DNA Structure and Replication The Innocence Project Uses DNA as evidence to free people wrongly convicted of crimes DNA testing is standard part of court cases Extremely accurate way to match crime scene evidence to perpetrators What is DNA Deoxyribonucleic acid DNA Hereditary molecule that is passed from parents to offspring Common to all living organisms Serves as the instruction manual for how to build an individual DNA Found in the nucleus of eukaryotic cells In the form of a chromosome Single DNA molecule wrapped around proteins DNA is made up of DNA and proteins Human DNA Humans have 23 pairs of chromosomes 23rd chromosome pair determines sex XX Female XY Male 46 chromosomes in total One chromosome from each pair is inherited from the biological mother One chromosome from each pair is inherited from the biological father Each person s DNA is unique Consider its structure to understand why The structure of DNA DNA is composed of nucleotides building blocks of DNA Each nucleotide consists of a sugar a phosphate and a base Nucleotides have one of four bases Adenine A Thymine T Guanine G Cytosine C Only the base will ever change Two strands of nucleotides pair up and twist around each other to form a spiral shaped double helix spiral structure formed by two strands of DNA nucleotides bound together Sugars and phosphates form the outside backbone Bases form the internal rungs Two strands of DNA double helix are held together by base pairing hydrogen bonding between the bases of each strand Complementary base pairing fitting together two strands of DNA are said to be complementary in that A always pairs with T and G always pairs with C A always pairs with T 2 hydrogen bonds C always pairs with G 3 hydrogen bonds Specific sequence of nucleotides along a strand of DNA is unique to each individual Extract the DNA from the cells to create an individual s DNA profile Visual representation of a person s unique DNA sequence Need many copies of their DNA DNA Replication Natural process by which cells make an identical copy of a DNA molecule Take advantage of complimentary base pairing rules First hydrogen bonds that hold base pairs together are broken and the helix is unwound DNA polymerase reads the DNA and adds complementary nucleotides using the rules of base pairing makes a new copy of DNA that matches Semi conservative mechanism Produces two copies of the original DNA molecule Each molecule consists of one of the strands of the original DNA molecule and a new strand The Polymerase Chain Reaction PCR PCR is a laboratory technique used to replicate and amplify a specific DNA segment Primers short segments of DNA that guide DNA polymerase to the section of DNA to copy PCR Heating Strand separation DNA replication DNA profiling sequence Genome Allows DNA replication to occur many times Can make billions of copies from a starting sample of just a few molecules of DNA DNA profiling takes advantage of the fact that no two people have the exact same DNA One complete set of genetic instructions encoded in the DNA of an organism Determining sequence of entire genome is extremely time consuming and expensive Use shortcut Use PCR to amplify only specific segments of DNA Short tandem repeats STR STRs are sections of a chromosome in which DNA sequences are repeated For example sequence AGCT may be repeated over and over again STRs are in the same places along chromosomes Exact length of STR varies from person to person Making a DNA profile 1 Collect cells and extract DNA 2 Use PCR to amplify multiple STR regions 3 Separate STRs using gel electrophoresis size Laboratory technique that separates fragments of DNA by 4 Compare STR banding patterns Separated fragments of DNA create a specific pattern of bands Visible using fluorescence Unique to each person Compare patterns of DNA Different individuals have different DNA banding patterns DNA profiling Look at multiple STRs Combined pattern of STR repeats at multiple sites is unique to a person The Innocence Project DNA evidence is more reliable than other forms of evidence Error rates for bite mark identification can be as high as 91 Hair analysis can only exclude a suspect not positively identify one Except for identical twins no two people share exactly the same DNA Summary DNA is the hereditary molecule of all living organisms DNA in a eukaryotic cell is packaged into chromosomes located in the nucleus Humans have 23 pairs of chromosomes in their cells one chromosome of each pair inherited from the mother the other from the father DNA is a double helix Each strand is made of nucleotides The two linear strands of a DNA molecule are bound together by complementary pairing of the nucleotides Complementary pairing of DNA strands guides DNA replication PCR enables scientists to increase the number of copies of specific DNA sequences Forensic scientists use STRs to create a DNA profile Genes to Proteins Pharming What is protein Amin Acids Using genetically modified animals to make pharmaceutical drugs Human protein antithrombin is extracted from the goats milk A macromolecule made of repeating amino acids and subunits Many functions For example muscle contraction facilitate chemical reactions fight infection Building blocks of proteins 20 different amino acids All have the same basic core structure Each also has a unique chemical side group Bond together to form linear chains Chain folds into a 3 D protein based on the sequence of amino acids Determine the shape and function of a protein Changing an amino acid in the sequence changes the 3 D shape of protein Shape of the protein determines its function Where do proteins come from Instructions to make proteins are encoded by genes found in DNA which is found in the nucleus A sequence of DNA that contains the instructions to make at least one protein Gens are found on chromosomes DNA and proteins packed together Each chromosome carries a unique set of genes Synthesis of a protein from a gene is called gene expression Antithrombin Protein Antithrombin protein helps prevent blood clots thrombosis Antithrombin gene is on chromosome 1 Gene is expressed by cells in the liver Release antithrombin into bloodstream Inherit genetic defect causes an antithrombin deficiency One of both copies of antithrombin gene defective Humans have two copies of every gene Either identical in nucleotide sequence or slightly different Different version of same gene is called allele Allele Alternative versions of the same gene