Replication, Transcription, and Translation DNA and RNA Replication, Transcription, and Translation

Genetic Controversy Two schools of thought a. Some said protein was material b. Some said DNA was material How was the controversy settled? - The scientific experiments of Griffith, Avery, Hershey and Chase

Griffith and Transformation - 1928 - England - Trying to develop a vaccine against pneumonia causing bacteria - Two strains - S(smooth) and R(rough)

Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Control (no growth) Harmless bacteria (rough colonies) Disease-causing bacteria (smooth colonies) Heat-killed, disease-causing bacteria (smooth colonies) Dies of pneumonia Lives Dies of pneumonia Lives Live, disease-causing bacteria (smooth colonies)

RESULTS - Showed that heat killed S strain and live R strain would kill mice - Something was “transforming” the R strain to an S strain - Called it transformation - What was the material?

Oswald Avery - 1944 - Wanted to identify Griffith’s transforming material - Used two enzymes a. protein killing b. DNA killing - Showed that no transforming took place when DNA “killed”

D. Hershey and Chase - 1952 - Working with a bacteriophage - Virus that infects bacteria - Made of only two things a. protein coat b. DNA (genetic) core

Hershey and Chase Phage infects bacterium Bacteriophage with phosphorus-32 in DNA Radioactivity inside bacterium Phage infects bacterium No radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat

Recap: Was DNA or protein injected? - DNA has phosphorus - Protein has sulfur - Used radioactive phosphorus 32P and radioactive sulfur 35S - Let virus infect bacteria - New viruses full of 32P DNA was being injected!

The Components and Structure of DNA 1. Called deoxyribonucleic acid 2. Long and thread-like (twisted) 3. Many subunits linked together 4. Subunits called nucleotides 5. 1000’s in a chain-like structure

The structure of a nucleotide 1. Phosphate group - same in all 2. Five carbon sugar a. deoxyribose sugar 3. Nitrogenous base - 4 different ones that name the nucleotide

Nitrogenous Bases 1. Are different in each nucleotide 2. Names of the four bases a. adenine (A) b. guanine (G) c. thymine (T) d. cytosine (C) Two classes of bases A. purines 1) large double ring 2) A & G B. pyrimidines 1) small single 2) T & C

Purine and Pyrimidine Structure

H. Chargaff - 1949 - Studying the amounts of bases in DNA of living things - His results showed that: a. A always = T b. C always = G - Called Chargaff’s rule - Also called the base pair rule

The molecule is completed… - Franklin and her X-ray diffraction picture showed a helix Watson and Crick adds that it is a double helix with bases in the middle - Called it a “spiral staircase” - Strands are complements of each other - Think of a step ladder a. “sides” are alternating sugar and phosphate groups b. “rungs” are base pairs 1) A = T 2) C = G

Sugar-phosphate backbone Nucleotide Hydrogen bonds Sugar-phosphate backbone Adenine Thymine Cytosine Guanine

Chromosomes and DNA Replication A. DNA Can Make Copies of Itself 1. Process called replication 2. Done during S phase 3. Needed for new cells 4. DNA unwound using helicases 5. Hydrogen bonds broken between bases 6. DNA polymerase puts new nucleotides in place (A to T and C with G) 7. New copy just like original

From Genes To Proteins RNA DNA Single-stranded Double-stranded Ribose Uracil 3 forms of RNA mRNA (messenger) tRNA (transfer) rRNA (ribosomal) DNA Double-stranded Deoxyribose Thymine

From Genes To Proteins… 1. Transcription: making mRNA from DNA to carry information to the ribosomes.

- ALL organisms have a genetic code made of three nucleotide sequences called codons. - Codons correspond to particular AA and stop signals.

From Genes To Proteins… 2. Translation: Using tRNA to build proteins from the information in mRNA. - Each tRNA molecule carries an amino acid to the ribosomes, by matching its anticodon to a specific codon from the mRNA http://www.youtube.com/watch?v=983lhh20rGY

GENETIC MUTATIONS Mutations (gene or chromosomal) Changes in DNA Effect depends on where mutation occurs (body or sex cell) & what type of mutation Can be helpful, harmful, or neutral

Different Types of Gene Mutations Substitutions = UGU to UGC Effect depends on translation Insertions = nucleotides added Deletions = nucleotides deleted Transposons= DNA segments move spontaneously from one location to another in the same DNA molecule

Ex. THE CAT ATE THE RAT (meaningful) Deletion of C = THE ATA TET HER AT (meaningless)

Types of Chromosomal Mutations Deletions (whole or part deleted) Duplications (extra copies of parts) Inversions (reverses parts of chromosomes) Translocations (parts break off and relocate) 27

Causes of Mutations? Spontaneous Mutagens (come from environment) UV light Chemicals Carcinogens (cancer causing)

RNA (ribonucleic acid) 3 forms of RNA mRNA (messenger) tRNA (transfer) rRNA (ribosomal) RNA is used to take the information in DNA and make proteins (gene expression) 2 stages of gene expression Transcription Translation

The Big Idea… During gene expression, the info in DNA is first transcribed as mRNA and then translated via tRNA and used to build a protein.

The Genetic Code

The Genetic Code