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CHAPTER 12DNA and RNAEssential QuestionsHow do genes work?What are they made of and how do they determine the characteristics of organisms?Are genes single molecules or are they longer structures made up of many molecules?

12-1 DNAGriffith and Transformation1928, Frederick Griffith, investigated pneumoniaTwo different pneumonia bacteriaColonies with rough edges- harmlessColonies with smooth edges- pneumonia

RoughSmooth

Smooth

Smooth

Rough

Transformation- when a bacteria picks up foreign DNA. This changes the bacteria.

Griffiths hypothesis- 1) some factor was transmitted from the heat-killed cells to the harmless living cells. 2) This factor must contain information that would change the harmless cells into disease-causing cells. 3) This factor could be passed onto offspringOswald Avery, 1944

Smooth

Rough

Destroy: ProteinsLipidsCarbohydratesRNAOswald Avery, 1944

Smooth

Rough

Destroy: DNA

Averys conclusionDNA must store and transmit genetic information from one generation to the nextHershey-Chase ExperimentAlfred Hershey and Martha Chase, 1952What transmits hereditary information: DNA or proteins?Bacteriophage- a virus that infects bacteriaComposed of DNA or RNA coreProtein coat

A bacteriophage will inject virus DNA or RNA into a bacteria. The viral genes will use the cell to make more viruses and also destroy the cell.

Components and Structure of DNA

Components Structure of DNA5-carbon sugarsDeoxyribosePhosphatesNitrogenous bases

Components Structure of DNANucleotide:5-carbon sugar (deoxyribose) PhosphateNitrogenous base

Nitrogenous basesPurines (2 rings):AdenineGuaninePyrimidines (1 ring):CytosineThymine

Chargaffs RuleErwin Chargaff% of Guanine = % of Cytosine% of Adenine = % of ThymineSourceATGCStreptococcus29.831.620.518.0Yeast31.332.918.717.1Herring27.827.522.222.6Human30.929.419.919.8Rosalind FranklinEarly 1950sUsed x-ray diffraction to Study the structure of DNA

James Watson and Francis Crick1953 created a model to explain the structure of DNA

They used Franklins photographs

Double Helix2 strands wrapped around each other

Nucleotides are linked togetherG bind to CT binds to ABases are connected to opposite bases by hydrogen bondsG to C by three bondsT to A by two bonds

12-2 Chromosomes and DNA ReplicationDNAProkaryotes- one single chromosome, DNA is circular

Eukaryotes- multiple chromosomes, DNA is linear

DNA LengthE. Coli4,600,000 base pairs4,000 genes1.6mm longHuman DNA3,000,000,000 base pairs35,000 genes2 meters longChromatin- substance of tightly packed DNA and protein

Histones- protein that DNA is coiled aroundNucleosome- histone with DNA wrapped around it

What do histones and nucleosomes do?Histones: DNA held tightly= turned offDNA held loosely= turned onNucleosomes: aid in folding and packing of DNA

DNA ReplicationProkaryotes- one site to begin replication

DNA ReplicationProkaryotes- two complete complementary DNA strands created.

DNA ReplicationEukaryotes- multiple sites along the linear DNA strand begin replicationDNA ReplicationComplementary bases are added to the template strand.

CATGTGATCATAGATA- template strandDNA ReplicationComplementary bases are added to the template strand.CATGTGATCATAGATA- template strandGTACACTAGTATCTAT- copied strand

DNA ReplicationDNA is unwound by an enzyme- HelicaseHelicase breaks the hydrogen bonds between bases

Replication bubble- Where the helicase unwinds the DNA to begin copying

Replication fork-The end of the bubble where DNAis being unwound.

DNA ReplicationDNA polymerase- an enzyme that adds new nucleotides on the complementary strandDNA polymerase- proof reads the new strand to make sure no mistakes are made. It ensures that the right base is added on the complementary strand.

CATGTGATCATAGATA- template strandGTACACT- copied strand

TGTTTTTAAAAACCCCCCGGGGGGG12-3 RNA and Protein SynthesisGenes- coded DNA instructions that control the production of proteins within the cell

The Structure of RNASimilarities between RNA and DNABoth are composed of nucleotides (5-carbon sugar, phosphate, nitrogenous base)Differences between RNA and DNA

1. 5-carbon sugar is ribose (not deoxyribose)

Differences between RNA and DNA

2. Usually single stranded (not double stranded)

Differences between RNA and DNA

3. Contains uracil instead of thymine

Types of RNAMessenger RNA (mRNA)

Contains instructions for assembling amino acids into proteinsLong single strand of RNA

Types of RNARibosomal RNA (rRNA)

Proteins and rRNA make up ribosomes

Amino acids are linked together to make proteins at the ribosome.

