Structure and Replication What is DNA? Structure and Replication

DNA Structure DNA is a macromolecule. It is a type of nucleic acid. DNA is a polymer (many units connected to each other) of nucleotides. DNA Stands for Deoxyribonucleic acid.

People important to the discovery of DNA Structure Watson, Crick, & Wilkins were awarded a Nobel Prize because they were the first to make a model of the double helix shape Chargaff did experiments to come up with the base pairing rules (A-T, C-G). Franklin took x-ray pictures of DNA, first to show the shape was a double helix, called image 51

What is the monomer of DNA? DNA is a large molecule made of small parts called nucleotides. Each nucleotide contains three parts: 1. sugar (deoxyribose) 2. phosphate group 3. nitrogen base (any of 4, adenine, thymine, cytosine or guanine)

Complementary Base Pairing DNA has two sides or strands. We say that one strand is complementary to the other, meaning that they use Chargaff’s base pairing rule to match up. Chargaff’s rule states that: adenine always pairs with thymine (A-T) & cytosine always pairs with guanine (C-G) The two strands of DNA are held together by hydrogen bonds.

DNA Replication DNA replication is the process where a molecule of DNA makes an exact copy of itself. (see foldable model) DNA "unzips", which means it breaks hydrogen bonds and opens up. New nucleotides come in and bond to the open strands using the base pairing rules.

Semi-Conservative Replication Each new molecule that results is half "new" and half "old" - this helps minimize mistakes in copying - we call this semi-conservative replication

DNA Replication Steps of DNA Replication: The parental DNA molecule unwinds and unzips. Both parental strands serve as templates for new strands. Free nucleotides link to complementary bases on each strand. Two identical DNA molecules result, each composed of one parental strand, adn one new strand.

Practice Use Chargaff’s rule to write the complementary bases below the single strands. 1. ATTGCTAGTCATGCAGTCA 2. ATCGGTCATGCATCCGGAT TAACG... 3. TGTCACAGTAGCATGGTAC 4. DNA stands for _____________________. It is a _____________ of nucleotides. They consist of three parts; ____________, ______________, ________________. 5. The word we use for DNA copying is ________________. 6. DNA replication is considered to be __________-____________. This means that the daughter DNA molecule is half the original molecule and half the new molecule.

Practice KEY Write the complementary bases below the strand that is given. 1. ATTGCTAGTCATGCAGTCA 2. ATCGGTCATGCATCCGGAT TAACGATCAGTACGTCAGT TAGCCACTACGTAGGCCTA 3. TGTCACAGTAGCATGGTAC ACACTGTCATCGTACCATG 4. DNA stands for __deoxyribonucleic acid__. It is a _polymer_ of nucleotides. They consist of three parts; __nitrogen bases__, __deoxyribose sugar__, __phosphate__. 5. The word we use for DNA copying is ___replication___. 6. DNA replication is considered to be __semi-conservative__. This means that the daughter DNA molecule is half the original molecule and half the new molecule.