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KEY CONCEPT DNA was identified as the genetic material through a series of experiments. DNA & RNA Units of Life A. B. C. D. E. F. History of DNA DNA Discovery RNA Transcription Translation Mutations DNA: Blueprint for Life A. History of Discovery 1. Frederick Griffith: Mice Transformation 2. Avery: DNA Identified 3. Hershey-Chase: DNA and Viruses 4. Rosalind Franklin: X-ray Evidence 5. Chargaff’s Rules: Base Pairing 6. Watson and Crick:The Double Helix Discovery of DNA: A History FREDERICK GRIFFITH (1928) • Studied way in which bacteria cause pneumonia and recognized process of transformation. • Showed through experiments that one strain of bacteria could be transformed into another. • Hypothesized that there was a transforming factor involved. Avery identified DNA as the transforming principle. • Avery isolated and purified Griffith’s transforming principle. • Avery performed three tests on the transforming principle. – Qualitative tests showed DNA was present. – Chemical tests showed the chemical makeup matched that of DNA. – Enzyme tests showed only DNA-degrading enzymes stopped transformation. Griffith finds a ‘transforming principle.’ • Griffith experimented with the bacteria that cause pneumonia. • He used two forms: the S form (deadly) and the R form (not deadly). • A transforming material passed from dead S bacteria to live R bacteria, making them deadly. Section 12-1 Griffith’s Experiment Heat-killed, disease-causing bacteria (smooth colonies) Control Disease-causing Harmless bacteria Heat-killed, disease(no growth) bacteria (smooth (rough colonies) causing bacteria colonies) (smooth colonies) Dies of pneumonia Lives Lives Harmless bacteria (rough colonies) Dies of pneumonia Live, disease-causing bacteria (smooth colonies) Section 12-1 Griffith’s Experiment Heat-killed, diseasecausing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Dies of pneumonia Harmless bacteria (rough colonies) Lives Heat-killed, disease-causing bacteria (smooth colonies) Lives Control (no growth) Harmless bacteria (rough colonies) Dies of pneumonia Live, disease-causing bacteria (smooth colonies) DNA Discovery: A History AVERY (1944) • Repeated Griffith’s experiments and identified DNA as the transforming factor-identified DNA • DNA-stores and transmits genetic information from one generation to another. DNA Discovery: A History HERSHEY-CHASE (1952) • Experiments with bacteria-killing viruses (bacteriophages) • Confirmed again that DNA was the molecule that contained the genetic code. Hershey and Chase confirm that DNA is the genetic material. • Hershey and Chase studied viruses that infect bacteria, or bacteriophages. – They tagged viral DNA with radioactive phosphorus. – They tagged viral proteins with radioactive sulfur. • Tagged DNA was found inside the bacteria; tagged proteins were not. Hershey-Chase Experiment Bacteriophage with phosphorus32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Hershey-Chase Experiment Bacteriophage with phosphorus32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Hershey-Chase Experiment Bacteriophage with phosphorus32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium Watson and Crick determined the three-dimensional structure of DNA by • They realized that building models. DNA is a double helix that is made up of a sugar-phosphate backbone on the outside with bases on the inside. DNA Discovery: A History ROSALIND FRANKLIN and MAURICE WILKINS (1950’S) • Studied DNA molecule by using a purified DNA sample and x-ray pictures of molecule. • Found it was a twisted “X” structure. • Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff. – Franklin’s x-ray images suggested that DNA was a double helix of even width. – Chargaff’s rules stated that A=T and C=G. DNA Discovery: A History ERWIN CHARGAFF (early 1950’s) • Observed in any DNA sample, the number of adenine molecules was equal to the number of thymine; same for guanine and cytosine. • Developed nitrogen base pairing rules Percentage of Bases in Four Organisms Source of DNA A T G C Streptococcus 29.8 31.6 20.5 18.0 Yeast 31.3 32.9 18.7 17.1 Herring 27.8 27.5 22.2 22.6 Human 30.9 29.4 19.9 19.8 DNA Discovery: A History WATSON-CRICK (1953) • Tried to build 3D DNA model couldn’t quite solve it • Used Franklin’s pictures to develop the double helix model • Double helix model explained much about DNA structure, including placement of nitrogen bases and the formation of bonds. • Received Nobel Prize along with Wilkins (Franklin didn’t—why?) DNA: Blueprint for Life B. The Structure of DNA 1. Nucleotides – basic unit of DNA 2. Nitrogen Bases 3. DNA Replication DNA is composed of four types of nucleotides. • DNA is made up of a long chain of nucleotides. • Each nucleotide has three parts. – a phosphate group – a deoxyribose sugar – a nitrogen-containing base phosphate group deoxyribose (sugar) nitrogen-containing base • The nitrogen containing bases are the only difference in the four nucleotides. Structure of DNA DNA made of nucleotides, the basic unit Nucleotide is made of three