dna also known as deoxyribonucleic acid history of dna in the mid 1900’s scientists started asking...
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DNADNAAlso known as deoxyribonucleic acid
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History of DNAHistory of DNA
• In the mid 1900’s scientists started asking the question:– “How do genes work?”– Like many scientific stories, the
discovery of DNA was an accident while a scientist was trying to find out something else
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Frederick GriffithFrederick Griffith
• Griffith was working on what was causing the deadly disease pneumonia
• Griffith isolated two separate strains:– A disease causing strain– A harmless strain
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Disease-causing bacteria (smooth
colonies)
Harmless bacteria (rough colonies)
Heat-killed, disease-causing bacteria (smooth colonies)
Control(no growth)
Heat-killed, disease-causing bacteria (smooth colonies)
Harmless bacteria (rough colonies)
Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)
Dies of pneumonia
Figure 12–2 Griffith’s ExperimentFigure 12–2 Griffith’s Experiment
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Griffith’s ExperimentGriffith’s Experiment
• He found that mice injected with the disease-causing strain died of pneumonia
• However, if he heated the disease-causing strain and injected the mice with it they did not die at all
• This suggested that the disease wasn’t caused by a chemical toxin released by the bacteria
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Griffith’s ExperimentGriffith’s Experiment
• When he injected mice with the heat killed disease-causing bacteria they did not die– When he added
the harmless bacteria to the heat killed bacteria they did develop pneumonia and die!
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Griffith’s ExperimentGriffith’s Experiment
• Somehow the heat killed bacteria passed on their ability to cause disease to the harmless strain!!
• Griffith called this process transformation – one strain of bacteria changing into another
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Griffith’s ExperimentGriffith’s Experiment
• Griffith hypothesized that some “factor” was transferred from the heat-killed bacteria to the live, harmless bacteria
• He hypothesized that this factor was a gene that the live bacteria obtained from the heat-killed bacteria
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Oswald Avery’s ExperimentOswald Avery’s Experiment
• In 1944 Avery repeated Griffith’s experiment – He changed it by creating an extraction
of the “combined” bacteria and treating it with enzymes
– These enzymes destroyed all of the proteins, fats, carbs, and RNA
– Leaving only the DNA!!
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Oswald Avery’s ExperimentOswald Avery’s Experiment
• After he destroyed most of the organic components, transformation still occurred!
• He performed it one more time:– This time he destroyed the DNA in the
mixture– As he had guessed, the mice lived – He concluded that it was the DNA that
was responsible for the disease
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Oswald Avery’s ExperimentOswald Avery’s Experiment
• Avery’s Conclusion:– DNA is the nucleic acid that stores and
transmits genetic information from one generation of organism to the next
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Hershey-Chase ExperimentHershey-Chase Experiment
• Alfred Hershey and Martha Chase wanted to explain Avery’s findings further– They worked with bacteriophages
• “bacteria eater”• They attach to the outside of a bacterium
and inject their DNA into the cell• The DNA instructs the cell to make copies
of itself until the cell bursts with more bacteriophages
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Hershey-Chase ExperimentHershey-Chase Experiment
• They put radioactive markers on the outside of the bacteriophage as well as on the DNA inside
• These markers can be seen or followed during an experiment to determine which is left “inside” the bacterium to “infect” it
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Bacteriophage with phosphorus-32 in DNA
Phage infectsbacterium
Radioactivity inside bacterium
Bacteriophage with sulfur-35 in protein coat
Phage infectsbacterium
No radioactivity inside bacterium
Hershey-Chase Experiment
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Hershey-Chase ExperimentHershey-Chase Experiment
• Hershey and Chase concluded that the genetic material of the bacteriophage was DNA and not protein
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The Structure of DNAThe Structure of DNA
• DNA is a long molecule made up of nucleotides
• Each nucleotide is made up of three parts:– A 5-carbon sugar
called deoxyribose– A phosphate group– And a nitrogenous
base
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The Nitrogenous BasesThe Nitrogenous Bases
• There are 4 kinds of Nitrogenous Bases:– The Pyrimidines:
• Cytosine• Thymine
– The Purines:• Adenine• Guanine*the sugar phosphate forms the
“backbone” of the molecule
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PurinesAdenine Guanine
Phosphate group
Pyrimidines
Cytosine Thymine
Deoxyribose 5-Carbon Sugar
The NucleotidesThe Nucleotides
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Chargaff’s RulesChargaff’s Rules
• According to Erwin Chargaff:– Adenine always pairs with Thymine
– Cytosine always pairs with Guanine
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The Double HelixThe Double Helix
• James Watson and Francis Crick– Using the X-ray taken by Rosalind
Franklin– And compiling data and research over
many years– Watson and Crick “unlocked” the secret
structure of DNA in 1953• The building blocks of ALL life
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The Double HelixThe Double Helix
• base pairing- hydrogen bonds forming only between certain “base pairs”
Sugar-phosphate backbone
Hydrogen bonds
Nucleotide
Key
Adenine (A)
Thymine (T)
Cytosine(C)
Guanine (G)
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Chromosomes and DNA Chromosomes and DNA ReplicationReplication
• DNA is the genetic material for the cell and the organism
• It is found in the nucleus of Eukaryotic cells– If Prokaryote cells don’t have a
nucleus, then where is the DNA stored?
