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DNA

DNA. DNA-Deoxyribonucleic Acid- molecule that contains genetic information. Genes are segments of DNA. Chromosomes are strands of DNA. In the 1950’s it was understood that DNA was the molecule that stored genetic information but the structure was unknown. DNA. Structure of DNA.

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DNA

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  1. DNA • DNA-Deoxyribonucleic Acid- molecule that contains genetic information. • Genes are segments of DNA. Chromosomes are strands of DNA. • In the 1950’s it was understood that DNA was the molecule that stored genetic information but the structure was unknown.

  2. DNA

  3. Structure of DNA • James Watson and Francis Crick discovered the structure of DNA. • Double Helix structure. • DNA and RNA are classified as nucleic acids. • Each strand of DNA is made of nucleotides- subunits of a nucleic acid. • Each nucleotide is made of a phosphate group, a five carbon sugar (deoxyribose), and a nitrogen-containing base.

  4. Structure of DNA • There will be the same number of sugars, phosphates, and bases. • Sugar-phosphate and sugar-bases are held by strong covalent bonds. • Base pairs are held by weak hydrogen bonds.

  5. Pairing between bases • Erwin Chargaff noticed that the amount of A=T and the amount of G=C. • In DNA Adenine is always paired with Thymine and Guanine is always paired with Cytosine. • One purine (two rings, A and G) is always paired with one pyrimidine (one ring-T and C).

  6. Pairing between Bases • A - T, and G - C are complimentary base pairs • What is the significance? • The sequence on one strand will determine the sequence on the other strand.

  7. DNA Replication "...It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” -Watson, J.D., and Crick, F.H.C. 1953."Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid" Nature, April 25, 1953. vol. 171:737-738.

  8. DNA Replication • DNA replication is the copying of DNA before cell division. • DNA Replication takes place in the S phase of the cell cycle before Mitosis and Meiosis • Jobs: • DNA is split. • Hold DNA apart. • Make new nucleotides. • Check for errors.

  9. DNA Replication • DNA is split by an enzyme known as DNA helicase. • DNA is held apart by proteins at the replication fork. • The enzyme DNA polymerase moves along each strands, and adds the complimentary nucleotides until two new identical copies are produced. (semi-conservative) • DNA polymerase can backtrack to correct incorrect nucleotide base pairings. • http://www.maxanim.com/genetics/Dna%20Replication/Dna%20Replication.htm

  10. Meiosis • Meiosis is a form of cell division that produces gametes. • Homologous chromosomes are pairs that are similar is size, shape, and genetic information. • Before meiosis begins DNA is replicated. • Chromosomes are replicated and exist as two identically attached chromatids.

  11. Stages of Meiosis I • Prophase I- Nuclear envelope breaks down, Homologous chromosomes pair, spindles form. • Metaphase I- Homologous chromosomes are moved to the equator. • Anaphase I- Spindle fibers separate the pairs of chromosomes, chromosomes are not split along the centromere. • Telophase I- chromosomes move to the poles, new nuclear membrane is formed, cytoplasm is divided.

  12. Stages of Meiosis • Prophase II- new spindle forms, nuclear membrane breaks down. • Metaphase II- The chromosomes line up along the equator, attached at the centromere. • Anaphase II- each individual chromatid is pulled apart at the centromere • Telophase II- nuclear envelopes forms, spindle breaks down, cytoplasm splits, four haploid cells

  13. Meiosis • Crossing over is the when a piece of a chromatid on one homologous chromosome is broken and exchanged with another, occurs in prophase I. • Spermatogenesis is meiosis in male testes that produce 4 sperm. • Oogenesis is meiosis in female ovaries that produces 1 egg and 3 polar bodies.

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