1. Chapter 9 DNA and the Molecular Structure of Chromosomes
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2. Chapter Outline Functions of the Genetic Material
Proof That Genetic Information Is Stored in DNA
The Structures of DNA and RNA
Chromosome Structure in Prokaryotes and Viruses
Chromosome Structure in Eukaryotes
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3. Functions of the Genetic Material
The genetic material must replicate, control the growth and development of the organism, and allow the organism to adapt to changes in the environment.
Genotypic Function: Replication
Phenotypic Function: Gene Expression
Evolutionary Function: Mutation (Gene modifications)
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4. Chromosomes Genes are located on chromosomes.
Chromosomes contain proteins and nucleic acids.
The nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
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5. Proof that Genetic Information is Stored in DNA
In most organisms, the genetic information is encoded in DNA. In some viruses, RNA Is the genetic material. Proteins?
Chromosomes-nuclear fraction-DNA
Cytosol-proteins-RNA
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6. DNA Mediates Transformation
Griffith’s experiment
(in vivo)
Mice
Streptococcus pneumoniae
--type IIIS (virulent)
--type IIR (avirulent)
“Transforming principles”
Sia and Dawson’s experiment
(in vitro)
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7. DNA Mediates Transformation
Griffith’s experiment
(in vivo)
Mice
Streptococcus pneumoniae
--type IIIS (virulent)
--type IIR (avirulent)
“Transforming principles”
Sia and Dawson’s experiment
(in vitro)
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8. Avery, MacLeod and McCarty’s experiment (in vitro)
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9. The Genetic Material of Bacteriophage T2 is DNA
Hesley-Chase’s experiment (in vitro) > Transfection ( Infection)
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10. The Genetic Material of Tobacco Mosaic Virus (TMV) is RNA
Retroviruses ( RNA------> DNA)
(in vitro)
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11. The genetic information of most living organisms is stored in deoxyribonucleic acid (DNA).
In some viruses, the genetic information is present in ribonucleic acid (RNA).
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12. The Structures of DNA and RNA
DNA is double-stranded,
with adenine paired with thymine and guanine paired with cytosine.
RNA is usually single-stranded and contains uracil in place of thymine.
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13. © John Wiley & Sons, Inc.

14. Deoxyribonucleotides
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15. Structure of a Polynucleotide Chain
DNA composition: [A]=[T] ; [C]=[G]
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16. Chargaff’s Rules © John Wiley & Sons, Inc. %A = %T and %G = %C.
%A ~ %T and %G ~ %C are valid for each of the two DNA strands
methyltransferases methylate and/or deaminate
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17. Structure of a Polynucleotide Chain
DNA composition: [A]=[T] ; [C]=[G]
X-ray Diffraction Pattern of DNA
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18. The Double Helix Phosphodiester [C-O-P-O-C] Polynucleotide chain
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19. © John Wiley & Sons, Inc.

20. Complementary and Antiparallel
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21. © John Wiley & Sons, Inc.

22. DNA Structure Complementary Base Pairs (A with T, G with C)
Anti-parallel Strands
Right-handed double helix (B-DNA)
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23. DNA replication DNA-RNA duplexes Elevated content of C:G
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24. DNA Structure: Supercoils
Unique structure of a DNA molecule
Is produced after one or both strand
of DNA are cleaved
DNA will rotate or twist
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25. © John Wiley & Sons, Inc.

26. DNA usually exists as a double helix, with the two strands held together by hydrogen bonds between the complementary base pairs: adenine paired with thymine and guanine paired with cytosine.
The complementarity of the two strands of a double helix makes DNA uniquely suited to store and transmit genetic information.
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27. The two strands of a DNA double helix have opposite chemical polarity.
RNA usually exists as a single-stranded molecule containing uracil instead of thymine.
The functional DNA molecules in cells are negatively supercoiled.
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28. Chromosome Structure in Prokaryotes and Viruses
The DNA molecules of prokaryotes and viruses (RNA?) are organized into negatively supercoiled domains.
Prokaryotes are monoploid and are part of the nucleoids.
Most viruses and prokaryotes have a single set of genes stored in a single chromosome, which contains a single molecule of nucleic acid.
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29. The E. coli Chromosome
Folded genome: is the functional state of a isolated bacterial chromosome
Mild conditions
(no ionic detergents)
1M salt
Polyamines(-)
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30. Model of E. coli Chromosome
folded=coiled
protein
Nicked=single strand
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31. The DNA molecules in prokaryotic and viral chromosomes are organized into negatively supercoiled domains (loops).
Bacterial chromosomes contain circular molecules of DNA segregated into 50 to 100 domains.
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32. Chromosome Structure in Eukaryotes
Eukaryotic chromosomes contain huge molecules of DNA that are highly condensed during mitosis and meiosis.
The centromeres and telomeres of eukaryotic chromosomes have unique structures.
Each chromosome is unineme (Theory)
Each chromosome contains a single large double
helix (strand) of DNA molecule
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33. Chromatin Composition
Histones:
H1, H2a, H2b, H3, H4
(protamines in sperm)
Structural
(+)
Nonhistone proteins:
Non structural
Regulation
Nucleosomes: DNA + histones
except H1
(-)
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34. Nucleosomes
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35. Methyl groups Acetyl groups
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36. Structure of the Nucleosome Core
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37. Human Metaphase Chromosomes
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38. The 30 nm Fiber
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39. Micrococcal nuclease releases individual nucleosomes from chromatin as particles.
Intermediate
Structures?
Endonucleases

