Chapter 12 DNA

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Chapter 12 DNA

• Also known as deoxyribonucleic acid

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History of DNA

• In the mid 1900s 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 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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Figure 122 Griffiths Experiment
Heat-killed, disease-causing bacteria (smooth
colonies)
Harmless bacteria (rough colonies)
Control(no growth)
Harmless bacteria (rough colonies)
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)
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Griffiths 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 wasnt caused by
  a chemical toxin released by the bacteria

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Griffiths 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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Griffiths 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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Griffiths 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 Averys Experiment

• In 1944 Avery repeated Griffiths 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

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Oswald Averys 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 Averys Experiment

• Averys 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 Experiment

• Alfred Hershey and Martha Chase wanted to explain
  Averys 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 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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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
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Hershey-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 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 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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The Nucleotides
Purines
Pyrimidines
Adenine
Guanine
Cytosine
Thymine
Phosphate group
Deoxyribose
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Chargaffs Rules

• According to Erwin Chargaff
• Adenine always pairs with Thymine
• Cytosine always pairs with Guanine

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The 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 Helix
Nucleotide
Hydrogen bonds
Sugar-phosphate backbone
Key Adenine (A) Thymine (T) Cytosine(C) Guanine
(G)

• base pairing- hydrogen bonds forming only between
  certain base pairs

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Chromosomes and DNA Replication

• DNA is the genetic material for the cell and the
  organism
• It is found in the nucleus of Eukaryotic cells
• If Prokaryote cells dont have a nucleus, then
  where is the DNA stored?

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Its time to check for understanding

• We will now go to a DNA site
• www.dnaftb.org/dnaftb/
• We will go thru the Molecules of Genetics portion
  of the site and view slides 15-23.
• Then go to DNA site
• www.dnai.org/

• We will go thru two of the slides and the
  activities that are part of the interactive then
  you will view the rest on your own.
• A worksheet and quiz will follow.

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Chromosomes and DNA Replication

• 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!!!

Chromosome
E. coli bacterium
Bases on the chromosome
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Eukaryotic 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 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 DNA

• Chromatin DNA tightly coiled around proteins
  called histones
• Nucleosome DNA and histones forming a beadlike
  structure

Nucleosome
Chromosome
DNA double helix
Coils
Supercoils
Histones
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DNA 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 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 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 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 Replication
Original strand
New strand
DNA polymerase
DNA polymerase
Replication fork
Replication fork
Nitrogenous bases
New strand
Original strand
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Chapter 12 3 RNA and Protein Synthesis

• 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 its relationship with RNA
• Ribonucleic acid

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RNA and Protein Synthesis

• 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 RNA

• RNA is much like DNA in that it is a long chain
  of nucleotides
• There are THREE main differences
• gt the sugar in RNA is ribose
• gt RNA is single stranded
• gt RNA has Uracil in place of Thymine

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Three Types of RNA
RNA
can be
also called
also called
which functions to
also called
which functions to
which functions to
from
to
to make up
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Transcription

• 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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Transcription

• 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 RNA

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

• Promoters specific sites where the RNA
  Polymerase binds to the strand of DNA to begin
  transcription

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RNA 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 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 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 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 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 Code
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Translation

• 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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Figure 1218 Translation
Messenger RNA Messenger RNA is transcribed in
the nucleus.
Nucleus
mRNA
Lysine
tRNA
Phenylalanine
Methionine
Transfer RNA
Ribosome
Start codon
mRNA
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Translation

• As a strand of DNA is read during transcription a
  complimentary strand of RNA is made
• TACAAGTTT (DNA)
• AUGUUCAAA (RNA)

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Translation

• That strand of RNA is known as mRNA and leaves
  the cell nucleus where it attaches to a ribosome
• AUGUUCAAA (mRNA)

Ribosome
mRNA
Start codon
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Translation

• Each strand of mRNA is separated into three base
  pairs called codons
• AUG - UUC --- AAA (mRNA)
• This is where transfer RNA comes in (tRNA)

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Translation

• tRNA is responsible for getting the right
  anticodon with each of the mRNA codons
• An amino acid is attached to each anticodon

Lysine
tRNA
Ribosome
mRNA
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Figure 1218 Translation
The Polypeptide Assembly Line The ribosome
joins the two amino acids breaks the bond
between the tRNA its amino acid
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
Ribosome
Translation direction
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Translation

• 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
  its tRNA
• This happens until a stop codon is reached and
  there is a long chain of amino acids (a
  polypeptide)

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Mutations

• 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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Mutations

• Mutations that only affect one nucleotide are
  called point mutations
• Point mutations generally only affect one amino
  acid in the sequence
• THE DOG BIT THE CAT
• THE DOG BIT THE CAR
• Normal AUG-AAG-GGC-UAA
• Protein Met - Lys - Gly - Stop
• Normal AUG-AAG-AGC-UAA
• Protein Met - Lys - Ser - Stop

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Mutations

• 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 gene
• THE 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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Gene MutationsSubstitution, Insertion, and
Deletion
Substitution
Deletion
Insertion

• Mutations can be very dangerous
• and VERY SCARY!!

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Mutations

• 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 Mutations
Deletion
Duplication
Inversion
Translocation
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THE END