What can be studied in Biology

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Housekeeping

• Lab Due at beginning of class
• Notebooks due
• Assigned problem (fly lab) due
• Thursday 12/05/02 Ch 17
• Tuesday 12/10/02 paper
• FINAL 12/17/02
• Review session?
• Whats on the exam?

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What do we know so far?

• We inherit traits from our parents
• Mendel
• Our inherited information is on chromosomes
• Different inheritance mechanisms
• Our chromosomes contain genes-reveal our traits

What is this inherited information made of? What
is the molecular basis of our inheritance?
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What is this inherited information made of? What
is the molecular basis of our inheritance?
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What molecule passes our traits from one
generation to another?
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Genome
Encode for proteins
Encode for a character
Genes
DNA
Traits
Nucleotides
Arrangement gives variation
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What molecule passes our traits from one
generation to another?
Need an appropriate study model
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Bacteria and Viruses

• Simpler units of life
• Easy to grow
• Easy to maintain
• Easy to clone (make an exact copy)

http//www.dph.state.ct.us/BRS/food/fpbact.htm
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What experiments did they do to suggest that DNA
provides our hereditary information?
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Frederick Griffith

• Streptococcus pneumoniae
• Pathogenic isolate (smooth cells)
• Nonpathogenic isolate (rough cells)

What was being transferred to allow nonpathogenic
cells to kill?
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What was being transferred to allow nonpathogenic
cells to kill?

• DNA is the transforming agent
• Transformation Transfer of external DNA to a
  cell
• Change genotype Change phenotype
• Nonpathogenic to pathogenic

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Scientists wanted more proof.
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Hershey and Chase

• Bacteriophage
• T2 (DNA and protein)
• T2 infects Escherichia coli
• When E. coli is infected, the cell will make more
  virus (T2)

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What component of T2 gets into the cell?
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Radioactive components Sulfurin proteins
Phosphorousin DNA
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What were the results?Where was the radioactive
protein? Where was the radioactive DNA?
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Conclusions

• Radioactive protein Supernatant
• Radioactive DNA Pellet

DNA is the hereditary molecule to allow for
reproduction of virus
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How about eukaryotes? Does DNA play the same role?
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DNA is the hereditary information

• Chargaff
• DNA diversity in different organisms
• different orders of nucleotides

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Now that we know what DNA does, What does it look
like??
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Watson and CrickThe double helix
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What does DNA look like??

• NUCLEOTIDES
• Nitrogenous base
• Purines adenine, guanine
• Pyrimidines thymine, cytosine
• Phosphate group
• Sugar
• Deoxyribose DNA
• Ribose RNA

How they are ordered in the strand creates
diversity!
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How is the double helix created?
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The double helix

• Purine binds to a Pyrmidine
• Adenine binds to thymine
• Guanine binds to Cytosine

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Why?
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Double Helix-two strands of nucleotides
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Now we know what DNA looks like, how does
inheritance work (DNA replication during
Interphase)?
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Watson and Cricks hypothesis

• DNA replicates by
• 1. Two strands separate
• 2. Each strand acts as a template

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Models of Replication

• Semiconservative model (Watson and Crick)
• One old strand (template)
• One new strand
• Conservative model
• New strand-totally new DNA
• Dispersive model
• New strand and old strand-become a mixture of old
  and new DNA

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What do we need to get DNA to replicate?
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What is needed for DNA replication

• A start site

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A start site...

• Origin of replication
• One site in bacteria (circular chromosomes)
• Many sites in eukaryotes
• Specific sequence of nucleotides
• Open up the DNA
• Replication fork-where the DNA are elongating
  (copying)

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What is needed for DNA replication

• A start site
• A primer

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A primer

• Preexisting chain to start replication
• Small piece of RNA
• Need Primase
• Connects primer to DNA

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What is needed for DNA replication

• A start site
• A primer
• Enzymes

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Enzymes

• Helicase
• Unwinds the DNA
• Single-strand binding protein
• Keeps the DNA unwound (binds to the unwound DNA)
• DNA polymerase
• Elongate, add nucleotides to the single strands
• Lagging strand
• DNA ligase

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DNA polymerase

• Need nucleotides in the environment
• Align with complementary bases
• A-T
• G-C
• Get added onto the strand

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DNA polymerase
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DNA is antiparallel!What is antiparallel?
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DNA is antiparallel

• Run in opposite directions!
• At one end-5 (phosphate group)
• At other end-3 (hydroxyl group)
• Nucleotides are added from 5-3 by DNA
  polymerase

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Leading strand DNA replication
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Leading strand Lagging strand Okazaki
fragments DNA ligase
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What do we need to replicate a strand of DNA?

• Origin of replication
• DNA helicase
• Single-strand binding protein
• Primase adds a primer
• DNA polymerase adds nucleotides
• Lagging strand replication-primase and DNA ligase

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How does DNA replication occur without so many
mistakes??
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DNA repair

• Error rate normal 110,000
• Use Mismatch repair
• Nuclease DNA cutting enzyme
• DNA polymerase fill in nucleotides
• DNA ligase seals strand

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What happens with the ends of linear DNA?? How
are we able to get full replication?DNA can
only add nucleotides to a primed 3 end
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The ends of our chromosomes

• Telomeres DNA sequence located at the end of
  chromosomes (repeat sequences)
• Telomerase enzyme that lengthens the telomere
  ends- contains an RNA primer

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In sum

• DNA is the inheritable information
• Need to replicate DNA to pass this information on
  to offspring