DNA Structure DNA Some DNA Basics DNA stands

DNA Structure

DNA

Some DNA Basics… DNA stands for Deoxyribonucleic Acid n DNA’s basic function is to store and transmit genetic information. n This information tells an organism’s cells what proteins to make and when to make them. n Proteins form pretty much everything the body needs…like? n

DNA Structure… n DNA is composed of 2 chains or strands of repeating nucleotides n A nucleotide = sugar + phosphate + nitrogen containing base

DNA Structure… n Deoxyribose is a sugar molecule. n The phosphate group is phosphorus surrounded by oxygen atoms. n The nitrogen containing base is just that, a base containing nitrogen atoms.

The DNA Backbone n Putting the DNA backbone together – refer to the 3 and 5 ends of the DNA • the last trailing carbon 5 PO 4 CH 2 base O C O –O P O O CH 2 base O OH 3

Directionality of DNA n You need to number the carbons! – it matters! nucleotide PO 4 N base 5 CH 2 4 O deoxyribose 3 OH 2 1

Anti-Parallel Strands n Phosphate to sugar bond involves carbons in 3 & 5 positions – DNA molecule has “direction” – complementary strand runs in opposite direction “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. ” Watson & Crick

Nitrogen Containing Bases… n In DNA, the nitrogen containing bases come in 4 varieties. – – Adenine Guanine Cytosine Thymine (__A__) (__G__) (__C__) (__T__)

Purines vs. Pyrimidines Adenine and Guanine are Purines n (2 carbon rings). n Purine Cytosine and Thymine are Pyrimidines n (1 carbon ring). n Pyrimidine

Complementary Base Pairing… (Remember Chargaff? ) DNA bases pair in a standard manner. The 2 base pairing rules are: n Adenine pairs with Thymine by 2 hydrogen bonds n Guanine pairs with Cytosine by 3 hydrogen bonds n

Bonding in DNA 5’ hydrogen bonds 3’ phosphodiester bonds 3’ 5’ …. strong or weak bonds? How do the bonds fit the mechanism for copying DNA?

DNA Replication is the process in a cell where DNA copies itself. n To accomplish this feat, DNA must unwind, split into two chains, and each chain serves as a template for two new strands of DNA. n In Eukaryotic cells, replication occurs during the Synthesis (S) phase of Interphase during the Cell Cycle. n

Semi-Conservative Replication n Messelsohn & Stahl Experiment – 15 N 1958 strands replicated in 14 N medium – Showed that each new molecule is ½ old and ½ new

Replication Overview n n n In Lecture 28 you will complete a self-guided tutorial on DNA Replication We will introduce this topic though using this animation… http: //www. wiley. com/college/pratt/0471393878/stude nt/animations/dna_replication/index. html http: //highered. mcgrawhill. com/olcweb/cgi/pluginpop. cgi? it=swf: : 535: : /si tes/dl/free/0072437316/120076/micro 04. swf: : DNA%2 0 Replication%20 Fork http: //highered. mcgrawhill. com/olcweb/cgi/pluginpop. cgi? it=swf: : 535: : /si tes/dl/free/0072437316/120076/bio 23. swf: : How%20 N ucleotides%20 are%20 Added%20 in%20 DNA%20 Rep lication