Chapter 18

(a) Draw the monomer 1,2 -dibromoethene. (b) Draw the polymer formed from this monomer, making it at least three monomer units long.

(a) Draw the monomer 1-butene. (b) Draw the polymer formed from this monomer, making it at least three monomer units long. (Hint: There are no double bonds in the polymer.)

What is a polymer? How does it differ from a monomer?

What is meant by the term macromolecule? Are polymers macromolecules? Explain.

What is a monomer? How does a monomer unit differ from a monomer? Give an example of each.

In the polymer polyethylene, there are no double bonds. Why, then, is it called polyethylene?

Draw a polymer made from the monomer propene. Make your chain at least three monomer units long. What is this polymer called?

What is plastic wrap made of? Draw the free radical derived from the monomer.

This polymer is called silicone and has a noncarbon, "inorganic" backbone of alternating silicon and oxygen atoms: (a) Put a set of parentheses around one monomer unit. (b) Another name for this polymer is polydimethylsiloxane. Explain why it has this name.

Ethylene is a gas, but polyethylene is a solid. How do you explain this?

What is it about the monomers used to make nylon that allows them to be linked into large macromolecules?

What is an amide bond? Show an amide bond between dimethylamine and acetic acid chloride.

Define monosaccharide, disaccharide, and polysaccharide and give an example of each.

How does glucose differ structurally from sucrose?

Which carbohydrate do plants use to help maintain their shape, starch or cellulose? Explain why.

Consider the term carbohydrate. (a) What does it mean literally? (b) Are sugar molecules examples of carbohydrates? Explain.

How are cellulose and starch similar? How do they differ from each other?

When you burn wood, what are you actually burning? What are the combustion products?

In an amino acid, a carbon atom bound directly to the carbonyl carbon of the acid function is called the alpha carbon \((\alpha\) -carbon \() .\) Draw glycine, point out the \(\alpha\) -carbon, and then explain why all 20 amino acids used to build human proteins are called \(\alpha\) -amino acids. Then draw the simplest \(\beta\) -amino acid.

What is the difference between the amino acids glycine and alanine?

What does the expression essential amino acid mean?

What is a peptide linkage?

What is a polypeptide? How does it differ from a protein?

What two peptides are possible from the combination of alanine and glycine? Draw both of them.

What are some of the functions of proteins in living organisms?

How does the sequence of amino acids influence a protein. Can swapping just two amino acids in a very large protein molecule affect its function? Explain by giving an example.

How does DNA serve as the master blueprint for building proteins?

What is the backbone of the DNA polymer made of? Name the parts, and draw two monomer units of the backbone.

What type of bond holds the two strands of a DNA molecule together? What would be wrong with holding the strands together with covalent bonds?

How many DNA bases are there? Name them and give their abbreviations.

The DNA bases always hydrogen-bond in specific pairs. What are those pairs?

What is meant by the term codon? What is the function of a codon?

What do viruses do (on the cellular level) to make you sick?

How might viruses be used for good purposes?

If a functional group A forms a strong covalent bond with a functional group B, (a) Can the monomers \(\mathrm{A}-\mathrm{xx}-\mathrm{B}\) and \(\mathrm{A}-\mathrm{xx}-\mathrm{B}\) form a polymer? (b) Can the monomers \(\mathrm{A}-\mathrm{xx}-\mathrm{A}\) and \(\mathrm{B}-\mathrm{xx}-\mathrm{B}\) form a polymer? For each "yes" answer, draw a short segment of the polymer and indicate the monomer unit.

Nylon fabric owes much of its strength to the formation of hydrogen bonds between the polymer chains. Suppose functional groups \(\bar{A}\) and \(\mathrm{B}\) bond covalently with each other. Draw two different monomers that can form a polymer in which the interchain attractive forces are stronger than those in nylon. (Hint: Each of your monomers can contain all A, all B, or any number of A combined with any number of B.)

