Chapter 23

What is a lipid? What roles do lipids play in living organisms?

What effect do double bonds have within the hydrocarbon chain of a fatty acid?

Explain the difference, in terms of both structure and properties, between a saturated fat and an unsaturated fat.

Describe the basic structure of phospholipids and glycolipids. What functions do these lipids have in living organisms?

What is a steroid? List some functions of steroids.

What are carbohydrates? What role do they play in living organisms?

How do monosaccharides and disaccharides differ? Aldoses and ketoses?

How do simple and complex carbohydrates differ?

How do cellulose, starch, and glycogen differ? Describe the function of each.

Describe the basic structure of an amino acid. How are amino acids linked together to form proteins?

Draw the structure of a neutral amino acid and its dipolar ion.

Draw the structure of any two amino acids, showing how they link together to form a dipeptide.

Why is protein structure important?

How do fibrous proteins and globular proteins differ?

Describe the various levels of protein structure (primary, secondary, tertiary, and quaternary).

Describe the secondary structures known as a-helix and b-pleated sheet.

What is the function of nucleic acids in living organisms?

What is the general structure of a nucleic acid?

The bases in nucleic acids are complementary. What does this mean?

What is a codon? A gene? A chromosome?

Do most cells contain complete copies of an organism’s DNA? Do most cells express all of the genes contained in their DNA?

Explain the mechanism by which DNA is replicated.

Explain the mechanism by which proteins are synthesized from the information contained within DNA.

Draw structures showing the reaction of glycerol with myristic acid to form the triglyceride trimyristin. Would you expect this triglyceride to be a fat or an oil?

Draw structures for the straight-chain and ring forms of fructose.

How many different tripeptides can form from serine, glycine, and cysteine? List the amino acid sequence of each one. MISSED THIS? Read Section 23.4

How many dipeptides can form from leucine and serine? List the amino acid sequence for each one.

Draw the reaction by which valine and asparagine form a peptide bond.

Draw a structure for each tetrapeptide. a. Ser-Ala-Leu-Cys b. Gln-Met-Cys-Gly c. Gly-Cys-Met-Gln

An amino acid on a protein strand forms a hydrogen bond to another amino acid that is four amino acid units away. The next amino acid on the chain does the same, hydrogen-bonding to an amino acid that is four amino acids away from it. This pattern repeats itself over a significant part of the protein chain. The resulting pattern in the protein is an example of which kind of structure? (primary, secondary, tertiary, or quaternary)

A dimeric protein is composed of two individual chains of amino acids. The way these two chains fit together is an example of which kind of structure? (primary, secondary, tertiary, or quaternary)

Draw the structures of the two purine bases in nucleic acids. MISSED THIS? Read Section 23.6

Draw the structures of the three pyrimidine bases in nucleic acids.

A monomeric protein contains 154 amino acids. How many codons code for these amino acids? How many nucleotides? MISSED THIS? Read Sections 23.6,23.7

A dimeric protein contains 142 amino acids in one strand and 148 in the other. How many codons code for these amino acids? How many nucleotides?

Determine the class of biochemical compound that contains each type of linkage. a. peptide bonds b. glycosidic linkage c. ester linkage

Name the type of polymer associated with each monomer. a. nucleotide b. amino acid c. saccharide

What is the difference between a codon and a nucleotide? A codon and a gene?

What is the difference between a fatty acid and a triglyceride? A triglyceride and a phospholipid?

Draw each molecule and identify the chiral centers within them. a. ribose b. galactose c. 5 -deoxyribose (Hint: The 5 indicates that the oxygen is removed from the 5 th carbon.

Eukaryotic DNA is equipped with special ends called telomers. Telomers are made up of hexanucleotide sequences that repeat at the ends of the DNA. For example, human DNA features repeating AGGGTT sequences. Functionally, telomers protect the ends of chromosomes from being treated as a broken piece of DNA in need of repair. Interestingly, telomers are cut off each time the DNA is replicated, indicating a possible cellular clock that allows only a certain number of cellular replications. Telomerase is the enzyme that catalyzes the synthesis of telomers. Telomerase is present in limited quantities within certain cells such as fetal tissue, adult male germ cells, and stem cells. It is also found in over \(85 \%\) of tumor cells. Researchers speculate that the telomerase activity may be linked to cancer. Propose an explanation for why telomerase activity could be associated with cancer and speculate on ways in which cancer treatments in the future may capitalize on research on this enzyme.

Write the major equilibrium that is established in a solution of glycine at \(\mathrm{pH}=2\) and at \(\mathrm{pH}=10 .\) The \(\mathrm{p} K_{\mathrm{a}}\) of the COOH group is \(2.3,\) and the \(\mathrm{p} K_{\mathrm{a}}\) of the \(\mathrm{NH}_{3}{\underline{\phantom{xx}}}^{+}\) group is 9.6 . Determine the relative concentrations of each member of the relevant conjugate acid-base pair at \(\mathrm{pH}=2\) and \(\mathrm{pH}=10 .\) Calculate the \(\mathrm{pH}\) at which glycine is neutral.

How many different tetrapeptides can form from four different amino acids?

The genetic code is random, which means that a particular codon could have coded for a different amino acid. The genetic code is also nearly universal, meaning that it is the same code in nearly all organisms (and in the few where it differs, it does so only slightly). If scientists ever find life on another planet, they will be curious to know its genetic code. What would a completely different genetic code indicate about the origin of the life-forms? What would a genetic code identical to terrestrial life indicate?

Compare and contrast cornstarch with cotton balls, which are made of almost pure cellulose. Include at least three ways in which they are similar and three ways in which they are different. Mention aspects you have observed in daily life and aspects on the molecular scale.

Describe how a common object or toy (e.g., a train, building blocks, or beads on a string) could represent a protein. Describe how amino acids and peptide bonds are represented in your analogy. Also describe the representation of primary, secondary, tertiary, and quaternary structure in your analogy.

Working individually, draw an accurate structure for one of the following (don't tell other group members which one you choose): a monosaccharide, a disaccharide, a polysaccharide, a fatty acid, a triglyceride, a steroid, an amino acid, or a dipeptide. After each group member has completed drawing a structure, take turns showing your structure to the group. How many group members can correctly identify the structure you drew? How many of your group members' structures can you correctly identify?