Photo 51 Rosalind Franklin Maurice Wilkins James D. Watson Francis Crick

DNA deoxyribonucleic acid Chapter 12

DNA Functions Store and transmit genetic information DNA is the molecule that makes up genes DNA provides the codes for cells that tell the cell which proteins to make and when to make them. Every living thing has DNA within it Each type of cell uses different genes (portions of DNA) as instructions for its different functions.

DNA Structure DNA is an organic molecule made from long chains of nucleotides. *** The arrangement of these nucleotides is what makes us different from each other and other organisms*** Basic components of a nucleotide: 1.Deoxyribose – a 5 carbon sugar 2.Phosphate Group (P,O) 3.Nitrogen Base (N,C)

DNA Structure

Types of Nitrogenous Bases: 1.Purines: 2 Rings of C & N 1.Adenine 2.Guanine 2.Pyrimidines: 1 Ring of C & N 1.Cytosine 2.Thymine cytosine thymine

DNA Structure Chargaff’s Rule What general statement can you make about the data?

DNA Structure DNA forms the shape of a “double helix” It is often compared to a ladder or spiral staircase Backbone of the ladder: 1. Ribose Sugar 2. Phosphate Group -these are held together by covalent bonds

DNA Structure Rungs of the Ladder: -consist of two nitrogenous bases held together by hydrogen bonds. Base Pair Rules: Adenine :: Thymine Guanine ::: Cytosine

DNA Structure Homework 1.Draw a diagram of DNA and Label all parts of the nucleotide and the bonds that are formed. 2.Write a paragraph with at least 5 Sentences. Your paragraph must include the following words- UNDERLINE them!!! nucleotide, deoxyribose sugar, phosphate group, covalent bond, hydrogen bond, purines, pyrimidines, adenine, guanine, cytosine, thymine, double helix *** You will be turning this in so make it neat***

Prokaryotes Prokaryotes lack a nucleus so the DNA is located in the cytoplasm of the cell. Most prokaryotes have a single circular DNA molecule. This is the cell’s chromosome. DNA Structure

Eukaryotes – The nucleus of a eukaryotic cell contains more than 1 meter of DNA How does it all fit???????

Levels of DNA 1 nm = 1 x m Or m 1 mm = 1000 nm

DNA Replication Before a cell divides it must make a copy of its DNA so that each new cell gets a complete copy. This process is called replication.

DNA Replication 1.The enzyme helicase unwinds the double stranded DNA molecule and breaks the hydrogen bonds holding the base pairs together. 2.Single Strand Binding Proteins hold the DNA strands straight until the new DNA strands are made.

DNA Replication The two “old” DNA strands are used as templates to build two “new” complimentary strands using the base pair rules for adding nucleotides. -The DNA strands are antiparallel. Even though replication occurs simultaneously on both strands, it can only occur in 1 direction 5’ to 3’. Because of this one strand is called the “leading strand”, the other, the “lagging strand”.

DNA Replication 3. The leading strand: The enzyme primase begins the replication process by attaching a primer. The enzyme DNA polymerase then helps to elongate (add nucleotides) continually in the 5’ to 3’ direction towards the replication fork to build the complimentary strand.

DNA Replication 4. The lagging strand As the replication bubble opens, DNA polymerase can add nucleotides in short segments moving away from the replication fork. As the bubble continues to widen, another short strand can be synthesized. These short strands are known as Okazaki fragments. 5. These fragments are eventually joined by an enzyme called ligase.

DNA Replication DNA helix unwinds, providing single-stranded DNA templates (helicase and single-strand binding proteins) Synthesis of Leading Strand 1.Priming (primase) 2.Elongation (polymerase) Synthesis of Lagging Strand 1.Priming Okazaki fragment (primase) 2.Elongation of fragment (polymerase) 3.Fragments joined (ligase)

DNA Replication What and accomplishment!!! Your DNA contains about 6 billion bases (this would fill about 900 of your textbooks if you were to just type the first letter of each base) It takes your cell a few hours to copy all of the DNA Error Rate – About 1 per billion nucleotides!!!