Biology, 9th ed,Sylvia Mader Ch. 12 - DNA - Structure & Function Biology, 9th ed,Sylvia Mader Chapter 13 Chapter 13 DNA Structure & Function DNA Structure & Function

DNA as Genetic Material Biology, 9th ed,Sylvia Mader DNA as Genetic Material Chapter 13 DNA Structure & Function Johann Miescher (1869) Removed nuclei from pus cells Found they contained a chemical he called nuclein This was rich in phosphorus and had no sulfur; thus it could not be a protein Later scientists realized there were two types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

Biology, 9th ed,Sylvia Mader Frederick Griffith (1931) Chapter 13 DNA Structure & Function Investigated virulence of Streptococcus pneumoniae in mice in following manner: 1. S strain bacteria have a smooth capsule & are capable of killing mice 2. R strain have no capsule & don’t kill mice 3. Injected heat-killed S strain bacteria into mice; they did not die 4. Injected mice with mixture of heat-killed S strain & live R strain. These mice had living S strain bacteria & died Concluded that virulence passed from the dead strain to the living strain; transformation had occurred

Griffith’s Transformation Experiment Biology, 9th ed,Sylvia Mader Chapter 13 DNA Structure & Function Griffith’s Transformation Experiment

Avery, MacLeod & McCarty (1944) Biology, 9th ed,Sylvia Mader Avery, MacLeod & McCarty (1944) Chapter 13 DNA Structure & Function (Refer to transparency here first) Discovered that DNA is the transforming substance. 1. Took DNA only from the S bacteria and mixed it with R bacteria. 2. S strain DNA was then incorporated into genome of living R strain bacteria and they were then transformed into S strain bacteria. 3. Enzymes that degrade proteins or RNA did not prevent transformation while those that digest DNA did.

Reproduction of Viruses Biology, 9th ed,Sylvia Mader Reproduction of Viruses Chapter 13 DNA Structure & Function Viruses consist of a protein coat (capsid) surrounding a nucleic acid core Bacteriophages are viruses that infect bacteria

Biology, 9th ed,Sylvia Mader Hershey and Chase (1952) Chapter 13 DNA Structure & Function Did an experiment to determine whether the bacteriophages inject the protein or DNA into the bacteria. Radioactively labeled the DNA core and protein capsid of a bacteriophage 1. Radioactive P (found in DNA & not in protein) was found inside cells 2. Radioactive S (found in protein & not in DNA) was found mainly outside of cells Results indicated that DNA, not the protein, enters the host The DNA of the phage contains genetic information for producing new phages

Hershey and Chase Experiments Biology, 9th ed,Sylvia Mader Hershey and Chase Experiments Chapter 13 DNA Structure & Function

Biology, 9th ed,Sylvia Mader Structure of DNA Chapter 13 DNA Structure & Function DNA contains: Two nucleotides with purine bases. These are double ring nitrogenous bases. Adenine (A) Guanine (G) Two nucleotides with pyrimidine bases. These are single ring nitrogenous bases. Thymine (T) Cytosine (C)

Nucleotide Composition of DNA Biology, 9th ed,Sylvia Mader Nucleotide Composition of DNA Chapter 13 DNA Structure & Function

Biology, 9th ed,Sylvia Mader Chargaff’s Rules Chapter 13 DNA Structure & Function The amounts of A, T, G, and C in DNA: Identical in identical twins Varies between individuals of a species Varies more from species to species In each species, there are equal amounts of: A & T G & C All this suggests DNA uses complementary base pairing to store genetic information. Human chromosome estimated to contain, on average, 140 million base pairs. Number of possible nucleotide sequences 4^140,000,000.

Biology, 9th ed,Sylvia Mader Diffraction Data Chapter 13 DNA Structure & Function Rosalind Franklin: Studied structure of DNA using X-rays. Found that if a concentrated solution of DNA is made it forms into a crystal like structure. When X-rayed, an X-ray diffraction pattern results. The pattern of DNA shows that it is a helix.

X-Ray Diffraction of DNA Biology, 9th ed,Sylvia Mader X-Ray Diffraction of DNA Chapter 13 DNA Structure & Function

Watson and Crick Model (1953) Biology, 9th ed,Sylvia Mader Watson and Crick Model (1953) Chapter 13 DNA Structure & Function Using data provided by Franklin’s X-ray diffraction and other knowledge about DNA, they eventually determined that DNA is a double-helix Sugar-phosphate backbones make up the sides Hydrogen-bonded bases make up the rungs. Complementary bases (A-T; C-G) pair up. Model matched data of both Franklin & Chargaff Received a Nobel Prize in 1962

Watson/Crick Model of DNA Biology, 9th ed,Sylvia Mader Watson/Crick Model of DNA Chapter 13 DNA Structure & Function

Biology, 9th ed,Sylvia Mader DNA Replication: Chapter 13 DNA Structure & Function Replication = process of copying a DNA molecule 1. During DNA replication, each old DNA strand of the parental molecule (original double helix) serves as a template for a new strand in a daughter molecule. 2. DNA replication is termed semiconservative replication because one of the old strands is conserved, or present, in each daughter DNA molecule.

