DNA: The Molecule of Heredity PDF

DNA: The Molecule of Heredity Deoxyribonucleic Acid Genetic info “instructions for life” for all cells In nucleus of eukaryotes; in cytoplasm of prokaryotes DNA Controls the cell by giving instructions to make proteins Codes for traits (characteristics) DNA =TRAITS!!!! Structure of DNA DNA is a...

DNA: The Molecule of Heredity Deoxyribonucleic Acid Genetic info “instructions for life” for all cells In nucleus of eukaryotes; in cytoplasm of prokaryotes DNA Controls the cell by giving instructions to make proteins Codes for traits (characteristics) DNA =TRAITS!!!! Structure of DNA DNA is a nucleic acid made of nucleotide subunits Made of Phosphate group Sugar (deoxyribose) Nitrogen Base A, T, C, G Draw for your notes! Nucleotides are linked together to form DNA 4 Nitrogen Bases- Double ringed bases (purines) 1. Adenine (A) 2. Guanine (G) Single ringed bases (pyrimidines) 3. Thymine (T) 4. Cytosine (C) Structure of DNA 4 Nucleotides of DNA Discovery of DNA Structure In the 1940’s- scientists knew : DNA was the molecule of life DNA was a nucleic acid DNA was made of A, T, C, G What they didn’t know was how it all fit together in the molecular structure of DNA! Discovery of DNA Structure Late 1940s - Erwin Chargaff In any cell, the amount of A always =T and C always =G -This shed light on how bases bind to each other Discovery of DNA Structure 1952: Rosalind Franklin Took X-ray photos of crystalized DNA Added info about shape of DNA: It must be a helix (“twisted ladder”) Came very close to solving DNA structure, but was beaten to publication by Watson and Crick -images suggested that there were two strand, nitrogenous bases in middle, and twisted 10 X-ray Crystallography DNA is purified from sample of interest Stretch fibers in a thin glass tube to make most of the strands parallel An X-ray beam is directed at the DNA. Some of it passes through, but some is scattered (diffracted) when it contacts particles in the DNA. The scattering pattern of the X-ray is recorded on a film and used to determine molecular structure ------- Discovery of DNA Structure 1953 James Watson and Francis Crick discovered DNA is a double helix using Franklin’s X-rays, Chargaff rules, and toy models DNA Double Helix: 2 strands of DNA in a “twisted ladder” Backbone – repeating phosphates and sugars Covalent bonds Nitrogen base pairs are the steps of the ladder Hydrogen bonds Discovery of DNA Structure Base Pairing (Chargaff’s) Rule A pairs with T (“straight w/ straight”) C pairs with G (“curvy with curvy”) “Always Together” “Great Combination” Chargaff is scientist who discovered that % of A= % of T and % of C = % of G 17 Practice Base Pairing Rule Write the Complementary Strand of DNA Build a DNA Molecule http://learn.genetics.utah.edu/content/basics/builddna/ DNA Double-Helix DNA Replication DNA is found in each and every cell of an organism Each cell has an exact copy of the DNA When the cell divides in 2, both new cells must have a correct copy of the DNA Found in each single-celled organism and in every cell of a multicellular organism 23 DNA Replication DNA makes an exact copy of itself Results in 2 identical copies of DNA Occurs in the nucleus Only occurs right before CELL DIVISON so each cell has one complete set of DNA!!!! Steps of DNA Replication 1. Unzipping-The enzyme helicase breaks apart the hydrogen bonds that hold the bases together Steps of DNA Replication 2. New nucleotides are added to both sides of the original strand by the base pairing rule by the enzyme DNA polymerase Steps of DNA Replication Result- 2 identical copies of DNA - each with 1 original DNA strand and 1 new strand --semi-conservative replication Discovery of DNA Structure DNA Double Helix: 2 strands of DNA in a “twisted ladder” Backbone – repeating phosphates and sugars Covalent bonds Nitrogen base pairs are the steps of the ladder Hydrogen bonds Protein Synthesis proteins DNA gets all the glory, Proteins do all the work Gene - small piece of DNA that codes for a protein. Each gene codes for a different protein What protein you make determines what trait you express 2 Genes are expressed when the protein a gene codes for is made Genes on Chromosomes Important Proteins muscles antibodies enzymes transport The simple steps to make a protein: DNA RNA Protein 5 What is RNA? Ribonucleic Acid Single strand of nucleotides (looks like ½ of a DNA strand) Contains ribose sugar ***Uracil replaces Thymine*** U binds with A DNA RNA DNA vs. RNA Comparing DNA and RNA DNA RNA # of strands Sugar Bases present Where found RNA doesn’t use T 2 (double helix) deoxyribose A, T, C and G Only in the nucleus 1 ribose A, U C and G U = uracil Can leave the nucleus 8 3 Forms of RNA Messenger RNA - mRNA Takes message from the DNA in the nucleus to the ribosome Complementary sequence to DNA 3 Forms of RNA Ribosomal RNA- rRNA makes up ribosomes 3 Forms of RNA Transfer RNA- tRNA Carries specific amino acids to ribosome to make proteins PRACTICE: DNA sequence: A A T G G C C G T RNA sequence: What process did you just do? Transcription!! (DNA to mRNA) Just like replication, except all T’s are replaced with U’s! U U A A C C C G G What is a Scribe? A person who serves as a professional copyist. To transcribe is to make a complementary mRNA copy of the DNA sequence Steps of Protein Synthesis 1. Transcription: Convert DNA into mRNA *****Occurs in the nucleus DNA unzips at certain gene RNA nucleotides bind with complementary bases on DNA (enzyme: RNA polymerase) mRNA strand leaves the nucleus and goes to ribosome DNA zips back up Transcription Video: https://www.youtube.com/watch?v=5MfSYnItYvg Animation: http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf https://staff.concord.org/~btinker/workbench_web/models/eukTranscription.swf https://www.youtube.com/watch?v=ztPkv7wc3yU Good video, but has U in DNA instead of T in animation 15 Interactive http://learn.genetics.utah.edu/content/basics/transcribe/ Use this to practice at home! What is a Translator? A person who translates from one language into another The ribosome translates the mRNA “language” into the protein “language” 2. Translation: convert mRNA to protein **Occurs at the ribosome** mRNA is “read” 3 bases at a time (called a codon) (ex: ACG, CGU) 1 codon = 1 amino acid (look at chart) tRNA carries amino acid to ribosome to make a protein Goes from start (AUG) to stop codon Steps of Protein Synthesis 20 Amino Acids Steps of Translation mRNA attaches to ribosome and is read 3 bases at a time (AUG = start codon) tRNA matches to codons on mRNA and brings in corresponding amino acid Ribosome (rRNA) links amino acids together with peptide bonds to build the protein (aka polypeptide) Continues until a stop codon is reached **Many amino acids connected together form a protein/polypeptide! A chain of amino acids 22 What is the difference between DNA Replication, Transcription and Translation? DNA Replication: The DNA unzips and creates an exact copy of the double helix. Transcription: The DNA double helix unzips and a single strand mRNA is made. Translation: The mRNA binds to the ribosome and tRNA carries over the corresponding amino acids to make a protein. Label the Parts of the Diagram Below 1.) One DNA 2 DNA molecules = replication. 2.) DNA mRNA = transcription. 3.) mRNA amino acid = translation. Label the Structures Below How does the tRNA know which amino acid to bring? Contains 3 RNA bases that are complementary to the mRNA codon (called the anticodon)