DNA and RNA

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DNA and RNA
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Early 1900s

• What was known
• Genes are the units of heredity
• Genes located on chromosomes
• Chromosomes made of DNA and protein

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Early 1900s

• What was not known
• What are genes made of?
• Protein? (these regulate cell processes)
• DNA? (may be too simple to hold code)
• How does the code work?

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The Golden Age of Genetics 1900-WWII

• 3 Experiments
• Griffith
• Avery
• Hershey and Chase

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Frederick Griffiths Transformation experiment,
1928
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Somehow, heat-killed bacteria had passed
disease-causing ability to harmless
strain----transformation.
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Oswald Averys Experiment---1944

• Repeated Griffiths experiment
• Which molecule is responsible for causing
• transformation?
• carbohydrate?
• lipid?
• RNA?
• protein?
• DNA?

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Oswald Averys Experiment---1944
DNA must be the transforming factor. DNA must
store and transmit genetic information from one
generation to the next
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Martha Chase and Alfred Hershey, 1953
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• The Hershey-Chase Experiment

label with 32P
protein coat label with 35S
a bacteriophage
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• Hershey Chase Experiment

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Radioactive 32P found in bacteria. Hershey and
Chase concluded that genetic material is DNA, not
protein.
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The Structure of DNA
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• Erwin Chargaff
• In any sample of DNA,
• amount of adenine amount of thymine
• amount of cytosine amount of guanine
• in every organism
• A T
• C G

Chargaffs Rules
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• Rosalind Franklin
• X-ray Diffraction

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Cracking the code!

• Race to understand the structure of DNA
  Griffith,
• Avery,
• Hershey and Chase,
• Chargaff,
• Franklin,
• and others contributed to the
  discovery of the structure
• of DNA

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Watson and Crick

• Francis Crick,
• British physicist
• James Watson,
• American biologist
• Built 3-D models of
• tin, wire, cardboard

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Watson and Crick

• When shown Franklins x-ray photograph of DNA
• DNA structure must be a helix

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1953
Watson Crick awarded Nobel Prize in 1962
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A nucleotide
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Nitrogenous (nitrogen-containing) bases
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• http//www.genomenewsnetwork.org/articles/06_02/dn
  a_jewelry_art.shtml

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http//kimberlychapman.com/crafts/knit-gallery.htm
l
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DNA Replication
 
 
 
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Figure 1211 DNA Replication
Section 12-2
Original strand
DNA polymerase
New strand
Growth
DNA polymerase
Growth
Replication fork
Replication fork
Nitrogenous bases
Original strand
New strand
Go to Section
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DNA Replication in Prokaryotes
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Protein Synthesis

• Code of DNA directs protein synthesis
• What is the importance of proteins?
• Proteins are the key to almost everything that
  living cells do

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Importance of proteins

• Examples
• blood type hemoglobin
• color of hair, eyes, enzymes
• flower hormones makes up
  skin size of organism
• antigens makes up hair
• antibodies body tissues
• skin color
• regulate growth
• Incorrect proteins result in a number of
  disorders

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Protein

• A protein is a polymer of amino acids

Peptide bonds connect amino acids in a chain
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Essential Amino Acids must be part of diet
Non-essential Amino Acids
Alanine Asparagine Aspartate Cysteine Glutamate Gl
utamine Glycine Proline Serine Tyrosine
Arginine Histidine Isoleucine Leucine Lysine Methi
onine Phenylalanine Threonine Tryptophan Valine
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RNA compared to DNA
RNA - Single stranded - Bases A-U, C-G - Sugar
is ribose
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3 kinds of RNA

• mRNA
• tRNA
• rRNA

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2 Main Steps in Protein Synthesis

• Transcription (in nucleus)
• Translation (at ribosome)

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Transcription
Adenine (DNA and RNA) Cystosine (DNA and
NA) Guanine(DNA and RNA) Thymine (DNA
only) Uracil (RNA only)
RNApolymerase
DNA
RNA
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Figure 1218 Translation
Section 12-3
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
Go to Section
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Figure 1218 Translation (continued)
Section 12-3
The Polypeptide Assembly Line The ribosome
joins the two amino acidsmethionine and
phenylalanineand 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
Go to Section
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The Genetic Code
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Pre-RNA
mRNA
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rRNA
DNA
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Mutations

• Changes in DNA sequence that affect genetic
  information
• Two types
• Gene mutations (single gene changed)
• Chromosomal mutations (whole chromosome
• affected)

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Point mutation - substitution
Example Sickle Cell Anemia
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Point mutation - deletion
Example Duchenne muscular dystrophy
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Point mutation - insertion
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Inversion
Example hemophilia
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 Chromosomal Mutations
Deletion
Duplication
Inversion
Translocation
Go to Section
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Barbara McClintock Jumping Genes

• Worked with Indian corn (maize)
• Theorized that genes are transposable (can
  move around) --- transposons
• Her theory was proven using molecular techniques
  in the 1970s
• Nobel Prize in 1983 -- first American woman to
  win an unshared Nobel Prize
• Helps explain how bacteria becomes resistant to
  certain antibiotics
• Helps explain how genes can turn healthy cells
  into cancerous ones.

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Gene Regulation

• What determines which genes will be expressed
  (transcribed into RNA)?
• Prokaryotes
• Lac operon in E. coli
• Turns on when lactose is present
• Eukaryotes
• Much more complex/not yet well understood
  Example Hox genes control development

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• Hox genes help lay out the basic body forms of
  many animals, including humans, flies, and worms.
  They set up the head-to-tail organization. You
  can think of them as directing instructions as an
  embryo develops Put the head here! Legs go over
  there!

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Mutation in hox genes of fruit fly
Edward Lewis, 1940s

• A single mutation in a complex of genes which
  act as master switches, turning on and off arrays
  of genes involved in body shape and arrangement
  of segments and appendages.
• http//www-tc.pbs.org/wgbh/evolution/library/03/4/
  pdf/l_034_06.pdf

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• http//www.biologycorner.com/bio4/notes/homeobox.p
  hp

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The Central Dogma of Molecular Biology

• DNA makes RNA makes protein

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The Central Dogma of Molecular Biology
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An exception to the Central Dogma AIDS

• HIV uses reverse transcriptase to transcribe DNA
  from RNA
• (opposite of normal transcription!!)

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Protein Synthesis Overview
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Transcription A molecule of DNA is copied into a
complementary strand of RNA
To cytoplasm
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Translation
P
A
 
 
 
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Figure 122 Griffiths Experiment
Section 12-1
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)
Go to Section
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Figure 124 Hershey-Chase Experiment
Section 12-1
Bacteriophage with phosphorus-32 in DNA
Phage infectsbacterium
Radioactivity inside bacterium
Bacteriophage with sulfur-35 in protein coat
Phage infectsbacterium
No radioactivity inside bacterium
Go to Section
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Figure 125 DNA Nucleotides
Section 12-1
Purines
Pyrimidines
Adenine
Guanine
Cytosine
Thymine
Phosphate group
Deoxyribose
Go to Section
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Figure 127 Structure of DNA
Section 12-1
Nucleotide
Hydrogen bonds
Sugar-phosphate backbone
Key Adenine (A) Thymine (T) Cytosine (C) Guanine
(G)
Go to Section
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Prokaryotic Chromosome Structure
Section 12-2
Chromosome
E. coli bacterium
Bases on the chromosome
Go to Section