What carries hereditary information? n By the 1940s, scientists knew that chromosomes carried genes. n They also knew that chromosomes were made of DNA and protein. n They did NOT know which of these molecules actually carried the genes. n Since protein has 20 types of amino acids that make it up, and DNA only has 4 types of building blocks, it was a logical conclusion. n Most Scientists thought protein carried genes
Avery’s Experiment 1. Avery repeated Griffith’s experiments with an additional step to see what type of molecule caused transformation. 3. When Avery added enzymes that destroy DNA, no transformation occurred. 2. Avery used enzymes to destroy the sugars and transformation still occurred—Sugar did not cause transformation. Avery used enzymes to destroy lipids, RNA, and protein one by one. Every time transformation still occurred—none of these had anything to do with the transformation. So…he knew that DNA carried hereditary information!
n The experiment involved viruses to see if DNA or protein was injected into the bacteria in order to make new viruses. n One group of viruses was infected with radioactive protein and another group with radioactive DNA. n Then the viruses attack the bacteria. n Radioactive DNA shows up in the bacteria, but no radioactive protein. Hershey-Chase Experiment
Chargaff’s Rules n The amount of adenine (A) equals the amount of thymine (T). n The amount of cytosine (C) equals the amount of guanine (G).
Rosalind Franklin n Took X-ray pictures of DNA. n The photos revealed the basic helix, spiral shape of DNA.
Maurice Wilkins n Worked with Rosalind Franklin. n Took her x-ray photos and information to Watson and Crick
Watson and Crick n Used Franklin’s pictures to build a series of large models. n Stated that DNA is a double-stranded molecule in the shape of a double helix, or twisted ladder. n Won the Nobel Prize for their work in 1962.
Basic DNA Structure S P A C S P S P T n A nucleotide is the monomer of DNA n A nucleotide is made of –a sugar called deoxyribose –a phosphate –and a base (ATCG)
Deoxyribose n Simple sugar molecule like glucose that has 5 carbons n The five carbons are numbered clockwise starting from the first one after the oxygen
Phosphate n The negatively charged phosphate bonds to the 5’ Carbon of the deoxyribose.
Bases n There are two main types of bases purines and pyrimidines. –Purines have two rings in their structure. Adenine and guanine are purines. –Pyrimidines only have one ring. Thymine and Cytosine are pyrimidines. Pyrimidines Purines
Basic DNA Structure S P A C S P S P T n To form one strand of DNA, the phosphate of one nucleotide covalently bonds to the 3’ Carbon of the deoxyribose from another nucleotide.
S P A C S P S P T G S P S P AT S P n The two strands of DNA are held together by hydrogen bonds
Base Pairs n The nucleotides that bond together by their bases are called base pairs. –Adenine only bonds to Thymine –Guanine only bonds to Cytosine
Does each of your cells have the same DNA? n YES
DNA Replication n Before a cell divides, DNA must make a copy of itself so that each new cell has a complete set of DNA.
What is an enzyme? n A protein that helps speed up chemical reactions in a cell.
Step 1-Unzip DNA n An enzyme called helicase untwists the ladder and breaks the hydrogen bonds between the bases and “unzips” DNA down the middle. Helicase Enzyme
Step 2-Prime the DNA n An enzyme called DNA primase put a few nucleotides of RNA on the DNA. n This is only to create a starting place and these will later be removed.
Step 3-Elongation n The two strands of the Parent DNA become templates for the new strands. n New nucleotides are added by an enzyme called DNA polymerase.
Step 3-Elongation n DNA polymerase only adds nucleotides in the 5’ to 3’ direction on both strands beginning at the RNA primer.
Step 4 – Fine tuning n RNA primer is removed and any gaps are sealed by an enzyme called ligase. n DNA polymerase proof reads the new copy and fixes any mistakes.
Helicase unwinds and unzips DNA S P A C S P S P T T G S S P P S P A
DNA Polymerase Adds New Nucleotides T G S S P P S P A S P A C S P S P T T S P G S P S P A S P AC S P S P T
n Are the two copies of DNA the same? n Why would it be important for the two copies of DNA to be the same?
What is a Gene? n A gene is a code found in DNA n Genes code for proteins that give people their traits.
How does DNA code for so many traits with only 4 bases? n Can you spell 20 words with the letters A, T, C and G? n Each combination of bases codes for a different amino acid. n Putting the 20 amino acids in different orders makes different proteins.
RNA n Single-stranded nucleic acid n Made of nucleotides n Has ribose instead of deoxyribose n Has uracil instead of thymine
Protein Synthesis n Two Steps to making a protein n Transcription –Writing DNA code n Translation –Decoding DNA’s message into a protein
Transcription n Transcription happens in the nucleus where the DNA is.
Transcription n DNA’s code is copied by messenger RNA (mRNA). n mRNA has complementary bases to the DNA (Remember RNA has a U instead of T). n Three bases of mRNA make a codon.
Translation n After mRNA is made in Transcription, the mRNA goes to the ribosome where the protein is made.
Translation n Translation begins at the start codon (AUG) of mRNA. n Then each codon codes for an amino acid in a protein that is brought in by a tRNA (transfer). n tRNA has an anticodon with complementary bases to the mRNA codon. n Translation is terminated by stop codon.
Which Amino Acid does each codon code for? n GGU Glycine n AAA Lysine n CUG Leucine n UGG Tryptophan
Mutations n Mutation-alteration in DNA n Mutagens-physical and chemical agents that mutate DNA n Deletion-mutation caused by deleting DNA that should be there n Insertion-mutation caused by inserting DNA that should not be there n Substitution-mutation caused by substituting DNA
Gene Regulation n Genes are not expressed all the time. n Some genes are usually on, but can be turned off by repressors when they are not needed. n Some genes are usually off, but they can be turned on by enhancers when they are needed.