Structure and function of
nucleic acids
Nucleotides
There are monomers located in DNA and RNA. It has three components; phosphate group,
sugar (deoxyribose in DNA and ribose in RNA), and nitrogenous base.
DNA
DNA is a double helix and is has two backbones made of sugar and phosphate. In the centre
of the molecule, nucleotides base forms complementary base pairs which is held together
by hydrogen bonds. Adenine always pairs with thymine (A-T), and guanine always pairs with
cytosine (G-C) DNA is made of two linked strands that wind around each other to resemble a
twisted ladder. Each strand has a backbone made of sugar (deoxyribose) and phosphate
groups. DNA molecule has two polynucleotides' chains made of four types of nucleotide
subunits. It is negatively charged which allows it to associate with the positivity charged
histone proteins. Hydrogen bonding allows strands to separate for DNA replication and
transcription. Complementary base pairing allows for accurate copying of the sequence of
nucleotides. DNA contains instructions that is needed for organisms to grow, survive and
reproduce. It has all the genes needed to pass onto the next generation. DNA also contains
DNA sequences involved in controlling the expression of proteins. This is a picture of DNA
nucleotides. Nucleotides join to make a DNA molecule by the two strands held together by
hydrogen bonds G-C and A-T base pairs.
, DNA replication
It is when DNA molecules are copied to make two identical copies. It takes place before the
cell divides so each cell has a copy of the DNA molecule. This is so daughter cells have the
exact genetic information as the parent cell. Replication happens in three stages; Initiation,
elongation, and termination.
Initiation
Two strands must be separated by enzyme helicase (breaks hydrogen bonds down between
two strands). This makes a replication fork. Then primase binds the 3 ends of exposed DNA
strands. Primase adds a short sequence (primer- acts as a foundation for replication to start)
of RNA complementary to DNA. After that DNA polymerase binds and start adding
nucleotides to a free 3`-OH group.
Elongation
One strand (leading s) synthesis continuously. Another strand (lagging s) is synthesised
discontinuously in sections Okazaki fragments. This is because DNA polymerase can only add
DNA nucleotides in a 5` to 3` direction.
Lagging strand- DNA polymerase adds nucleotides till it reaches 5` end of the recently made
Okazaki fragments. Then another DNA polymerase removes the RNA primer of the Okazaki
fragment and replaces the RNA nucleotides with DNA nucleotides,
Termination
nucleic acids
Nucleotides
There are monomers located in DNA and RNA. It has three components; phosphate group,
sugar (deoxyribose in DNA and ribose in RNA), and nitrogenous base.
DNA
DNA is a double helix and is has two backbones made of sugar and phosphate. In the centre
of the molecule, nucleotides base forms complementary base pairs which is held together
by hydrogen bonds. Adenine always pairs with thymine (A-T), and guanine always pairs with
cytosine (G-C) DNA is made of two linked strands that wind around each other to resemble a
twisted ladder. Each strand has a backbone made of sugar (deoxyribose) and phosphate
groups. DNA molecule has two polynucleotides' chains made of four types of nucleotide
subunits. It is negatively charged which allows it to associate with the positivity charged
histone proteins. Hydrogen bonding allows strands to separate for DNA replication and
transcription. Complementary base pairing allows for accurate copying of the sequence of
nucleotides. DNA contains instructions that is needed for organisms to grow, survive and
reproduce. It has all the genes needed to pass onto the next generation. DNA also contains
DNA sequences involved in controlling the expression of proteins. This is a picture of DNA
nucleotides. Nucleotides join to make a DNA molecule by the two strands held together by
hydrogen bonds G-C and A-T base pairs.
, DNA replication
It is when DNA molecules are copied to make two identical copies. It takes place before the
cell divides so each cell has a copy of the DNA molecule. This is so daughter cells have the
exact genetic information as the parent cell. Replication happens in three stages; Initiation,
elongation, and termination.
Initiation
Two strands must be separated by enzyme helicase (breaks hydrogen bonds down between
two strands). This makes a replication fork. Then primase binds the 3 ends of exposed DNA
strands. Primase adds a short sequence (primer- acts as a foundation for replication to start)
of RNA complementary to DNA. After that DNA polymerase binds and start adding
nucleotides to a free 3`-OH group.
Elongation
One strand (leading s) synthesis continuously. Another strand (lagging s) is synthesised
discontinuously in sections Okazaki fragments. This is because DNA polymerase can only add
DNA nucleotides in a 5` to 3` direction.
Lagging strand- DNA polymerase adds nucleotides till it reaches 5` end of the recently made
Okazaki fragments. Then another DNA polymerase removes the RNA primer of the Okazaki
fragment and replaces the RNA nucleotides with DNA nucleotides,
Termination
