1. Chapter 16 188 The Molecular Basis of Inheritance
DNA is the molecule of inheritance.
In 1868, Friedrich Miescher, a Swiss biochemist, discovered the cell nucleus contained protein and deoxyribonucleic acid, which he called nuclein.
In 1914, Robert Feulgen, a German chemist, devised a method of staining nucleic acid. The solution was later called Feulgen stain.

2. Fig. 16-1
Figure 16.1 How was the structure of DNA determined?

3. 188
In 1928, Fred Griffith, an English pathologist, discovered the process of transformation between S-type (S: smooth; virulent) and R-type (R: rough; avirulent) pneumococci (Streptococcus pneumoniae).
In 1944, O.T. Avery, Colin MacLeod, and Maclyn McCarty of the Rockefeller Institute, discovered the so-called transforming factor was DNA.

4. Fig. 16-2 EXPERIMENT RESULTS
Mixture of heat-killed S cells and living R cells
EXPERIMENT
Living S cells (control)
Living R cells (control)
Heat-killed S cells (control)
RESULTS
Figure 16.2 Can a genetic trait be transferred between different bacterial strains?
Mouse dies
Mouse healthy
Mouse healthy
Mouse dies
Living S cells

5. 188
DNA as the genetic material was confirmed by Alfred D. Hershey and Martha Chase of the Carnegie Laboratory of Genetics.

6. Fig. 16-3 Phage head Tail sheath Tail fiber DNA 100 nm Bacterial cell
Figure 16.3 Viruses infecting a bacterial cell
DNA
100 nm
Bacterial
cell

7. Fig. 16-4-1 EXPERIMENT Radioactive protein Phage Bacterial cell DNA
Batch 1: radioactive sulfur (35S)
DNA
Radioactive DNA
Figure 16.4 Is protein or DNA the genetic material of phage T2?
Batch 2: radioactive phosphorus (32P)

8. Fig. 16-4-2 EXPERIMENT Empty protein shell Radioactive protein Phage
Bacterial cell
Batch 1: radioactive sulfur (35S)
DNA
Phage DNA
Radioactive DNA
Figure 16.4 Is protein or DNA the genetic material of phage T2?
Batch 2: radioactive phosphorus (32P)

9. Fig. 16-4-3 EXPERIMENT Empty protein shell
Radioactivity (phage protein) in liquid
Radioactive protein
Phage
Bacterial cell
Batch 1: radioactive sulfur (35S)
DNA
Phage DNA
Centrifuge
Radioactive DNA
Pellet (bacterial cells and contents)
Figure 16.4 Is protein or DNA the genetic material of phage T2?
Batch 2: radioactive phosphorus (32P)
Centrifuge
Radioactivity (phage DNA) in pellet
Pellet

10.
Additional evidence that DNA is the genetic material is based on the discovery of the doubling of DNA in eukaryotes prior to mitosis, and that gametes of the same organism have half the amount of DNA as the diploid cells. Chargaff’s rules: the amount of adenine approximately equaled the amount of thymines, and the amount of guanines approximately equaled the amount of cytosines.

11. 189
In 1953, James Watson and Francis Crick proposed the double helix molecular model for DNA.
Nucleotide: Phosphate-Sugar-Nitrogenous base
Nitrogenous bases:
Adenine (A)
Purines
Guanine (G)
Cytosine (C)
Pyrimidines Thymine (T)
RNA contains uracil (U) instead of thymine.

12. Fig. 16-8 Adenine (A) Thymine (T) Guanine (G) Cytosine (C)
Figure 16.8 Base pairing in DNA
Guanine (G)
Cytosine (C)

13. Sugar–phosphate backbone 5 end Sugar (deoxyribose) 3 end
Fig. 16-5
Sugar–phosphate backbone  end
Nitrogenous bases
Thymine (T)
Adenine (A)
Figure 16.5 The structure of a DNA strand
Cytosine (C)
Phosphate
DNA nucleotide
Sugar (deoxyribose)  end
Guanine (G)

14. Fig. 16-7a 5 end Hydrogen bond 3 end 1 nm 3.4 nm 3 end 0.34 nm
Figure 16.7 The double helix
3 end
0.34 nm
5 end
(a) Key features of DNA structure
(b) Partial chemical structure

15. Table 16-1

16. 190 DNA Replication On 3’ to 5’ strand:
1. DNA helicase untwists and breaks the
hydrogen bonds.
2. Primase synthesizes RNA primer
(about 10 bases long).
4. DNA polymerase III
5. DNA polymerase I erases RNA primer
and replaces it with DNA nucleotides.
This new strand of DNA that runs from 5’ to 3’ direction is called a leading strand.

