The importance of DNA as an information-carrying molecule and its use in gene
technologies (25 marks)
DNA, or deoxyribose nucleic acid, is a polypeptide chain. The polynucleotide strand that
makes up a DNA molecule carries an organism's genetic material. All cellular organisms
contain DNA and it is vital for their survival as it allows them to grow and reproduce.
In eukaryotic cells, the DNA is arranged in a double helix structure, which is a tertiary
structure. Each DNA nucleotide is composed of a hexose sugar, in DNA this is deoxyribose,
a phosphate and a complementary base. Hydrogen bonds hold complementary base
pairings between two nucleotides together and phosphodiester bonds form between the
phosphate of one nucleotide and the sugar of another, making up the sugar phosphate
backbone. This arrangement helps the process of DNA replication and helps to ensure that
the DNA is replicated correctly to reduce the chances of mutations, a change in a gene or
chromosome, which can be harmful to the organism. As DNA replicates its genetic
information, the hydrogen bonds between each complementary base pair is broken easily.
As the complementary bases are exposed, only the complementary bases will be attracted
and attached to the correct base, ensuring that the sequence is copied correctly. This
ensures that only adenine and thymine are paired up and only cytosine and guanine are
paired up. In prokaryotic cells, the DNA is circular and is organised into one single
chromosome whereas eukaryotic DNA is organised into many chromosomes however, they
both carry the organism's genetic information and are both essential in htis survival, growth
and replication.
DNA replication is vital for survival, as it can allow organisms to adapt to their environment to
improve their chances of successful reproduction, and therefore survival. As DNA contains
the organism's genetic information, it controls how the cells within it function. During DNA
replication, mutations can arise.There are a number of mutations that can arise. An addition
mutation is where a base is added and deletion is where a base is removed, these both
cause a frameshift and cause the polynucleotide strand after the mutation to change, which
may result in dysfunctional proteins such as enzymes that no longer catalyse a reaction due
to a change in their tertiary structure. Substitution mutations is where one base is essentially
swapped for another and due to the genetic code being degenerate, this may mean that
although the triplet coding for an amino acid has changed, the same amino acid may still be
coded for. Mutations can be harmful as they can lead to a number of issues.They can lead to
genetic disorders such as cystic fibrosis, which can often lead to a reduced life expectancy.
Also, as these disorders are genetic, they can be passed onto offspring. Mutations can also
lead to the formation of an abundance of rapidly growing cells known as tumours. This can
be caused by mutations in genes such as oncogenes, which help control cell growth. The
mutated genes that increase the chances of tumours can also be inherited. However, some
mutations can be beneficial. In many African countries, there are high numbers of people
with sickle cell anaemia, which is when the structure of red blood cells is altered making it
less able to carry oxygen. As this is an autosomal recessive gene, people can have some
cells that function normally and some that are mutated, ensuring that they can survive. This
mutation makes people in this region more resistant to malaria. Thuis then increases the
chance of survival in this area and this advantageous mutation is more likely to be passed
onto offspring, giving them a better chance of survival.
