Chapter 8: DNA and the Language of Life

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Chapter 8 DNA and the Language of Life
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Fredrick Griffith

• In 1928, Fredrick Griffith was studying two forms
  or strain of a bacterial species one strain was
  fatal to mice, while the other strain was
  harmless.

Strain 1 Strain 2
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Griffiths Experiment

• When he injected heat-treated bacteria into mice,
  the mice remained healthy.
• Heat kills the deadly strain of bacterium, making
  it harmless.

Strain 1 Strain 2 Heated Strain 1
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Griffiths Transforming Factor

• When he injected mice with a mixture of the
  harmless strain and the heat-treated deadly
  strain, he expected the mice to survive.
• However, the mixture killed the mice. Some of the
  harmless bacteria had been transformed,
  becoming deadly.

• Strain 1 Strain 2 Heated Strain 1
  Strain 2 heated Strain1

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DNA or Protein?????

• After Griffiths experiment, scientists began to
  search for the transforming factor.
• Attention focused on two types of chemicals
  protein and DNA.
• In 1952, biologists Alfred Hershey and Martha
  chase provided more evidence to distinguish
  between the two possibilities.
• They conducted a series of experiments using
  viruses.

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Virus

• A virus is package of nucleic acid wrapped in a
  protein coat.
• Unlike living things, viruses are not made of
  cells.
• A virus can only reproduce by infecting a living
  cell with its genetic material.
• A virus that infects bacteria is called a
  bacteriophage.
• Phage consists of a protein coat that encloses
  the genetic
• material. When a phage infects a bacterium, it
  inserts
• its genetic material into the bacterium, while
  its coat
• remains outside.

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Hershey and Chases Experiment

• In the first experiment, phages with
  radioactive-labeled DNA, infected bacteria.
• In a second experiment, phages with
  radioactive-labeled protein infected bacteria.
• In both experiments, bacteria were separated from
  the phage coats by blending.
• In the first experiment, most radioactivity was
  found in the infected bacteria, while in the
  second experiment most radioactivity was found in
  the phage coat.
• These experiments demonstrated that DNA is the
  genetic material of phage and that protein does
  not transmit genetic information.

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DNA Structure

• The heritable genetic information of an organism
  is stored in DNA.
• The DNA molecule is made up of two strands that
  are held together by hydrogen bonds.
• These strands are parallel to each other but run
  in opposite directions, called antiparallel.
• Each strand of DNA consists of a large number of
  nucleotides.

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DNA Structure

• Each nucleotide is made up of a deoxyribose
  (sugar), a phosphate group and a nitrogenous
  base.
• There are 4 kinds of nitrogenous bases, Thymine
  (T), Cytosine (C), Adenine (A), and Guanine (G).
• Bases Thymine (T) and Cytosine (C) are
  single-ring structure called pyramidines.
• Bases Adenine (A) and Guanine (G) are double-ring
  structures called purines.
• In the double stranded DNA, A always pairs with T
  and C always pairs with G. This is called
  complementary base pairing.

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DNA Strands

• Nucleotides are joined to one another by covalent
  bonds that connect the sugar of one nucleotide to
  the phosphate group of the next.
• This repeating pattern of sugar-phosphate is
  called a sugar-phosphate backbone.
• Knowing the main components of DNA, Watson and
  Crick tried to figure out how the elements fit
  together?
• One clue came from X-ray photographs of DNA taken
  by Rosalind Franklin suggested that the structure
  of DNA was a double helix.

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DNA Replication

• The process of copying the DNA molecule.
• This process can be divided into 3 major parts
• Binding of enzymes to existing DNA
• Unwinding the double helix
• Synthesis of a new matching strand for each
  existing strand

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DNA Replication

• 1. What do the yellow strands of DNA represent?
• new DNA strands
• 2. What will the two daughter DNA molecules
  consist of?
• Each consists of one original (parent) strand
  and one new strand.

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• RNA                       DNA
  
• Single-stranded                 
  Double-stranded
• Ribose                                   
  Deoxyribose
• A, C, G and U                     
  A, C, G and T

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Types of RNA

• 1.  mRNA - messenger RNA - carries information
  from DNA to the ribosome where the protein is
  made.
• 2.  tRNA - transfer RNA - carries amino acids to
  mRNA at the ribosome to assembly the protein
  being made.3.  rRNA - ribosomal RNA - major
  structural component of the ribosome where
  protein synthesis occurs.

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The Central Dogma
DNA is maintained by DNA replication, DNA is
transcribed into RNA, RNA is translated into
protein.
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What are proteins?

• We are protein.
• Our hair, our nails, our skin, our blood, our
  enzymes and hormones are protein
• indeed, our bodies contain some ten thousand to
  fifty thousand kinds of protein.

