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Replication Transcription Translation DNA 1. Double Stranded Helix 2. Hydrogen Bonds between Nitrogenous Base Pairs 3. Adenine-Thymine and Guanine-Cytosine Adenine shares 2 hydrogen bonds with Thymine Guanine shares 3 hydrogen bonds with Cytosine Gene • A gene is a segment of DNA • A gene is a sequence of nucleotides that codes for a functional product (usually a protein) • 1 gene = 1000’s of base pairs • 41000 possibilities of combinations A Gene is a Segment of DNA When a gene is expressed, DNA is transcribed to produce RNA and RNA is then translated to produce proteins. Replication • The duplication of DNA which occurs during the S phase of Interphase. • 1 Strand 2 Complementary Strands • Where? In the nucleus Hydrogen bond (H-bonds) thymine adenine cytosine guanine phosphate deoxyribose sugar Sugar / phosphate “strand” Nitrogenous base “rung” DNA nucleotide Deoxyribose sugar phosphate RNA nucleotide ribose sugar Nitrogenous base (guanine) phosphate Nitrogenous base (uracil) Step 1: Hydrogen bonds between complementary bases break DNA “unzips” DNA strands pull apart from each other Step 2: DNA nucleotides in the cell match up with each side of the “unzipped” DNA each “unzipped’ strands forms a template for a new strand Step 3: Each “old’ strand forms a template for a “new” strand two identical DNA molecules form “new” strand, identical sequence to the original “old” (original) strand RNA Review • Like DNA, RNA is a chain of nucleotides. • RNA contains the base Uracil, instead of Thymine. • RNA is small enough to exit through nuclear pores, unlike DNA. • RNA can be found in the nucleus, in the cytoplasm, or in the ribosomes (rRNA). Transcription • The process by which a gene found in DNA is copied into a complementary strand of RNA. • 1 Strand DNA 2 Strands RNA • Where? In the nucleus DNA RNA Label the Following Step 1: Hydrogen bonds between complimentary bases break DNA “unzips” as the strands pull apart from each other Step 2: RNA nucleotides in the cell match up with only one side of the “unzipped” DNA each “unzipped’ strands forms a template for a mRNA strand RNA nucleotide mRNA strand Step 3: mRNA strand breaks off from the DNA strand One side of DNA strand Step 4: mRNA strand leaves the nucleus for the ribosome Step 5: Once the mRNA leaves, the DNA “zips” back together • Transcription is different from DNA replication – during the process of transcription, only a segment of DNA, or gene, is transferred into an RNA message (whereas replication copies the whole chromosome). • mRNA then takes the gene’s coded message to the ribosome for protein synthesis. • Transcription not only produces mRNA – tRNA and rRNA are also made through the process of transcription. Translation • The process that converts, or translates, an mRNA message into the amino acid sequence of a protein. • 1 Strand RNA Amino Acid Chain Protein • Where? Cytoplasm or Rough E.R. – at the ribosomes Definitions Codon • Three-base segment of mRNA that code for amino acids. Anticodon • Three-base segment of tRNA that is complementary to an mRNA codon. • Pairing results in deposition of amino acid. Amino Acid • Monomer of protein The problem: How does a particular sequence of nucleotides specify a particular sequence of amino acids? By means of transfer RNA (tRNA) molecules, each specific for one amino acid and for a particular triplet of nucleotides in mRNA called a codon. The family of tRNA molecules enables the codons in a mRNA molecule to be translated into the sequence of amino acids in the protein. Step 1 – The mRNA codon attracts and pairs up with a complementary tRNA anticodon Step 2 – The ribosome helps forms a peptide bond between the two amino acids carried by the tRNA molecules Step 3 – The ribosome pulls the mRNA strand to expose the next codon, and the steps repeat until the protein is complete RNA and Protein Synthesis • RNA is a singlestranded nucleic acid • RNA acts as a messenger between DNA and ribosomes • The process of translation takes amino acids and forms proteins Why Is It Necessary? • DNA in the Nucleus • Ribosomes in the Cytoplasm • Need a Messenger Protein Synthesis • Proteins are coded directly from the mRNA with 3 bases (one codon) for each amino acid. What’s up with that? Mutation • A change in the nitrogenous base sequence of DNA; that change causes a change in the product coded for by the mutated gene. Mutations What happens when you get insertions or deletions of bases in the DNA sequence? Usually you end up with a mess. THE BIG FAT CAT ATE THE RAT AND GOT ILL Deletion of one base THE IGF ATC ATA TET HER ATA NDG OTI LL And its all pops and buzzes. Sickle-Cell Anemia Definitions • Carcinogens Substances and preparations which, if they are inhaled or ingested or if they penetrate the skin; may induce cancer or increase its incidence and can affect any cells or tissues • Mutagens may induce hereditary genetic defects or increase their incidence and effect the germ cells (gonads) • Teratogens may induce non-hereditary congenital malformations or increase their incidence and effect the growing fetus Mutagens • • • • • • • Tobacco products Nitrous Acid Mold Toxins X-rays Gamma Rays UV Radiation Some Artificial Sweeteners