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DNAChapter 12
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DNA
Holds our genetic information Like a library
Important for mitosis to occur
Biologists had to discover the chemical nature of DNA to determine that it is responsible for our genetic information
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Griffith and Transformation
Transformation: when a strain of bacteria is changed by a gene or genes from another bacteria
Experiment Inject mice with bacteria containing virus for
pneumonia Smooth colonies = have bacterial infection Rough colonies = harmless bacteria
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Griffith and Transformation If the virulent colonies were killed with heat and mixed
with harmless bacteria, then the harmless bacteria get transformed into virulent bacteria
Some factor of the bacteria was tranformed to harmless bacteria
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Avery and DNA
Wanted to repeat Griffith’s experiment
Treated heat-killed virulent bacteria with enzymes One enzyme destroyed RNA and proteins Another enzyme destroyed ONLY DNA
Lethal Virus
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Avery and DNA
Results showed that bacteria treated with DNA destroying enzyme did not transform harmless bacteria into virulent bacteria
It is the DNA that stores the genetic information from one generation to the next
Lethal Lethal Non Lethal
Lethal Virus
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Hershey-Chase
Bacteriophage: a virus that infects bacteria ONLY
Scientists wanted to see what gets injected into a bacteria to cause infection Used a radioactive
marker for DNA and protein
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Hershey Chase After infection, the bacteria that had radioactive marker
on DNA showed that it is the DNA that is inserted into the bacteria
Results: DNA from the virus is what causes infection
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DNA Structure
Monomer of DNA is a nucleotide 5-carbon sugar Phosphorous group Nitrogenous base
4 Nitrogenous bases in DNA Adenine Guanine Thymine Cytosine
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DNA Structure
Backbone of DNA is the sugar and phosphate
Nitrogenous bases stick out of side to form latter rungs These bases are
repeated in a pattern that form our genetic code
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DNA Structure
Chargaff’s Rule Scientist that discovered a pattern between the 4
bases Same percentage of Adenine as Thymine Same percentage of Guanine as Cytosine
Scientists still not sure how they match up though
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DNA Structure
Rosalind Franklin Scientist that worked with X-ray diffraction Used X-rays on a portion of DNA and the results
showed an X pattern
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DNA Structure
Watson & Crick Scientists that
were able to understand Rosalind’s X-ray picture
Result: DNA has a double helix pattern where the nitrogenous bases face each other
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DNA Structure
DNA has a double helix pattern Looks like a ladder twisted up
The sides of the ladder are the sugar and phosphate and the rungs of the ladder are the nitrogenous bases paired up
The adenine binds to thymine
The guanine binds to cytosine
This concluded Chargaffs’s rule base pairing
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DNA and Chromosomes
Prokaryotes Lack nucleus and organelles DNA floats as a circle in the
cytoplasm
Eukaryotes 1000 times more DNA than
prokaryotes DNA is located in nucleus Specific number of
chromosomes Ex: Humans have 46
chromosomes
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DNA and Chromosomes DNA Length
DNA is very long DNA is coiled up into a
very small space because it is in chromatin form
Chromosome Structure Tightly packed
chromatin is wrapped around small proteins called histones
When chromatin gets super coiled you create a chromosome
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DNA Replication
Each strand of DNA is needed to be a template for a new strand of DNA to be produced
Since you can use one strand to make the other side, they are said to be complementary
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Duplicating DNA
Before mitosis occurs, DNA needs to be duplicated first during interphase
When DNA duplicates, its called replication
DNA molecules separates into two strands, then produces two new complementary strands following the rules of base pairing
Each strand serves as a template for the new strand
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How Replication Occurs Enzymes help make new strands of DNA
One enzyme called helicase “unzips” the DNA, separating the base pairs
DNA polymerase adds new bases to pair up with the template
This enzyme also proofreads to make sure everything matches
What would be the matching bases to the part of DNA shown below?
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RNA & Protein Synthesis
Sections 3-4
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Structure of RNA
Made of nuleotides
Three differences between DNA & RNA Sugar
DNA = deoxyribose sugar RNA = ribose sugar
RNA is single stranded RNA uses Uracil instead of
Thymine to bond with Adenine
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Types of RNA
Three types of RNA mRNA
Messenger RNA rRNA
Ribosomal RNA tRNA
Transfer RNA
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Types of RNA
Messenger RNA This is a copy of complimentary strand of DNA Eventually will code for a protein to be made
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Types of RNA
Ribosomal RNA RNA found in ribosomes (organelles in the cell) Ribosomes are the factory for protein synthesis
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Types of RNA
Transfer RNA Help produce a protein from mRNA Brings amino acids (monomer of protein) to
ribosome to bond them together and make a whole protein
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Transcription
Taking DNA and making an RNA copy Occurs in the cell’s nucleus RNA polymerase opens the DNA and adds RNA
copy to the template Once this is made it is called pre-mRNA
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RNA Editing Pre-mRNA is a rough draft to the final copy of
mRNA Some parts of pre-mRNA are not needed to make
a protein These unnecessary parts are called introns Introns get cut out of pre-mRNA
Before leaving the nucleus, mRNA needs to get a cap and tail to finalize the RNA strand
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The Genetic Code Proteins are made of 20 possible amino acids In order to make a protein from a strand of mRNA, the
mRNA is read in a 3 letter sequence called codons
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The Genetic Code
Each three letter codon represents an amino acid DNA = AGCGTGCCA RNA = Codons = Amino acids =
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The Genetic Code
RNA knows when to start and stop based on the codons read There is ONE start codon: AUG There are THREE stop codons: UAA, UAG, UGA
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Translation
Taking mRNA and making a protein
Occurs in the cytoplasm on a ribosome
tRNA brings specific amino acids to ribosome If mRNA = AUG, then tRNA = UAC The tRNA has the anti-codon
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Translation As new tRNA brings amino acids to the ribosome, past
ones break off leaving just amino acids bonded to each other
This continues until one of the three STOP codons is met Finished amino acid strand goes through protein folding
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Mutations
Changes in the DNA sequence that affect the cell
Two types of mutations Gene mutation Chromosomal mutation
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Gene Mutation
Point mutation A change in one nucleotide in a DNA
sequence Occur only in a single point of the DNA Can sometimes be a problem
Frameshift mutation A change in the reading frame of DNA Since DNA is read in 3 letter codons, if
there is an insertion, deletion, or large change in these codons the frame is changed
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Chromosomal Mutation A change in the number of chrom0somes in the
cell
Four types Duplication Deletion Inversion Translocation