DNA

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DNA

• Deoxyribonucleic Acid

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DNA

• DNA is like the architects master plan for a
  building. Why?

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• Chromosomes are microscopic, threadlike strands
  composed of the chemical DNA

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Names to Know

• Frederick Griffith 1928 Transformation -
  showed that some factor was responsible for
  transferring the virulent strain to the harmless
  strain.
• Oswald Avery - 1944 used enzymes to destroy
  lipids, carbohydrates, proteins, RNA, and DNA to
  determine that genes are composed of DNA.

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Hershey and Chase (1952)

• Alfred Hershey and Martha Chase used radioactive
  markers to conclude that the genetic material of
  the bacteriophage was DNA, not protein.

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• In 1953, James Watson and Francis Crick
  established the structure of DNA.  The shape of
  DNA is a double helix, which is like a twisted
  ladder.
• The sides of the ladder are made of alternating
  sugar and phosphate molecules.  The sugar is
  deoxyribose.
• The rungs of the ladder are pairs of 4 types of
  nitrogen bases.    The bases are known by their
  coded letters A, G, T, C.

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Structure of DNA

• DNA is a polymer made of monomers called
  nucleotides, each containing 3 basic parts
• Simple sugar - deoxyribose
• Phosphate group
• Nitrogenous (nitrogen-containing) base
• 1. adenine
• 2. guanine
• 3. cytosine
• 4. thymine
• The DNA helix is actually made of repeating units
  called nucleotides.

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What does an elm, an elk, and an eel have in
common?

• Then..
• What makes them different?

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Sequence of the four different nucleotides.
The closer the relationship between two
organisms, the greater the similarity in
the Order of DNA nucleotides.
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What does Chemical Analysis Reveal about DNA?

• Compare the amounts of A, T, G, and C in each
  kind of DNA. Why do you
• think the relative amounts are so similar in
  human liver and thymus cells?
• What fact can you state about the overall
  composition of DNA, regardless of its
• source?

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Chargaffs Rule and the Principle of Base Pairs

• Chargaffs Rule - There typically exists a 11
  ratio of the base pairs
• AdenineThymine
• CytosineGuanine
• The bases can occur in any order as long as the
  base pair principle is followed.
• Base order is the code which contains
  instructions. For instance ATGCACATA would code
  for a different gene than AATTACGGA. A strand of
  DNA contains millions of bases.

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The two sides of the DNA ladder are held together
loosely by hydrogen bonds.
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In simple terms, DNA controls the production of
proteins within the cell.  These proteins form
the structural units of cells (building blocks)
and control all chemical processes within the
cell.  How you look is largely determined by
the proteins that are made. Proteins are made
according to sequence of DNA in the nucleus.
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DNA Replication

• The DNA can actually "unzip" when it needs to
  replicate - or make a copy of itself.
• Why would DNA need to be replicated?

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• Each new strand formed is a complement of one of
  the original, or parent strand. The result is
  the formation of two DNA molecules, each is
  identical to the original DNA molecule.

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• The sequence of nitrogen bases on one strand of a
  DNA molecule is
• GGCAGTTCATGC
• What would be the sequence of bases on the
  complementary strand?

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RNA

• RNA is like the actual blueprints taken to the
  jobsite. Why?

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RNA

• DNA is too big to go through the nuclear pores.
  Messenger RNA  (mRNA) is small enough to go
  through the nuclear pores.  It takes the
  "message" of the DNA to the ribosomes and "tells
  them" what proteins are to be made.  Recall that
  proteins are the body's building blocks. Imagine
  that the code taken to the ribosomes is telling
  the ribosome what is needed - like a recipe.

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DNA vs RNA
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• RNA is similar to DNA, except that it is a
  single strand.
• Instead of thymine, mRNA contains the base
  Uracil.
• RNA has the sugar ribose instead of deoxyribose.
  RNA stands for Ribonucleic Acid.

