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 Located in the nucleus 1

HISTORY OF DNA 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 2

DNA STRUCTURE 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 Phosphate GroupNitrogen Base 3

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

DNA STRUCTURE 5 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

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

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

8

NUCLEOTIDE SEQUENCES 9 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 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

HOW DNA REPLICATES 11 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

12

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 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

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

16