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Genetic Alphabets

• Genetic "Alphabets" - there are three alphabets
  involved in the entire process of protein
  synthesis
• 1)  DNA - A, C, G and T
• 2)  RNA - A, C, G and U
• 3)  Protein - Twenty different amino acids
• Triplet Code - three nucleotides code for one
  amino acid
• 1. Codon a triplet in mRNA, pairs with triplet
  on a tRNA molecule carrying the correct amino
  acid.
• 2. Anticodon a triplet in tRNA    

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The Genetic Code

• Example 1
• 1)  mRNA Codon AUG
• 2)  Amino Acid Met 
• Example 2
•   C U A G G C A A C U U A
• Amino Acids 2
• Leu - Gly - Asn - Leu
• Example 3
• UUACGCCGUAAG
• Leu Arg Arg - Lys

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Transcription

• Purpose to synthesize RNA from a DNA template
• It starts when the enzyme RNA polymerase attaches
  to a specific region of the DNA.
• As a result, a single complementary strand of RNA
  is made.

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Editing the mRNA message

• Transcribed mRNA must first be edited before it
  can leave the nucleus for the cytoplasm.
• The initial RNA transcripts have stretches of
  noncoding nucleotides that interrupt nucleotide
  sequences that actually code for amino acids.

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Splicing

• Splicing - Introns are removed and Exons are
  joined together.
• Intron - segment of mRNA which does NOT code for
  protein therefore, it is removed.
• Exon - segment of mRNA which does code for
  protein therefore, it remains for expression
  in protein.

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Translation

• It is the final step on the way from DNA to
  protein.
• It is the synthesis of proteins directed by a
  mRNA template.
• tRNA translates the three-letter codons of mRNA
  to the amino acids that make up proteins.
• It happens on ribosomes.

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tRNA during Translation

1. A tRNA molecule must become bound to the
   appropriate amino acid.
2. It has to recognize the appropriate codon in the
   mRNA.
3. During translation, the anticodon on tRNA
   recognizes a particular codon on mRNA by using
   base-pairing rules.

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Ribosome

• A ribosome has two subunits
• Small subunit binding site for mRNA
• Large subunit consist of two binding sites for
  tRNA
• P site holds the tRNA carrying the growing
  polypeptide chain.
• A site holds the tRNA carrying the next amino
  acid to be added to the chain.

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Steps of Translation

• First, the ribosome attaches at a specific site
  on the mRNA. This site is the start codon, AUG.
• Next, amino acids are added one by one to the
  growing chain of amino acids.
• During translation, the ribosome moves down the
  mRNA, codon by codon, until translation is
  completed.
• This process continues until the ribosome reaches
  a stop codon UAA, UAG, or UGA.

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Mutation

• A mutation is any change in the nucleotide
  sequence of DNA.
• Mutations can change the meaning of genes.
• Mutations can involve large regions of a
  chromosome or just a single nucleotide.
• Mutation can be divided into 2 general categories.

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1. Base Substitution

• Base substitution replacement of one base or
  nucleotide with another.
• It results in a change that affects the function
  of a protein.

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2. Base Insertion or Deletion

• 2. Base insertion or deletion adding or
  subtracting nucleotides.
• Its usually more disastrous than the effects of
  base substitutions.

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What Causes Mutation?

• May occur when errors are made during DNA
  replication.
• May occur when errors happen during chromosome
  crossovers in meiosis.
• Physical or chemical agents that cause mutations
  are called mutagens.
• Most common physical mutagen is high-energy
  radiation. Ex X-rays
• Mutations are the ultimate source of genetic
  diversity in the living world.

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EXTRAS!!!!!!!!!!!!!
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Transcription Translation

• http//learn.genetics.utah.edu/units/basics/transc
  ribe/
• Translation video-http//www.biostudio.com/demo_fr
  eeman_protein_synthesis.htm
• Protein synthesis- http//www.wisc-online.com/obje
  cts/index_tj.asp?objIDAP1302

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Sickle cell disease

• Sickle cell disease is an example of a disorder
  caused by inheritance of a genetic mutation.
• In sickle cell disease, the hemoglobin in red
  blood cells tends to bind together when oxygen
  levels are low.
• The hemoglobin crystals deform the red blood
  cells into sickle, or crescent shapes.
• The sickle shaped cells clog tiny blood vessels,
  dangerously blocking the normal flow of blood.

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Replication of the Double Helix

• More than a dozen enzymes are involved in DNA
  replication.
• Each incoming nucleotide pairs with its
  complementary nucleotide on the parent strand.
• Enzymes called DNA polymerase make the covalent
  bonds between the nucleotides of the new strand.
• DNA replication begins at specific sites called
  origins of replication. The copying proceeds
  outward