Food Chemistry II - Amino Acids, Proteins, Carbohydrates, and Lipids

Flashcards covering key concepts from Food Chemistry II, including amino acid properties, protein structure, denaturation, enzyme catalysis, carbohydrate chemistry, lipid properties, and lipid oxidation.

What percentage of total body protein does skin typically account for in mammals?

Skin often accounts for about $10\%$ of total body protein.

Where are the basic amino group and acidic carboxyl group attached on amino acids found in proteins?

Both the amino and carboxyl groups are attached to the $\alpha$-carbon atom.

Which three aromatic amino acids absorb light significantly in the ultraviolet range?

Tryptophan, tyrosine, and phenylalanine.

Why is spectrophotometric measurement at $280\,nm$ used to estimate protein concentration?

Most proteins contain tyrosine residues, which absorb light significantly in the ultraviolet range at $280\,nm$.

How is a peptide bond formed between two amino acids?

It is formed when the amino group of one amino acid reacts with the carboxyl group of another amino acid, releasing a molecule of water.

How many different proteins are estimated to exist in nature?

It is estimated that only $2000$ different proteins exist in nature.

What defines the secondary structure of a protein?

The three-dimensional manner in which relatively close members of the protein chain are arranged.

Why is the formation of an $\alpha$-helix structure in proteins spontaneous?

Because the $\alpha$-helix structure possesses the lowest feasible free energy.

Which bond type is the strongest in maintaining the tertiary structure of a protein?

Covalent disulfide ($-S-S-$) linkages.

What bonding mechanism present in tertiary protein structure is generally absent in maintaining quaternary structure?

Disulfide bonds.

What are the density ranges for high density, low density, and very low density lipoproteins?

High density is $1.063\text{ -- }1.21\,g/ml$; low density is $1.019\text{ -- }1.063\,g/ml$; very low density is $1.0006\text{ -- }1.019\,g/ml$.

What types of bonds join proteins to heterosaccharides in glycoproteins?

Either O-glycosidic bonds to hydroxylamino acids (serine or threonine) or N-glycosidic bonds to the side chain amide of asparagine residues.

What proportion of iron is contained in the storage metalloprotein ferritin?

Ferritin consists of about $20\%$ iron.

What physiological significance does the decarboxylation of histidine have?

It produces histamine, which is one of the major mediators of allergy, shock, and similar states in humans.

What is the Van Slyke reaction used for in protein chemistry?

It uses nitrous acid ($HNO_2$) to produce one mole of nitrogen per mole of amino acid, which is used to follow the release of free amino groups during proteolysis.

How is protein denaturation defined?

Any modification in secondary, tertiary, or quaternary conformation not accompanied by the rupture of peptide bonds involved in primary structure.

By how much does the rate of protein denaturation increase with a $10\,^\circ\text{C}$ temperature rise in typical denaturation ranges?

The rate increases about $600$ times.

At what hydrostatic pressure levels do ovalbumin and trypsin denature?

Ovalbumin denatures at $50\,kPa$ and trypsin denatures at $60\,kPa$.

What are the conditions for standard acid hydrolysis of proteins?

Refluxing in a $20.5\%$ solution of hydrochloric acid for $12\text{ -- }70$ hours (or $8\text{ -- }10$ hours at $120\,^\circ\text{C}$).

Which amino acid is completely lost during acid hydrolysis of proteins?

Tryptophan.

How many biochemical reaction types are enzymes known to catalyze?

Enzymes are known to catalyze more than $5000$ biochemical reaction types.

How many amino acid residues of an enzyme structure are directly involved in catalysis?

Around $2\text{ -- }4$ amino acids.

Which GRAS microorganisms are used to produce invertase and lactase?

Saccharomyces cerevisiae produces invertase, and Saccharomyces fragilis produces lactase.

What percentage of total caloric intake is provided to humans by starch?

Starch provides $75\text{ -- }80\%$ of the total caloric intake of humankind.

How are oligosaccharides and polysaccharides distinguished by degree of polymerization?

Oligosaccharides have a degree of polymerization ranging from $2$ to about $10$, while polysaccharides contain more than $10$ monosaccharide residues.

What sugar mixture is produced when D-glucose undergoes alkaline enolization?

A mixture of $65\%$ D-glucose, $31\%$ D-fructose, and $2.4\%$ D-mannose.

What is the relative sweetness of fructose and glucose compared to sucrose ($1.00$)?

Fructose has a relative sweetness of $1.30$, and glucose has a relative sweetness of $0.60\text{ -- }0.80$.

What are the systematic names for palmitic acid and oleic acid?

Palmitic acid is hexadecanoic acid; oleic acid is octadeca-9-enoic acid (or octadeca-cis-9-enoic acid).

What are the three stages of lipid autoxidation?

Initiation (formation of free radicals), Propagation (free radical chain reaction), and Termination (formation of non-radical products).

What are the maximum regulatory limits for single and combined synthetic antioxidants added to foods based on fat content?

A single antioxidant may not exceed $0.01\%$, and combined total antioxidants may not exceed $0.02\%$.

What does the peroxide value test measure in quality control of lipids?

It measures primary oxidation products (hydroperoxides), indicating early-stage oxidation.

What does the p-anisidine value test measure in lipid quality control?

It determines the amount of reactive aldehydes and ketones in the lipid portion, reflecting secondary oxidation.