Finger Print of Life

 What does DNA look like?  macroscopic view:  nanoscopic view:

  DNA is an organism’s “blueprint”  Tells your cells what proteins they need to make  Proteins determine what physical traits and characteristics you (and all organisms) have General Function of DNA

  There are three parts to every nucleotide:  There are four nitrogenous bases:  Adenine, Thymine, Cytosine, Guanine Nucleotides a phosphate group a 5-carbon sugar “deoxyribose” 1 of 4 nitrogenous (nitrogen-containing) bases

DNA (DeoxyriboNucleic Acid) is a double helix  Backbone is made of sugar-phosphate  Base pairs bind the backbone together  Adenine always pairs with Thymine  Guanine binds with Cytosine

  Published in 1871  First to isolate and identify DNA and suggested its role in heredity. Friedrich Miescher

  Published in 1950  Found that the amount of adenine was the same as thymine and the amount of cytosine was the same as guanine in any DNA sample Erwin Chargaff

  Worked together ~1950  Studied DNA using x-ray diffraction techniques  Both worked together (on and off again) at King’s College in London Maurice Wilkins & Rosalind Franklin

  Published in 1953  Determined the structure of DNA (a double helix) and published a one-page article in Nature in April 1953 James Watson & Francis Crick

The Double Helix  Watson & Crick explained that hydrogen bonds hold the nitrogen bases together:  A always pairs with T  C always pairs with G  Hydrogen bonds provide just enough force to hold the strands together, yet can be easily broken if needed.

  Before a cell divides, it must make a copy of its genetic material.  DNA is copied in a process called DNA Replication  “Each strand has all the information needed to reconstruct the other half by the process of base-pairing!” -Watson & Crick How does DNA make copies?

 1.DNA helicase (an enzyme) “unzips” the base pairs, unwinding the DNA double helix 2.Free DNA nucleotides find their complementary bases along the new strands 3.DNA polymerase (an enzyme) helps assemble the sugar-phosphate backbone to complete the new DNA strands DNA Replication

  The result is two DNA molecules identical to each other and to the original molecule  Each DNA molecule has one original strand and one new strand; we call this the semi-conservative replication process. DNA Replication

  Watch the following video clip to see an animation of how DNA replication works! DNA Replication

Base pairs  A - T – double hydrogen bond  G - C – triple hydrogen bond  Nucleotide (3 chemical groups)  Sugar – deoxyribose  contains 5 Carbon atoms  Phosphate group  A base (A, T, G, C)

How Does DNA Copy Itself?

 History of Replication  Watson & Crick – realized that complementary base pairing provided a way for DNA to copy itself - base pairing could allow a new strand to be built on an old strand - 3 possible models of DNA replication

 3 Models of Replication

 3 Models of Replication: Semi-conservative Replication  Each strand in a DNA molecule is used as a template to build a new strand using complementary base pairing  Results in new molecule with one original DNA strand and one new strand

 3 Models of Replication: Conservative Replication  Leaves the original DNA intact and produces another molecule of DNA identical to the first

 3 Models of Replication: Dispersive Replication  Creates two molecules that are a mix of new and old DNA interspersed along each strand of the molecule

 The Question is Answered  1957 Matthew Meselson & Franklin Stahl -conducted an experiment proving replication is semiconservative - each DNA molecule has one new strand and one old strand

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 DNA Replication: Process  Replication begins when the enzyme DNA helicase opens the DNA forming replication bubbles

 DNA Replication: Process  Multiple replication bubbles are opened simultaneously allows the molecule to be replicated quickly

 DNA Replication: Process  The nitrogen bases on the original DNA strands are exposed in the replication bubbles.  They serve as a template to build new DNA strands

 DNA Replication  The ends of the replication bubbles known as the replication fork is where replication begins

 DNA Replication – DNA Polymerase  The enzyme DNA polymerase brings new nucleotides to the replication fork - it pairs them according to base pairing rules A pairs with T C pairs with G

 DNA Replication – Leading Strand  The process of replication proceeds from 5’ to 3’  leading strand- replication is continuous – it is built toward the replication fork

 DNA Replication – Lagging Strand  lagging strand- replication occurs in short segments - called Okazaki fragments - the new DNA strand grows away from the replication fork

 DNA Replication- The Big Picture Each Bubble has 2 Forks – each fork has a leading and lagging strand

 DNA Replication  The process continues until 2 complete copies of the DNA are produced  Each copy of the DNA contains one strand of DNA from the original DNA molecule and one new strand that was produced by replication  Known as semi-conservative replication

 DNA Replication

 DNA Replication- Vocabulary  replication  DNA helicase  replication bubble  replication fork  DNA polymerase  leading strand  lagging strand  Okazaki Fragment  semi-conservative replication

 DNA replication

Multiple Replication Forks During Eukaryotic DNA Synthesis Multiple Replication Forks During Eukaryotic DNA Synthesis

MUTATIONS Changes in DNA that affect genetic information

Gene Mutations Point Mutations – changes in one or a few nucleotides – Substitution THE FAT CAT ATE THE RAT THE FAT HAT ATE THE RAT – Insertion THE FAT CAT ATE THE RAT THE FAT CAT XLW ATE THE RAT – Deletion THE FAT CAT ATE THE RAT THE FAT ATE THE RAT

Chromosome Mutations Changes in number and structure of entire chromosomes Original Chromosome ABC * DEF DeletionAC * DEF DuplicationABBC * DEF TranspositionACB * DEF InversionAED * CBF TranslocationABC * JKL GHI * DEF

Significance of Mutations Most are neutral Eye color Birth marks Some are harmful Cystic Fibrosis Down Syndrome Some are beneficial Sickle Cell Anemia to Malaria Immunity to HIV

What Causes Mutations? There are two ways in which DNA can become mutated: – Mutations can be inherited. Parent to child – Mutations can be acquired. Environmental damage Mistakes when DNA is copied