chapter 9 dna and the molecular structure of chromosomes © john wiley & sons, inc

Chapter 9

DNA and the Molecular Structure of Chromosomes

© John Wiley & Sons, Inc.

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


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.


Genotypic Function: ReplicationPhenotypic Function: Gene ExpressionEvolutionary Function: Mutation (Gene

modifications)

Chromosomes

Genes are located on chromosomes.

Chromosomes contain proteins and nucleic acids.

The nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).


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

DNA Mediates Transformation


Griffith’s experiment (in vivo) MiceStreptococcus pneumoniae--type IIIS (virulent)--type IIR (avirulent)

“Transforming principles”

Sia and Dawson’s experiment (in vitro)


Avery, MacLeod and McCarty’s experiment (in vitro)

The Genetic Material of Bacteriophage T2 is DNA


Hesley-Chase’s experiment (in vitro)-----------> Transfection ( Infection)

The Genetic Material of Tobacco Mosaic Virus (TMV) is RNA


Retroviruses ( RNA------> DNA)

(in vitro)

• 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).


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.


Deoxyribonucleotides


Structure of a Polynucleotide Chain


DNA composition: [A]=[T] ; [C]=[G]

Chargaff’s Rules


%A = %T and %G = %C.

%A ~ %T and %G ~ %C are valid for each of the two DNA strands

methyltransferases methylate and/or deaminate

Structure of a Polynucleotide Chain


DNA composition: [A]=[T] ; [C]=[G]

X-ray Diffraction Pattern of DNA

The Double Helix


Phosphodiester [C-O-P-O-C]

Polynucleotide chain


Complementary and Antiparallel

DNA Structure

Complementary Base Pairs (A with T, G with C)

Anti-parallel StrandsRight-handed double helix (B-DNA)



DNA replication DNA-RNA duplexesElevated content of C:G

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

• 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.


• 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.


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.

The E. coli Chromosome


Folded genome: is the functional state of a isolated bacterial chromosome

Mild conditions(no ionic detergents)

1M salt Polyamines(-)

Model of E. coli Chromosome


folded=coiled

protein

Nicked=single strand

• 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.


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.


Each chromosome is unineme (Theory)

Each chromosome contains a single large double

helix (strand) of DNA molecule

Chromatin Composition


(+)

(-)

Histones:H1, H2a, H2b, H3, H4

(protamines in sperm)

Structural

Nonhistone proteins:Non structuralRegulation

Nucleosomes: DNA + histonesexcept H1

Nucleosomes



Methyl groups Acetyl groups

Structure of the Nucleosome Core


Human Metaphase Chromosomes


The 30 nm Fiber


Micrococcal nuclease releases individual nucleosomes from chromatin as particles.

Endonucleases

IntermediateStructures?

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

DNA Around a Scaffold of Non-histone Proteins


heterochromatin

Levels of DNA Packaging

2-nm double-stranded DNA molecule 11-nm nucleosomes 30 nm chromatin fiber Organization around a central scaffold


H1

DNA repeats


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

http://en.wikipedia.org/wiki/Tandemly_arrayed_genes

http://en.wikipedia.org/wiki/Non-coding_DNA

http://en.wikipedia.org/wiki/Non-coding_DNA

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.


Telomere Structure


-TTAGGG

-500 to 3000 repeats

-G-rich overhang

-T-loop (D-loop)

-Telomeres specificProteins ( protection)

POT1

TRF1 and 2

TIN2 and TPP1

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)


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

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

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

chapter 9 dna and the molecular structure of chromosomes © john wiley & sons, inc

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