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DNA Structure and Function

DNA Structure and Function. Oak Ridge High School Biology: DNA Structure & Function Chapter 10. Key Concepts:. Each DNA strand consists of two strands of nucleotides twisted together Hereditary information is encoded in the sequence of nucleotides

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DNA Structure and Function

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  1. DNA Structure and Function Oak Ridge High School Biology: DNA Structure & Function Chapter 10

  2. Key Concepts: • Each DNA strand consists of two strands of nucleotides twisted together • Hereditary information is encoded in the sequence of nucleotides • Nitrogen bases have specific pairing arrangements • DNA is replicated before a cell divides • DNA contains the information of heritable traits in all cells

  3. Discovery of DNA Function • Griffith’s experiments • Transfer of hereditary material from dead S cells to living R cells

  4. Evidence for DNA as The Substance for Heredity • Radioisotope incorporated into protein and picked up by bacteriophage • Viral DNA inside the cell picked up radioisotope

  5. Hershey – Chase Experiment • Bacteriophage viruses contain DNA core and Protein outer coat • Steps using RadioIsotopes • Tag DNA-Phosphate • Tag Protein-Sulfur • Infection • Blending • Centrifugation Only phosphate detected inside cells, sulfur remains outside cell. Therefore DNA is genetic material.

  6. DNA Inside the Nucleus • A cells DNA is contained inside the cells nucleus. • Each chromosome is a coiled mass if DNA and protein. • The DNA molecule is a tightly coiled double helix.

  7. Nucleotide Structure • DNA helix is made up of four bases, Adenine, Guanine, Cytosine, & Thymine. • A nucleotide consists of a phosphate, Sugar, & Nitrogen base. • These bases form a “ladder” like structure that is twisted.

  8. DNA Structurea Summary • Pairing Arrangement • A - T • C – G • Nucleotides • Deoxyribose • Phosphate Group • Nitrogen base • Purines • Adenine A • Guanine G • Pyrimidines • Thymine T • Cytosine C

  9. DNA Nucleotide Sequence Codes for Alleles • Look at the replication fork to the right. • The strand on the left reads TGCCATCCTA…… • Each three base sequence is a codon and codes for a specific amino acid. • If there was a different DNA of the same species the same sequence might read TGCAATCGTA…… and code for a protein that would produce a different allele.

  10. DNA Structure Continued • The DNA side groups are arranged in alternating sets of phosphate and sugar molecules. One side is 5’-3’ and the other side is 3’ - 5’. • Base pairs make up the rungs of the ladder A—T and G– C. The genetic code is arranged as sets of three base codes together. For example AAA, CGC, ATC, CCC, would all code for four different amino acids. • Each gene and therefore allele has a different sequence which codes for a different protein that is expressed in the organism; as the persons phenotype.

  11. Central Dogma • DNA can be replicated by using one side of the molecule as a template to copy a new side. • RNA, know as mRNA can be transcribed from a DNA strand. This mRNA will then leave the nucleus to find a ribosome in the cytoplasm. • mRNA coded message can be translated into a protein sequence.

  12. DNA Replication • Enzyme regulated • Helicases unwind parent stand • Binding proteins stabilize complementary strands by breaking hydrogen bonds between nitrogen base pairs. • DNA Polymerase enzymes bind to the complementary strands and copy each side of the original “old” strand in the 5’ - 3’ direction. Each strand acts as a template for “new” base pairs to attach according to base paring rules. • DNA Ligase binds the new bases to the old bases so that each strand is half old and half new and are identical.

  13. DNA Replication and Repair • Enzyme regulated • Hydrogen bonds break • Attachment of nucleotides to new strands • DNA polymerases DNA ligases • New strand is half old, half new

  14. Detailed Look at Replication • In this replication fork the helicases have unwind the DNA. • Binding proteins are breaking the base pairs. • DNA polymerase is copying each strand; one side continuous and the other in smaller fragments. • DNA ligase binds smaller fragments together to produce identical copies.

  15. In Conclusion • Hereditary information is located in DNA • DNA consists of nucleotides • DNA molecule consists of two nucleotide strands twisted into a double helix • The bases of DNA strands pair in a constant fashion • DNA of one species has specific nucleotide sequences

  16. In Conclusion • Enzymes unwind the two strands of DNA and assemble a new strand during DNA replication • Resulting new DNA molecule has an old strand and a new strand • Some of the enzymes in DNA replication also repair DNA • developed by M. Roig & S. Iverrson

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