IBDP Bio (2025) - D1.1 AHL DNA replication

Base sequencing

the procedure of determining the order of nucleotides in a DNA section.

DNA gyrase

an enzyme that relieves the stress in a DNA molecule by adding negative supercoils as it is being unwound.

DNA polymerases I

an enzyme that removes the RNA primers and replaces with dNTP's.

DNA polymerase III

an enzyme that starts replication by attaching at the 3' end of the RNA primer and adding dNTP's in a 5' --> 3' direction. Moving away from the replication fork.

RNA primase

an enzyme that starts DNA replication by adding short lengths of RNA, attached by complementary base pairing, to the template DNA strand.

DNA Helicase

a prokaryote enzyme that unwinds the DNA helix at the replication fork, breaking the hydrogen bonds, to allow the resulting single strands to be copied.

Lagging strand

the strand of the DNA double helix that, because of its orientation that is opposite to the working orientation of DNA polymerase III, is synthesized in a series of short fragments known as Okazaki fragments.

Leading strand

DNA strand being replicated by a continuous process in a 5' to 3' direction.

Nucleotides

the building blocks of a nucleic acid, consisting of a carbon pentose sugar covalently bonded to a nitrogenous base and a phosphate group.

RNA Primer

a segment of RNA that is complementary to a given DNA sequence and that is needed to initiate replication by DNA polymerase.

Replication fork

a site on a DNA molecule at which the unwinding of the helices and synthesis of daughter molecules are both occurring during DNA replication.

Antiparallel strands

The description given to the orientation of the two polynucleotide strands in DNA running in the opposite direction.

DNA ligase

An enzyme that links Okazaki fragments during replication.

Okazaki fragments

Newly formed DNA fragments that form part of the lagging strand during replication and which are linked together by DNA ligase to produce a continuous strand.

Deoxynucleoside triphosphate (dNTP's)

Free building units that are added to the 3' end of the DNA when forming a new strand of DNA.

5 to 3 prime

leading strand

3 to 5 prime

lagging strand

polynucleotide

A polymer consisting of many nucleotide monomers in a chain; nucleotides can be those of DNA or RNA.

phosphodiester bond

the type of bond that links the nucleotides in DNA or RNA. joins the phosphate group of one nucleotide to the hydroxyl group on the sugar of another nucleotide

continuous replication

replication of the leading strand in the same direction as that of unwinding, allowing new nucleotides to be added continuously to the 3' end of the new strand as the template is exposed

discontinuous replication

Replication of the lagging strand in the direction opposite that of unwinding, which means that DNA must be synthesized in short stretches (Okazaki fragments).

proof reading enzymes

During DNA replication, these scan the newly synthesized DNA for mistakes and repair them.