chapter 9 dna and the molecular structure of chromosomes © john wiley & sons, inc
TRANSCRIPT
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Chapter 9
DNA and the Molecular Structure of Chromosomes
© John Wiley & Sons, Inc.
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Chapter Outline
Functions of the Genetic MaterialProof That Genetic Information Is
Stored in DNAThe Structures of DNA and RNAChromosome Structure in Prokaryotes
and VirusesChromosome Structure in Eukaryotes
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Functions of the Genetic MaterialThe genetic material must
replicate, control the growth and development of the organism,
and allow the organism to adapt to changes in the environment.
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Genotypic Function: ReplicationPhenotypic Function: Gene ExpressionEvolutionary Function: Mutation (Gene
modifications)
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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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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?
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Chromosomes-nuclear fraction-DNA
Cytosol-proteins-RNA
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DNA Mediates Transformation
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Griffith’s experiment (in vivo) MiceStreptococcus pneumoniae--type IIIS (virulent)--type IIR (avirulent)
“Transforming principles”
Sia and Dawson’s experiment (in vitro)
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DNA Mediates Transformation
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Griffith’s experiment (in vivo) MiceStreptococcus pneumoniae--type IIIS (virulent)--type IIR (avirulent)
“Transforming principles”
Sia and Dawson’s experiment (in vitro)
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Avery, MacLeod and McCarty’s experiment (in vitro)
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The Genetic Material of Bacteriophage T2 is DNA
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Hesley-Chase’s experiment (in vitro)-----------> Transfection ( Infection)
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The Genetic Material of Tobacco Mosaic Virus (TMV) is RNA
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Retroviruses ( RNA------> DNA)
(in vitro)
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• 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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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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Deoxyribonucleotides
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Structure of a Polynucleotide Chain
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DNA composition: [A]=[T] ; [C]=[G]
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Chargaff’s Rules
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%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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Structure of a Polynucleotide Chain
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DNA composition: [A]=[T] ; [C]=[G]
X-ray Diffraction Pattern of DNA
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The Double Helix
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Phosphodiester [C-O-P-O-C]
Polynucleotide chain
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Complementary and Antiparallel
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DNA Structure
Complementary Base Pairs (A with T, G with C)
Anti-parallel StrandsRight-handed double helix (B-DNA)
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DNA replication DNA-RNA duplexesElevated content of C:G
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DNA Structure: Supercoils
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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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• 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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• 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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Chromosome Structure in Prokaryotes and Viruses
The DNA molecules of prokaryotes and viruses (RNA?) are organized into negatively
supercoiled domains.
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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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The E. coli Chromosome
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Folded genome: is the functional state of a isolated bacterial chromosome
Mild conditions(no ionic detergents)
1M salt Polyamines(-)
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Model of E. coli Chromosome
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folded=coiled
protein
Nicked=single strand
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• 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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Chromosome Structure in EukaryotesEukaryotic chromosomes contain huge molecules of DNA that are highly condensed during mitosis and meiosis.
The centromeres and telomeres of eukaryotic chromosomes have unique structures.
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Each chromosome is unineme (Theory)
Each chromosome contains a single large double
helix (strand) of DNA molecule
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Chromatin Composition
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(+)
(-)
Histones:H1, H2a, H2b, H3, H4
(protamines in sperm)
Structural
Nonhistone proteins:Non structuralRegulation
Nucleosomes: DNA + histonesexcept H1
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Nucleosomes
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Methyl groups Acetyl groups
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Structure of the Nucleosome Core
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Human Metaphase Chromosomes
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The 30 nm Fiber
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Micrococcal nuclease releases individual nucleosomes from chromatin as particles.
Endonucleases
IntermediateStructures?
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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 saltsH1
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DNA Around a Scaffold of Non-histone Proteins
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heterochromatin
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Levels of DNA Packaging
2-nm double-stranded DNA molecule 11-nm nucleosomes 30 nm chromatin fiber Organization around a central scaffold
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H1
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DNA repeats
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Centromeric: specific repeated regions (non-coding DNA sequences=heterochromatin) of chromosome for attachment of spindle microtubules ( 5000 to 15000 bp).
Satellite sequences:--Tandemly repeating --Non-coding DNA
Alpha-------171 ( unit repeat as base pair)Beta----------68Satellite 1---48Satellite 2-----5Satellite 3-----5
Most satellite DNA is localized to the telomeric or the centromeric region of the chromosome
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TelomeresFunctions 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.
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Telomere Structure
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-TTAGGG
-500 to 3000 repeats
-G-rich overhang
-T-loop (D-loop)
-Telomeres specificProteins ( protection)
POT1
TRF1 and 2
TIN2 and TPP1
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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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The heritable factors that Mendel studied are now known as:
a) Nucleic acidsb) Amino acidsc) Genesd) Unit factorse) Peptides
Different forms of the same gene are known as:
a) Peptidesb) Amino acidsc) Proteinsd) Allelese) Gene differences
The building blocks of genes are:
a) Proteinsb) Amino acidsc) Nucleic acidsd) Lipidse) Carbohydrates
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The main components of a membrane in a cell are:
a) Lipidsb) Proteinsc) Carbohydratesd) Lipids and Proteinse) Lipids and Carbohydrates
Prokaryotes can be characterized by:1.The lack of a true nucleus or compartment in which the DNA is located2. The unique cell walls composed of murein3. The lack of mitochondria4. All of these
a) 1b) 2c) 3d) 4e) 1 and 3
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Which large organic molecules are essential chromosome components?
a) Lipids and proteinsb) Proteins and nucleic acidsc) Nucleic acids and polysaccharidesd) Proteins and polysaccharides
Which of the following is a type of nucleic acid?
a) DNAb) RNAc) DNAsed) RNAsee) DNA and RNA
In Sia and Dawson's 1931 experiment:a) Mice were required to demonstrate the transforming principleb) Used serum to precipitate IIIS cells from a mixture of heat-killed IIIS and living IIR cellsc) They showed that mice play no direct role in the transforming principled) Heat-killed IIR cells mixed with living IIIS cells gave rise to IIR coloniese) None of these