Unit 11A:
Explain the nucleotide structure and the main features of DNA and RNA:
Structure of DNA:
Base pairs
Sugar phosphate backbone
DNA, also known as deoxyribose nucleic acid, is made up of two strings which form a double
helix structure. They are known as polymers which are large molecules made up of smaller
repeating blocks. The main structure of DNA is a sugar molecule which is attached to
phosphate group as well as a nitrogenous base.
DNA is made up of four bases which is adenine, cytosine, guanine and thymine - (ACGT).
Each of the bases pair with one another to form the basic structure of the nucleotide. The
main structure consists of the sugar and phosphate molecules as the sides, whilst the base
pairs are the rungs. The main difference between DNA and RNA is that DNA is made up of
deoxyribose sugars whilst RNA is only made up of ribose sugar.
The main structure of DNA is that it is made up of two sugar phosphates. These phosphate
groups help to form the backbone of the structure. The two structures go in opposite
directions and therefore, is referred to as being anti-parallel. The two sugar phosphates
which help to form the backbone are joined together by nitrogenous bases which are then
connected through hydrogen bonds.
Both bases, adenine and guanine are known as purines, whilst cytosine and thymine are
known to be pyrimidine. A purine base binds with a pyrimidine base, and this helps to
ensure that they each remain the same width. Adenine and thymine bond together and this
is joined by 2 hydrogen bonds and guanine binds with cytosine which is joined together by 3
hydrogen bonds. Both adenine and thymine and cytosine and guanine are known as
complementary base pairs.
The main features of DNA:
The main features of DNA are the base pairs and the sugars which help it to form its
structure. The base pairs that help to form the structure of DNA is adenine, thymine,
cytosine, and guanine. Another main feature of DNA is its twisted shape due to its double
helix. DNA is essential for the growth and development of organisms, in addition, the three
, components that help to form DNA are the sugars, phosphate groups, and the nitrogenous
bases.
During DNA replication the structure of the DNA consists of one new strand and one old
strand, and this is due to the replication process being semi-conservative. During this stage,
no cell division has occurred, this is due to cell replication occurring before cell division takes
place.
Within the replication process, there are three main steps which includes opening and
separation of the double helix strands, template of the strands being prepared, and
formation of the new DNA. Within the first stage of DNA replication, the double helix
strands start to uncoil themselves and this is completed at the origin, which is the specific
location at which this process occurs.
The next stage, which involves the preparation of the template strands, different proteins as
well as enzymes help to organise the strands that have uncoiled for replication of the DNA.
The final stage is assembling the DNA. During this stage the nucleotides within the DNA and
the base pairs help to form the new copy of the DNA molecule (Nature, n.d).
Structure of RNA:
RNA also known as ribose nucleic acids is made up of four bases, adenine, cytosine, guanine,
and uracil. Unlike DNA they do not have the pyrimidine base thymine and therefore, is
replaced with uracil instead. Just like how cytosine and guanine pair together, adenine and
uracil pair together. There are three main types of RNA, this includes mRNA, tRNA, and
rRNA. Within RNA, the main sugar that makes up its structure is ribose sugar, unlike
deoxyribose sugar which is in the structure of DNA. For RNA the main structures which are
important for gene replication are small interfering RNA and micro-RNA.
The main role of mRNA is to carry genetic codes towards the ribosomes from the DNA
within the nucleus. This type of RNA is known as the messenger RNA. Once the genetic
information has been transported to the ribosomes, the genetic code of the base triplets is
read, once this occurs, the amino acids are aligned in order to form a polypeptide sequence.
The next type of RNA structure is tRNA. The main function of this is to transport the amino
acids to the cells of the ribosomes, and this is carried from the cytoplasm. After this occurs,
amino activation occurs which requires enzymes and a sufficient amount of ATP. When
amino activation takes place, tRNA attaches itself to the amino acids. The final type of RNA
is rRNA which is known as ribosomal RNA. This helps to form part of the organelle of
ribosomes. The structure also helps to carry out protein synthesis.
The final type of RNA is siRNA. siRNA is an interfering RNA. The main purpose of it is to
destroy mRNA and this is to help regulate expressions of genes. It can also be known as a
silencing RNA and it prevents the process of gene expression from occurring. Unlike other
RNA, siRNA is a double stranded structure and usually is 25 nucleotides long, furthermore,
their structure also helps to prevent protein synthesis from occurring. SiRNA is also helpful
in protecting the cell from attacks from mRNA.
