Chapter 8 From DNA to Proteins GENETIC MATERIAL ● In the middle of the 1900’s Scientists were asking questions about genes ● What is a gene made of? ● How do genes work? ● How do genes determine characteristics of organisms? ● At the time most scientists believed that proteins had to be the molecules that made up genes Frederick Griffith - 1928 ● Was trying to develop a vaccination for the pneumococcus bacteria. ● He was working with two strains of bacteria. ● Rough - bacteria had a appearance in culture, non-virulent (doesn't kill) ● Smooth - bacteria had a smooth appearance in culture, virulent (kills) Transformation ● Griffith reasoned that some chemical factor that could change harmless bacteria into disease-causing bacteria was transferred from the heat-killed cells of the S strain into the live cells of the _ R strain. ● Griffith called the process of one type of bacteria changing permanently into another Oswald Avery 1944 ● Oswald Aery set out to determine which molecule in the heat killed bacteria was most important for transformation. He treated the mixture with enzymes that destroyed a protein, lipids, carbohydrates, and RNA but transformation still occurred. ● When repeated and the mixture was destroyed, transformation did not occur. He discovered that DNA stores and transmits genetic info from one generation to the next. ● Avery’s conclusion was not widely accepted; scientists continued to question whether the transforming material was DNA or proteins DNA as hereditary material ● The Genetic Material is DNA – Alfred Hershy and Martha chase 1952. ● Hershey and Chase worked with viruses that bacteria called bacteriophages ● Through a series of experiments, they were able to show that DNA, not protein, is the hereditary molecule. DNA Structure ● Hershey & Chase’s experiment insured confidence in scientists that DNA was the genetic material, but they questioned how nucleotides came together to form DNA and how DNA could communicate information. ● Nucleotide's basic structure was determined by P.A. Levine in the 1920’s. Nucleotides ● Consist of a five-carbon sugar a phosphate group, and a nitrogenous base ● DNA –sugar (deoxyribose), phosphate group, and nitrogenous base (Adenine Guanine Cytosine and Thymine) ● RNA –sugar (ribose), phosphate group, and a nitrogenous base (Adenine, Guanine, Cytosine, or _____ Uracil). Structure of DNA ● Double stranded helix ● Structure of DNA was determined in 1953 by Watson and Crick Nucleotides repeating units composed of: ● Deoxyribose sugar ● Phosphate group ● Nitrogen base Adenine pairs with Thymine Cytosine pairs with Guanine ● Deoxyribose sugar and phosphate group on sides of ladder. ● Weak hydrogen bonds hold nitrogen bases together on a rung ● Sequence of nucleotides determines genotype of organism. Erwin Chargaff ● Chargaff's rules showed that A = T_ and G = C so there was complementary base pairing of a purine with a pyrimidine DNA Orientation ● On the top rail, the strand is said to be oriented 5 to 3 ● The strand on the bottom runs in the opposite direction and is oriented 3 to 5 The orientation of the two strands is called antiparallel Nitrogenous Bases Two types: ● Purines (2 rings) ● Pyrimidines (one ring) ● Purines- Adenine and Guanine ● Pyrimidines - Thymine and Cytosine Practice Pairing… A C G G T A 12.2 DNA Replication DNA Replication ● The process of a cell duplicating its DNA before a cell divide. ● DNA polymerase is the principal enzyme involved in DNA replication It joins individual nucleotides to produce a new strand of DNA DNA Replication ● Enzyme (DNA helicase) breaks hydrogen bonds that hold the nucleotides together by the nitrogen bases. DNA unzips. ● Free nucleotides pair with exposed nucleotides on both strands. ● Sugars and phosphates of adjacent nucleotides forming adjacent strands. ● Each of 2 double stranded DNA molecules spiral forming a helix. From DNA to Protein … Genes and Proteins ● DNA determines your genes your amino acid sequence, and your protein production. 3 Types of RNA ● Messenger RNA (mRNA): brings _________ from DNA in nucleus to the cytoplasm. ● Ribosomal RNA (rRNA): attach to mRNA using its information to assemble the amino acids in order. ● Transfer RNA (tRNA): transfers amino acids to the ribosome to be assembled into protein Transcription ● Process of _________ making a single stranded _______ in the nucleus. The Genetic Code 20 different amino acids and 4 different nitrogen bases code for all the gazillion proteins. ● Each set of 3 nitrogen bases forms a triplet called a codon There are 64 different codons. ● AUG is the start codon. ● UAA, UGA, UAG are the stop codons. 60 other codons code for the 20 different amino acids. Translation from mRNA to protein ● mRNA codon of AUG attaches to __________. _ tRNA anticodon of UAC attaches to AUG ● Second codon of mRNA GCA attaches to tRNA anticodon of CGU. ● Amino acids on the other side of tRNA are joined by peptide bonds. ● Process continues until UAA the stop codon is read, and the protein is then complete. Genetic Changes ... Mutation: A Change in DNA ● Simple error radiation can produce mutations (changes in DNA). ● In reproductive cells (eggs or sperm), mutations may be harmful or they may produce a useful adaptation. ● In body cells, mutations may or may not cause harm. If mutation affects cell division, cancer results. Two types of gene mutations: ● Point mutation - change in a single nitrogen base pair in DNA, resulting in the change of one amino acid of a protein. ● single mutation - one nitrogen base is added or deleted, resulting in a drastic change in the amino acid sequence. Usually more Harmful than point mutations. Chromosomal Mutations ● Nondisjunction - organism has one more or one less chromosome than it should. ● Piece of chromosome could break away and become lost, or it could rejoin upside down. Causes of Mutations ● Mutagens - agent that causes change in DNA. 1. Radiation - x-rays, cosmic, ultraviolet and nuclear often cause deletions and substitutions. 2. Chemicals - asbestos (used in insulation) and formaldehyde (used as preservative) usually cause _________________. Repairing DNA ● Often occurs naturally by the enzymes of the organism. However, if the exposure to the mutagen is very high, the chance for repair is slim.
