Nucleic Acids Competency 208.5.1 Melissa Kelleher, RN

The Structure of DNA • DNA is composed of units called nucleoCdes, (Wolfe, 2000). • NucleoCdes are composed of a phosphate group, a deoxyribose sugar, and a nitrogenous base, (Wolfe, 2000). – Purines – nitrogenous bases that composed of two rings, (Wolfe, 2000). – Pyrimadines – nitrogenous bases composed of one ring, (Wolfe, 2000).

The Structure of DNA • DNA is a double helix structure of nucleoCdes wound together in an anCparallel direcCon, (Wolfe, 2000). – Hydrogen bonds form between the nitrogenous bases, (Wolfe, 2000). – Base pairs only bond in specific pairs, (Wolfe, 2000). • Adenine bonds only with thymine, (Wolfe, 2000). • Guanine bonds only with cytosine, (Wolfe, 2000).

• Deoxyribose sugars line up in one direcCon, considered the 51 to 31 direcCon, in one strand of DNA, and in the opposing direcCon, considered the 31 to 51 direcCon, creaCng and anCparallel orientaCon, (Wolfe, 2000).

The Structure of DNA

DNA ReplicaCon • DNA replicaCon is a semi-­‐conservaCve process, by which each strand of DNA is used as a template for the new strand of DNA being replicated, (Wolfe, 2000). • DNA replicaCon bubbles form in various secCons along the DNA strand, and these are the sites of replicaCon, (Wolfe, 2000).

• Helicase is the enzyme that uncoils the DNA strands at the replicaCon bubbles, (Wolfe, 2000). • Single strand binding protein binds to each of the DNA strands to prevent it from winding into a helix shape again, (Wolfe, 2000).

– Various enzymes are involved in the replicaCon process, (Wolfe, 2000).

DNA ReplicaCon

DNA ReplicaCon • Within each replicaCon bubble the enzyme primase adds a secCon of RNA primer to each strand, (Wolfe, 2000). • DNA polymerase is the enzyme that adds new chunks of DNA to each strand, starCng where the RNA primer has been added, (Wolfe, 2000). – DNA polymerase reads from the 31 to 51 end of the DNA strand, (Wolfe, 2000). – DNA polymerase adds new nucleoCdes in the 51 to 31 direcCon, maintaining the anCparallel characterisCc of DNA, (Wolfe, 2000).

– DNA polymerase can not add nucleoCdes directly to the DNA strand without an RNA primer, (Sander, 2013).

DNA ReplicaCon • The leading strand is the strand of DNA that reads in the 31 to 51 direcCon, (Wolfe, 2000). – DNA polymerase adds new nucleoCdes to this strand conCnuously working towards the replicaCon fork, (Wolfe, 2000).

• The lagging strand is the strand of DNA that reads in the 51 to 31 direcCon, (Wolfe, 2000). – DNA polymerase adds new nuceloCdes disconCnuously along this strand towards the replcaCon fork, (Wolfe, 2000).

DNA ReplicaCon

DNA ReplicaCon • The lagging strand of DNA is built disconCnuously in segments called Okazaki fragments, which were named aXer the scienCst who discovered them, (Wolfe, 2000). • Primase adds RNA polymerase to the DNA strand and DNA polymerase adds new nucleoCdes in the direcCon away from the replicaCon fork, (Sanders, 2013). – As helicase and single strand binding protein unwind more secCons of DNA at the replicaCon fork, primase and DNA polymerase work to create new secCons of DNA, (Wolfe, 2000). – The new secCons along the lagging strand are the Okazaki fragments, (Wolfe, 2000).

DNA ReplicaCon

Role of Ligase • DNA replicaCon can not be completed unCl the RNA primer is replaced in the new DNA strand, and the Okazaki fragments have been connected, (Sanders, 2013). • DNA Polymerase I, which was the first DNA polymerase enzyme discovered, replaces RNA primer with DNA nucleoCdes along the new DNA strand, (Sanders, 2013). • Ligase then comes along and connects the Okazaki fragments that have their chunks of RNA primer replaces, to create a conCnuous DNA strand, (Sanders, 2013).

Role of Ligase

Role of Ligase

Role of mRNA • DNA holds the “recipes” for our cells to make proteins, (Wolfe, 2000). • To preserve our DNA so that it is not leaving the cell nucleus and exposed to the enzymes in the cytoplasm that could alter it, RNA polymerase binds to the parent DNA strand and creates mRNA, (Wolfe, 2000). • The process of creaCng mRNA from DNA is called transcripCon, (Sanders, 2013).

Role of mRNA

Role of mRNA • Following creaCon of the mRNA strand in the cell nucleus, it then leaves the nucleus and enters the cytoplasm surrounding the nucleus, (Sanders, 2013). • Ribosomes and rRNA molecules bind to the strand of mRNA and begin “reading” the “recipe”, (Wolfe, 2000). • Amino acids are then brought by tRNA molecules to the cell based on the codon, or 3 nucleoCde combinaCon read by the ribosome, (Wolfe, 2000). • The ribosome travels down the mRNA strand linking more and more amino acids together, creaCng the new protein coded in that stand of mRNA, (Wolfe, 2000). • This process of translaCon occurs mulCple Cmes along the mRNA strand, and many proteins can be built from one strand of mRNA, (Wolfe, 2000).

Role of mRNA

Death Cap Mushrooms • Death cap mushrooms are poisonous when ingested due to the toxin alpha-­‐amanaCne, (Hudon-­‐Miller, 2013). • In order for cell funcCon to conCnue, mRNA must be created by RNA polymerase, and then must be used to create new proteins, (Hudon-­‐Miller, 2013). – Proteins maintain electrolyte balance, build enzymes, build new structures in the body, among other things, (Hudon-­‐Miller, 2013).

• The alpha-­‐amanaCne toxin inhibits the RNA polymerase molecule from making mRNA in the cell, and leads to a stop in cell funcCon, and ulCmately death, (Hudon-­‐Miller, 2013).

References • Hudon-­‐Miller, S. (2013, 07 16). Death cap mushrooms. Retrieved from h`p:// wgu.hosted.panopto.com/Panopto/Pages/ Viewer.aspx?id=45c5aef2-­‐370e-­‐43eb-­‐ ad9c-­‐40f073926331 • Sanders, J. (2013, 7 16). Dna replica1on. Retrieved from h`p://wgu.hosted.panopto.com/ Panopto/Pages/Viewer.aspx? id=2c8cb82e-­‐03f8-­‐4524-­‐aecd-­‐c3d314612141 • Wolfe, G. (2000). Thinkwell biochemistry. Retrieved from h`p://wgu.thinkwell.com