DNA Flashcards
Which nucleotide bases have a purine ring?
Cytosine
Uracil
Thymine
Which nucleotide bases have purine rings
Guanine
Adenine
What is a NUCLEOSIDE?
A nucleoside is a purine or pyramidine base attached to a sugar
What is a NUCLEOTIDE?
This is when a phosphate is esterified to the OH group on a sugar attached to a nucleoside
Which direction is DNA read?
IN The 5’ to The 3’ direction
How is The DNA backbone formed!
Formed when nucleotides join by 3’ to 5’ phosphodiester bonds.
What is chargaffs rule
[A]= [T]
[G] = [ C]
What is the difference between heterochromatin and Euchromatin?
Heterochromatin is dense and transcriptionally silent and dark under a light microscope
Euchromatin is transcriptionally active and less dense. It is light under a light microscope
Explain how DNA replicates
First, an initiator protein binds to the origin of replication to begin the unwinding process.
Next, DNA Helicase continues to unwind the DNA with the help of DNA gyrase (topoisomerase) which goes ahead of DNA helicase to remove any supercoils
Single stranded DNA binding proteins stabilise the single DNA strands, allowing them to act as templates. A replication fork is formed at this point.
An RNA primer that is complimentary to the DNA template is synthesised when DNA Primase binds to the leading strand.
DNA polymerase III uses the RNA primer to initiate DNA synthesis by adding deoxyribonucleotides to its 3’ end. Since DNA synthesis is in the 5’-3’ direction, only one RNA primer is needed by the leading strand
A RNA primer is made for the lagging strand which is then extended by DNA polymerase III
In the lagging strand, DNA synthesis is discontinuous as it is synthesised in the 3’-5’ direction making Okazaki fragments. These grow until they reach the adjacent fragment and the RNA primer is replaced with DNA polymerase I
DNA ligase joins adjacent Okazaki fragments.