parts: 1. One Phosphate 2. One 5-Carbon Sugar (deoxyribose) 3. One Nitrogen base Adenine(A), Guanine(G) – Purines Thymine(T), Cytosine(C) – Pyrimidines Structure of DNA Sugar and Phosphate are the “backbone” of DNA Two parallel strands of sugarphosphate groups with pairs of nitrogen bases linking the two strands together with weak hydrogen bonds, forming a double helix. WHY WEAK BONDS? Nucleotides always pair in the same way. • The base-pairing rules show how nucleotides always pair up in DNA. – A pairs with T – C pairs with G • Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width. G A C T Structure of DNA Nitrogen Base Pairing ‘Rulz’: A=T (one purine/ pyrimidine) C=G (one purine/ pyrimidine) DNA strands are complementary because of base pairing rules Nitrogen bases attached to sugars. • The backbone is connected by covalent bonds. • The bases are connected by hydrogen bonds. hydrogen bond covalent bond DNA Nucleotides Purines Adenine Guanine Phosphate group Pyrimidines Cytosine Thymine Deoxyribose Structure of DNA Nucleotide Weak Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) DNA Replication A Perfect Copy When a cell divides, each daughter cell receives a complete set of chromosomes. This means that each new cell has a complete set of the DNA code. Before a cell can divide, the DNA must be copied so that there are two sets ready to be distributed to the new cells. DNA Replication Complementary strands of DNA serve as a pattern for a new strand. DNA replication carried out by enzymes which “unzip” the two strands by breaking the hydrogen bonds. Then, appropriate nitrogen bases are inserted. Enzymes also proofread the bases to make sure of correct base pairing. Chromosome Structure Chromosome Nucleosome DNA double helix Coils Supercoils Histones DNA Replication New strand Original strand DNA polymerase Growth DNA polymerase Growth Replication fork Replication fork New strand Original strand Nitrogenous bases DNA Replication Copied DNA C G G T A A C A T T A DNA G C C A T T G T A A T enzymes Copied DNA C G G T A A C A T T A DNA G C C A T T G T A A T RNA: The Other Code C. RNA and Protein Synthesis A.The Structure of RNA B. DNA and RNA Similarities/Differences C. Transcription D. Types of RNA E. Protein Synthesis F. Translation RNA: The Other Code A. RNA similar to DNA • • long chain made of nucleotides each nucleotide consists of: a sugar a phosphate a nitrogen-containing base • sugar and phosphate still backbone of RNA RNA: The Other Code B. RNA different from DNA • Different type of sugar (ribose) • Single strand rather than a double strand RNA molecule is a disposable copy of DNA • Nitrogen base THYMINE found in DNA replaced by a similar base URACIL (U) in RNA ex. ( A - U ) and ( C - G ) Why RNA? C. Why does DNA need to transfer genetic information to RNA? 1. DNA is found in the nucleus. Ribosomes are outside the nucleus. 2.DNA does not leave nucleus-too large for nuclear pores. 3.Messenger must bring genetic information from the DNA to the ribosomes to make proteins/amino acid 4.Special molecule, messenger RNA (mRNA), performs this task. RNA: The Other Code RNA - The Other Part of the Code A. RNA –“messenger” between the DNA in the nucleus and the ribosomes. (mRNA) B. Ribosomes –organelles outside the nucleus that make proteins from amino acids. C. Proteins/Amino Acids –used to build and repair cells. • Discovery education streaming • Standard Deviants School Biology: The Cell –RNA Polymerase segment RNA Synthesis Transcription- process by which one strand of DNA is copied into a complementary strand of mRNA in the nucleus. enzymes mRNA C G G U A A C A U U A DNA G C C A T T G T A A T Copied DNA C G G T A A C A T T A enzymes mRNA G C C A U U G U A AU enzymes Transcription Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNA polymerase DNA RNA Types of RNA Transfer RNA (tRNA) A. Carries amino acids to ribosome B. Single strand looped back on itself C. Anticodon-three nucleotides on tRNA are complementary to the three on the mRNA. D. Matching of codon (mRNA) to anticodon (tRNA) allows the correct amino acid to be put in place. Ribosomal RNA (rRNA) A. makes up majority of ribosome Types of RNA RNA can be Messenger RNA also called Ribosomal RNA which functions to mRNA Carry instructions also called which functions to rRNA Combine with proteins from to to make up DNA Ribosome Ribosomes Transfer RNA also called which functions to tRNA Bring amino acids to ribosome Protein Synthesis A. Nucleotides in DNA have all the information to make proteins. B. DNA code copied into mRNA C. Proteins are made of amino acids which are coded from mRNA. D. mRNA code is read in triplet form called a CODON which specifies certain amino acids using a decoder (p.201) Protein Synthesis: Translation Only 20 amino acids make all life as we know it! How can this be? *AUG - codes for amino acid methionine or be an “initiator codon” and will always start mRNA *Some are “stop” codons which end mRNA Translation -the decoding of mRNA code into an amino acids--proteins Translation Nucleus Messenger RNA Messenger RNA is transcribed