Types of RNATransfer RNA (tRNA)

A molecule that carries an amino acid to a ribosome in order to make a protein

TranscriptionTranscription- Transcribing a DNA sequence into an RNA sequenceRNA polymerase- separates DNA strands and copies one strand of the DNA. It creates a complementary strand of RNA.

How does RNA polymerase know where to copy?RNA polymerase starts copy by binding to promoter- a specific sequence of DNA RNA polymerase stops copying when it reaches a terminator- a specific sequence of DNA

TranscriptionRNA polymerase creates a mRNA (messenger RNA). The mRNA strand is complementary for the DNA sequence from which it was copied. It has U instead of T.RNA- GUACCAUGAUCAUGDNA- CATGGTACTAGTACmRNA editingThe mRNA is edited:5 Cap- A cap is added to the front. It includes a Guanine and three phosphates. Poly A Tail- A tail is added to the end. It is a long string of A nucleotides.

5 G-P-P-P- CAGUAGAUCAUGA-AAAAAAAA

mRNA editingThe mRNA is edited:Introns- parts of the mRNA that are cut outExon- parts of the mRNA that are left in

5 G-P-P-P- CAGUCGUACUAUGACACUAGAUCAUGA-AAAAAAAA5 G-P-P-P- CAGUC UGACAC AUGA-AAAAAAAA5 G-P-P-P- CAGUCUGACACAUGA-AAAAAAAA

mRNA editing

Genetic CodeThere are 20 amino acidsA string of amino acids forms a proteinAmino acids are held together by peptide bonds.A polypeptide is another name for a protein

aminoacid- aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacid-aminoacidGenetic CodeThe sequence of mRNA can be translated into an amino acid sequence.The mRNA sequence is divided into groups of three nucleotides.Three nucleotides = codon

Genetic CodeEach codon is equal to a certain amino acid.

UCGCACGGUUCG-CAC-GGUSerine-Histidine-Glycine

Genetic CodeThere are 4 bases (C,A,U,G)Each codon is 3 bases long.64 possible codon combinations (4x4x4)There are 64 codons but only 20 amino acids

Genetic CodeMultiple codons are linked to the same amino acid. There is one start codon- AUGThere are three stop codons- UAA, UAG, UGA

AUG-xxx-xxx-xxx-xxx-xxx-xxx-xxx-xxx-UAAStartStopTranslationTranscription- creating a mRNA sequence that is complementary to a DNA sequence.Translation- creating an amino acid sequence (protein) from a mRNA sequence.

TranslationTranscription: mRNA is transcribed from DNA in the nucleusmRNA is edited and then goes into the cytoplasam

Translation: 1. mRNA attaches to a ribosomeTranslation2. A tRNA brings an amino acid to the ribosomeA tRNA has an anticodonThe anticodon is the complementary sequence of a codon

tRNA anitcodon:UACmRNA codon: AUG

tRNA anitcodon:UACAAGUUUmRNA codon: AUG UUC AAA3. The tRNA with the correct anticodon will bind to the codon on the mRNA4. The tRNA will release its amino acid

tRNA anitcodon:UACAAGUUUmRNA codon: AUG UUC AAA5. The amino acid from the tRNA will create a peptide bond with the amino acid next to it.

tRNA anitcodon:UACAAGUUUmRNA codon: AUG UUC AAA6. The empty tRNA will leave the ribosome to pickup another amino acid.7. Amino acids will continue to be added until a stop codon on the mRNA is reached.

12-4 MutationsMutation- change in the genetic material

Are all mutations bad?

12-4 MutationsGene Mutations- Change in the sequence of the DNA of one or a few nucleotides

Chromosome Mutations- Change in the structure of the chromosome and usually involves many genes

Gene Mutations-Point Mutation- a change in one nucleotide of the DNASubstitution- changing one nucleotide for another

CATGACTAGGCAATTAGGC originalCATGACTACGCAATTAGGC mutationGene Mutations- Point Mutation- Insertion- adding one nucleotideCAT-GAC-TAG-GCA-ATT-AGG originalCAT-GAC-TAG-GCCA-ATT-AGG mutation

Deletion- removing one nucleotideCAT-GAC-TAG-GCA-ATT-AGG originalCAT-GAC-TAG-GC-ATT-AGG mutation

What are the consequence of mutations?DNA AAAAAGAATmRNA UUUUUCUUAProtein PhePheLeu

Silent mutation- does not change the amino acidSubstitution mutation can change a proteinCAT-GAC-TAG-GCA-ATA-AGG original DNACAT-GAC-TAC-GCA-ATA-AGG mutation DNA

CAT-GAC-TAG-GCA-ATA-AGG original DNAGUA-CUG-AUC-CGU-UAU-UCCoriginal mRNAVal----Leu----Ile---Arg---Tyr---Seroriginal protein