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Chromosomes and DNA Chromosomes and DNA ReplicationReplication
• This E. coli bacterium has DNA but, it is compacted into the cytoplasm of the cell
• Most bacteria have a single, circular DNA molecule– E. coli has 4,639,221 base pairs!!!
E. coli bacterium
Chromosome
Bases on the chromosome
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Eukaryotic DNAEukaryotic DNA
• Eukaryotic DNA has as many as 1000 times more base pairs as Prokaryotic DNA– It exists in the nucleus of the cell in
the form of chromosomes– How many chromosomes make up a
diploid human cell?
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Eukaryotic DNAEukaryotic DNA
• How does the nucleus of a cell contain more than 1 meter of DNA?
• Eukaryotic chromosomes contain DNA and protein in a substance called chromatin
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Eukaryotic DNAEukaryotic DNA• Chromatin – DNA tightly coiled around
proteins called histones• Nucleosome – DNA and histones forming
a beadlike structure
DNA
double
helix
Histones
Coils
Nucleosome
Supercoils
Chromosome
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DNA ReplicationDNA Replication
• The way that DNA is constructed allows for exact duplication
• When DNA is separated one side can be “copied” because of base pairing
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DNA ReplicationDNA Replication
• If you had a strand of DNA, but only one half of the strand, how would you create a complimentary strand?
– Suppose you had the base pairs:• ATGCCCGTAATGTAACCGTTGAA
• What would be the complimentary strand?
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DNA ReplicationDNA Replication
• Replication – process by which DNA duplicates or “copies” itself– during replication the strand of DNA
separates into two strands– While this is happening two new
strands are being formed simultaneously
– This occurs at the replication fork
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DNA ReplicationDNA Replication• DNA is “unzipped” by a special enzyme
called DNA polymerase
– The polymerase adds new nucleotides to pair with the “old” strand
– It also proofreads it before it finishes to make sure there are no mistakes
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DNA ReplicationDNA Replication
Replication fork
DNA polymerase
DNA polymerase
Replication fork
New strand
New strand
Nitrogenous
bases
Original strand
Original strand
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Chapter 12 – 3 Chapter 12 – 3 RNA and Protein RNA and Protein
SynthesisSynthesis• At this point we all know that DNA
provides the genetic code for all life on the planet
• So, “how does it work?”
• The key is it’s relationship with RNA– Ribonucleic acid
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RNA and Protein RNA and Protein SynthesisSynthesis
• DNA is like a “library” of information in every cell of an organism
• RNA would be the “person” reading the individual ‘books’ in the library– The manufacture of proteins is
ESSENTIAL for the life of the organism!
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Structure of RNAStructure of RNA
• RNA is much like DNA in that it is a long chain of nucleotides
There are THREE main differences:> the sugar in RNA is ribose > RNA is single stranded> RNA has Uracil in place of Thymine
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from to to make up
Three Types of RNAThree Types of RNA
also called which functions to also called also called which functions towhich functions to
can be
RNA
Messenger RNA
Ribosomal RNA
Transfer RNA
mRNA Carry instructions
rRNACombine
with proteins
tRNABring
amino acids to
ribosome
DNA Ribosome Ribosomes
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TranscriptionTranscription• Transcription is the process of
“making” RNA molecules by creating a complimentary strand to a section of DNA
• The enzyme responsible for “reading” the DNA code is RNA polymerase
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TranscriptionTranscription• During transcription, RNA
polymerase attaches to the DNA and separates the strands
• The RNA polymerase then uses one strand of DNA as a template to make complimentary nucleotides into a strand of mRNA
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TranscriptionTranscriptionAdenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)
RNA DNA
RNApolymerase
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TranscriptionTranscription• Promoters – specific sites where the
RNA Polymerase binds to the strand of DNA to begin transcription
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RNA EditingRNA Editing
• The “finished” mRNA strand has been edited before it goes to work
• The pieces that are kept are called exons
• The pieces that are “cut” are called introns
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The Genetic CodeThe Genetic Code
• Proteins are assembled in polypeptides– These are long chains of amino
acids
– There are 20 different types of amino acids
– The properties of proteins are determined by which order these amino acids are joined
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The Genetic CodeThe Genetic Code
• mRNA is the key to the genetic code and it provides for the manufacture of all proteins in the body
• A strand of mRNA is read three base pairs at a time– UCGAAGCUUACA would be …..– UCG-AAG-CUU-ACA
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The Genetic CodeThe Genetic Code• Each of these amino acids that
mRNA “codes” for recognizes the three base pair sequence
• A codon consists of three consecutive nucleotides that specify a single amino acid
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The Genetic CodeThe Genetic Code
• Along with the twenty amino acids there are “special” base pair sequences that “code for” start and stop codons
• Stop codons are like the “period at the end of a sentence”.– They signify the end of a
polypeptide
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The Genetic CodeThe Genetic Code
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TranslationTranslation• The decoding of a strand of mRNA
into a protein is known as translation
• At this point we have taken a strand of DNA and created a strand of mRNA by the process of transcription – DNA mRNA polypeptide chain– Polypeptide chain Protein
• The next step is to make proteins!!
