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Discovery of DNA

Discovery of DNA. 1850’s Gregor Mendel discovered hereditary “factors”, but did not know that DNA was what genes were made of . 1928…Frederick Griffith showed genes were responsible for heredity 1944…Oswald Avery showed DNA was responsible for heredity.

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Discovery of DNA

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  1. Discovery of DNA • 1850’s GregorMendel discovered hereditary “factors”, but did not know that DNA was what genes were made of. • 1928…Frederick Griffith showed genes were responsible for heredity • 1944…Oswald Avery showed DNA was responsible for heredity. • 1952…Alfred Hershey and Martha Chase backed up Avery’s experiments

  2. Discovery of DNA • 1949 Edwin Chargaff noticed that A&T and G&C appear almost equally in DNA, no matter what the organism! • Early 1950’s…Rosalind Franklin took first Xray of DNA molecule • 1953 James Watson and Francis Crick announced double helix shape (based on RF’s Xray).

  3. DNA Structure • Deoxyribonucleic Acid • Makes up chromosomes • Chromosomes have small areas called genes • Genes are a section of DNA that is a code for a protein that does some function in your body (more about this in next unit)

  4. DNA Structure

  5. DNA Structure • Double helix like a twisted ladder made of subunits called nucleotide. Has three parts: • deoxyribose(sugar) • phosphate group • nitrogen base • 4 different bases: adenine guanine cytosine thymine • Bases match each other (complementary), A matches with T, G matches with C • Order of bases called the base sequence • (DNA overview)

  6. DNA Replication • DNA Copies itself during the S phase of the cell cycle, so daughter cells have complete copy of all genes. • DNA Helicase(an enzyme) “unzips” the DNA molecule by breaking the hydrogen (weak) bonds between nitrogen bases. • Area where “unzips” is called replication fork. • DNA polymerase (another enzyme) matches base pairs with their complement (A with T, G with C…Chagraff’s Rule) on both strands at once. The base pairs are already in the nucleus.

  7. DNA Replication

  8. DNA Replication • Because one strand is upside down (antiparallel), one strand is copied as one whole piece (leading strand) and one is copied in chunks (Okazaki fragments) and pieced together (lagging strand) • DNA polymerase continues until whole strand is copied. Since two new strands have 1 original and 1 new, it’s called semi-conservative replication. • (DNA Replication)

  9. Prokaryotic DNA • In Prokaryotes (bacteria), DNA is a ring and replication starts at one point and goes around both ways until it’s done. • Thus there will be only two replication forks. • In eukaryotes, replication will start in many places, so there are multiple replication forks. • (Replication Forks)

  10. Mistakes • Mistakes in copying DNA can be (and often are) made, but are usually caught by DNA polymerase and fixed. • If not fixed, called mutation, and the base sequence changes. • Sometimes this is good and leads to a new adaptation (evolution) • Sometimes its bad (cancer, other genetic disorders)

  11. Mistakes • (Mutation) • There are also mutations to chromosomes, but we’ll talk about all of this in the next unit.

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