DNA (Deoxyribonucleic Acid)

Transformation of Bacteria

Chromosomes are made of DNA and protein

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 G S P S P AT S P n A nucleotide is the monomer of DNA n A nucleotide is made of –a sugar called deoxyribose –a phosphate –and a base (ATCG) n The two strands of DNA are held together by hydrogen bonds

DNA Replication 1. The DNA molecule separates into its 2 strands by breaking the hydrogen bonds. 3. An enzyme called DNA polymerase adds new complementary nucleotides to each original strand. 2. Each old strand becomes a template for a new strand. DNA makes a copy of itself.

DNA Splits S P A C S P S P T T G S S P P S P A

Add New Nucleotides Fill in the correct nucleotides that will be added. 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

Questions 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.

What organelle makes proteins? n Ribosomes

Which molecule makes proteins? n RNA

RNA n Single-stranded nucleic acid n Made of nucleotides n Has ribose instead of deoxyribose n Has uracil instead of thymine

Transcription n DNA’s code is transcribed onto mRNA. n mRNA has complementary bases to the DNA. n Each codon is made of three bases.

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. n tRNA has complementary bases to mRNA 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 n Inversion-DNA is inverted or flipped

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.

The End!