Ch' 11'1 DNA: History

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Ch. 11.1 DNA History and Structure Replication

• What weve learned so far
• Cells make proteins
• Genetic information is passed on through
  chromosomes
• Compacted DNA and proteins chromosomes
• Genetic information is stored in the nucleus
• Genetic information is essential so that each
  cell is identical (mitosis)

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The transition...

• To truly understand genetics, biologists first
  had to discover the chemical nature of the gene.
• How do genes control what you look like?

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11-1 DNA

• Vocabulary
• Transformation
• Bacteriophage
• Nucleotide
• Base pairing

• Key Concepts
• What did scientists discover about the
  relationship between genes and DNA?
• What is the overall structure of the DNA molecule?

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DNAs Experiment History

• For thousands of years, humans have noticed that
  parents pass on traits to their offspring
• What is the process and/or molecule that makes
  this possible??

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DNAs Experiment History

• Griffith How do certain types of bacteria cause
  pneumonia?
• The experiment that tested this question led to
  new knowledge.
• Genetic information could be transformed from one
  bacterium to another.

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Genetic Info. Transferred
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Transformation

• Heat killed bacteria had passed their disease
  causing ability to the harmless strain
• Griffith called this TRANSFORMATION
• One strain of bacteria (harmless) had changed
  into the other (disease causing)
• Some factor was transferred from the heat killed
  cells to the live cells
• This factor might contain a GENE with information
  that could change harmless bacteria into disease
  causing ones!

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Avery DNA

• Avery and a group of scientists decided to repeat
  Griffiths experiment
• to determine which molecule in the heat killed
  bacteria was needed for transformation
• Made an extract (juice) from heat killed bacteria
  and added enzymes that destroy proteins,
  carbohydrates, lipids
• Transformation still occurred!
• Repeated the experiment but added enzymes that
  destroy DNA
• Transformation DID NOT occur!!

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Averys Conclusion

• What was the transforming factor?
• DNA!
• Averys Conclusion DNA is the substance that
  stores and transmits genetic info. from
  generation to generation

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Hershey-Chase Experiment

• Studied viruses specifically bacteriophages
• Bacterio bacteria
• Phage eater
• Viruses are made up of
• DNA protein coat
• Research Question Which part of the virus enters
  the infected bacteria cell?

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• Grew viruses in the presence of radioactive
  markers 32P and 35S.
• Sulfur is found in protein coat
• Phosphorus is found in DNA

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No Sulfur!
Phosphorus!
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Hershey-Chase Conclusion

• Genetic information of the bacteriophage that
  they infected with bacteria was DNA
• NOT protein!

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What does DNA do?

• Carries information from one generation to the
  next
• Puts that information to work by determining
  TRAITS
• Must be easily copied since almost every new cell
  gets a copy.

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DNA Structure

• Made up of nucleotides (monomer)
• Each nucleotide composed of 3 parts
• Sugar (DEOXYRIBOSE)
• Phosphate group
• Nitrogen-containing base
• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)

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DNA Structure DOUBLE HELIX (twisted ladder)

• Backbone
• Deoxyribose Phosphate Group of each nucleotide
• Steps of Ladder
• bases
• Any base sequence is possible!

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Chargaffs Rules

• What do these data suggest to you?

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• A T (A pairs with T)
• C G (C pairs with G)

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What DNA Looks Like

• Rosalind Franklin used X-ray diffraction
  patterns to discover that DNA strands twisted
  around each other like a HELIX

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• Watson Crick while trying to build a 3-D model
  of DNA, Watson saw Franklins photograph and
  measurements and within weeks, he and Crick
  figured out the structure of DNA

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Whats holding the strands together?

• HYDROGEN BONDS!!!
• Hydrogen Bonds form between A and T base pairs as
  well as between C and G base pairs

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DNA Replication

• Vocabulary
• Chromatin
• Replication
• DNA polymerase

• Key Concept
• What happens during DNA Replication?

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The Review

• Prokaryotic cells do not have a nucleus
• DNA molecules are located in the cytoplasm
• Usually a circular DNA molecule and it is
  referred to as the cells chromosome
• Eukaryotic cells have a nucleus
• Can have 1000x more DNA than prokaryotic cells
• DNA is located in the form of a number of
  chromosomes
• of chromosomes varies widely from species to
  species

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DNA molecules are longhow does DNA fit in the
nucleus?

• It forms chromosomes!
• DNA coils around proteins called histones and
  then this chromatin supercoils around itself
  until chromosomes form

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DNA Replication

• before a cell divides, it must copy its DNA so
  that all cells have a copy of the genetic
  instructions
• this process involves A LOT of ENZYMES!
• each half of the DNA double helix can serve as a
  "template" for the replication of another DNA
  double helix molecule
• The strands are said to be complementary

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DNA REPLICATION THE PROCESS

• An enzyme unwinds "unzips" DNA (separates the 2
  DNA strands) by breaking the hydrogen bonds
  between base pairs

Hydrogen Bonds Breaking!
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• the complementary base is inserted to each side
  of the DNA strand with the help of DNA Polymerase

Why does the blue always pair with the green?
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• The sugar-phosphate groups are covalently bonded
  to the growing DNA chain (new "backbone")

1 nucleotide
COVALENT BOND
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• an enzyme (DNA polymerase) will "proof-read" the
  order of bases make corrections

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SIMPLIFIED VERSION
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A Little More Complicated