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DNA STRUCTURE AND REPLICATION
CHAPTER
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What is DNA? composed of? Proteins and DNA
Hereditary material present in all living cells Composed of monomers called nucleotides Is part of the chromosomes What are chromosomes composed of? Proteins and DNA Before ~ 1940 people did not really know what the genetic material was
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Nucleic Acids Elements C, H, O, N, P Monomers: Nucleotides
Polymers: Nucleic acids Examples: DNA, RNA, ATP. Deoxyribonucleic acid Ribonucleic acid Adenosine triphosphate
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Monomer - nucleotide DNA -adenine, guanine, cytosine and THYMINE
Nucleotide consists of Ribose sugar (deoxy in DNA) Phosphate group One of 5 nitrogenous bases DNA -adenine, guanine, cytosine and THYMINE RNA adenine, guanine, cytosine and URACIL
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DNA is a double helix A sugar and phosphate
“backbone” connects nucleotides in a chain. P T P A 3’ 5’ 5’ 3’ P C P G A pairs with T and G pairs with C P C P G Two nucleotide chains together wind into a helix. P T P A Hydrogen bonds between paired bases hold the two DNA strands together. G P P C P C P G DNA strands are antiparallel.
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A history of DNA Friedrich Miescher, 1871 isolated nuclei from pus and
identified nuclein later called nucleic acid. what is pus? Archibald Garrod, 1902 linked inheritance of “inborn errors of metabolism” with the lack of particular enzyme proteins. Shows that something must be passed on from parent to offspring
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WHICH IS MORE LIKELY TO BE GENETIC MATERIAL?
Protein DNA
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FREDERICK GRIFFITH’S EXPERIMENTS in 1928
Worked with two types of pneumonia causing bacteria: S-strain covered by a capsule and causes pneumonia and death of mice R-strain had no capsule and does not cause pneumonia Mice were injected with the bacteria to see if they contracted pneumonia
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Griffith’s experiment identifying the “transforming principle”
Bacterial colonies Rough nonvirulent (strain R) + Rough nonvirulent (strain R) Heat-killed smooth virulent (strain S) Smooth virulent (strain S) Heat-killed smooth virulent (strain S) Injection Results Mouse healthy Mouse healthy Mouse dies Mouse dies Live strain S bacteria in blood sample from dead mouse
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FREDERICK GRIFFITH’S RESULTS
R bacteria (safe) mixed with heat-killed S bacteria (capsule still present) killed the mouse Griffith’s discovery: TRANSFORMATION, Something (presumably the hereditary material) from the heat killed S bacteria transferred to the safe R bacteria and changed its genetic composition to give pneumonia
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AVERY et al’s EXPERIMENT
Repeated Griffith’s experiments, utilizing enzymes to destroy DNA, RNA, and protein, respectively Protease to destroys all proteins DNAse to destroys all DNA
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What is the “transforming principle”?
Conclusion: DNA could be the genetic material.
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HERSHEY-CHASE EXPERIMENT in 1953
When a virus infects a bacteria, it produces more viral particles which are identical to the parent virus. So …. Virus composed of Protein and DNA STEP 1: Viral proteins and DNA “marked” with two different radioactive elements S35 for proteins – coats radioactive P32 for DNA – genetic material radioactive
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Experiment 1 Experiment 2
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HERSHEY-CHASE EXPERIMENT
Conclusion: Examined infected bacteria Found radioactive DNA inside the bacteria Radioactive proteins – outside the bacteria Nobel Prize!
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Chargaff’s Experiment
Erwin Chargaff observed: # of adenine = # of thymine # of guanine = # of cytosine Complementary bases pair: A and T pair C and G pair
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Rosalind Franklin’s Experiment
Rosalind Franklin’s X-ray images Conclusion: Repeating double helix structure Franklin (died in 1958 of cancer) did not get the Nobel Prize in 1962
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WATSON AND CRICK: “THE DOUBLE HELIX”
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DNA Structure DNA made up of two twisted strands
Adenine pairs w/Thymine Cytosine pairs w/Guanine Two strands held together by weak hydrogen bonds The sugar and phosphate make the backbone (or sides of ladder)of the molecule Nitrogen bases make the middle or (rungs of ladder)
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WHAT IS THE COMPLEMENTARY STRAND?
A C G C C A G T A
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WHAT IS THE COMPLEMENTARY STRAND?
A C G C C A G T A T G C G G T C A T
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What is the role of the genetic material and what is a gene?
The genetics material has to be able to carry out two jobs Faithfully duplicate itself to transfer the same genetic information to daughter cells during cell division Express itself and make proteins for the cell to carry out it duties A gene is a segment of the DNA containing an unique sequence of bases that directs the formation of an unique protein which will do the cellular work
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REPLICATION OF DNA
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DNA REPLICATION REPLICATION: Process by which DNA is copied
When during the cell cycle is the DNA copied? Result: Each new cell contains a complete, exact copy of DNA of the parent cell
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STEPS IN DNA REPLICATION
Helix unwinds and unzips making Y-shaped “replication forks” Replication fork
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STEPS IN DNA REPLICATION
Nucleotides base pair with the parent DNA strands Attach with H bonds A-T, G-C DNA Polymerase makes the covalent bonds to join the backbone
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STEPS IN REPLICATION Two new identical helixes form each with one parent strand and one daughter strand Semi-conservative replication
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