dna structure and replication
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DNA Structure and Replication . Frederick Griffith (1927) showed that avirulent strains of Diplococcus pneumoniae could be transformed to virulence. Section 10.3. Avery, MacLeod, and McCarty (1944) demonstrated that the transforming principle was DNA and not protein. . - PowerPoint PPT PresentationTRANSCRIPT
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DNA Structure and Replication
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• Frederick Griffith (1927) showed that avirulent strains of Diplococcus pneumoniae could be transformed to virulence.
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Section 10.3
• Avery, MacLeod, and McCarty (1944) demonstrated that the transforming principle was DNA and not protein.
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Figure 10.4
• Avery, Macleod, and McCarty Experiment (1944)
• DNA not protein is the heritable material
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Section 10.3
• Hershey and Chase (1952) demonstrated that DNA, and not protein, enters the bacterial cell during bacteriophage infection and directs viral reproduction.
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Figure 10.5
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Figure 10.6
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Genes Are Made of DNA
1. Heritable information is carried in units called genes
2. Genes are parts of structures called chromosomes
3. Chromosomes are made of deoxyribonucleic acid (DNA) and protein
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DNA
• DNA is made of chains of small subunits called nucleotides
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DNA
• Each nucleotide has three components:1. Phosphate group2. Deoxyribose sugar3. One of four nitrogen-containing bases
– Thymine– Cytosine– Adenine– Guanine
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Chargaff’s Rule
• In 1940, biochemist E. Chargaff determined that:
– In a DNA molecule, amounts ofA = T, G = C
– “Chargaff’s Rule”
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Early DNA Studies• Rosalind Franklin and Maurice Wilkins studied DNA
structure using X-ray scattering
• From X-ray diffraction patterns they deduced that DNA – Is long and thin– Has a uniform diameter of 2 nanometers – Is helical, and is twisted like a corkscrew– Consists of repeating subunits
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DNA Is a Double Helix• James Watson and
Francis Crick :
– DNA is made of two strands of nucleotides
– Deoxyribose and phosphate portions make up the sugar-phosphate backbone
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Bases Form Ladder Rungs in DNA
• Nitrogen-containing bases protrude inward from sugar-phosphate backbone
ghr.nlm.nih.gov
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Hydrogen Bonds
• Hydrogen bonds hold certain nitrogenous base pairs together
– A bonds with T, G bonds with C
– Bonding bases called complementary base pairs
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DNA is a Double Helix
• Ladder-like structure of the two DNA strands are twisted into a double helix
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• How can a molecule with only 4 simple parts be the carrier of
genetic information?
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DNA Replication
• All cells come from pre-existing cells
• Cells reproduce by dividing in half
• Each of two daughter cells gets an exact copy of parent cell’s genetic information
• Duplication of the parent cell DNA is called replication
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DNA Replication
• DNA helicases
• DNA polymerases
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ncbi.nlm.nih.gov
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DNA Replication
• Base pairing is the foundation of DNA replication
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Semiconservative Replication
• The two resulting DNA molecules have one old parental strand and one new strand (semiconservative replication)
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Replication And Proofreading
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Types of Mutations
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• Point mutation - individual nucleotide in the DNA sequence is changed
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• Insertion mutation - one or more nucleotide pairs are inserted into the DNA double helix
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• Deletion mutation - one or more nucleotide pairs are removed from the double helix
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• Inversion - piece of DNA is cut out of a chromosome, turned around, and re-inserted into the gap
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• Translocation - chunk of DNA (often very large) is removed from one chromosome and attached to another
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