CAT-GAC-TAC-GCA-ATA-AGG mutation DNAGUA-CUG-AUG-CGU-UAU-UCCmutant mRNA Val----Leu---Met---Arg---Tyr---Sermutant protein

Insertion or Deletion mutations cause frame shiftFrame shift- a change in the reading frame of the codons caused by an insertion or deletion mutation

CAT-AAG-GAC-TAG-GCA-ATA-AGG original DNAC T-AAG-GAC-TAG-GCA- ATA-AGG mutation DNACTA-AGG-ACT-AGG-CAA-TAA-GG mutation DNA

Insertion or Deletion mutations cause frame shiftCAT-AAG-GAC-TAG-GCA-ATA-AGG original DNACTA-AGG-ACT-AGG-CAA-TAA-GG mutation DNA

CAT-AAG-GAC-TAG-GCA-ATA-AGG original DNAGUA-UUC-CUG-AUC-CGU-UAU-UCC original mRNAVal----Phe---Leu----Ile---Arg---Tyr---Ser original protein

CTA-AGG-ACT-AGG-CAA-TAA-GG mutation DNA GAC-UCC-UGA-UGC-GUU-AUU-CC mutant mRNA Asp--Ser- Stopmutant protein

Chromosomal MutationsMutations of Chromosomes:Deletion- Removal of a chromosome segment

Chromosomal MutationsMutations of Chromosomes:Duplication- More than one copy of a chromosome segment

Chromosomal MutationsMutations of Chromosomes:Inversion- Rearrangement of a chromosome segment

Chromosomal MutationsMutations of Chromosomes:Translocation- Movement of a chromosome segment to another chromosome

Chromosomal Mutations

Phases of Meiosis4N2N2N2N2N2NNNNNErrors in meiosis

Sometimes chromosomes do not separate correctly.Errors in meiosisHaploid- one set of chromosomesDiploid- two sets of chromosomes

Polyploidy- an organism with an extra set of chromosomesTriploid- three sets of chromosomesTetraploid- four sets of chromosomes

PolyploidyPolyploidy is more common in plants than animals.Polyploid plants are often stronger and larger than diploid plants.12-5 Gene Regulation97% of DNA does not code for a functional proteinNon-coding DNAUsed for structure and regulation of genesGenes can be turned on or offOn- RNA polymerase binds to the DNA, a mRNA copy is made (transcription), the mRNA is translated into an amino acid sequence (protein)Off- RNA polymerase does not bind to the DNA. No protein is made

Why are genes turned on or off?If a protein is not needed- the cell does not want to waste energy making it.PromoterPromoter- where RNA polymerase binds to begin transcription

RNA promoterStart Trans. Stop Trans.

---PPPPPP----GGGGGGGGGGGGGGGGGGG--Lac operonOperon- a group of genes that work togetherE. coli can use lactose as a source of food.

RNA promoterLactose genes

---PPPPPP----LLLLLL---LLLLLL--LLLLLL--

Lac operonIf there is lactose present- it transcribes and translates the lactose processing genesIf there is not lactose- it does not transcribe and translate the lactose processing genesHow does E. coli control the transcription of the lac genes?Operator- a site on the DNA where a repressor protein can bind. This prevents the transcription of the DNA by RNA polymerase

PPPP---OOOO--LLLL-----LLLLLL----LLLLLLHow does E. coli control the transcription of the lac genes?Lactose binds to the repressor protein and causes it to be removed so RNA polymerase can transcribe the lactose genes.

PPPP---OOOO--LLLL-----LLLLLL----LLLLLL

Eukaryotic Gene RegulationEukaryotic cells do not have operonsTATA Box- a DNA sequence 30 base pairs long, with T and A. It is in front of the gene sequence.

-------TATATATA--GGGGGGGGGGGGGGG----

Eukaryotic Gene RegulationPromoter sequences regulate genes in eukaryotesAccelerate transcription- cause the RNA polymerase to bind to the DNA quickly and oftenStop transcription- prevents the RNA polymerase from binding to the DNA

---PPPPP----TATATATA----GGGGGGGGGGGGG----Eukaryotic Gene RegulationWhy do cells need to control transcription?Prokaryotes- do not want to waste energy by producing unnecessary proteinsEukaryotes-????Eukaryotic Gene RegulationWhy do cells need to control transcription?Prokaryotes- do not want to waste energy by producing unnecessary proteinsEukaryotes-different cells must produce different proteins

Different cells in an eukaryote all have the same DNA.Liver cells must produce only the proteins necessary to be a liver cell

Development and DifferentiationDifferentiation- cells become specialized in structure and functionHox genes- control the differentiation of cells and tissues in the embryo

Hox gene mutationsCauses developmental abnormalities

Hox genes are very similar in different organisms.The same type of gene controls the development of the same type of structure.