CELS 191 Lecture 10 Flashcards
what are Chargaffs rules
[A] = [T] and [C] = [G]
the composition of DNA varies between species
why couldn’t 2 purine join together (or 2 pyrimidines)
because the diameter of the helix is constant and pyrimidines have only 1 carbon ring each whereas purines have 2 carbons rings each so if they were bonded the diameter of the double helix wouldn’t be constant
how are nucleotide monomers joined together and what do they form
they are joined together with phosphodiester bonds to form a polynucleotide or nucleic acid
the hydroxyl group of the __ carbon of one of the nucleotides reacts with the phosphate group attached to the ___ on another nucleotide
3rd - 5th
in which direction are DNA and RNA strands synthesised and why
5’ to 3’ direction - because the 3’ end is chemically reactive
what is the name of the enzyme adding nucleotides together
DNA polymerase 3
how are nucleotides added to the DNA strand
before the nucleotide is added it has three phosphate groups attached and in order to attach to the DNA stand we cleave between the first and second phosphate groups so there is just one phosphate on the molecule. this releases a lot of energy that is then used to chemically bond the nucleotide onto the DNA strand
each DNA strand has a direction depending on the position of the 3’ and 5’ carbons, how are the two strand arranged
they are antiparallel
what type of bonds hold together the bases of DNA and are they strong
hydrogen bonds are very weak but many of them combined can be relatively strong
how many hydrogen bonds are there between A and T
2
how many bonds are there between C and G
3
what is the Watson and crick model of DNA
DNA has a double stranded helical structure. the sugar phosphate backbone is on the outside. the bases are on the inside. the structure is stabilise by hydrogen bonds. the two polynucleotide strands are oriented in opposite directions
what is the model for DNA replication called
semi-conservative model
