DNA: Structure and Function Biology’s Biggest Moment of the 20th Century!

DNA stands for: D: Deoxyribo (se) N: Nucleic A: Acid Every living thing has DNA. That means you have something in common with every other living thing.

Intro to Viruses Genetic material, DNA or RNA enclosed within a capsid Viruses are not considered to be living organisms, they are not made up of cells and can not reproduce on their own. Genetic material, DNA or RNA enclosed within a capsid

Intro to Bacteria Single circular chromosome DNA found in the cytoplasm Plasmids extra circular pieces of DNA that may code for antibiotic resistance

DNA is made up of Nucleotides 3 components of a nucleotide: Nitrogen Base 5-C sugar

4 Bases of DNA Nucleotides Purines(2 rings) Adenine (A) Guanine (G) Pyrimidines(1 ring) Thymine (T) Cytosine (C)

Basic Nucleotide Pairings What do you notice? Pyrimidine Purine Pyrimidine = Purine

Chargaff’s Rule Base Pair Rule Amount of A = Amount of T Amount of G = Amount of C Base Pair Rule

Research of DNA Structure Rosalind Franklin’s Photo 51 1952 DNA is a double helix, 2 complementary strands twisted around each other

Watson & Crick’s Model 1953 Sequence on one chain is complementary to the sequence on the other (paired bases form rungs of a ladder) Sugar-Phosphate forms a twisted ladder Covalent bonds hold nucleotides together (formed by dehydration synthesis) Hydrogen bonds hold bases together

Watson and Crick’s Model: Why it makes sense Makes copies of itself - Replication Encodes Information - Transcription Controls Cells - Translation Change by Mutation - Evolution

How is DNA packaged? Each cell has about 6 feet = 1.8m of DNA. The average human has 75 trillion cells. 150 billion kilometers of DNA (250 billion miles) Enough DNA to go from the earth to the sun more than 400 times. DNA has a diameter of only 0.000000002 m.

Chromosomes are made up of: Histones (Proteins) Nucleosomes (DNA & Histones)

The most amazing molecule on the planet!! Nobel Prize awarded to Watson, Crick and Wilkins in 1962

Replication DNA is able to copy itself Happens every time a cell divides Occurs during the S phase of the cell cycle

Overview 1. Enzymes “unzip” the molecule 2.Each strand becomes a template for a new strand to be made from 3. DNA polymerase is the main enzyme but there are many others 4. DNA polymerase adds new bases to the opened up strands

Replication practice

Key to DNA Structure and Function Lies Partly with the Carbons within Deoxyribose The Carbons also are the key to antiparallelism

Orientation of DNA Model Antiparallel M.C. Escher captured antiparallelism

The Classic DNA Experiments Griffith (1928) Avery (1944) Hershey/Chase (1950) Is the Genetic Material DNA or Protein?

Griffith’s Experiment 1928 There is a transforming agent from the smooth strain that causes the rough strain to become virulent.

Step 2 - Treated the strains with Proteases Avery 1944 - Hypothesized that the transforming agent is a nucleic acid Step 1 - Treated the Type R and Type S bacterial with DNASE Result - Transformation did not occur Step 2 - Treated the strains with Proteases Result - DNA transformed the bacteria + DNAse Rough Heat-killed nonvirulent + smooth virulent (type R) (type S) + Protease

Doubting Griffith and Avery, Hershey & Chase set out in 1953 to prove them wrong using viruses. Phage (virus) particles infecting a bacteria cell Bacteriophage - virus that infects bacteria

The Classic Blender Experiment 1. Labelled phage particles in 2 batches: a. radioactive sulfur (proteins) b. radioactive phosphorus (nucleic acids) 2. Then allowed each batch to separately infect bacteria. 3. Used a blender to knock phage from bacteria then centrifuged. 4. Tube with sulfur found to have virus capsids labeled but bacteria were not. 5. The bacteria were labeled with phosphorus. What was the conclusion? The virus part that enters the cell is nucleic acid and not protein.