in the nucleus. Phenylalanine tRNA mRNA Transfer RNA Methionine The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon. Ribosome mRNA Lysine Start codon Translation (continued) The Polypeptide “Assembly Line” The ribosome joins the two amino acids— methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids. Lysine Growing polypeptide chain Ribosome tRNA tRNA mRNA Completing the Polypeptide mRNA Ribosome Translation direction The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain. The Genetic Code Decoder BACK Translation DNA T A C T T T G T A A C T mRNA A U G A A A C A U U G A enzymes Determining the Sequence of a Gene •DNA contains the code of instructions for cells. •Sometimes, an error occurs when the code is copied. •Such errors are called mutations. Mutations • Mutations can occur on individual chromosomes by way of gene mutations. – Base sequence gets rearranged and may cause insertion, deletion, or substitution of genes • Mutations can also occur with entire chromosomes. Gene Mutations: Substitution, Insertion, and Deletion Deletion Substitution Insertion • Original The fat cat ate the wee rat. • • • • • The fat hat ate the wee rat. The fat caa tet hew eer at. The fat __ ate the wee rat. The fat cat xlw ate the wee rat The fat tar eew eht eta tac. Point Mutation Frame Shift Deletion Insertion Inversion Chromosome Mutations Deletion Duplication Inversion Translocation Mutagen. • Ultraviolet light, nuclear radiation, and certain chemicals can damage DNA by altering nucleotide bases so that they look like other nucleotide bases Environmental Impact • Ultraviolet light, nuclear radiation, and certain chemicals can damage DNA by altering nucleotide bases so that they look like other nucleotide bases. Mutagens are environmental agents that can cause mutations in the genetic code. • High energy radiation from radioactive elements, X-rays, gamma rays, microwaves, and ultraviolet light (please use sunscreen and wear a hat). • Industrial chemicals such as PCB's (support the ban). • Pollutants such as cigarette smoke (please don't smoke and if you do work hard to quit) • Pesticides (eat organic). • Food Additives (read food labels). • Drugs (use only when necessary). • Viruses (wash your hands and practice safe sex). Mutagen • An agent, such as a chemical, ultraviolet light, or a radioactive element, that can induce or increase the frequency of mutation in an organism. • Spontaneous DNA replication and repair errors, spontaneous modification of nucleotides • All types of mutations produced UV irradiation • Pyrimidine dimers induce error prone repair (SOS) Mainly G-C to A-T transitions, but all other types of mutations including deletions, frameshifts, and rearrangements Impact of Genetics Autosome Disorders caused by Recessive alleles Dominant alleles Codominant alleles include include include Huntington’s disease Sickle cell disease Galactosemia Albinism Cystic fibrosis Phenylketonuria Tay-Sachs disease Achondroplasia Hypercholesterolemia Pedigrees A circle represents a female. A horizontal line connecting a male and female represents a marriage. A half-shaded circle or square indicates that a person is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait. A square represents a male. A vertical line and a bracket connect the parents to their children. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. Blood Groups A. Four major blood groups: A, B, O, AB B. Each type carries certain Antigens C. Antigens are markers on surface of cells that identify the type of cell. Allows antibodies to attack if they aren’t identified correctly. D. Antibodies found in the body, they provide protection from diseases and foreign substances. As you are exposed to diseases, your body builds up antibodies—resistance. Blood Groups E. Blood Type A B AB O Antigen A B AB none Antibodies b a none a and b F. Type O blood is the universal donor blood Why? There are no markers (but O can only receive O) G. Type AB is the universal recipient blood Why? Carry both markers; lack antibodies Blood Groups Phenotype (Blood Type Genotype Antigen on Red Blood Cell Safe Transfusions To From Blood Groups-Rh Factor • Rh factor identified in rhesus monkey and later found in human blood. • Rh+ is dominant over Rh• If you have Rh+ blood (O+, A+, etc)= O+O+, A+O- , B+O+, etc • If you have Rh- blood (O-, B-, etc)= O-O-, B-O- ,A-O- , etc Blood Types-Rh Factor • Blood types must match up correctly when getting blood or death results. • Important during pregnancy: if mom is Rh- and has Rh+ fetus, mom’s antibodies don’t recognize Rh+ and begin to attack. Could result in death. This can be detected early and treated with blood supplements. • What was the dad’s Rh type? Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II Sex-Linked Traits: Colorblindness Father (normal vision) Normal Colorblind vision Male Female Mother (carrier) Daughter (normal vision) Son (normal vision) Daughter (carrier) Son (colorblind) Sex-Linked Traits: Colorblindness Father (normal vision) Normal Colorblind vision Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind)