precipitation Signup and view all the answers

Proteins in solution form hydrogen bonds with water, and adding organic solvents reduces this interaction.

True Signup and view all the answers

In Robert's test, _____________ precipitates in the presence of an inorganic salt like ammonium sulphate.

Albumin Signup and view all the answers

Match the following denaturation methods with their effects on proteins:

By Alcohol = Reduces the concentration of water molecules available for keeping proteins in solution By Heating = Coagulation and denaturation of proteins Salt Denaturation = Precipitation of proteins by disrupting salt bridges Signup and view all the answers

What factors affect surface tension?

Temperature, Dissolved Substances Signup and view all the answers

_____ salts slightly raise surface tension of water, though potassium permanganate lowers it.

Inorganic Signup and view all the answers

What effect do organic substances typically have on surface tension?

Lower it Signup and view all the answers

Ammonia increases surface tension.

False Signup and view all the answers

Match the following amino acids with their groups:

Glycine = Aliphatic amino acids Serine = Hydroxy amino acids Cysteine = Sulfur-containing amino acids Signup and view all the answers

What is the physiological importance of surface tension?

Involved in digestion, helps emulsification Signup and view all the answers

What test is used to detect the presence of lead sulfide?

Lead Sulfide Test Signup and view all the answers

Tungstic acid and Hager’s reagent are referred to as powerful protein _____.

precipitating agents Signup and view all the answers

What can denaturation of proteins lead to?

All of the above Signup and view all the answers

What does the isoelectric point (I.E.P.) of a protein represent?

The pH at which the molecule is electrically neutral (net charge is zero) Signup and view all the answers

Denaturation is brought about by certain ______ agents.

physical, chemical, and mechanical Signup and view all the answers

What can denaturation cause in terms of biological activities?

All of the above Signup and view all the answers

Denaturation is always irreversible.

False Signup and view all the answers

Study Notes

Colloids

Colloids are suspensions of particles that are larger than true solutions but still smaller than to settle out by gravity.
A colloidal system consists of two components: dispersed phase and dispersion phase.
The dispersed phase consists of macromolecular solids like proteins and nucleic acids, and liquids like oily fats.
The dispersion phase is the medium in which insoluble materials are dispersed.

Types of Colloids

Suspensoid: a colloidal system where the dispersed particles have little or no affinity towards water.
Emulsoid: a colloidal system where the dispersed particles have an affinity towards water.
Foam Formation: stable foam (emulsoid) and unstable foam (suspensoid).

Dialysis

Dialysis is a process where solvent molecules, other small molecules, and hydrated ions pass from a solution through a semipermeable membrane.
Dialyzing membranes are semipermeable with larger pores than osmotic membranes.
They hold back colloid particles and large molecules but allow solvent, hydrated ions, and small molecules to pass through.

Osmosis and Diffusion

Osmosis is the spontaneous flow of solvent through a semipermeable membrane from a solution of low concentration to one of higher concentration.
Diffusion is the movement of molecules from a higher concentration to a lower concentration.
Diffusion is faster for small molecules than larger ones.

Protective Colloids

When a large amount of hydrophilic colloids carrying opposite charges is added to hydrophobic colloids, they get adsorbed on the hydrophobic particles and form a protective layer around it.
This adsorption layer prevents the precipitating ions from reaching the sol particles and hence preventing coagulation.

Surface Tension

Surface tension is the property of a liquid that causes it to behave as if it has an elastic skin at its surface.
Factors affecting surface tension: temperature, dissolved substances, and interfacial tension.
Physiological importance of surface tension: involved in the process of digestion, assisting emulsification, and increasing the surface area for lipase activity.

Biochemistry Lab - Midterm

Methylene Blue: a monovalent cationic dye used for dyeing silk, leather, paper, and cotton, and for production of ink.
Adsorption: a process where a solid is used for removing a soluble substance from water.
Membranes for Dialysis: cellulose-based, regenerated cellulose-based, and composite membranes.