Biology, 9th ed,Sylvia Mader Steps of Replication Chapter 13 DNA Structure & Function 1. Unwinding DNA replication begins at numerous points along linear chromosome called replication forks. DNA unwinds and unzips into two strands. Weak hydrogen bonds between paired bases are broken. A special enzyme, DNA helicase, unwinds the DNA.

Biology, 9th ed,Sylvia Mader Replication (cont’d) Chapter 13 DNA Structure & Function 2. Complementary base pairing Each old strand of DNA serves as a template for a new strand New complementary nucleotides are positioned by process of complementary base pairing A special enzyme, called DNA polymerase, helps to position the complementary base pairs

Biology, 9th ed,Sylvia Mader Replication (cont’d) Chapter 13 DNA Structure & Function 3. Joining The complementary nucleotides join to form new strands. This is also helped by DNA polymerase

Semiconservative Replication of DNA Biology, 9th ed,Sylvia Mader Semiconservative Replication of DNA Chapter 13 DNA Structure & Function

Meselson & Stahl’s experiment (1958) Biology, 9th ed,Sylvia Mader Meselson & Stahl’s experiment (1958) Chapter 13 DNA Structure & Function Confirmed semiconservative replication theory They grew bacteria in a medium containing heavy N-15 so only heavy DNAs were found. Switched bacteria to N-14 medium. After 1 division, only hybrid DNA was found After 2 divisions, half the DNA is light & half is hybrid These are the results expected if DNA replication is semiconservative.

Meselson and Stahl’s DNA replication experiment Biology, 9th ed,Sylvia Mader Meselson and Stahl’s DNA replication experiment Chapter 13 DNA Structure & Function

DNA Replication Animation DNA Replication Video DNA Replication Animation http://www.courses.fas.harvard.edu/~biotext/animations/replication1.html

Details of DNA Replication Biology, 9th ed,Sylvia Mader Details of DNA Replication Chapter 13 DNA Structure & Function Carbon atoms are numbered in the deoxyribose molecule. DNA strands are antiparallel. One of the strands runs from 3’ to 5’ in one direction, and the other strand runs from 3’ to 5’ in the opposite direction. During replication, DNA polymerase has to synthesize the daughter strand in the 5’ to 3’ direction. Why? DNA polymerase can only join a nucleotide to a free 3’ end of a previous nucleotide.

Biology, 9th ed,Sylvia Mader Chapter 13 DNA Structure & Function

Details of DNA Replication (cont’d) Biology, 9th ed,Sylvia Mader Details of DNA Replication (cont’d) Chapter 13 DNA Structure & Function This also means that DNA polymerase cannot start the synthesis of a DNA chain. An RNA polymerase lays down a short amount of RNA, called an RNA primer, that is complementary to DNA. Then DNA polymerase can join DNA nucleotides to the 3’ end of the growing daughter strand.

Details of DNA Replication (cont’d) Biology, 9th ed,Sylvia Mader Details of DNA Replication (cont’d) Chapter 13 DNA Structure & Function As helicase unwinds DNA, one parental strand runs in the 3’ to 5’ direction toward the fork. Thus, the new complementary daughter strand will be synthesized from the 5’ to 3’ direction. This strand is called the leading strand. The other parental strand, however, is running in the opposite direction (3’ to 5’ AWAY from the fork). The daughter strand must begin at the fork and run in the opposite direction to the leading strand. This is called the lagging strand.

Antiparallel Replication of DNA Biology, 9th ed,Sylvia Mader Chapter 13 Antiparallel Replication of DNA DNA Structure & Function

Details of DNA Replication (cont’d) Biology, 9th ed,Sylvia Mader Details of DNA Replication (cont’d) Chapter 13 DNA Structure & Function Replication of the lagging strand is discontinuous. It results in segments called Okazaki fragments. While proofreading, DNA polymerase will remove the RNA primers and replace them with complementary DNA nucleotides. DNA ligase will then join the fragments together.

Antiparallel Replication of DNA Biology, 9th ed,Sylvia Mader Chapter 13 Antiparallel Replication of DNA DNA Structure & Function

DNA Replication: Prokaryotic Biology, 9th ed,Sylvia Mader DNA Replication: Prokaryotic Chapter 13 DNA Structure & Function Prokaryotic Replication Bacteria have a single circular loop Replication moves around the circular DNA molecule in both directions. Takes about 40 minutes. Produces two identical circles Cell divides between circles, as fast as every 20 minutes

Replication: Prokaryotic vs. Eukaryotic Biology, 9th ed,Sylvia Mader Replication: Prokaryotic vs. Eukaryotic Chapter 13 DNA Structure & Function

Biology, 9th ed,Sylvia Mader Replication Errors Chapter 13 DNA Structure & Function Genetic variations are the raw material for evolutionary change Mutation: A permanent (but unplanned) change in base-pair sequence Some due to errors in DNA replication. Proofreading occurs which eliminates most errors. Mistake rate is only 1 per 1 billion base pairs. Others are due to DNA damage like UV radiation DNA repair enzymes are usually available to reverse most errors

DNA Replication Animation II Videos for Chapter 13 I DNA Replication Animation II http://highered.mcgraw-hill.com/olc/dl/120076/bio23.swf