DNA Structure & Replication Notes PDF

DNA: Structure & Replication  DNA Controls ALL activities of cell Found in nucleus in eukaryotes. Prokaryotes/Bacteria - DNA is in the cytoplasm DNA is an abbreviation for Deoxyribonucleic Acid  It is a nucleic acid (1 of the 4 biomolecules)  Made of smaller bui...

DNA: Structure & Replication  DNA Controls ALL activities of cell Found in nucleus in eukaryotes. Prokaryotes/Bacteria - DNA is in the cytoplasm DNA is an abbreviation for Deoxyribonucleic Acid  It is a nucleic acid (1 of the 4 biomolecules)  Made of smaller building blocks = nucleotides  3 parts to a nucleotide 1. Deoxyribose sugar (5 carbons - pentagon shaped) 2. Phosphate group 3. Nitrogen base Simple Nucleotide Structure There are 4 types of nitrogenous bases. – thymine (T) – adenine (A) – cytosine (C) – guanine (G) Nucleotide Building Block! =  DNA Structure Nucleotide building blocks bond to form the DNA molecule. Double helix shape - looks like a spiral staircase When unwound, it looks like a ladder: rails/backbone are alternating sugars & phosphates Rungs/ladder steps = complementary pairs of nitrogenous bases – bases held together with hydrogen bonds that can easily be broken when it is time for replication  The Chemical Structure of DNA  Complementary Nitrogen - Base Pairing There is only ONE way the nitrogen bases will bond! A only bonds to T C only bonds to G So, for every A there is a T and for every C there is a G. This is known as Chargaff’s rule (after the scientist that Structure Note #1: Nitrogen base pairs between 2 sugar – phosphate backbones Structure Note #2: Overall shape is hydrogen bonds a double helix Structure Note #3: A=T C=G held together with H-bonds Structure Note #4: – One side is upside down DNA is anti-parallel compared to the other. Summary of DNA Structure:  DNA is the universal genetic code! ALL organisms have DNA made up of the same structure. The only difference between species or individuals is the sequence (order) of the nitrogen bases. – The A, T, C and G’s are just arranged differently.  DNA Replication DNA must be copied in preparation for cell division, a process called replication. This happens during the S-phase of interphase in the cell cycle. Enzymes are necessary for this process to be carried out. The Cell Cycle S = Synthesis Phase DNA Replication occurs here!  DNA Replication Steps 1. the enzyme helicase unzips a section of DNA 2. DNA polymerase (another enzyme) brings in complimentary nucleotides to each side of the split DNA molecule. 3. At the end of replication, there are 2, new identical molecules of DNA – One half of each is from the original DNA. – The other half is the newly formed copy. Practice: If a DNA strand has the base sequence of TACCGTAGT, the complimentary strand would be: _______________________  DNA Replication Enzyme = Enzyme = helicase polymerase Remember: Helicase opens up the helix. Polymerase builds the new polymer (a molecule with a lot of building blocks).