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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. • 1952…Alfred Hershey and Martha Chase backed up Avery’s experiments

Discovery of DNA

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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. - PowerPoint PPT Presentation

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Page 1: 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.

• 1952…Alfred Hershey and Martha Chase backed up Avery’s experiments

Page 2: Discovery of DNA

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).

Page 3: Discovery of DNA

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)

Page 4: Discovery of DNA

DNA Structure

Page 5: Discovery of DNA

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 guaninecytosine thymine

• Bases match each other (complementary), A matches with T, G matches with C

• Order of bases called the base sequence

• (DNA overview)

Page 6: Discovery of DNA

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.

Page 7: Discovery of DNA

DNA Replication

Page 8: Discovery of DNA

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)

Page 9: Discovery of DNA

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)

Page 10: Discovery of DNA

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)

Page 11: Discovery of DNA

Mistakes

• (Mutation)• There are also mutations to chromosomes, but

we’ll talk about all of this in the next unit.