Amino acids are a sort of self-contradiction because they contain both a basic group (the \(\mathrm{NH}_{2}\) end) and an acidic group (the \(\mathrm{CO}_{2} \mathrm{H}\) end \()\) in the same molecule. Therefore, it should not surprise you that, when dissolved in water, an amino acid can react with itself to form what is known as a zwitterion. Based on this information, (a) Draw the structural formula for the form of the amino acid alanine you would expect to find in a neutral water solution. What is the net electrical charge on this species? (b) Enough concentrated \(\mathrm{HCl}\) is added to the solution of part (a) to make it strongly acidic. Draw the structural formula for the form of alanine you expect to find in this solution. What is the net charge on the alanine? (c) Enough concentrated \(\mathrm{NaOH}\) is added to the solution of part (a) to make it strongly basic. Draw the structural formula for the form of alanine you expect to find in this solution. What is the net charge on the alanine now?

Protein molecules are usually quite large and yet often water-soluble. They are soluble in water because they can fold themselves into spherical shapes in which the polar (hydrophilic) side chains are on the surface and the nonpolar (hydrophobic) side chains are buried inside the sphere. Of the amino acids Ala, Ser, Phe, lle, Arg, and Asp, (a) Which would you expect to find on the surface of a water-soluble protein? (b) Which would you expect to find buried deep inside the protein structure? (c) Which might be in either location depending on the solution pH?

The artificial sweetener aspartame is a slightly modified dipeptide. Which two amino acids are used to make it?

How many different tripeptides can be made that contain the amino acids alanine, serine, and glycine?

How many different tetrapeptides can be made from two alanines and two glycines?

Carbomer, a polymer used to thicken cosmetic lotions and creams, is a polymer of the monomer known as acrylic acid, shown below. Polymerization occurs due to the \(\mathrm{C}=\mathrm{C}\) double bond as it does for polyethylene. (a) Draw the polymer. (b) When this polymer is exposed to aqueous base, it deprotonates, and the resulting carboxylate anion hydrogen bonds to water very well, causing thickening of the aqueous solution. Draw this polymer in its deprotonated form, and show how water would hydrogen bond to it.

Are \(\alpha\) -glucose and \(\beta\) -glucose properly called isomers of one another? Explain. What would it take to convert one into the other?

Below are shown the hydrogen bonds that form between the \(C-G\) and \(A-T\) pairs of bases. What type of functional groups are involved in hydrogen bonding? Why does the A-T pair form only two hydrogen bonds and not three?

Proteins, like DNA, often adopt a coiled-like structure, known as an a-helix. This helical structure is stabilized by the formation of intramolecular hydrogen bonds between the backbone amino group of one amino acid and the \(\mathrm{C}=\mathrm{O}\) group of another amino acid a bit further down the chain. The amino acid proline is often referred to as a "helix breaker" because when it is part of a protein molecule, the \(\alpha\) -helix begins to unravel at its position. What is so different about this particular amino acid that would cause this disruption of the helix structure and earn it that name?

In the olden days (the \(1970 \mathrm{~s})\), the sequence of amino acids in a protein was determined by running a series of chemical reactions known as the Edman degradation. This technique worked only on short peptide chains, however, and large proteins had to be broken down into small parts in order to be sequenced. One way to chop large proteins into small chains was with enzymes known as proteases. The protease trypsin breaks the amide bond on the \(\mathrm{CO}_{2} \mathrm{H}\) side of arginine and lysine, and the protease chymotrypsin breaks the amide bond on the \(\mathrm{CO}_{2} \mathrm{H}\) side of tyrosine, phenylalanine, and tryptophan. An octapeptide treated with trypsin breaks down to the peptides Ala-Gly-Trp-Gly-Lys and Thr-Val-Lys, and the same octapeptide treated with chymotrypsin breaks down to the peptides Gly-Lys and Thr-Val-Lys-Ala-Gly-Trp. What is the sequence of the octapeptide?