Chapter 4 Genes & DNA

Section 1 What Does DNA Look LikeGenesGives instructions for building and maintaining cellsAble to be copied so cell can divide

NucleotidesDNA made of subunits called nucleotidesEach nucleotide has:SugarPhosphateBase4 Nucleotides due to 4 different basesAdenine (A)Thymine (T)Guanine (G)Cytosine (C)

Key PlayersErwin Chargaff1950s biochemistChargaffs RulesAmount of adenine = amount of thymineAmount of guanine = amount of cytosineRosalind FranklinX-ray diffraction to see DNA moleculesDNA has a spiral shape

Key Players ContdJames Watson & Francis CrickUsed Franklins imagesDNA is a long, twisted ladderMade the double helix modelJames WatsonFrancis Crick

DNA StructureDouble helix - twisted ladder modelSides of ladderAlternating sugar and phosphate partsRungs of ladderPairs of basesA + T OR C + G

Copying DNAReplication making copies of DNABase pairs are complementaryEach base only pairs with its corresponding baseAT or CGFor example:ATGCA only pairs with TACGT

ReplicationDNA molecule is unzipped down the middleLadder rungs are cut in halfComplementary nucleotides are added to the 2 strands1/2 of DNA molecule is old DNA and 1/2 is new DNAProteins in the cell control the replication process

Section 2 How DNA WorksEvery cell in your body has about 2 meters or 6 feet of DNA!Packaging DNAWound around proteins histonesCoiled into strandsBundled into chromosomesGene a string of nucleotides

Genes & ProteinsDNA read in 1 direction from one end to otherAmino acidsGroups of 3 bases give code to form amino acidFor example CCA is code for amino acid proline20 different amino acidsHuman body can only produce 10Other 10 come from our food Essential amino acidsProteins long strings of amino acids linked together

Proteins & TraitsProteins have several functionsChemical triggersMessengers for processes in a cellProteins help determine traitsGenes are the codes for making proteins

RNA & Making ProteinsRNA Ribonucleic acidMolecule that helps make proteinsMessenger RNA mRNACopy of a piece of DNAMoves from nucleus into cytoplasmGoes into ribosome 3 bases at a timeTransfer RNA tRNAtranslates RNA message into proteinSpecific tRNA molecules have certain amino acids attachedtRNA matches up with complementary bases on mRNAAmino acids released by tRNAAmino acids link up to produce a protein

MutationsMutation change in the nucleotide-base sequence in the gene or DNA molecule3 kinds of mutations

Substitution wrong base used Insertion extra base added in Deletion base left out

Do Mutations Matter?Mutation change in a gene or DNA3 possible outcomesImproved traitNo changeHarmful traitMost errors are fixed by proteinsSome become part of genetic codeMutation in sex cells are passed on to offspring

How do Mutations HappenRegularly due to random errors during replicationMutagens physical or chemical agents that cause mutationsHigh energy radiation x-ray, UV ray, cosmic rayAsbestosCigarette smokeHarmful mutations sickle cell disease, cancers

Genetic EngineeringManipulating individual genes in organismsCreate new productsBacteria engineered to produce drugsPlants or animals bred for superior qualitiesGene therapyReplace defective genes with healthy genesAre there possible dangers?

Genetic IdentificationDNA Fingerprinting identify unique pattern in each persons DNACrime scenesFamily relationshipsTrace hereditary disease

CloningClone is an exact copy of another organisms DNAIdentical twins are genetic clones3 types of cloningSomatic cell nuclear transfer put DNA from one cell into another cell to create an exact copy of the original organismDNA cloning put a piece of DNA into another organism. Fluorescent DNA from jellyfish into bacteria to make the bacteria glowTherapeutic cloning produce human embryos for medical research using stem cellsScientific and ethical issues surrounding cloning