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Transcription

• mRNA carries information from the DNA to the
  cells ribosomes for manufacturing proteins.
• Transcription occurs in the nucleus RNA
  polymerase (enzyme) makes an RNA copy of a
  portion of DNA

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Translation

• Proteins are made from the message on the RNA

mRNA codon tRNA anticodon
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Cracking the code

• Codon (group of 3 nucleotides) codes for one
  amino acid.
• The order of nitrogen bases in the mRNA will
  determine the type and order of amino acids in a
  protein.
• 64 combinations (20 amino acids)

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Genetic Code
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• Some codons do not code for amino acids they
  provide instructions for assembling the protein.
• UAA stop codon
• AUG start codon (amino acid methionine)

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• Where within the cell
• Are the DNA instructions
• located?
• Does transcription occur?
• Does translation occur?

Explain why specific base pairing is essential to
the processes of transcription And translation.
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Changing the Genetic Code

• Sometimes the DNA does not replicate exactly or
  the chromosomes do not pair correctly.
• Mutation
• Any change in the DNA sequence that changes the
  protein it codes
• Mutagen anything that causes a mutation

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Mutations

• In reproductive cells - changes the sequence of
  nucleotides within a gene in a sperm or an egg
  cell. If involved in fertilization, the altered
  gene would become part of the genetic makeup of
  the offspring.
• New trait
• Incorrect protein production

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Mutations in Body Cells

• Mutation is not passed on to offspring but may
  cause problems for the individual.
• Impaired cell function
• Cancer cells growing and dividing rapidly
  (uncontrolled dividing of cells)
• Ultraviolet radiation in sunlight

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Types

• Point mutation change in a single base pair in
  DNA changes the code
• Incorrect amino acid could be inserted changing
  the protein
• The Dog Bit the Cat.
• The Dog Bit the Car.

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• Frameshift Mutation mRNA fails to read a base
  from the DNA or adds a base while reading -
  causing the mRNA code to be out of position by
  one base
• Result codons are different possibly coding for
  a different protein
• THE DOG BIT THE CAT. (Delete the G)
• THE DOB ITT HEC AT.

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• Sickle-cell anemia
• Molecules of hemoglobin that are misshapen as a
  result of change in protein shape
• DNA
• Normal hemoglobin GGG CTT CTT TTT
• Sickled hemoglobin GGG CAT CTT TTT
• Is this a framshift mutation or a point mutation?

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Genetic Technology

• Applied genetics selective breeding
• (chooses best orgs to mate to produce desired
  traits in offspring)
• inbreeding mating between closely related
  orgs offspring are more prone to phenotypic
  problems due to smaller gene pool
• plant hybrids are usually bigger and better

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Genetic Technology

• Selective Breeding increases the frequency of a
  desired allele (trait) within a population
• Disease-resistant (plants)
• Best producer (cows, hens)
• May take many generations for the trait to be
  consistently expressed in a population

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Genetic Engineering

• Involves cutting (cleaving) DNA from one organism
  into small fragments into a host organism of the
  same or a different species Recombinant DNA
• Inserted into the host organisms chromosomes and
  that organism will use the foreign DNA as its own.

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Transgenic organisms

• Plants and animals that contain functional
  recombinant DNA
• Ex. Glowing tobacco plant

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Recombinant DNA technology

• Also called Genetic Engineering
• Method that involves cutting DNA from one org
  into small fragments and inserting the fragments
  into a host org (of same species or of a
  different species)
• -this is a much faster and more reliable method
  for increasing the frequency of a specific allele
  in a population but, is it ETHICAL???

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Gene Cloning

• Clones are genetically identical copies
• Single Gene
• Bacteria making human insulin

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Dolly

• Page 364

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The Human Genome

• International effort to completely map and
  sequence the human genome DNA
• Finished April 2003
• 20,000 100,000 genes on the 46 human
  chromosomes.(?)
• Why?
• Detecting, treating, and curing genetic disorders
• DNA fingerprinting