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* * * 1866 – Mendel’s Laws of Heredity * 1869 – Miescher discovers nuclein * 1928 – Griffith discovers bacterial transformation * 1944 – Avery et. al. reveals DNA carries genetic information * 1950 – Chargaff develops base pairing rule * 1952 – Hershey & Chase confirm Avery’s * 1952 – Franklin produces images of DNA structure * 1953 – Watson & Crick confirm and publish the DNA structure * 1961 – Nierenberg “cracks” the genetic code * 1984 – Jeffreys develops DNA fingerprinting * 1990 to 2003 – Human genome project * * Began studying white blood cells in 1869 * White blood cells are a major component of pus * Collected pus samples from bandages at a local hospital * Isolated a substance he called “nuclein” from the nuclei of the white blood cells * After chemical analysis, nuclein was later re-named DNA * * In 1928, discovers bacterial transformation while studying streptococcus pneumonieae. * Tried to learn how certain types of bacteria caused pneumonia * He isolated two different strains * S-strain: * R-strain: Smooth cells; caused pneumonia Rough cells; harmless * His experiments led to the discovery of substance known as DNA * * In 1944, repeated Griffith’s experiment with purified cell extracts * Discovered that the transforming principle is DNA * * Discovered that DNA consists of 4 nitrogen bases (Adenine, Guanine, Cytosine, Thymine) * Adenine (A) always pairs with Thymine (T) * Guanine (G) always pairs with Cytosine (C) * Chargaff’s Rule * The concentration of Adenine is equal to the concentration of Thymine * The concentration of Guanine is equal to the concentration of Cytosine * * Performed x-ray diffraction studies to identify the 3-dimensional structure of DNA * Discovered that DNA is helical * * In 1953, described the structure of DNA as a long double helix with a sugar-phosphate backbone bonded to nitrogenous bases. * They were awarded the Nobel Prize in 1962 for their discovery. * * Launched in 1990 * Goals: * Identify all of the estimated 30,000 genes in the human DNA * Determine the sequence of the 3 billion chemical base pairs of DNA * Storage of this information in databases for future analysis * Address any legal, ethical, or social issues that arise from this study * Completed in April, 2003 * ● DNA is located in the nucleus, tightly wound to form genes, which are located on chromosomes ●DNA is described as a double helix (a twisted ladder) * * DNA is a complex molecule made up of units called nucleotides * Nucleotides * Sugar (deoxyribose) * Phosphate * Nitrogen Base (4) * Adenine Purines * Guanine * Thymine Pyrimidines * Cytosine * DNA bases pair up in a specific way *A – T *G - C * DNA is built like a twisted ladder, called a double helix * It is made up of 2 chains of nucleotides joined together by weak hydrogen bonds * Human cells contain about 6.6 billion base pairs in their DNA * The order of the bases makes up the genetic code * Differences in the order of the bases is what makes one species different from another * *Pass on the genetic code *Replication *Codes for protein synthesis *Making proteins * * Each strand of the double helix has all the information needed to make copies or REPLICATE the DNA * Sites where separation and replication occur are called replication forks * DNA helicase splits the 2 DNA strands at the hydrogen bonds * DNA polymerase joins individual nucleotides and proofreads the base pairings as they form * DNA ligase seals the two newly formed strands together * * DNA unwinds and unzips, the weak hydrogen bonds break * Bases of the unzipped nucleotides are exposed to free nucleotides also found in the nucleus * New nucleotides attach to the exposed nucleotides from the original parent strand * DNA polymerase proofreads the newly formed strands * Results in two new strands that are identical to each other and to the original parent strand. * * DNA holds the code for the making of proteins * The monomers of proteins are amino acids *Amino Acids * There are 20 known amino acids * 3 consecutive DNA bases act as the code for 1 amino acid - this is known as a codon * There are 64 possible codons * Since there are only 20 amino acids, some amino acids are represented by more than one codon * Universal Code – a codon representing an amino acid in one organism represents the same amino acid in another organism * *Protein synthesis occurs in the ribosomes. Since the DNA code is locked up in the nucleus, how does the code get to the ribosome? * * RNA is composed of nucleotides like DNA * There are several differences between DNA and RNA DNA RNA Sugar Deoxyribose Ribose A pairs with T (thymine) U (uracil) Appearance Double stranded Single stranded Location Nucleus Nucleus, Cytoplasm, Ribosomes * * DNA unzips and unwinds * TRANSCRIPTION (takes place in the nucleus) * The DNA code is transcribed to the RNA message * RNA nucleotides called messenger RNA (mRNA) match up with the exposed DNA nucleotides * mRNA breaks away from the DNA in order to move through the cytoplasm to the ribosomes * TRANSLATION (takes place in the ribosomes) * The RNA code is translated to correctly join amino acids * RNA nucleotides called transfer RNA (tRNA) are bonded to amino acids * tRNA located in the ribosomes brings amino acids to the mRNA * Amino acids bond to each other to form protiens *Codon = 3 base sequence of mRNA *Anticodon = 3 base sequence of tRNA that carry an amino acid DNA A G C T T A T C C mRNA (codon) tRNA (anticodon) Amino Acid * * A mutation is a change in the DNA sequence * An organism’s DNA affects how it looks, how it behaves, and its physiology. Therefore, mutations serve as a source of genetic variation * Mutations are an essential mechanism of evolution; without mutations, evolution cannot occur * Mutations can affect organisms in three ways * Beneficial: create traits to allow an organism to adapt/survive * Detrimental: cause no functionality, disease or death * Neutral: cause no harm and no benefit (most common) * * Point Mutations * Mutations that occur at a specific base pair in the genome * An exchange of one base for another * Chromosomal Mutations * One DNA fragment is moved from one site on the genome to another * * Substitution * Silent/neutral mutation * A new codon codes for the same or a similar amino acid as the original; the protein remains unchanged * Missense mutation * A new codon codes for a different amino acid; the protein is slightly altered * Nonsense mutation * The new codon is a stop codon, creating a non-functional protein * * Insertion/Deletion * Insertion = adding in a base into the sequence * Deletion = removing a base from the sequence * A frameshift mutation * A change in the reading frame of the mRNA * Many amino acids may be changed * Drastically alters the protein, unless a whole codon is inserted/deleted * * Causes of chromosomal mutations * Spontaneous mutations * Result from errors occurring during DNA replication that are not corrected by DNA polymerase * Caused by errors made during crossing over * Induced mutations * Caused by a mutagen (external factors that cause mutations) * Radiation, Chemicals, Infectious agents (viruses) * Physical mutagen – physically damage DNA strands * Chemical mutagen – alter the molecular structure of DNA without physically altering it * * Translocation * A fragment of one chromosome switches places with a fragment of another chromosome * Usually occurs between two non-homologous chromosomes * Results in… * The inactivation of genes * The creation of a protein with a completely altered function * * Inversion * A section of a chromosome has reversed its orientation * Results in… * Inactivation or disruption of genes * The gene may come under alternate control * * Duplication * A portion of a chromosome is replicated, resulting in multiple copies of that region * Results in… * Disruption of genes * May have no affect at all