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Chapter 9 DNA and the Molecular Structure of Chromosomes. José A. Cardé- Serrano, PhD Universidad Adventista de las Antillas Biol 223 - Genética Agosto 2011. Chapter Outline. Functions of the Genetic Material Proof That Genetic Information Is Stored in DNA The Structures of DNA and RNA
Chapter 9DNA and the Molecular Structure of Chromosomes José A. Cardé- Serrano, PhDUniversidad Adventista de las Antillas Biol 223 - Genética Agosto 2011
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
The genetic material must replicate, control the growth and development of the organism, and allow the organism to adapt to changes in the environment. Functions of the Genetic Material
Functions of the Genetic Material • Genotypic Function: Replication • Copies; Generations • Phenotypic Function: Gene Expression • Development, Transcription; Translation • Evolutionary Function: Mutation • Changes, variations, adaptability
Chromosomes • Genes are located on chromosomes. • Chromosomes contain proteins and nucleic acids. (Chromatin) • The nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Key Points • 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. Proof that Genetic Information is Stored in DNA
The Genetic Material of Bacteriophage T2 isDNA (Hershey/Chase) Observaciones Pregunta Diseño Experimental Racional Experimento Resultados Conclusión (Hipotesis)
Viroids and Prions • Viroids are infectious, naked RNA molecules. • Prions are heritable, infectious proteins that do not contain nucleic acids.
Key Points • 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. The Structures ofDNA and RNA
Naturaleza Química del DNA o sus subunidades • Nucleótidos • Fosfato • Pentosa • Base Nitrogenada
Structure of aPolynucleotide Chain 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)
Estructuradel DNA: La DobleHéliceX-ray Diffraction Pattern of DNA • 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
DNA Structure • Complementary Base Pairs (A with T, G with C • Antiparallel Strands • Right-handed double helix (B-DNA)
Key Points • 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.
Key Points • 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. Chromosome Structure in Prokaryotes and Viruses
The DNA of Prokaryotes and Viruses • 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.
Key Points • 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. Chromosome Structure in Eukaryotes
Histone Proteins • 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
Eukaryotic Chromosomes • Each chromosome is unineme • Each chromosome contains a single large molecule of DNA
Autoradiography • 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.
Levels of DNA Packaging • 2-nm double-stranded DNA molecule • 11-nm nucleosomes • 30 nm chromatin fiber • Organization around a central scaffold
Centromeres • Constricted region of the chromosome • Necessary for proper segregation of chromosomes in mitosis and meiosis