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Messenger RNA :
Messenger RNA is transcribed in the nucleus.
Transfer RNA
mRNA Start codon
Ribosome
MethioninePhenylalanine tRNA Lysine
Nucleus
Figure 12–Figure 12–18 Translation18 Translation
mRNA
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TranslationTranslation• As a strand of DNA is read during
transcription a complimentary strand of RNA is made
–TACAAGTTT (DNA)TACAAGTTT (DNA)–AUGUUCAAA (RNA)AUGUUCAAA (RNA)
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TranslationTranslation• That strand of RNA is known as mRNA
and leaves the cell nucleus where it attaches to a ribosome
• AUGUUCAAA (mRNA)AUGUUCAAA (mRNA)
Ribosome
mRNAStart codon
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TranslationTranslation• Each strand of mRNA is separated
into three base pairs called codons
• AUG —- UUC --- AAA AUG —- UUC --- AAA (mRNA)(mRNA)
• This is where This is where transfer RNAtransfer RNA comes in comes in (tRNA)(tRNA)
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TranslationTranslation• tRNA is responsible for getting the right
anticodon with each of the mRNA codons• An amino acid is attached to each
anticodon
tRNAtRNA
mRNA
Ribosome
LysineLysine
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The Polypeptide “Assembly Line” The ribosome joins the two amino acids & breaks the bond between the tRNA & it’s amino acid
mRNARibosome
Translation direction
Lysine tRNA
tRNARibosome
Growing polypeptide chain
mRNA Completing the Polypeptide
The process continues until the ribosome reaches one of the three
stop codons. The result is a growing polypeptide chain.
Figure 12–Figure 12–18 Translation18 Translation
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TranslationTranslation• The ribosome acts like an
assembly line worker and attaches each amino acid to the next one.
• The ribosome also detaches the amino acid from it’s tRNA
• This happens until a stop codon is reached and there is a long chain of amino acids (a polypeptide)
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MutationsMutations• Mutations are
changes in the DNA sequence that affect genetic information
• Genetic mutations result from changes in a single gene
• Chromosomal mutations involve changes in whole chromosomes
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MutationsMutations• Mutations that only affect one
nucleotide are called point mutations– Point mutations generally only affect one
amino acid in the sequenceTHE DOG BIT THE CAT
THE DOG BIT THE CAR
Normal: AUG-AAG-GGC-UAA
Protein: Met - Lys - Gly - StopNormal: AUG-AAG-AGC-UAA
Protein: Met - Lys - Ser - Stop
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MutationsMutations• Frameshift mutations are much
more dangerous to the genetic code!
• They occur when a nucleotide is added (inserted) or deleted
• This “shifts” the reading frame of the geneTHE DOG BIT THE CAT
** What happens if you remove the “G” in DOG
THE DOB ITT HEC AT**The same would happen if you added a
letter
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SubstitutionInsertion
Deletion
Gene Mutations:Gene Mutations:Substitution, Insertion, Substitution, Insertion,
and Deletionand Deletion
Mutations can be very dangerousMutations can be very dangerous
and and VERY SCARY!!VERY SCARY!!
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MutationsMutations• Chromosomal mutations involves
the change in the number or structure of chromosomes
• There are Four Types:– Deletion – the loss of all or part of a
chromosome– Duplication – when a segment of a
chromosome is repeated– Inversion – When part of a chromosome
becomes oriented in the reverse direction– Translocation – when part of a
chromosome breaks off and attaches to another
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Chromosomal Chromosomal MutationsMutations
Deletion
Duplication
Inversion
Translocation
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THE ENDTHE END