DNA

1. DNA HISTORY, STRUCTURE, & REPLICATION

2. WHAT IS DNA? • Deoxyribose Nucleic Acid • Polymer made out of sugars (deoxyribose), phosphates, and nitrogen bases • Heredity material for all organisms • Makes up chromosomes • Located in the nucleus

3. HISTORY OF DNA • James Watson & Francis Crick (1953)- proposed that DNA is made of two chains of nucleotidesjoined together by the nitrogen bases • Just like theteethof azipperhold the two sides of the zipper together • Also discovered that each strand was a template for each other. During cell division, the strands unzip, and then it is able to copy its genetic material

4. DNA STRUCTURE • Nucleotides have 3 parts- a simple sugar, a phosphate group, and a nitrogen base • Sugar unit→ deoxyribose • Phosphate group→ 1phosphorus atom surrounded by four oxygen atoms • Nitrogen base→carbon ring structure that contains one or more atoms of nitrogen Phosphate Group Nitrogen Base

5. NITROGEN BASES • 4 different nitrogen bases • DNA→ Adenine (A) Guanine (G) Thymine (T) Cytosine (C)

6. DNA STRUCTURE • Nucleotides come together to form long chains • Phosphate group of one nucleotide bonding to the deoxyriboseof an adjacent nucleotide • Forms the “backbone” or the “hand rails of the ladder” • Nitrogen bases make up the “steps of the ladder” or the teethof the zipper

7. DOUBLE HELIX • Watson and Crick proposed that DNA is shaped like a long zipper that is twistedinto a coil, like a spring • DNA is composed of two strands twistedtogether, its shaped is called double helix

8. NITROGEN BASE PAIRINGS • Nitrogen bases are very specificwith which other base they bind to Adenine → Thymine Guanine → Cytosine • You will always have the sameamount of adenine and thymine, and the same amount of guanine and cytosine– they are complementary base pairs

10. NUCLEOTIDE SEQUENCES • All organisms have DNA made up of the same 4 nucleotides with adenine, thymine, cytosine, and guanine • Organism differences result from the sequences of the four different nucleotidesarranged along the DNA strands • A-T-T-G-C-Acarries different information from a sequence of C-C-T-A-G-C

11. REPLICATION OF DNA • During mitosisor meiosis, the cell must make a copyof its chromosomes • Process calledDNA Replication

12. HOW DNA REPLICATES • Each strand serves as a template, or a pattern, to make a new DNA molecule • Helicase- enzyme that breaks the hydrogen bonds between the bases that hold the two strands together • “unzipping” the DNA • While the DNA is unzipping, nucleotidesthat are floating around become attachedto their base pairs by hydrogen bonds • DNA polymerase- enzyme that bonds the nucleotides into a chain • Continues until the whole molecule is unzippedandreplicated

14. HOW DNA REPLICATES • After the DNA has been copied, there are twocopies of the genetic material • Genetic materialcan now be passed on to new cells in mitosisor new generations in meiosis

15. COPYING DNA 1. Separating of strands: nucleotide strands separate when the hydrogen bonds are broken, DNA molecule unzips, the bases are exposed 2. Base pairing:the bases of free nucleotides pair with the exposed DNA strand. Each strand builds a complement by base pairing Adenine – Thymine Cytosine – Guanine

16. COPYING DNA 3. Bonding of bases: sugar and phosphate groups of adjacent nucleotides bond together with covalent bonds to form the backbone of the new strand Original strand is hydrogen bonded to the new strand 4. Results of replication: produces two molecules of DNA, each has one strand from the original and a newly synthesized complement