Biology of Milk Fermentation

Questions and Answers

What is the primary principle behind the separation of amino acids in this technique?

Differences in temperature resistance of amino acids

Differences in chemical structure of amino acids

Differences in molecular weight of the amino acids

Differences in charge and its magnitude of the amino acids (correct)

At pH 3, what state do most amino acids exist in during the separation process?

Cationic state (correct)

Anionic state

Zwitterionic state

Neutral state

How do positively charged amino acids interact with the negatively charged resin in the column?

They are repelled by the resin and pass through quickly

They dissolve into the resin matrix

They are chemically transformed by the resin

They are attracted to the resin and adsorbed onto it (correct)

Which amino acids will have more affinity for the negatively charged resin particles?

Amino acids with larger positive charges Signup and view all the answers

What will happen to amino acids with least positive charges at pH 3 during separation?

They will be bound more loosely compared to others Signup and view all the answers

What happens to proteins that have a net positive charge in an electric field?

They migrate towards the negative electrode. Signup and view all the answers

Which factor does NOT affect the velocity of migration of proteins in an electric field?

Temperature of the buffer solution Signup and view all the answers

At what point does electrophoretic mobility of a protein become zero?

At the isoelectric pH. Signup and view all the answers

How do molecules of the same charge but different molecular masses behave in an electric field?

The lighter ones move faster. Signup and view all the answers

Which component is essential for the conducting liquid in SDS-PAGE?

Buffer solution Signup and view all the answers

What is the role of frictional resistance in the migration of proteins?

It retards the movement of charged molecules. Signup and view all the answers

How do polar organic molecules behave in paper chromatography compared to non-polar solvents?

They dissolve more easily in water. Signup and view all the answers

What type of substances are used as support in SDS-PAGE?

Inert substances like paper and gel Signup and view all the answers

What procedure can be used to identify points of overlap in a polypeptide chain?

Partial hydrolysis Signup and view all the answers

What byproduct is produced during the fermentation of lactose by bacteria in milk?

Lactic acid Signup and view all the answers

What happens to the pH of milk as lactic acid concentration increases?

It decreases Signup and view all the answers

Which chemical agent hydrolyzes peptide bonds more effectively in certain amino acids pairs?

Dilute acids Signup and view all the answers

What type of amino acids does trypsin specifically cleave in peptide bonds?

Basic amino acids Signup and view all the answers

What is the consequence of blood proteins becoming isoelectric in an acidic environment?

They cannot perform their functions Signup and view all the answers

Which method does cyanogen bromide (CNBr) employ to cleave peptide bonds?

Cleaving at methionine residues Signup and view all the answers

How does extreme pH affect protein structure?

It causes swelling and unfolding Signup and view all the answers

What effect does urea have on proteins?

It disrupts hydrophobic interactions Signup and view all the answers

Which of the following peptide bonds does chymotrypsin specifically target?

Bonds with aromatic amino acids Signup and view all the answers

Which of the following amino acids does thermolysin cleave in addition to those cleaved by chymotrypsin?

Isoleucine Signup and view all the answers

What is the role of mercaptoethanol in protein denaturation?

It reduces disulfide bonds to sulfhydryl groups Signup and view all the answers

What happens to methionine after hydrolysis using cyanogen bromide?

It is converted to homoserine lactone Signup and view all the answers

Which type of pH condition results in greater unfolding of proteins?

Extremely alkaline pH Signup and view all the answers

Which method is commonly used in laboratories to cleave peptide bonds besides chemical methods?

Enzymatic hydrolysis Signup and view all the answers

What is a common result of protein denaturation in biological systems?

Loss of functional ability Signup and view all the answers

What happens to proteins at their isoelectric point (pI)?

They are least soluble. Signup and view all the answers

How can different proteins be separated based on their solubility characteristics?

By isoelectric precipitation. Signup and view all the answers

What effect does pH have on the solubility of β-lactoglobulin?

It is soluble at extremes of pH. Signup and view all the answers

Which of the following factors does NOT influence protein solubility?

Concentration of all solutes. Signup and view all the answers

What is the primary reason for the increased solubility of proteins outside their pI?

They repel due to net charges. Signup and view all the answers

What is the characteristic of a protein's solubility curve?

It varies with temperature and pH. Signup and view all the answers

Which mechanism describes the separation of bound proteins using substrates?

Affinity chromatography. Signup and view all the answers

Why do proteins precipitate at their isoelectric point, even with positive and negative charges present?

Ionic interactions and clumping occur. Signup and view all the answers

Study Notes

Milk Fermentation and Coagulation

Bacteria grow in stored milk, using lactose for energy during fermentation.
Lactic acid is produced, decreasing the milk's pH.
Lower pH causes milk proteins to become isoelectric and coagulate, forming curd.

Blood Protein Denaturation

Acidic or basic blood pH leads to denaturation of proteins like albumin and fibrinogen.
Denatured proteins lose functionality, risking oxygen transport by hemoglobin and survival.

Protein Unfolding at Extreme pH

High net charge at extreme pH causes swelling and unfolding of proteins.
Extreme alkaline conditions ionize buried groups, disrupting polypeptide structures more than extreme acidic conditions.

Organic Solvent Effects on Proteins

Detergents (e.g., sodium dodecyl sulfate) and organic solvents (e.g., alcohol, acetone) denature proteins.
Urea forms stronger hydrogen bonds with proteins, disrupting internal bonding.
Mercaptoethanol reduces disulfide bonds, altering three-dimensional protein structures.

Separation of Amino Acids

Separation is based on charge differences (positive, negative, neutral) of amino acids.
At pH 3, amino acids behave predominantly as cations and are exchanged for sodium ions in cation resin columns.
Basic amino acids have a stronger affinity for negatively charged resin, affecting separation rates.

Hydrolysis Techniques

Acidic hydrolysis can cleave peptide bonds but shows varying susceptibility among amino acids.
Cyanogen bromide specifically cleaves methionine-containing bonds, transforming methionine to homoserine lactone.
Proteolytic enzymes like trypsin and chymotrypsin hydrolyze bonds based on specific amino acid characteristics.

Protein Separation Methods

SDS-PAGE uses a strong electric field to separate proteins based on charge and size.
Proteins migrate towards opposite electrodes; net charge determines direction and speed.
Velocity of migration depends on electric field strength, protein charge, and frictional resistance.

Isoelectric Point and Separation

At isoelectric pH, protein charge is neutral, resulting in zero electrophoretic mobility.
Different proteins will migrate at varying rates based on charge and size.
Polarity influences chromatography; polar molecules prefer aqueous environments over non-polar solvents.

Solubility and Salting-Out of Proteins

Protein solubility varies with pH; proteins are least soluble at their isoelectric points (pI).
Salting-out techniques further exploit solubility differences influenced by pH and ionic strength.
β-lactoglobulin, a milk protein, has a pI of 5.3; it's soluble at extreme pH levels and precipitates at its pI.

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Description

This quiz explores the process of milk fermentation, focusing on the role of bacteria and lactic acid production. Understand how the growth of bacteria affects milk composition and leads to coagulation. Ideal for those studying food science or microbiology.