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Discovery of DNA1850s Gregor Mendel discovered hereditary factors, but did not know that DNA was what genes were made of.1928Frederick Griffith showed genes were responsible for heredity1944Oswald Avery showed DNA was responsible for heredity. 1952Alfred Hershey and Martha Chase backed up Averys experimentsDiscovery of DNA1949 Edwin Chargaff noticed that A&T and G&C appear almost equally in DNA, no matter what the organism!Early 1950sRosalind Franklin took first Xray of DNA molecule1953 James Watson and Francis Crick announced double helix shape (based on RFs Xray).

DNA StructureDeoxyribonucleic AcidMakes up chromosomesChromosomes have small areas called genesGenes 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)

DNA Structure

DNA StructureDouble helix like a twisted ladder made of subunits called nucleotide. Has three parts:deoxyribose (sugar)phosphate group nitrogen base4 different bases:adenineguaninecytosinethymineBases match each other (complementary), A matches with T, G matches with COrder of bases called the base sequence

(DNA overview) DNA ReplicationDNA 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 CChagraffs Rule) on both strands at once. The base pairs are already in the nucleus.

DNA Replication

DNA ReplicationBecause 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, its called semi-conservative replication.(DNA Replication)

Prokaryotic DNAIn Prokaryotes (bacteria), DNA is a ring and replication starts at one point and goes around both ways until its 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)

MistakesMistakes 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)Mistakes(Mutation)There are also mutations to chromosomes, but well talk about all of this in the next unit.