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DNA and Protein Synthesis CHAPTER 10 Biology and Society: Mix-and-Match Viruses In 2009, a cluster of unusual flu cases broke out around Mexico City. In June 2009, the World Health Organization (WHO) declared H1N1 a pandemic (global epidemic) and unveiled a massive effort to contain it. Scientists soon determined that H1N1 was a hybrid flu strain, made when a known flu virus mixed with an Asian swine flu virus. The hybrid H1N1 flu strain had a combination of genes that infected young, healthy people instead of the elderly or people who were already sick. Many countries produced a coordinated response, and the WHO declared the pandemic over in August 2010. What are genes made of? DNA was known to be a chemical in cells by the end of the nineteenth century, has the capacity to store genetic information, and can be copied and passed from generation to generation. The discovery of DNA as the hereditary material ushered in the new field of molecular biology, the study of heredity at the molecular level. I. DNA & the genetic code A. Definitions 1. Gene a. segment of DNA b. codes for a certain trait (protein) c. Ie. Hair color gene causes cell to make brown hair B. Structure of DNA deoxyribonucleic acid 1. STRUCTURE DISCOVERED BY WATSON AND CRICK 2. Many nucleotides joined together a. What is a nucleotide Three part molecule a-deoxyribose sugar a- phosphate a-nitrogen base 3. SHAPED INTO A DOUBLE HELIX (SPIRAL) -- LOOKS LIKE A TWISTED LADDER 4. 5. NITROGEN BASES MAKE UP THE STEPS OF THE LADDER 10 - 1,000 STEPS FOR ONE GENE 6. Four nitrogen bases make up the steps - adenine A-double ring structure - thymine T-single ring structure - guanine G-double ring structure - cytosine C-single ring structure 7. Bases always match with its compliment A—T G—C II. Two functions of DNA 1. replication 2. protein synthesis REPLICATION- in cell nucleus Purpose: when cells or organisms reproduce, a complete set of genetic instructions passes to next generation-DNA doubles 1. Hydrogen bonds b/w nitrogen bases break 2. DNA unzips 3. New nucleotides come in & join w/complimentary bases - uses enzyme DNA polymerase 4. 2 identical strands of DNA are present DNA Replication DNA replication cont. DNA replication ensures that all the body cells in multicellular organisms carry the same genetic information. DNA can be damaged by X-rays and ultraviolet light. DNA replication in eukaryotes begins at specific sites on a double helix (called origins of replication) and proceeds in both directions. Origin of replication Parent strand bubble Parent strands Daughter strand THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN DNA provides instructions to a cell and an organism as a whole. How an Organism’s Genotype Determines Its Phenotype An organism’s genotype is its genetic makeup, the sequence of nucleotide bases in DNA. The phenotype is the organism’s physical traits, which arise from the actions of a wide variety of proteins. How an Organism’s Genotype Determines Its Phenotype DNA specifies the synthesis of proteins in two stages: 1. 2. transcription, the transfer of genetic information from DNA into an RNA molecule and translation, the transfer of information from RNA into a protein. transcription DNA transcription RNA nucleus cytoplasm translation protein Transcription: From DNA to RNA Transcription makes RNA from a DNA template, uses a process that resembles the synthesis of a DNA strand during DNA replication, and substitutes uracil (U) for thymine (T). RNA nucleotides are linked by the transcription enzyme RNA polymerase. RNA polymerase DNA- colors represent genes RNA polymerase RNA nucleotides RNA DNA template RNA Steps of transcription 1. 2. 3. 4. 5. 6. DNA unzips by breaking hydrogen bonds One strand is active, one is inactive RNA nucleotides join to active strand Controlled by RNA polymerase mRNA is ready for processing Original DNA strands rejoin RNA processing RNA processing includes adding a cap and tail consisting of extra nucleotides at the ends of the RNA transcript,-this protects RNA from cell enzymes removing introns (noncoding regions of the RNA), and RNA splicing, joining exons (the parts of the gene that are expressed) together to form messenger RNA (mRNA). DNA Cap RNA transcript with cap and tail Transcription Addition of cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm Translation Translation is the conversion from the nucleic acid language to the protein language. Translation requires mRNA, ATP, enzymes, ribosomes, and transfer RNA (tRNA). How translation occurs 1. mRNA attaches to ribosome to be decoded - code is read in pieces called codons - codon – 3 nucleotides AUG CCU GGA - each codon codes for one amino acid 2. A new kind of RNA brings in the correct amino acid. - transfer RNA (tRNA) see diagram one end has the a.a. on it the other end has an anticodon Anticodon 3 nucleotides on tRNA that base pair with nucleotides on mRNA - see diagram of tRNA This is how the correct a.a. is brought in Steps of translation 1. Correct tRNA (carrying it’s specific a.a.)base pairs w/M-RNA (called initiation) 1st codon is always AUG (start codon) 2. Another tRNA base pairs w/the next codon (called elongation) 3. Peptide bond is formed b/w the a.a’s 4. 1st tRNA releases it’s a.a and leaves 5. mRNA moves over & process continues Process continues until a stop codon is reachedthe stop codon signals termination (3rd step) Protein is released –ribosome splits into its 2 subunits 6. 7. mutations Mutations can change the amino acids in a protein. Mutations can involve large regions of a chromosome or just a single nucleotide pair, as occurs in sickle-cell disease. A mutation is any change in the nucleotide sequence of DNA. Mutations within a gene can be divided into two general categories: 1. 2. nucleotide substitutions (the replacement of one base by another) and nucleotide deletions or insertions (the loss or addition of a nucleotide). Insertions and deletions can change the reading frame of the genetic message and lead to disastrous effects. Single base substitution- sickle cell anemia Deletions,insertions Causes of mutations What causes mutation? 1. Mutagen – substance that causes DNA to change -- drugs, X-rays, UV rays 2. Unknown - during replication DNA can make a mistake