DNA

History of DNA Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of 20 different amino acids in long polypeptide chains

Transformation In 1928, Fred Griffith worked with virulent S and nonvirulent R strain Pneumoccocus bacteria He found that R strain could become virulent when it took in DNA from heat-killed S strain Study suggested that DNA was probably the genetic material

Griffith Experiment

History of DNA Chromosomes are made of both DNA and protein Experiments on bacteriophage viruses by Hershey & Chase in 1952 proved that DNA was the cell’s genetic material Radioactive 32 P was injected into bacteria!

DNA Structure In 1950’s, Rosalind Franklin took x- ray diffraction photographs of DNA crystals  showed: 1) helical structure 2) molecules spaced at regular intervals

In 1953, Watson & Crick built the first model of DNA using Franklin’s work as a foundation

DNA STRUCTURE Two strands coiled called a double helix Sides made of a 5 carbon sugar deoxyribose, bonded to phosphate (PO 4 ) groups Center made of nitrogen bases bonded together by weak hydrogen bonds

DNA Double Helix Nitrogenous Base (A,T,G or C) “Rungs of ladder” “Legs of ladder” Phosphate & Sugar Backbone

DNA Stands for Deoxyribonucleic acid nucleotidesMade up of subunits called nucleotides Each nucleotide is made of:Each nucleotide is made of: Phosphate group 1.Phosphate group 5-carbon sugar 2.5-carbon sugar Nitrogenous base 3.Nitrogenous base

DNA Nucleotide O O=P-O OPhosphate Group Group N Nitrogenous base (A, G, C, or T) (A, G, C, or T) CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose)

Nitrogenous Bases Erwin Chargraff showed the amounts of the four bases on DNA ( A,T,C,G) In a body or somatic cell: A = 30.3% T = 30.3% G = 19.5% C = 19.9%

Chargaff’s Rule: Adenine ThymineAdenine must pair with Thymine Guanine CytosineGuanine must pair with Cytosine The bases form weak hydrogen bonds G C TA

DNA P P P O O O P P P O O O G C TA

Base-Pairings Three hydrogen bonds required to bond Guanine & Cytosine CG 3 H-bonds

T A Two hydrogen bonds are required to bond Adenine & Thymine

Question: Adenine CytosineIf there is 30% Adenine, how much Cytosine is present?

Answer: CytosineThere would be 20% Cytosine Adenine (30%) = Thymine (30%)Adenine (30%) = Thymine (30%) Guanine (20%) = Cytosine (20%)Guanine (20%) = Cytosine (20%) Therefore, 60% A-T and 40% C-GTherefore, 60% A-T and 40% C-G

Significance of DNA

DNA is often compared to a set of blueprints  it contains the genetic instructions used in the development and functioning of all known living organisms i.e. it contains the instructions to construct components of cells, such as proteins and RNA molecules.

DNA segments that carry genetic information are called genes Genes code for proteins proteins, which include enzymes, do specialized jobs, & control the activities of each cell

Different cells have different activities. By controlling protein synthesis within each cell, the genes that make up DNA control the life of the entire organism. Thus, sequence of DNA bases ultimately determines how the information in genes is read

Interesting Facts Every person has two copies of each gene, one inherited from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people. Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s unique physical features.

Biology 11 stop here – the remainder of the powerpoint is not part of our study

DNA Replication

Replication Facts DNA has to be copied before a cell dividesDNA has to be copied before a cell divides DNA is copied during the S or synthesis phase of interphaseDNA is copied during the S or synthesis phase of interphase New cells will need identical DNA strandsNew cells will need identical DNA strands

Synthesis Phase (S phase) S phase during interphase of the cell cycle Nucleus of eukaryotes Mitosis -prophase -metaphase -anaphase -telophase G1G1 G2G2 S phase interphase DNA replication takes place in the S phase.

DNA Replication Two strands open forming Replication Forks (Y-shaped region)Two strands open forming Replication Forks (Y-shaped region) New strands grow at the forksNew strands grow at the forks ReplicationFork Parental DNA Molecule 3’3’ 5’5’ 3’3’ 5’5’

DNA Replication As the 2 DNA strands open at the origin, Replication Bubbles formAs the 2 DNA strands open at the origin, Replication Bubbles form Eukaryotic chromosomes have MANY bubbles Prokaryotes (bacteria) have a single bubble Bubbles

DNA Replication Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bondsEnzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds Single-Strand Binding ProteinsSingle-Strand Binding Proteins attach and keep the 2 DNA strands separated and untwisted

DNA Replication Before RNA primersBefore new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides PrimasePrimase is the enzyme that synthesizes the RNA Primer DNA polymerase can then add the new nucleotides

Proofreading New DNA DNA polymerase initially makes about 1 in 10,000 base pairing errorsDNA polymerase initially makes about 1 in 10,000 base pairing errors Enzymes proofread and correct these mistakesEnzymes proofread and correct these mistakes The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errorsThe new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors

Semiconservative Model of Replication Idea presented by Watson & CrickIdea presented by Watson & Crick TheThe two strands of the parental molecule separate, and each acts as a template for a new complementary strand New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA Parental DNA DNA Template New DNA

DNA Damage & Repair Chemicals & ultraviolet radiation damage the DNA in our body cells Cells must continuously repair DAMAGED DNA Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA DNA polymerase and DNA ligase replace and bond the new nucleotides together

Question: What would be the complementary DNA strand for the following DNA sequence? DNA 5’-CGTATG-3’

Answer: DNA 5’-GCGTATG-3’ DNA 3’-CGCATAC-5’