DNA Importance, Structure, Function, Replication, and Discoveries

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DNAImportance, Structure, Function, Replication,
and Discoveries

• Mrs. Jacks

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What makes you the same as all other organisms?

• What makes you different than all other living
  organisms?

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Its your DNA
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Whats so special about DNA?

• Blueprint for life- contains instructions for
  making proteins in most living organisms
• Tells cells what protein to make and when and how
  to make it (genes!)
• Gene- segment of DNA in the chromosomes (which
  are in the nucleus) that codes for a protein,
  which contributes to a physical trait.

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Whats so special about DNA?

• Genes code for Protein
• Remember, proteins have many important functions
  in our living cells! (See next slide) ?
• ? All body cells have a complete copy of all the
  DNA. However, different genes are activated in
  different kinds of cells.

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Remember the importance of proteins

• Enzymes catalyze all reactions in living things
  (digestion, respiration.)
• Allow things into/out of cells
• Regulate our bodies
• Transport things like oxygen

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Structure of DNA

• Written in special code (A, T, C, G) that is the
  same in all living things
• But every organisms DNA is also unique.

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Structure of DNA

• DNA is made of nucleotides (The monomers are
  called nucleotides)
• Nucleotides have three parts
• A phosphate group
• A 5-carbon sugar
• A nitrogen-containing base

• The 4 nitrogenous bases are
• Adenine A
• Thymine T
• Guanine G
• Cytosine C
• Base Pair Rule
• A pairs with T
• G pairs with C

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DNA The Double Helix

• DNA Double helix resembles a twisted ladder
• ? Ladder sides alternating sugar
• phosphate molecules connected by
• covalent bonds
• Ladder rungs nitrogenous base pairs are
  connected by weak hydrogen bonds
• ? A single strand of DNA has millions of bases

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DNA Replication

• Replication DNA copies itself during the S phase
  of the cell cycle.
• ? Replication steps are controlled with enzymes
• Helicase enzyme unzips Hydrogen bonds
• DNA Polymerase (enzyme) binds free floating
  nucleotides to unzipped DNA strands using the
  base pair rule.
• Nucleotides are bonded together with covalent
  bonds to form complementary strands

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Replication

• Replication is semi-conservative new DNA
  molecule consists of a new strand and an original
  strand
• ? Replication produces two identical DNA strands,
  which are chromosomes

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DNA Replication--Biology

• Practice
• 1. 2. 3.
• A--T A- -T A--__ __--T
• G--C G- -C G--__ __--C
• C--G C- -G C--__ __--G
• C--G C- -G C--__ __--G
• T--A T- -A T--__ __--A
• A--T A- -T A--__ __--T
• C--G C- -G C--__ __--G
• Original Splits with helicase DNA polymerase

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Discovering DNA Deoxyribonucleic Acid The race
to figure out the structure

• After Scientists found that DNA is the molecule
  in charge of our genetic code, there was a race
  to find the details of its structure!

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Discovering the Structure of DNA

• Chargaff
• ? 1950 Discovered that in DNA, the number of T
  A G C.
• So A pairs across from T
• and G pairs across from C
• Chargaffs Rule is true for ALL organisms.

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Rosalind Franklin

• Rosalind Franklin pioneer female microbiologist
• ? 1951 worked with scientist Maurice Wilkins to
  produce an image of DNA using x-ray diffraction
• Discovered a scattered pattern, which gives clues
  to the fact that DNA strands are twisted around
  each other in a helix shape. The x-ray also
  suggested that the bases were inside the helix,
  not outside like Watson and Crick originally
  thought.
• She died young. Her information was (possibly
  unethically) used by Watson and Crick. They did
  not credit her work until decades later (well
  after her death).

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Watson Crick

• Watson Crick
• 1953 Franklins x-ray scattered image of DNA
  provided the missing clues Watson Crick needed
  to figure out the structure of DNA
• Made a model of what is known as the double helix
  structure of DNA.
• ? Watson, Crick Wilkins were awarded the Nobel
  Prize in 1962 for their scientific discovery.
  Franklin had died in 1958.

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• STOP HERE!

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But How Did Scientists Know that DNA was the
Material of Heredity?

• Several scientists thought protein was the
  molecule that was in charge of our heredity (the
  ability to pass on traits to the next
  generation).
• However, after several scientists conducted
  experiments, they found that it is DNA (not
  protein) that holds the secret of heredity!

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Griffith Discovers Transformation (1928)
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Griffith Discovers Transformation (1928)

• Researched ways to fight pneumonia
• Studied bacteria that cause pneumonia
  (pneumococcal)
• Two types that grew different in culture
• Rough type pretty harmless
• Smooth type very bad and harmful (virulent)

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Griffith Discovers Transformation (1928)

• Experimented by injecting mice with strains
• Live, smooth bacteriakills mouse
• Live, rough bacteria mouse lives
• Heat killed, smooth bacteriamouse lives
• Ok but get a load of this next one!

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Griffith Discovers Transformation (1928)

• Heat killed, smooth bacteria live rough
  bacteria mouse dies
• Hmm? Why? What happened?

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What Do You Think?
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That rough bacteria must have picked up something
from the dead, smooth bacteria that caused it to
become virulent.

• Griffith called this change from harmless to
  harmful

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TRANSFORMATION
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Griffith concluded that some molecules from the
dead harmful bacteria got picked up by the
harmless bacteria and transformed them into
harmful bacteria.

• But what was this transforming molecule?

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Avery

• Inspired by Griffiths experiments to identify
  the molecule of heredity
• Thought transforming molecule made up genes
• Tried to cause transformation with various
  macromolecules from smooth bacteria.
• He destroyed the macromolecules one at a time.

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He destroyed carbohydrates from the virulent
bacteria and got..
Mousey, it was nice knowing you!
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He destroyed proteins from the virulent bacteria
and got..
Hasta La Vista, Mousey!
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But when the DNA was destroyed the mouse stayed
healthy.
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Avery concluded that transforming factor was DNA!

• Avery said that GENES ARE MADE OF DNA!!

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Alfred Hershey and Martha Chase
1952

• Skeptical of Avery
• Experimented with Bacteriophage virus (infects
  bacteria)
• Blender Experiments

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Bacteriophage

• Contains both DNA and Protein
• Hershey and chase used radioactive labeling to
  see what infects the bacteria

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Hershey and Chase

• Radioactive phosphorous from the DNA ended up in
  the bacteria
• Said that DNA must be the genetic material