Chapter 6 Flashcards
What is a nucleotide made up of?
-a pentose sugar-a nitrogenous base-a phosphate group
What is the DNA double-helix backbone made up of?
Alternating sugars (5-carbons) attached to phosphate groups
5’ and 3’
5’: the 5 Prime End, a phosphate group is attached to the 5th carbon3’: the 3 Prime End, a hydroxyl (alcohol) is attached to the 3rd carbon -the DNA structure is anti-parallel because it goes 5’ to 3’ and 3’ to 5’
Nitrogenous Base Pairs structure in the double-helix
-the nitrogenous base pairs are attached to the 1st carbon of sugar-they are held together by hydrogen bonds-there are 3 h-bonds between C & G-2 h-bonds between A & T
Semi-Conservative model
If you start with 1 strand of DNA, when the replication process is over you’ll have 1 old strand and 1 new strand (olds never meet again with each other and news never meet)
DNA Replication Steps
-starts at the origin of replication forms a bubble-the helicase breaks the h-bonds and unzips the strands-the DNA polymerase puts down corresponding new nitrogenous bases -it can only add to the 3’ end of DNA -so it’s easy for it to lay down 5’ to 3’ on the old 3’ to 5’ strand-to lay down the new 3’ to 5’ on the old 5’ to 3’ strand, the lagging strand, it had to go in the opposite direction of the replication fork-the enzyme RNA polymerase puts down a primer for the DNA polymerase to attach to-then, the DNA polymerase puts nitrogenous bases in the correct direction away from the replication fork -it takes multiple sections of primer to copy the lagging strand-the lagging strand is actually a bunch of DNA fragments separated by primers. These fragments are called the Okasaki fragments-the primers between the Okasaki fragments are removed by the DNA ligase that seals the fragments together to make one continuous strand like the leading strand
