Chapter 9 DNA and the Molecular Structure of Chromosomes

José A. Cardé- Serrano, PhDUniversidad Adventista de las AntillasBiol 223 - GenéticaAgosto 2011

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

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 Copies; Generations

Phenotypic Function: Gene Expression Development, Transcription; Translation

Evolutionary Function: Mutation Changes, variations, adaptability

Genes are located on chromosomes.Chromosomes contain proteins and

nucleic acids. (Chromatin)The nucleic acids are

deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

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…

ObservacionesPreguntaDiseño ExperimentalRacionalExperimentoResultadosConclusión (Hipotesis)

Viroids are infectious, naked RNA molecules.

Prions are heritable, infectious proteins that do not contain nucleic acids.

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).

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

- Nucleótidos- Fosfato- Pentosa- Base Nitrogenada

Polímero: cadena de monomeros RNA – cadena sencilla usualmenteDNA – cadena doble

El tetranucleótido mostrado:Azucar 2’ Deoxiribosa vs RibosaEnlaces 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?

-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

Estructura del DNA: Enlaces Químicos importantes

Complementary Base Pairs (A with T, G with C

Antiparallel StrandsRight-handed double helix (B-DNA)

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.

The DNA molecules of prokaryotes and viruses are organized into negatively supercoiled domains.

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.

The DNA molecules in prokaryotic and viral chromosomes are organized into negatively supercoiled domains.

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.

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

Each chromosome is uninemeEach 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.

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

Constricted region of the chromosome Necessary for proper segregation of

chromosomes in mitosis and meiosis

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 moleculesMost telomeres contain repetitive

sequences and a distinct structure.

Eukaryotic chromosomes contain repetitive DNA

Evidence for repetitive DNA Satellite bands DNA renaturation experiments In situ Hybridization

in situ: telómeros

in situ: telómeros

Each eukaryotic chromosome contains one giant molecule of DNA packaged into 11-nm ellipsoidal beads called nucleosomes.

The condensed chromosomes that are present in mitosis and meiosis and carefully isolated interphase chromosomes are composed to 30-nm chromatin fibers.

At metaphase, the 30-nm fibers are segregated into domains by scaffolds composed of nonhistone chromosomal proteins.

The centromeres (spindle-fiber-attachment regions) and telomeres (termini) of chromosomes have unique structures that facilitate their functions.

Eukaryotic genomes contain repeated DNA sequences, with some sequences present a million times or more.