This is because DNA polymerase is able to extend the new DNA strand by reading the template 3′ to 5′, synthesising in a 5′ to 3′ direction as noted above. Along the leading strand, DNA primase only needs to synthesise an RNA primer once, at the beginning, to initiate DNA polymerase. This newly formed strand is referred to as the leading strand. One of the template strands is read in a 3’ to 5’ direction, therefore the new strand will be formed in a 5’ to 3’ direction.
#DNA STANDS FOR WRONG ANSWER FREE#
DNA polymerase is only able to extend the primer by adding free nucleotides to the 3’ end. the template strands), it is able to start synthesising new strands of DNA to match the templates. Once DNA Polymerase has attached to the two unzipped strands of DNA (i.e. This enzyme is ultimately responsible for the creation and expansion of new strands of DNA. It synthesises a small RNA primer, which acts as a ‘kick-starter’ for DNA polymerase. It does this by hydrolysing the ATP used to form the bonds between the nucleobases, thereby breaking the bond holding the two strands together.ĭNA primase is another enzyme that is important in DNA replication. This enzyme unwinds the double helix and exposes each of the two strands so that they can be used as a template for replication. Within the replication complex is the DNA helicase. Multiple origin sites exist within the DNA’s structure when replication of DNA begins, these sites are referred to as r eplication forks. These origins are targeted by initiator proteins, which go on to recruit more proteins that help aid the replication process, forming a replication complex around the DNA origin. When bound together, the two strands form a double helix structure.īy Difference_DNA_RNA-DE, via Wikimedia Commonsįig 1 – The Structure of RNA and DNA Stages of DNA replicationĭNA replication can be thought of in three stages: i nitiation, elongation and termination InitiationĭNA synthesis is initiated at particular points within the DNA strand known as ‘ origins’, which have specific coding regions.
In normal DNA strands, cytosine binds to guanine, and adenine binds to thymine. There are 4 different bases associated with DNA: Cytosine, Guanine, Adenine, and Thymine. These strands are attached to each other throughout their lengths via the bases on each nucleotide.
There are two strands of DNA, which run in opposite (antiparallel) directions to each other. N.B: 3′ is pronounced ‘three prime’ and 5′ is pronounced ‘five prime’. The bond formed is between the third carbon atom on the deoxyribose sugar of one nucleotide (known as the 3’) and the fifth carbon atom of another sugar on the next nucleotide (known as the 5’). These nucleotides are attached to each other in strands via phosphodiester bonds to form a ‘sugar-phosphate backbone’. These are molecules composed of a deoxyribose sugar, with a phosphate and a base (or nucleobase) attached to it. DNA StructureĭNA is made up of millions of nucleotides. In this article, we shall discuss the structure of DNA, the steps involved in DNA replication (initiation, elongation and termination) and the clinical consequences that can occur when this process goes wrong. This is an important process taking place within the dividing cell.
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