Qualitative Test for Proteins and Amino Acids

Proteins are made up of amino acid residues joined by peptide bonds.
Colour reactions of proteins: used for qualitative detection and quantitative estimation of proteins and their constituent amino acids.
Tests: ninhydrin, xanthoproteic, Hopkins-Cole, and biuret.

Amino Acids

Classification: neutral, acidic, basic, aliphatic, hydroxy, sulfur-containing, aromatic, and imino acids.
Solubility: largely dependent on the solution pH.
Ninhydrin test: a-amino acids give purple colour, while imino acids give yellow colour.

Proteins

Made up of amino acid residues joined by peptide bonds.
Classification: albumins, globulins, metaproteins, proteoses, and peptones.
Solubility: largely dependent on the solution pH.
Colour reactions: used for qualitative detection and quantitative estimation of proteins and their constituent amino acids.### Biochemistry of Proteins
Proteins can be denatured, leading to a loss of their biological activities and antigenic properties.
Denaturation can be caused by various agents, including:
- Physical agents: heat, ultraviolet rays, and ionizing radiations.
- Chemical agents: acids, alkalies, and certain acid solutions of heavy metals (e.g., mercury, lead).
- Mechanical means: vigorous shaking or grinding.

Tests for Proteins

Biuret test:
- Named after the reaction with biuret (NH2-CO-NH2).
- Violet color indicates the presence of proteins.
- Gelatin does not give this test due to lack of arginine.
Sakaguchi test:
- Specific for guanidino groups in arginine.
- Bright red color indicates the presence of arginine.
Lead sulfide test:
- Tests for sulfur-containing amino acids (cysteine and cystine).
- Black or brown precipitate indicates the presence of sulfur.
Acid test:
- TCA (trichloroacetic acid) test is used to detect proteins.
- Precipitation of proteins occurs in the presence of acid reagents.
Nitroprusside test:
- Specific for cysteine.
- Red or intense purple color indicates the presence of cysteine.

Precipitation of Proteins

Precipitation occurs in a stepwise process.
Addition of a precipitating agent and mixing causes protein solution to destabilize.
Mixing leads to collision between precipitant and target product, causing precipitation.
Enough mixing time is required for molecules to diffuse across the fluid.
Precipitation can occur due to:
- Heavy metal salts (e.g., Hg2+, Pb2+, Ag1+, Tl1+, Cd2+).
- Salts with high atomic weights.
- Alkaloidal reagents (e.g., Esbach's reagent, picric acid, citric acid).
- Acids (e.g., concentrated nitric acid).
Salting out and salting in are two opposing processes:
- Salting out: high salt concentrations precipitate proteins.
- Salting in: low salt concentrations increase protein solubility.

Denaturation of Proteins

Denaturation leads to a loss of protein structure and function.
Can be caused by:
- Heat.
- Acids (e.g., concentrated nitric acid).
- Alkalies.
- Organic solvents (e.g., alcohol, acetone).
- Heavy metal salts.
- Detergents.
Denaturation can be reversible or irreversible.
Coagulation is a type of irreversible denaturation.

Casein from Milk

Casein is the main protein in milk.
Present at a concentration of about 35 g/l.
Casein is a phosphoprotein.
Isolation of casein can be done using:
- Acetic acid.
- Ethanol.
- Calcium salt and calcium caseinate.

Protein Structure and Function

Proteins have a three-dimensional conformation.
Primary, secondary, tertiary, and quaternary structure are characteristic of native proteins.
Hydrogen bonds, ionic bonds, and hydrophobic bonds stabilize protein structure.
Denaturation disrupts these bonds, leading to a loss of protein function.

Isoelectric Point (I.E.P.)

The pH at which a protein molecule is electrically neutral (net charge is zero).
At the I.E.P., proteins tend to precipitate due to the absence of repelling forces.
The I.E.P. of a protein is important in protein purification and isolation.

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Description

Test your understanding of colloidal systems, including the dispersed phase and filtration. Also, explore the process of dialysis and its applications.