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Chapter 28: Problem 70

Briefly describe each of the following ideas, phenomena, or methods: (a) saponification; (b) chiral carbon atom; (c) racemic mixture; (d) denaturation of a protein.

Short Answer

Expert verified
Briefly, (a) Saponification is the hydrolysis of an ester to form an alcohol and soap, (b) a chiral carbon atom is a carbon atom attached to four different types/groups of atoms leading to chirality in molecules, (c) a Racemic mixture is a mixture containing equal amounts of left and right-handed enantiomers, and (d) Denaturation of a protein refers to the alteration of a protein's structure, leading to the loss of its function.

Step by step solution

01

Define Saponification

Saponification is the hydrolysis of an ester under basic conditions to form an alcohol and a soap (which is basically a salt). Thus, a typical reaction involving a fat might be expressed as: Fat + Base → Glycerol + Soap.
02

Define Chiral Carbon Atom

A chiral carbon atom is a carbon atom bound to four different types of atoms or groups of atoms. This leads to molecules that cannot be superimposed on their mirror images, exhibiting a property called chirality.
03

Define Racemic Mixture

A racemic mixture, or racemate, is a mixture of equal amounts of left and right-handed enantiomers. Enantiomers are molecules that are mirror images of each other but cannot be superimposed.
04

Define Denaturation of a Protein

Denaturation of a protein involves the alteration of the protein's structure due to application of external stress or compounds, such as strong acid or base, high temperature, organic solvents, and so on. The protein loses its structural conformation and hence its functional properties.

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Most popular questions from this chapter

A molecule in which the energy of metabolism is stored is (a) glucose; (b) DNA; (c) RNA; (d) glycerol; (e) ATP.

The coagulation of egg whites by boiling is an example of (a) saponification; (b) inversion of a sugar; (c) hydrolysis of a protein; (d) denaturation of a protein; (e) condensation of amino acids.

Refer to a typical Escherichia coli bacterium. This is a cylindrical cell about \(2 \mu\) m long and \(1 \mu\)m in diameter, weighing about \(2 \times 10^{-12}\)g and containing about \(80 \%\) water by volume. The cell is about \(15 \%\) protein by mass with \(90 \%\) of the protein in the cytoplasm. Assuming an average molecular mass of \(3 \times 10^{4}\) u, how many protein molecules are present in the cytoplasm?

Write the formulas of the species expected if the amino acid phenylalanine is maintained in (a) \(1.0 \mathrm{M}\) HCl; (b) \(1.0 \mathrm{M} \mathrm{NaOH} ;\) (c) a buffer solution with \(\mathrm{pH}=5.7\).

If \(\mathrm{D}-(+)\) -glyceraldehyde is treated with \(\mathrm{HCN}\) in aqueous solution under basic conditions for three days at room temperature, cyanohydrins are formed (see Chapter 27). The cyanohydrins are not isolated, but are hydrolyzed to hydroxyacids in the same reaction mixture using dilute sulfuric acid. In this process, a new stereocenter is formed in the molecule. The products are diastereomers, formed in unequal amounts, and separable from each other by recrystallization because of their different physical properties, including solubilities. The trihydroxybutanoic acids are separated and then oxidized to tartaric acid with dilute nitric acid, which oxidizes only the primary alcohol group. (a) Ignoring stereochemistry, draw the reaction sequence for the transformations described above and hence deduce the structure of tartaric acid. (b) Starting from the Fischer projection of \(\mathrm{D}-(+)-\) glyceraldehyde and using the reaction scheme from part (a), draw Fischer projections of the two trihydroxybutanoic acids formed and designate the chiral centers as \(R\) or \(S\). (c) Starting from the Fischer projection of \(\mathrm{D}-(+)-\) glyceraldehyde and using the reaction scheme from part (a), draw Fischer projections of the two forms of tartaric acid formed and designate the chiral centers as \(R\) or \(S\). (d) One form of tartaric acid obtained is optically active, rotating the plane of polarized light in a negative sense \((-) .\) The other isomer formed, called meso-tartaric acid, is not optically active. Explain why the other isomer is not optically active. Draw the dashed-wedged line structure that corresponds to the Fischer projection of meso-tartaric acid. Can you describe how the two halves of the molecule are related? Using Fischer projections, write equations for the conversion of \(L-(-)-\) glyceraldehyde to tartaric acid. Show clearly the stereochemistry of the tartaric acids that are formed, and indicate whether you expect them to be optically active.
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