DNA & RNA Units of Life

DNA & RNAUnits of Life History of DNA DNA Discovery RNA Transcription Translation Mutations

DNA: Blueprint for Life A. History of Discovery • Frederick Griffith: Mice Transformation • Avery: DNA Identified • Hershey-Chase: DNA and Viruses • Rosalind Franklin: X-ray Evidence • Chargaff’s Rules: Base Pairing • 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.

Griffith’s Experiment Section 12-1 Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Harmless bacteria (rough colonies) Control(no growth) Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Dies of pneumonia Dies of pneumonia Lives Lives Live, disease-causingbacteria (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-Chase Experiment Bacteriophage with phosphorus-32 in DNA Phage infectsbacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infectsbacterium No radioactivity inside bacterium

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.

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 DNA1. Nucleotides – basic unit of DNA 2. Nitrogen Bases 3. DNA Replication

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 sugar-phosphate groups with pairs of nitrogen bases linking the two strands together with weak hydrogen bonds, forming a double helix. WHY WEAK BONDS?

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.

DNA Nucleotides Purines Pyrimidines Adenine Guanine Cytosine Thymine Phosphate group 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 Nucleosome Chromosome DNA double helix Coils Supercoils Histones

DNA Replication Original strand DNA polymerase New strand Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases New strand Original strand

enzymes 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 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 • 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 • RNA –“messenger” between the DNA in the nucleus and the ribosomes. (mRNA) • Ribosomes –organelles outside the nucleus that make proteins from amino acids. • Proteins/Amino Acids –used to build and repair cells.

enzymes enzymes enzymes RNA Synthesis Transcription- process by which one strand of DNA is copied into a complementary strand of mRNA in the nucleus. mRNAC 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 mRNA G C C A U U G U A AU

Transcription Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNApolymerase 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

Messenger RNA Ribosomal RNA Transfer RNA Bringamino acids toribosome Combine with proteins tRNA mRNA Carry instructions rRNA DNA Ribosome Ribosomes Types of RNA RNA can be also called which functions to also called which functions to also called which functions to from to to make up

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. mRNA Lysine Phenylalanine tRNA Transfer RNA 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. Methionine Ribosome Start codon mRNA

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. Growing polypeptide chain Ribosome tRNA Lysine tRNA mRNA Completing the Polypeptide The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain. mRNA Translation direction Ribosome

The Genetic Code Decoder BACK

enzymes 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

Determining the Sequenceof 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 Insertion Substitution

Original The fat cat ate the wee rat. • Point Mutation The fat hat ate the wee rat. • Frame Shift The fat caa tet hew eer at. • DeletionThe fat __ ate the wee rat. • Insertion The fat cat xlw ate the wee rat • Inversion The fat tar eew eht eta tac.

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

Codominant alleles Recessive alleles Dominant alleles Tay-Sachs disease Huntington’s disease Sickle cell disease Galactosemia Albinism Cystic fibrosis Hypercholes- terolemia Phenylketonuria Achondroplasia Impact of Genetics Autosome Disorders caused by include include include

DNA & RNA Units of Life