The Molecular Basis of Inheritance

Explain how the sea urchin and salmon data demonstrate both of Chargaff’s rules.

Using Chargaff’s rules, fill in the table with your predictions of the missing percentages of bases, starting with the wheat genome and proceeding through E. coli, human, and ox. Show how you arrived at your answers.

: If Chargaff's rule—that the amount of A equals the amount of T and the amount of C equals the amount of G—is valid, then hypothetically, we could extrapolate this to the combined DNA of all species on Earth (like one huge Earth genome). To see whether the data in the table support this hypothesis, calculate the average percentage for each base in your completed table by averaging the values in each column. Does Chargaff's equivalence rule still hold true?

Given a polynucleotide sequence such as GAATTC. Explain what further information you would need in order to identify which is the 5’ end. (See Figure 16.5)

Griffith was trying to develop a vaccine for S. pneumonia when he was surprised to discover the phenomenon of bacterial transformation. Look at the second and third panel of Figure 16.2. Based on these results, what result was he expecting in the fourth panel? Explain.

What role does complementary base pairing play in the replication of DNA?

Identify two major functions of DNA pol III in DNA replication.

What is the relationship between DNA replication and the S phase of the cell cycle?

If the DNA pol I in a given cell were non-functional, how would that affect the synthesis of a leading strand? In the overview box in Figure 16.17, point out where DNA pol I would normally function on the top leading strand.

Describe the structure of a nucleosome, the basic unit of DNA packing in eukaryotic cells.

What two properties, one structural and one functional, distinguish heterochromatin from euchromatin?

Interphase chromosomes appear to be attached to the nuclear lamina and perhaps also the nuclear matrix. Describe these two structures. See Figure 6.9 and the associated text.

In his work with pneumonia-causing bacteria and mice, Griffith found that

1. the protein coat from pathogenic cells was able to transform non-pathogenic cells.
2. heat-killed pathogenic cells caused pneumonia. 
3. some substances from pathogenic cells were transferred to non-pathogenic cells, making them pathogenic.
4. the polysaccharide coat of bacteria caused pneumonia.

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?

1. Origins of replication occur only at the 5’ end. 
2. Helicases and single-strand binding proteins work at the 5’end. 
3. DNA polymerase can join new nucleotides only to the 3’end of a pre-existing strand, and the strands are antiparallel.
4. DNA ligase works only in the 3’ 5’ direction.

In analyzing the number of different bases in a DNA sample, which would be consistent with the base-pairing rules?

1. A=G
2. A+G=C+T. 
3. A+T=G+C.
4. A=C.

The elongation of the leading strand during DNA synthesis 

1. progress away from the replication fork.
2. occurs in the $3’\to 5’$direction.
3. produces Okazaki fragments.
4. depends on the action of DNA polymerase.

In a nucleosome, the DNA is wrapped around  

1. histones
2. ribosomes
3. polymerase molecules
4. a thymine dimer

E.coli grown on ^{a 15}N medium is transferred to a ¹⁴N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment? 

1. one high-density and one low-density band
2. one intermediate density band
3. one high density and one intermediate-density band
4. one low-density and one intermediate-density band

A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture? 

1. DNA polymerase
2. DNA ligase
3. Okazaki fragments
4. primase

The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage? 

1. nuclease, DNA polymerase, DNA ligase
2. telomerase, primase, DNA polymerase
3. telomerase, helicase, single-stranded binding protein
4. DNA ligase, replication fork proteins, adenylyl cyclase

Although the proteins that cause the E.coli chromosome to the coil are not histones, what property would you expect them to share with histones, given their ability to bind to DNA (see Figure 5.14)?

Some bacteria may be able to respond to environmental stress by increasing the rate at which mutations occur during cell division. How might this be accomplished? Might there be an evolutionary advantage to this ability? Explain. 

Model building can be an important part of the scientific process. The illustration shown above is a computer-generated model of a DNA replication complex. The parental and newly synthesized DNA strands are colour coded differently, as are each of the following three proteins DNA pol III, the sliding clamp, and single-stranded binding protein. 

1. Using what you've learned in this chapter to clarify this model, label each DNA strand and protein.
2.  Draw an arrow to indicate the overall direction of DNA replication.

The continuity of life is based on heritable information in the form of DNA, and structure and function are correlated at all levels of biological organization. In a short essay (100-150words), describe how the structure of DNA is correlated with its role as the molecular basis of inheritance.

This image shows DNA (grey) interacting with a computer-generated model of a TAL protein (multicolored), one of a family of proteins found only in a species of bacterium Xanthomonas. The bacterium uses proteins like this once to find specific gene sequences in cells of the organisms it infects, such as tomatoes, rice and citrus fruits. Given what you know about DNA structure and considering the image above, discuss how the TAL protein's structure suggests that it functions.