17. Nucleoside triphosphate
Fig
New strand 5 end
Template strand 3 end
5 end
3 end
Sugar A T A T
Base
Phosphate C G C G G C G C
DNA polymerase
3 end A T A
Figure Incorporation of a nucleotide into a DNA strand T
3 end C
Pyrophosphate C
Nucleoside triphosphate
5 end
5 end

18. 190 On 5’ to 3’ strand: 1. DNA helicase
2. RNA primer synthesized by primase
3. DNA polymerase III
4. DNA polymerase I (eraser enzyme) erases
RNA primer and replaces it with DNA
nucleotides to make Okazaki fragment (about
1,000 to 2,000 bases long)
5. DNA ligase joins the Okazaki fragments to
form a lagging strand

19. Fig. 16-UN3 DNA pol III synthesizes leading strand continuously3 5
Parental DNA
DNA pol III starts DNA synthesis at 3 end of primer, continues in 5  3 direction 5 3 5
Lagging strand synthesized in short Okazaki fragments, later joined by DNA ligase
Primase synthesizes a short RNA primer 3 5

20. Fig. 16-9-3 A T A T A T A T C G C G C G C G T A T A T A T A A T A T A
(a) Parent molecule
(b) Separation of strands
(c) “Daughter” DNA molecules, each consisting of one parental strand and one new strand
Figure 16.9 A model for DNA replication: the basic concept

21. Fig. 16-10 (a) Conservative model (b) Semiconserva- tive model
First replication
Second replication
Parent cell
(a) Conservative model
(b) Semiconserva- tive model
Figure Three alternative models of DNA replication
(c) Dispersive model

22. Bacteria cultured in medium containing 15N 2
Fig a
EXPERIMENT 1
Bacteria cultured in medium containing 15N 2
Bacteria transferred to medium containing 14N
RESULTS 3
DNA sample centrifuged after 20 min (after first application) 4
DNA sample centrifuged after 20 min (after second replication)
Less dense
Figure Does DNA replication follow the conservative, semiconservative, or dispersive model?
More dense

23. Semiconservative model
Fig b
CONCLUSION
First replication
Second replication
Conservative model
Semiconservative model
Figure Does DNA replication follow the conservative, semiconservative, or dispersive model?
Dispersive model

24. 193 Differences in DNA synthesis: Prokaryotes Eukaryotes
Rate of synthesis: base pairs base pairs
per second per second
Initial sites: one many

25. 194
Telomeres are the special nucleotide sequences at the ends of DNA. They do not contain genes. They consist of repeated sequence of typically TTAGGG in humans, which repeats from 100 to 1,000 times.
Telomere protects the organism’s genes from being eroded through successive DNA replications. The telomere and its associated proteins prevent the ends from activating the cells system for monitoring DNA damage.

26. Fig
Figure Telomeres
1 µm

27. 191
Eukaryotes produce telomerase, a special enzyme that contains a molecule of RNA along its protein, to lengthen the telomeres.
The RNA of the telomerase has a sequence which serves as the template for new telomere segments. Telomerase is present in germ line cells that give rise to gametes. The enzyme produces long telomeres in germ cells and in the newborn. The enzyme is also found in cancerous cells. It contributes to the immortality of the cells.

28. Chromatin is organized into fibers 10-nm fiber
195
Chromatin is organized into fibers
10-nm fiber
DNA winds around histones to form nucleosome “beads”
Nucleosomes are strung together like beads on a string by linker DNA
30-nm fiber
Interactions between nucleosomes cause the thin fiber to coil or fold into this thicker fiber
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29. Fig. 16-21a DNA, the double helix Histones
Nucleosome
(10 nm in diameter)
DNA double helix (2 nm in diameter) H1
Histone tail
Histones
Figure 16.21a Chromatin packing in a eukaryotic chromosome
DNA, the double helix
Histones
Nucleosomes, or “beads on a string” (10-nm fiber)

30. Fig. 16-21b 30-nm fiber Looped domains (300-nm fiber)
Chromatid
(700 nm)
30-nm fiber
Loops
Scaffold
300-nm fiber
Figure 16.21b Chromatin packing in a eukaryotic chromosome
Replicated chromosome (1,400 nm)
30-nm fiber
Looped domains (300-nm fiber)
Metaphase chromosome

31. 195 300-nm fiber Metaphase chromosome
The 30-nm fiber forms looped domains that attach to proteins
Metaphase chromosome
The looped domains coil further
The width of a chromatid is 700 nm
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32. Loosely packed chromatin is called euchromatin
195
Most chromatin is loosely packed in the nucleus during interphase and condenses prior to mitosis
Loosely packed chromatin is called euchromatin
During interphase a few regions of chromatin (centromeres and telomeres) are highly condensed into heterochromatin
Dense packing of the heterochromatin makes it difficult for the cell to express genetic information coded in these regions
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

33. Histones can undergo chemical modifications that result in changes in chromatin organization
For example, phosphorylation of a specific amino acid on a histone tail affects chromosomal behavior during meiosis
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

34. 195 Alternative Forms of DNA: Right-handed DNA:
A-DNA has 11 base pairs per turn.
B-DNA (the classic DNA proposed by Watson and Crick) has 10 base pairs per turn.
C-DNA has 9 base pairs per turn.
Left-handed DNA:
Z-DNA has 12 base pairs per turn.
The biological significance of these different
forms of DNA is not fully understood.