Ch (part 2) DNA Structure & Replication

Target #7- I can explain what Rosalind Franklin discovered about DNA Rosalind Franklin –Studied DNA using x-ray crystallography The DNA, when bombarded with x-rays, an image can be captured from the refracted light –X-ray photographs showed an X surrounded by a circle Used later by James Watson & Francis Crick to further develop the shape of DNA

Target #8- I can explain what Watson & Crick discovered about DNA James Watson & Francis Crick –One of the many scientists to study proteins and the structure of DNA –Built a model of DNA using wood and metal Found that DNA fits together like a puzzle –Double Helix: two strands of DNA wind around each other like a twisted ladder

Target #9- I can describe the structure of DNA A DNA strand: –Has a backbone made up of alternating phosphate and sugar molecules –Has two strands which form a double helix Held together by hydrogen bonds Run anti-parallel –In opposite directions 5’ end  marked by a phosphate group at the end 3’ end  marked by a sugar group and OH- molecule at the end

Target #10- I can explain the structure of nucleotides DNA is a chain of nucleotides –Made of 3 subunits: phosphate group, pentose sugar, nitrogen base –Purines  a group of nitrogen bases Adenine Guanine –Pyrimidines  a group of nitrogen bases Thymine cytosine

Target #11- I can state compliment ary base pairing rules Complimentary base pairing rules –A always pairs with T Forms 2 hydrogen bonds –G always pairs with C Forms 3 hydrogen bonds

Target #12- I can describe DNA replication DNA replication: the process of copying one DNA double helix into two identical double helices –Each original strand serves as a template for the formation of a complimentary new strand –Known as “semiconservative” A new double helix has one conserved old strand and one new strand –Results in two new DNA helices that are identical to each other and to the original molecule

Target #13- I can state what occurs during DNA replication Target #14- I can identify the enzymes involved with DNA Replication Step 1: before replication begins the two strands that make up parental DNA are hydrogen bonded to each other Step 2: The enzyme DNA helicase unwinds and “unzips” the double stranded DNA at the replication fork –Breaks the hydrogen bonds

Step 3: New complimentary DNA nucleotides fit into place via base pairing –Joined by the enzyme DNA polymerase –5’ strand is leading strand Replication occurs “forwards” –3’ strand is lagging strand Replication occurs “backwards” Works in a “piece by piece” fashion by creating fragments called okazaki fragments –Later connected using DNA ligase

Target #13 & #14- cont. Step 4: To complete replication, the enzyme DNA ligase seals any breaks in the sugar phosphate backbone Step 5: the two double helix molecules are identical to each other and the original DNA molecule