1. Chromosome Structure and
Benjamin A. Pierce
GENETICS
A Conceptual Approach
FIFTH EDITION
CHAPTER 11
Chromosome Structure and
Organelle DNA
© 2014 W. H. Freeman and Company

2. Large Amounts of DNA Are Packed into a Cell
DNA must be tightly packed to fit in small spaces (Fig. 11.1)
Supercoiling
Positive supercoiling, Figure 11.2 (b)
Negative supercoiling, Figure 11.2 (c)
Topoisomerase: The enzyme responsible for adding and removing turns in the coil.

3. Figure 11.2 Supercoiled DNA is overwound or underwound, causing it to twist on itself.

4. The Bacterial Chromosome
Most bacterial genomes have a single circular DNA molecule

5. Figure 11.3 Bacterial DNA is highly folded into a series of twisted loops.

6. Organelle DNA Has Unique Characteristics
Mitochondria and chloroplasts contain DNA
Encodes some polypeptides used by the organelle, rRNA, and some tRNAs

8. Organelle DNA Has Unique Characteristics
Endosymbiotic theory: proposes that mitochondria and chloroplasts were once free-living bacteria
Both organelles are similar to eubacteria, and DNA sequences found within them are also similar to eubacteria

10. Organelle DNA Has Unique Characteristics
Uniparental inheritance of organelle-encoded traits
Animal mtDNA inherited almost exclusively from female parent
Replicative segregation
Each cell has hundreds to thousands of organelles
Heteroplasmic cells: organelles segregate randomly

13. Traits Encoded by mtDNA
Petite mutations in yeast
Neurospora mutations
Human diseases: MERRF, LHON, NARP, KSS, CEOP
In plants, cytoplasmic male sterility

15. The Mitochondrial Genome
Mitochondrial genomes are small and vary greatly (Table 11.4)
Human mtDNA: circular, 16,569 base pairs; encodes two rRNAs, 22 tRNAs, and 13 proteins (Fig )
Yeast mtDNA: five times as large as human; encodes 2 rRNAs, 25 tRNAs, and 16 polypeptides (Fig )
Flowering-plant mtDNA: extensive size variation (Fig )

19. The Evolution of Mitochondrial DNA
High mutation rate in vertebrate mtDNA
Number of genes and organization remains relatively constant
Most copies of mtDNA identical

20. Damage to Mitochondrial DNA is Associated with Aging
Many human genetic diseases associated with mtDNA appear in middle age or later
Oxidative phosphorylation capacity declines with age; those with mutations in mtDNA start life with decreased oxidative phosphorylation capacity
Mechanism of age-related mtDNA damage unknown

21. The Chloroplast Genome
Many traits associated with chloroplasts exhibit cytoplasmic inheritance
Chloroplasts shown to have their own DNA in 1963
Sequence very similar to DNA sequences found in cyanobacteria

24. Large Amounts of DNA Are Packed
into a Eukaryotic Cell
Chromatin structure (Table 11.1)
Euchromatin
Heterochromatin
Histone proteins

26. Concept Check 2
Neutralizing their positive charges would have which effect on the histone proteins?
They would bind the DNA tighter.
They would separate from the DNA.
They would no longer be attracted to each other.
They would cause supercoiling of the DNA.

27. Concept Check 2
Neutralizing their positive charges would have which effect on the histone proteins?
They would bind the DNA tighter.
They would separate from the DNA.
They would no longer be attracted to each other.
They would cause supercoiling of the DNA.

28. Large Amounts of DNA Are Packed
into a Cell
Chromatin structure
The nucleosome
Chromatosome
Linker DNA
High-order chromatin structure
30 nm fiber
300 nm loops
250 nm wide fiber

29. Figure 11.4 Chromatin has a highly complex structure with several levels of organization.

30. Figure 11.5 The nucleosome is the fundamental repeating unit of chromatin.

31. Large Amounts of DNA Are Packed
into a Cell
Chromatin structure
Changes in chromatin structure
Polytene chromosome: created by repeated rounds of DNA replication with no cell division (Fig. 11.6)
Chromosomal puffs
DNase I sensitivity: correlates with gene activity (Fig. 11.7)
Epigenetic changes: methylation; capable of being reversed and often due to environmental factors (Fig. 11.8)

32. Figure Chromosomal puffs are regions of relaxed chromatin where active transcription is taking place.

33. Figure Chromosomal puffs are regions of relaxed chromatin where active transcription is taking place.

34. Eukaryotic Chromosomes Possess Centromeres and Telomeres
Centromere structure: constricted region of a chromosome where spindle fibers attach
Figure 11.9
Telomere structure: ends of chromosomes; provide a means to replicate the ends of linear chromosomes

37. Figure DNA at the ends of eukaryotic chromosomes consists of telometric sequences. (a) The G-rich strand at the telomere is longer than the C-rich strand. (b) In mammalian cells, the G-rich strand folds over and pairs with a short stretch of DNA to form a t-loop.

38. Eukaryotic DNA Contains Several Classes of Sequence Variation
Organisms differ in amount of DNA per cell (C value)
Denaturation
Melting temperature
Renaturation
Types of DNA sequences in eukaryotes:
Unique sequence DNA
Gene family: Similar but not identical copies of unique DNA sequences that arose through duplication of an existing gene

40. Eukaryotic DNA Contains Several Classes of Sequence Variation
Types of DNA sequences in eukaryotes:
Repetitive DNA
Moderately repetitive DNA: 150 ~ 300 bp long
Tandem repeat sequences
Interspersed repeat sequences
Short interspersed elements: SINEs: Alu element
Long interspersed elements: LINEs

41. Eukaryotic DNA Contains Several Classes of Sequence Variation
Types of DNA sequences in eukaryotes:
Repetitive DNA
Highly repetitive DNA: less than 10 bp long
Microsatellite DNA