DNA HISTORY STRUCTURE REPLICATION WHAT IS DNA Deoxyribose

DNA HISTORY, STRUCTURE, & REPLICATION

WHAT IS DNA? • Deoxyribose Nucleic Acid • Polymer made out of sugars (deoxyribose), phosphates, and nitrogen bases • Heredity material for all organisms • Makes up chromosomes 1 • Located in the nucleus

HISTORY OF DNA 2 • James Watson & Francis Crick (1953)proposed that DNA is made of two chains of nucleotides joined together by the nitrogen bases ❖Just like the teeth of a zipper hold 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

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

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

DNA STRUCTURE • Nucleotides come together to form long chains ❖Phosphate group of one nucleotide bonding to the deoxyribose of an adjacent nucleotide ❖Forms the “backbone” or the “hand rails of the ladder” • Nitrogen bases make up the “steps of the ladder” or the teeth of the zipper 5

DOUBLE HELIX • Watson and Crick proposed that DNA is shaped like a long zipper that is twisted into a coil, like a spring 6 • DNA is composed of two strands twisted together, its shaped is called double helix

NITROGEN BASE PAIRINGS • Nitrogen bases are very specific with which other base they bind to Adenine → Thymine Guanine → Cytosine 7 • You will always have the same amount of adenine and thymine, and the same amount of guanine and cytosine– they are complementary base pairs

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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 nucleotides arranged along the DNA strands 9 • A-T-T-G-C-A carries different information from a sequence of C-C-T-A-G-C

REPLICATION OF DNA 10 • During mitosis or meiosis, the cell must make a copy of its chromosomes ❖Process called DNA Replication

• 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, nucleotides that are floating around become attached to their base pairs by hydrogen bonds • DNA polymerase- enzyme that bonds the nucleotides into a chain • Continues until the whole molecule is unzipped and replicated 11 HOW DNA REPLICATES

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HOW DNA REPLICATES 13 • After the DNA has been copied, there are two copies of the genetic material • Genetic material can now be passed on to new cells in mitosis or new generations in meiosis

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 14 Adenine – Thymine Cytosine – Guanine

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 15 4. Results of replication: produces two molecules of DNA, each has one strand from the original and a newly synthesized complement

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