Presentation on theme: "DNA and the Language of Life Chapter 12. How did scientists learned that DNA is the genetic material?"— Presentation transcript:
DNA and the Language of Life Chapter 12
How did scientists learned that DNA is the genetic material?
Genes are Made of DNA Griffin’s experiment (1928) Avery’s experiment (1944) Hershey and Chase experiment (1952)
Griffith’s experiment - 1928
Griffith showed that although a deadly strain of bacteria could be made harmless by heating it, some factor in that strain is still able to change other harmless bacteria into deadly ones. He called this the "transforming factor."
Avery’s experiment - 1944 Transforming factor - Protein or DNA? Avery and colleagues treated a mixture of heat- treated deadly strain and harmless strain of bacteria with: Protein-destroying enzyme DNA-destroying enzyme
Hershey and Chase experiment -1952
The basic unit of the DNA molecule is called: NUCLEOTIDE
A NUCLEOTIDE in DNA has three parts: A ring-shaped sugar called deoxyribose A phosphate group A nitrogenous base (single or double ring of carbon and nitrogen atoms)
Nucleotide monomers join together by covalent bonds between the sugar of one nucleotide and the phosphate of the next, forming a sugar- phosphate backbone.
The bases pair up (A-T & G-C) forming the DOUBLE HELIX first described by Watson and Crick
Watson, Crick and Franklin
Various ways to model DNA structure http://www.umass.edu/molvis/tutorials/dna/dnapairs.htm manipulate DNAhttp://www.umass.edu/molvis/tutorials/dna/dnapairs.htm
Why does DNA need to be replicated? Growth – new cells - reproduction How does this process happens?
REPLICATION IN 3 STEPS DNA replication results in two new strands, each containing one new strand (yellow) and one original strand (blue)
Weak bonds Hydrogen bonds Comes apart easily Comes together easily
Overview of DNA replication DNA separates Complementary nucleotides are linked along separated strands
initiate Initiator protein guides unzipper protein (helicase) to correct position on DNA
untwister Untwister (topoisomerase) unwinds the DNA double helix in advance of the unzipper
Unzipper separates DNA strands, breaking weak bonds between the nucleotides unzip
assemble Builders (polymerases) assemble new DNA strand by joining nucleotides to their matching complements on the exposed strands
straightners Straighteners (single-strand DNA binding proteins) keep single strand of DNA from tangling
Phosphate provides energy Phosphate bond energy from the new nucleotides is used to make the new bonds
Leading vs. Lagging strand Leading (top) strand is built continuously as the builder follows behind the unzipper, but the Lagging (lower) strand builds in the opposite direction
Lagging strand Lagging (lower) builder makes a loop with the DNA strand and builds in opposite direction
Lagging strand Built in small sections Sections linked by enzyme ligase
Repairs of DNA Erasers (Repair Nuclease): find poorly matched or damaged nucleotides and cut them out
Repairs of DNA Builders (Polymerase): fill gaps using other DNA strand as a guide
Repairs of DNA Stitchers (Ligase): uses ATP to restore continuity of backbone of repaired strand
Big picture of DNA replication
REPLICATION IN 3 STEPS DNA replication results in two DNA molecules, each with one new strand (yellow) and one old strand (blue)