Molecular Basis of Genetics and Biotechnology

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Molecular Basis of Genetics and Biotechnology

• The central dogma of molecular biology describes
  the flow of genetic information from
  DNA?RNA?protein. This flow happens through
  precise mechanisms, although mistake can happen
  during the process. Many technologies take
  advantage of the properties of DNA to generate
  novel products and tools.

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Each group will be given a different experiment
or insight that led to the structure and function
of DNA.

• Griffith experiment (2 groups) (190-191)
• Avery experiment (191, additional handout)
• Hershey-Chase experiment (2 groups) (192-193)
• Chargaffs observation, structure of the 4 bases
  (195, 196)
• Wilkins and Franklins X-ray diffraction (196)
• Watson and Cricks DNA model and pairing between
  bases (196-197)

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Griffith experiment
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Avery experiment

• Repeated Griffith experiment to see which
  molecule actually transformed into the harmless
  strain
• Treated extract of heat killed smooth colonies
  with enzymes that broke down everything except
  for DNA. What happened?
• Did same with enzyme that broke down DNA. What
  happened?

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Hershey-Chase experiment
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Watson and Crick Model

• What did they know DNA was a molecule involved
  in genetic information
• What did they not know The structure of the
  molecule
• What evidence did they use?
• X-Ray diffraction Scattered pattern of DNA
  X-rays on film produced by Rosalind Franklin
  (showed coiled strand and angle of stands)
• Chargaffs rule

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Reading quiz Read through WB 34. I will stamp
SG 1 for full credit today only. I will also
stamp SG 3 on Thursday for full credit (if not
done)

• What is the basic unit (monomer) of a nucleic
  acid?
• What are the 3 subunits of a nucleotide. Draw
  them.
• Which of these subunits are the same in all
  nucleic acids?
• What are the 4 bases of DNA?
• What is the function of DNA, can it leave the
  nucleus?

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Analysis question 2

• Draw a labeled diagram of your DNA molecule. Keep
  the illustration in a straight ladder form as
  seen in figure 5. Do not attempt to draw the
  helical shape. Identify each nitrogen base.
• Do this on the back of WB 34

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Structure of DNA

• Double stranded helix
• Deoxyribose sugar
• Phosphate group
• 4 nitrogen bases
• Guanine Cytosine
• Adenine Thymine
• Hydrogen bonds connect bases

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DNA replication

• Each strand is complementary
• Replication steps
• DNA Helicase (enzyme) unzips the DNA strand,
  breaking the hydrogen bonds
• DNA polymerase adds complementary bases to each
  strand (5 to 3)
• Sugar phosphate links extend the chain and DNA
  polymerase proof reads new strand
• DNA ligase seals fragements together

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Reading quiz

• Person closest to the molecular modeling kit
• Read through WB 35
• Rebuild your double helix exactly as it was on
  Monday/Tuesday. (You can use your instructions).
  Make sure you have the correct base sequence and
  base pairing. THIS IS YOUR READING QUIZ!

• Everyone else at the table
• Read through WB 35 and define the following
  terms.
• 1. Anticodon
• 2. Codon
• 3. Nucleotide
• 4. Ribosome
• 5. Transcription

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Reading quiz answers

• DNA model
• Check with model up front

• 1. Anticodon 3 nucleotides on a tRNA
  complementary to the codon
• 2. Codon 3 nucleotides of an mRNA that codes for
  an amino acid
• 3. Nucleotide Monomer of a nucleic acid
  consisting of a sugar, base, and phosphate
• 4. Ribosome Organelle which is the site of
  protein synthesis
• 5. Transcription Process of producing an mRNA
  molecule from a DNA strand

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• Complete letters C-F using the DNA molecule just
  made
• Answer these questions on the back of WB 35 (yep,
  were conserving paper)
• 3. A partial DNA stand has the following
  sequence CACTTGCAC. What would be the
  complementary mRNA sequence
• 4. How can protein be synthesized in the
  cytoplasm of a cell when DNA is contained in the
  nucleus?

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Structure of RNA

• Can leave the nucleus
• Single stranded
• Ribose sugar
• Phosphate group
• 4 nitrogen bases
• Guanine Cytosine
• Adenine Uracil

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Transcription

• The process of copying part of a DNA strand into
  a complementary RNA strand, so the information
  can be taken outside of the nucleus without
  affecting the DNA molecule

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Reading quiz. Use study guide and WB 34-35.
Staple exam to back of test corrections and turn
in.

• Complete the following chart

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• Complete letter G
• Answer the following questions on the back of WB
  36
• 5. You have the following mRNA sequence
  GUGAACGUG. What would be the anticodon base
  sequence on the corresponding tRNAs? Circle each
  codon and anticodon.
• 6. Using a venn diagram, compare and contrast
  codons to anticodons (structure? Function?
  Location?)

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Genetic code
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Genetic code
English code

• Has a four letter alphabet
• There are 20 different amino acids (protein
  building blocks)
• How many letters codes for each amino acid?
• Codon 3 letter combination of mRNA strand

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tRNA

• Anticodon (complementary to mRNA)
• Attached amino acid
• Codon AAA, then
  anticodon is ____

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Reading quiz

• Left table of your group. Put together the mRNA
  molecule produced in letter F (hint, look at the
  diagram on WB 40 and think about which sugar to
  use)

• Right table of your group. Put together the tRNA
  molecules produced in letter G.
• Add appropriate amino acid (black) to each tRNA

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Translation

• Goal of genetic code is to produce a protein. How
  does this happen?
• 1) Transcription produces mRNA strand
• 2) mRNA binds with ribosome
• 3) tRNA anticodon binds with mRNA
• 4) Amino acids attached to tRNA bond together

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Hookin up amino acids

• mRNA and first tRNA bind to ribosome (but not
  each other yet). This is always the anti codon
  UAC (amino acid methionine)
• Ribosome scans mRNA and keeps first codon
  sequence (AUG) at the P site. Anticodon hydrogen
  bonds with 1st codon
• Anticodon complementary to the 2nd codon hydrogen
  bonds to it at the A site.
• Amino acid of 1st tRNA detaches and forms
  peptide bonds with amino acid of 2nd tRNA
• mRNA and 2nd tRNA move to the left as the 1st
  tRNA leaves ribosome
• When a stop codon is reached polypeptide chain
  leaves, other parts dissemble
• Polypeptide may be modified (where?) before it
  is a functional protein

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Write response in notebook

• Use the genetic code (on your desk) to find the
  amino acid sequence coded by the mRNA sequence
  AUGAAGUUU
• Use the genetic code (on your desk) to find the
  amino acid sequence coded by the DNA sequence
  TATCATGCC

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Mutations

• Point
• Frameshift
• THE CAT ATE THE RAT
• THC ATA TET HER AT
• Mutations constantly happen (about 1 in every
  1000 bases) and are important for variation
  Severity depends on location and number of
  mutations

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Chromosomal mutations
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Gene regulation

• All cells in an organism have the same genes
• Do all cells look the same and do the same job?
  Why?
• How is this possible?