Download Chapter 9 DNA and the Molecular Structure of Chromosomes

José A. Cardé- Serrano, PhD
Universidad Adventista de las Antillas
Biol 223 - Genética
Agosto 2011
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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
The 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: Replication
 Copies; Generations
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Phenotypic Function: Gene Expression
 Development, Transcription; Translation
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Evolutionary Function: Mutation
 Changes, variations, adaptability
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Genes are located on chromosomes.
Chromosomes contain proteins and nucleic
acids. (Chromatin)
The nucleic acids are deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA).
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The genetic material must perform three
essential functions: the genotypic function—
replication, the phenotypic function—gene
expression, and the evolutionary function—
mutation.
In most organisms, the genetic information is
encoded in DNA.
In some viruses, RNA Is the genetic material.
Viroids are infectious naked RNA molecules, and
prions are infectious, heritable proteins.
DNA: Principio de Transformación:
Avery, McLeod y McCarty…
Observaciones
Pregunta
Diseño Experimental
Racional
Experimento
Resultados
Conclusión (Hipotesis)
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Viroids are infectious, naked RNA molecules.
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Prions are heritable, infectious proteins that
do not contain nucleic acids.
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The genetic information of most living organisms is
stored in deoxyribonucleic acid (DNA).
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In some viruses, the genetic information is present in
ribonucleic acid (RNA).
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Viroids and prions are infectious naked molecules of
RNA and protein, respectively.
DNA is usually double-stranded, with adenine paired with
thymine and guanine paired with cytosine. RNA is usually
single-stranded and contains uracil in place of thymine.
Naturaleza Química
del DNA o sus
subunidades
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Nucleótidos
- Fosfato
- Pentosa
- Base Nitrogenada
Polímero: cadena de monomeros
RNA – cadena sencilla usualmente
DNA – cadena doble
El tetranucleótido mostrado:
Azucar 2’ Deoxiribosa vs Ribosa
Enlaces C-O-P-O-C (fosfodiester)
Polaridad: 5’ vs 3’ (PO4 unido al C5 o al C3)
-patrones de difracción de Rayos X
típico para cada tipo de átomo
-estructura repetitiva
-Como se conoce esta foto?
Estructura del DNA
-Doble helice espiral
-Complementaridad
-Polaridad
-Antiparalelismo
-Curva hacia la derecha
-0.34 nm entre bases
-10 base por giro = 3.4 nm
-Premio Nobel excepto Franklin
Estructura del DNA: Enlaces
Químicos importantes
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Complementary Base Pairs (A with T, G with C
Antiparallel Strands
Right-handed double helix (B-DNA)
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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.
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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.
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RNA usually exists as a single-stranded molecule
containing uracil instead of thymine.
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The functional DNA molecules in cells are
negatively supercoiled.
The DNA molecules of prokaryotes and viruses are organized into
negatively supercoiled domains.
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Prokaryotes are monoploid.
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 DNA molecules in prokaryotic and viral
chromosomes are organized into negatively
supercoiled domains.
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Bacterial chromosomes contain circular
molecules of DNA segregated into about 50
domains.
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.
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Structural role in chromatin
Present in amounts
equivalent to amounts of
DNA
Major histone types: H1,
H2a, H2b, H3, and H4
Basic proteins
Arginine and Lysine are
Abundant
Highly conserved proteins
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Each chromosome is unineme
Each chromosome contains a single large
molecule of DNA
DNA is labeled with 3H-thymidine, spread on a
microscope slide, and covered with emulsion.
 Molecules nearly as long as a Drosophila chromosome are
observed.
 These data support that each chromosome is one
molecule of DNA.
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2-nm double-stranded DNA molecule
11-nm nucleosomes
30 nm chromatin fiber
Organization around a central scaffold
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Constricted region of the chromosome
Necessary for proper segregation of
chromosomes in mitosis and meiosis
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Functions of telomeres
 Protect the ends of linear DNA molecules from
deoxyribonucleases
 Prevent fusion of chromosomes ends or terminals
 Facilitate complete replication of the ends of
linear DNA molecules
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Most telomeres contain repetitive sequences
and a distinct structure.
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Eukaryotic chromosomes contain repetitive
DNA
Evidence for repetitive DNA
 Satellite bands
 DNA renaturation experiments
 In situ Hybridization
in situ: telómeros
in situ: telómeros
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Each eukaryotic chromosome contains one giant molecule
of DNA packaged into 11-nm ellipsoidal beads called
nucleosomes.
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The condensed chromosomes that are present in mitosis
and meiosis and carefully isolated interphase chromosomes
are composed to 30-nm chromatin fibers.
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At metaphase, the 30-nm fibers are segregated into
domains by scaffolds composed of nonhistone
chromosomal proteins.
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The centromeres (spindle-fiber-attachment regions)
and telomeres (termini) of chromosomes have
unique structures that facilitate their functions.
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Eukaryotic genomes contain repeated DNA
sequences, with some sequences present a million
times or more.