1.5 Nucleic Acids and DNA Replication Flashcards
What bond forms between two nucleotides?
A phosphodiester bond
A purine must always bond with a pyrimidine. What are purines and pyrimidines and give examples.
Purines have a double carbon ringlet structure; they are larger; examples are bases adenine and guanine.
Pyrimidines have a single carbon ringlet structure; they are smaller; examples are bases thymine and cytosine.
What is meant by the DNA strand being antiparallel?
DNA strands run in opposite directions. The ‘O’ of the pentose sugar, or the point, acts as an arrow that points in the 5’ to 3’ direction
What’s the first step of DNA replication?
Enzyme DNA helicase unwinds the DNA strands by breaking down the hydrogen bonds between the bases. This results in a formation known as the replication fork. The separated strands of DNA provide a template for creating a new strand of DNA.
What’s the second step of DNA replication?
An enzyme called RNA primase starts the replication process. This enzyme catalyses the synthesis of a small piece of RNA, called a primer. A primer marks the starting point for the construction of the new strand of DNA.
What’s the third step of DNA replication?
An enzyme called DNA polymerase binds to the primer and begins making the new strand, joining two nucleotides together in a condensation reaction, forming a phosphodiester bond. DNA polymerase can only add nucleotides in one direction, from the 5’ end to the 3’ end. Therefore, the 5’ to 3’ strand, leading strand, is made continuously.
What’s the fourth step of DNA replication?
The 3’ to 5’ strand, the lagging strand, cannot be made continuously as it runs in the opposite direction. Therefore, the DNA polymerase can only make this strand in a series of chunks called Okazaki fragments. Each fragment is started with an RNA primer. DNA polymerase adds bases from this primer, in the 5’ to 3’ direction. The next primer is then added further down the lagging strand as the replication fork grows, and another Okazaki fragment is then made, and the process is repeated.
What’s the fifth step of DNA replication?
RNA primers are removed by enzyme DNA exonuclease, which act as proofreaders during this process. The DNA polymerase then fills in the gaps with nucleic acids.
What’s the sixth step of DNA replication?
Finally, the enzyme DNA ligase seals up the fragments of DNA in both strands to form a continuous double strand.
