Biochemistry of Nucleic Acids Flashcards
What is the central dogma?
The central dogma is concerned with the flow of information from DNA towards protein
What is the difference between a nucleoside and a nucleotide?
Nucleoside = base + sugar (e.g adenosine, guanosine) Nucleotide = nucleotide + phosphate group
What are the difference between purines and pyrimidines and which bases are in each group?
Purines are larger groups - include adenine and guanine
Pyrimidines are smaller groups - include uracil, thymine and cytosine
Which side can new nucleotides be added to?
New nucleotides can only be added to a free 3’ end of a nucleic acid (free 3’ hydroxy group)
What catalyses the addition of another nucleotide into a chain?
DNA polymerase III
What happens during polymerisation of nucleotides into a chain?
A phosphodiester bond is formed between a free 3’ OH group and a 5’ triphosphate. 1 phosphate group forms the bonds and 2 phosphates leave as PP pyrophosphate. This process consumes 2 high-energy bonds so supplies energy to drive the reaction forward
Naming DNA and RNA building blocks - name dATP (DNA form) and ATP (RNA form)
dATP = DEOXY-adenosine-triphosphate ATP = adenosine-triphosphate
What is the difference between the leading and lagging strand?
Leading strand continues adding from a free 3’ end
Lagging strand runs in the opposite direction from the leading strand so doesn’t have a free 3’ end so adding is discontinuous in short segments and requires many RNA primers
What are the short segments in the lagging strand called?
Okazaki fragments
Incorporating the wrong nucleotide can create mutations, so what can DNA polymerase do about this?
DNA polymerase has an exonuclease activity so can chow back from 3’ to 5’ when a mismatch is detected so it can remove the incorrect nucleotide
DNA replication is semi-conservative, what does this mean?
This means that the DNA strands split and finds a new pair
Should DNA be replicated before or after cell division?
DNA has to be replicated BEFORE cell division
What enzyme is need to unwind a DNA helix?
Helices
Eukaryotic genomes have many origins of replication, what does this mean?
This means that in eukaryotes, replication can simultaneously at various points in the genome - so replication is bidirectional as it can occur in both directions - this ensures that replication is finished quickly
What enzyme catalyses DNA replication and what enzyme starts replication?
DNA polymerase catalyses DNA replication but it is a RNA primase (synthesised by primase) that start replication
