DNA Structure and Function

Miescher Discovered DNA First discovered in 1868 by Miescher He discovered an acid with lots of phosphorus in the nucleus He called it nuclein We call it DNA (deoxyribonucleic acid)

Mystery of the Hereditary Material DNA was first thought to be a type of protein Thinking was –1000’s of different heritable traits –Therefore there must be 1000’s of different molecules –Proteins are made of 20 amino acids and an infinte number can be made

Griffiths Transformation Expt He injects living “harmless” bacteria into the mouse

Griffiths Transformation Expt He injects living “deadly” bacteria into the mouse.

Griffiths transformation Expt He injects “deadly” bacteria that have been heated treated to kill them into the mouse

Griffiths transformation Expt He then injects a mixture of living”harmless” and heat killed “deadly” bacteria into the mouse - the mouse dies and when they examne it - they find it is filled with living “deadly” bacteria

Transformation Griffiths conclusion was that “SOMETHING” had “Transformed” the harmless R cells into deadly S cells. It could not be protein because heat destroys protein – so he called it a transforming factor Turned out to be DNA

Oswald, Avery, Hershey & Chase All these scientists performed a variety of experiments to show that DNA and NOT protein was the Genetic Material.

Structure of DNA In Watson and Crick proposed that DNA is a double helix and built a model showing its structure.

DNA is made up of repeating NUCLEOTIDES Each nucleotide consists of –Deoxyribose (a 5-carbon sugar) –Phosphate group –One of four nitrogen-containing base Four bases –Adenine, Guanine, Thymine, Cytosine (A, T, G, C)

Nucleotide Bases phosphate group deoxyribose ADENINE (A) THYMINE (T) CYTOSINE (C) GUANINE (G)

DNA Structure Movie

Base Pairing Chargaff showed: –The Amount of adenine is always different to the amount of guanine in many different species –BUT - the amount of adenine always equals amount of thymine in many species –AND the amount of guanine always equals amount of cytosine in many different species A=T and G=C

Rosalind Franklin’s Work Was an expert in X-ray crystallography She looked at DNA fibers Concluded that DNA was some sort of helix

Rosalind Franklins “famous” X Ray Chrystallography Image of DNA

Watson-Crick Model Watson and Crick used the data from many different sources to build a model of DNA DNA consists of two nucleotide strands Strands run in opposite directions - antiparallel Regarding the nitrogen bases: A binds with T and C binds with G Strands are held together by hydrogen bonds between bases Molecule is a double helix

A diagram of Watson & Crick’s DNA Model

DNA Organization Movie

DNA Structure Helps Explain How It Duplicates DNA is two nucleotide strands held together by hydrogen bonds Hydrogen bonds between two strands are easily broken Each single strand then serves as template for new strand Every DNA molecule is half “old” and half “new”

DNA Replication Movie

DNA Replication new old Half Old and Half New

DNA Replication Overview - Movie

Enzymes in Replication Enzymes unwind the two strands DNA polymerase attaches complementary nucleotides DNA ligase fills in gaps Enzymes wind two strands together

DNA Replication Movie