40. High salts H1 The path of nucleosomes in the chromatin fiber
Both the 10 nm fiber and
the 30 nm fiber were first seen by electron microscopy.
Higher packing of the
nucleosomes into “inactive
heterochromatin” may involve
Non-histone proteins.
The path of nucleosomes in the chromatin fiber
High salts H1
Figure: 20.17
Title:
Chromatin is a thread of nucleosomes
Caption:
The 10 nm fiber in partially unwound state can be seen to consist of a string of nucleosomes. Photograph kindly provided by Barbara Hamkalo.

41. DNA Around a Scaffold of Non-histone Proteins
heterochromatin
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42. Levels of DNA Packaging
2-nm double-stranded DNA molecule
11-nm nucleosomes
30 nm chromatin fiber
Organization around a central scaffold H1
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43. DNA repeats
Centromeric: specific repeated regions (non-coding DNA sequences=
heterochromatin) of chromosome for attachment of spindle microtubules
( 5000 to bp).
Satellite sequences:
--Tandemly repeating
--Non-coding DNA
Alpha ( unit repeat as base pair)
Beta
Satellite
Satellite
Satellite
Most satellite DNA is localized to the telomeric or
the centromeric region of the chromosome
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44. Telomeres Functions of telomeres
Protect the ends of linear DNA molecules from deoxyribonucleases
Prevent fusion of chromosomes
Facilitate complete replication of the ends of linear DNA molecules
Most telomeres contain repetitive sequences and a distinct structure.
© John Wiley & Sons, Inc.

45. Telomere Structure -TTAGGG -500 to 3000 repeats -G-rich overhang
-T-loop (D-loop)
-Telomeres specific
Proteins ( protection)
POT1
TRF1 and 2
TIN2 and TPP1
© John Wiley & Sons, Inc.

46. Repeated DNA Sequences
Eukaryotic chromosomes contain repetitive DNA ( 15 to 80 %), Human (~50%)
--Satellite bands (tandem repeats)
--Transposable genetic elements (transposon)
---Retrotransposon, ---DNA transposon
--Genomic island (G+C)
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47. The heritable factors that Mendel studied are now known as:
a) Nucleic acids
b) Amino acids
c) Genes
d) Unit factors
e) Peptides
The building blocks of genes are:
a) Proteins
b) Amino acids
c) Nucleic acids
d) Lipids
e) Carbohydrates
Different forms of the same gene are known as:
a) Peptides
b) Amino acids
c) Proteins
d) Alleles
e) Gene differences

48. The main components of a membrane in a cell are:
a) Lipids
b) Proteins
c) Carbohydrates
d) Lipids and Proteins
e) Lipids and Carbohydrates
Prokaryotes can be characterized by:
1.The lack of a true nucleus or compartment in which
the DNA is located
2. The unique cell walls composed of murein
3. The lack of mitochondria
4. All of these
a) 1
b) 2
c) 3
d) 4
e) 1 and 3

49. Which large organic molecules are essential chromosome components?
a) Lipids and proteins
b) Proteins and nucleic acids
c) Nucleic acids and polysaccharides
d) Proteins and polysaccharides
Which of the following is a type of nucleic acid?
a) DNA
b) RNA
c) DNAse
d) RNAse
e) DNA and RNA
In Sia and Dawson's 1931 experiment:
a) Mice were required to demonstrate the transforming principle
b) Used serum to precipitate IIIS cells from a mixture of heat-killed IIIS and living IIR cells
c) They showed that mice play no direct role in the transforming principle
d) Heat-killed IIR cells mixed with living IIIS cells gave rise to IIR colonies
e) None of these