8.2 Structure of DNA TEKS 3F, 6A, 6B The student is expected to: 3F research and describe the history of biology and contributions of scientists; 6A identify components of DNA, and describe how information for specifying the traits of an organism is carried in the DNA; 6B recognize that components that make up the genetic code are common to all organisms

8.2 Structure of DNA TEKS 3F, 6A, 6B KEY CONCEPT DNA structure is the same in all organisms.

8.2 Structure of DNA TEKS 3F, 6A, 6B DNA DNA is one of the 4 types of macromolecules known as a nucleic acid.DNA is one of the 4 types of macromolecules known as a nucleic acid. DNA stands for deoxyribonucleic acid.DNA stands for deoxyribonucleic acid.

8.2 Structure of DNA TEKS 3F, 6A, 6B DNA is composed of four types of nucleotides. DNA is made up of a long chain of nucleotides. Each nucleotide has three parts. –a phosphate group –a deoxyribose sugar –a nitrogen-containing base phosphate group deoxyribose (sugar) nitrogen-containing base

8.2 Structure of DNA TEKS 3F, 6A, 6B The nitrogen containing bases are the only difference in the four nucleotides.

8.2 Structure of DNA TEKS 3F, 6A, 6B

The chain has a direction determined by whether the deoxyribose is right side up, or upside down. The “top” of the molecule will have a phosphate sticking out. It is known as the 5’ end (5 prime).

8.2 Structure of DNA TEKS 3F, 6A, 6B If there is no phosphate sticking out, it is the 3’ end (3 prime). If there is no phosphate sticking out, it is the 3’ end (3 prime).

8.2 Structure of DNA TEKS 3F, 6A, 6B Constructing the DNA Polymer 5’3’5’3’ 3’5’3’5’

8.2 Structure of DNA TEKS 3F, 6A, 6B It looks like a twisted ladder. The strands run in opposite directions; called antiparallel (like opposite flows of traffic )

8.2 Structure of DNA TEKS 3F, 6A, 6B Watson and Crick determined the three-dimensional structure of DNA by building models. They realized that DNA is a double helix that is made up of a sugar- phosphate backbone on the outside with bases on the inside.

8.2 Structure of DNA TEKS 3F, 6A, 6B Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff. –Franklin’s x-ray images suggested that DNA was a double helix of even width. –Chargaff’s rules stated that A=T and C=G.

8.2 Structure of DNA TEKS 3F, 6A, 6B Chargaff’s Rules: Erwin Chargaff ( ) discovered that in any DNA sample the amount of guanine is always equal to the amount of cytosine, the amount of adenine was always equal to the amount of thymine. A = T G = C

8.2 Structure of DNA TEKS 3F, 6A, 6B T A C G Nucleotides always pair in the same way. The base-pairing rules show how nucleotides always pair up in DNA. Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width. – A pairs with T – C pairs with G

8.2 Structure of DNA TEKS 3F, 6A, 6B This eventually led to our base pairing rules: 1.Each base pair is made of 1 purine and 1 pyrimidine. 2. Adenine from one strand and thymine from the other always pair together with two hydrogen bonds

8.2 Structure of DNA TEKS 3F, 6A, 6B 3. guanine on one strand and cytosine on the other strand always bond together with three hydrogen bonds.

8.2 Structure of DNA TEKS 3F, 6A, 6B The backbone is connected by covalent bonds. hydrogen bond covalent bond The bases are connected by hydrogen bonds.