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Biology DNA Unit PDE Big Idea 8A The basic molecular and the associated genetic code structure of DNA are universal, revolutionizing our understanding of disease, heredity, and evolution. Griffith’s Experiments • Frederick Griffith did a series of experiments with Streptococcus pneumoniae (pneumonia) in 1928. • He noticed that one strain (the S strain) of the bacteria caused disease, the other (the R strain) didn’t. Griffith’s Experiments • Griffith did four experiments using mice and various mixtures of the disease causing and non disease causing bacteria. Experiment 1 • He injected a mouse with live S strain bacteria. • As a result, the mouse died. Experiment 2 • He injected a mouse with live R strain bacteria. • As a result, the mouse lived. Experiment 3 • Mouse was injected with heat killed S strain cells • The mouse lived Experiment 4 • Mouse was injected with heat killed S strain cells and live R strain cells • The mouse died Griffith’s Conclusion • Griffith concluded that there was some hereditary factor released by the dead S cells and absorbed by the live R cells • Today we call this transfer of genetic material from one organism to another transformation Avery’s Experiment • Oswald Avery later did three experiments in which he used enzymes to deactivate protein, RNA and DNA and injected them into mice • He found that DNA was the hereditary factor from Griffith’s conclusion Watson and Crick • James Watson and Francis Crick discovered the double helix shape of DNA in 1953 DNA Anatomy • Further studies of DNA showed that it contains three parts 1. Deoxyribose (sugar) 2. Phosphate 3. A nitrogenous base - Put all three parts together and you have a nucleotide, the building blocks of DNA Nucleotides • The four nucleotides of DNA are known as Adenine (A), Guanine (G), Cytosine (C) and Thymine (T) • RNA also has nucleotides, but Thymine is replaced with Uracil (U) Purines and Pyrimidines • Purines have 2 rings and Pyrimidines have 1. • Purines and Pyrimidines Hydrogen bond to one another Base Pairing • Because of the bonding pattern of the purines and pyrimidines, how the bases pair up can easily be predicted • C and G always pair up • In DNA, A and T pair up • In RNA, A and U pair up G–C A–T C–G T–A G–C A–U C–G U–A DNA and RNA Functions • DNA contains the directions for making all of the proteins in the body, but it can not leave the nucleus • RNA is made from DNA and contains selected information from the DNA • RNA leaves the nucleus and is used to make protein in the cytoplasm Replication - The process in which copies of DNA are made - The enzyme helicase unzips the DNA into two separate strands. - New strands are then built onto the old strands - Each new double helix has half of the old one - Because of this, we say that the process is conservative Replication Example Old Strand New Strand GATTACATCCGTA CTAATGTAGGCAT Transcription • This is when DNA is used to make RNA, which will be used to make protein • The base thymine (T) is replaced with uracil (U) Transcription Example DNA Strand RNA Strand GTAC GCTAT TCG CAUGCGAUAAGC Transcription Makes Three Main Types of RNA • mRNA – the blueprint for making protein (messenger) • tRNA – (transfer)carries amino acids to ribosomes (transfer) • rRNA – becomes part of the ribosome (ribosomal) Translation • Making protein from RNA • mRNA is read by the ribosome (part rRNA) in order to construct a new protein made from amino acids which are supplied by the tRNA mRNA • In order to determine the order of the amino acid sequence, scientists had to crack the genetic code • Within the mRNA there is a code that specifies what amino acid goes where in the protein Codons • Examples: AGA = arginine GGA = glycine UGC = cysteine * See page 207 in your textbook • Scientists found that the mRNA was organized into segments 3 bases long, that they called codons • Each codon specifies an amino acid • The genetic code has a lot of repetition Start Codon • Transcription often makes long strands of mRNA that may have directions for many proteins • The cell needs to know where to begin translating • The “on switch” is known as the start codon Start Codon = AUG AUG = methionine Stop Codons • The cell also needs to know where to stop translating • Because of this there are 3 “off switches” or stop codons • They are UAA, UAG and UGA Anticodons • The tRNA knows where to attach to the mRNA because it contains the complimentary bases to the codon • These bases are called an anticodon Codon AUG GAC UCA Anticodon UAC CUG AGU Translation • mRNA slides between the large and small subunit of a ribosome until AUG is found Translation • A tRNA brings in the necessary amino acid and its anticodon binds to the codon Translation • The next codon slides through the ribosome Translation • The next tRNA brings its amino acid. Its anticodon binds to the codon and a peptide bond forms between the amino acids. Translation • The next codon slides through the ribosome and the first tRNA is released. Translation • The process continues over and over again until a stop codon is reached. Then the polypeptide is released and the ribosome can start over. Transcription/Translation Practice DNA AGTACGCTTCGACTGT mRNA U C A U G C G A A G C U G A C A Protein Structure • After proteins are made, they often bend, twist, fold and interact with other proteins to make a useable product for an organism Primary Protein Structure • This refers to the order of the amino acids in the polypeptide (protein) chain Secondary Protein Structure • Certain amino acids have charged regions and will form hydrogen bonds • This causes the protein chain to fold, twist or change shape in some way Tertiary Protein Structure • Most protein chains include many different features (twists, sheets, and folds) • The final 3-dimensional shape of the entire protein is the tertiary structure Quaternary Protein Structure • In many cases, different proteins will bind together to make a final product • Quaternary structure is the interaction between two or more protein chains Enzymes • Enzymes are special proteins that catalyze (speed up) chemical reactions • The beginning substances they work on are called substrates • The substrates are changed into different molecules Enzymes • Enzymes catalyze more than 4,000 biochemical reactions • Enzymes are essential to the survival of many organisms • For example, without them we could not digest our food, get rid of carbon dioxide or send messages through our nerves How Enzymes Work