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DNA RNA Protein Scientists call this the: Central Dogma of Molecular Biology!

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Presentation on theme: "DNA RNA Protein Scientists call this the: Central Dogma of Molecular Biology!"— Presentation transcript:


2 DNA RNA Protein Scientists call this the: Central Dogma of Molecular Biology!

3 How do we know that all of our genetic information comes from DNA? What type of experiment would you design to determine that DNA is the source of all genetic information?

4 Griffiths Experiment with Pneumonia and the accidental discovery of Transformation Frederick Griffiths was a bacteriologist studying pneumonia He discovered two types of bacteria: –Smooth colonies –Rough colonies CONCLUSION: The smooth colonies must carry the disease!

5 Griffiths Experiment with Pneumonia and the accidental discovery of Transformation When heat was applied to the deadly smooth type… And injected into a mouse… The mouse lived!

6 Griffith injected the heat-killed type and the non-deadly rough type of bacteria. The bacteria transformed itself from the heated non-deadly type to the deadly type. Griffiths Experiment with Pneumonia and the accidental discovery of Transformation

7 Griffiths Experiment did not prove that DNA was responsible for transformation How would you design an experiment to prove that DNA was responsible for transformation?

8 Avery, McCarty, and MacLeod Repeated Griffiths Experiment Oswald Avery Maclyn McCarty Colin MacLeod

9 Avery, McCarty, and MacLeod Added the non-deadly Rough Type of Bacteria to the Heat-Killed Smooth TypeCarbohydratesLipidsProteinsRNADNA To the Heat-Killed Smooth Type, added enzymes that destroyed…

10 S-Type Carbohydrates Destroyed S-Type Lipids Destroyed S-Type Proteins Destroyed S-Type RNA Destroyed S-Type DNA Destroyed Conclusion: DNA was the transforming factor!

11 The Hershey-Chase Experiment Alfred Hershey & Martha Chase worked with a bacteriophage: A virus that invades bacteria. It consists of a DNA core and a protein coat DNA Protein coat

12 The Hershey-Chase results reinforced the Avery, McCarty, and MacLeod conclusion: DNA carries the genetic code! However, there were still important details to uncover…

13 How did DNA: 1. Store information? 2. Duplicate itself easily? These questions would be answered by discovering DNAs structure

14 The Race to Discover DNAs Structure

15 Linus Pauling 1940s Discovered the alpha- helical structure of proteins.

16 The Race to Discover DNAs Structure 1950 Chargaffs Rule: Equal amounts of Adenine and Thymine, and equal amounts of Guanine and Cytosine Erwin Chargaff Why do you think the bases match up this way? Purine + Purine = Too wide Pyrimidine + Pyrimidine = Too Narrow Purine + Pyrimidine = Perfect Fit from X-ray data

17 The Race to Discover DNAs Structure Maurice Wilkins Rosalind Franklin X-Ray diffraction image of DNA taken by Franklin in 1951

18 The Race to Discover DNAs Structure James Watson Francis Crick 1953 Compiled data from previous scientists to build a double-helical model of DNA

19 DNA Structure Deoxyribonucleic acid Double helix (twisted ladder or strands) of nucleotides (Sugar (deoxyribose), phosphate and a nitrogen base) Each strand has a sugar and phosphate backbone covalently bonded to a nitrogen base

20 One single strand of DNA…

21 DNA Structure Double helix is made of covalently bonded strands that are hydrogen bonded to complementary covalently bonded strands One strand bonds to the second strand via hydrogen bonds (weak enough to break in order to separate the 2 strands) Each strand measures 3.4 nm/twist or 10 base pairs

22 DNA Double Helix

23 DNA Structure Strands of DNA are different – they are oriented in opposite directions to each other – they are ANTIPARALLEL Each end has a number (5 or 3 – you say 5 prime or 3 prime)

24 Four Nitrogen Bases Adenine (A), Guanine (G), Cytosine (C), Thymine (T) Purines (double ring structures) – Adenine and Guanine Pyrimidines (single ring structures) – Cytosine and Thymine Chargaff rules: A –T and T – A G – C and C - G

25 AdenineGuanine Cytosine Thymine Phosphate Sugar (deoxyribose) PurinesPyrimidines Nitrogenous Bases

26 Chromosome Structure DNA packs tightly around histones to form chromatin. DNA and histones form bead-like structures called nucleosomes. Nucleosomes pack together to form supercoils. Supercoils condense to form chromosomes.

27 Chromosome Nucleosome Coils Supercoils Histones DNA Chromosome Structure

28 DNA Replication The double helix did explain how DNA copies itself We will study this process, DNA replication, in more detail

29 How does DNA replicate? ConservativeSemi-ConservativeDispersive Hypotheses:

30 DNA Replication DNA copies itself in the S phase of interphase. 1 parent DNA molecule produces 2 daughter DNA molecules, each daughter being made up of parent DNA and a strand of new DNA (semiconservative process)

31 Steps of DNA Replication 1. DNA unzips – Helicase enzyme breaks hydrogen bonds, unzipping the double helix at the origin of replication (about 100 on a human chromosome). A replication bubble is formed when DNA unzips DNA polymerization is bi-directional because of the antiparallel orientation of the DNA strand.

32 DNA Replication Section 12-2 Growth Replication fork DNA polymerase New strand Original strand DNA polymerase Nitrogenous bases Replication fork Original strand New strand

33 DNA Replication

34 Steps of DNA Replication 2. Bases pair up – DNA Polymerase bonds free nucleotides to complementary bases DNA POL reads DNA in 3 to 5 direction, thus a new strand elongates only in the 5 to 3 direction Nucleotides are added at a rate of about 50 per second in mammals and 500 per second in bacteria.

35 Steps of DNA Replication Leading strand has continuous elongation starting at RNA primer since it is read in 3 to 5 direction (towards replication fork) by DNA polymerase Lagging strand has discontinuous elongation DNA strand is read 3 to 5 away from the replication fork in a series of segments called Okazaki fragments Once fragments are finished, they are joined to previous fragment with enzyme Ligase.

36 DNA Replication

37 Steps of DNA Replication 3. Proofreading and repair DNA polymerase proof-reads newly created DNA strand and identifies incorrect base pairs. Nuclease (exonuclease) enzyme cuts out the identified incorrect nucleotides. DNA polymerase places correct nucleotides into DNA strand. Ligase fuses these corrected nucleotides into the DNA strand

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