2.3 Nucleic Acids

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2.3 Nucleic Acids
The monomer units in nucleic acids are called nucleotides.
They consist of a pentose sugar (deoxyribose/ribose) a phosphate group and a nitrogenous
base that is either a pyrimidine or a purine.
These three components are joined in condensation reactions by covalent bonds.
Nucleotide derivatives
ATP and ADP are
derivatives and
are often present
in coenzymes
such as NADP ­
phosphate which
is used in

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DNA structure
DNA is made of two polynucleotide strands, antiparallel to each other.
The monomers in DNA include deoxyribose sugar, a phosphate group and the bases
cytosine, thymine, adenine and guanine.
The monomers are bonded by covalent phosphodiester bonds.
The bases are bonded with hydrogen bonds in complementary base pairing. These
hydrogen bonds are weak but together are stronger as there is a large number of them.
It stores genetic information and hereditary material in the sequence of its bases.…read more

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RNA Structure
The pentose sugar is ribose (has oxygen).
Uracil, cytosine, adenine and guanine are the
nitrogenous bases.
The polymer is single stranded.
RNA carries information between organelles
in a cell and is not a store of information.
DNA Replication
DNA uses semiconservative
replication as both of the
original strands are used in the
two daughter strands.
DNA is a selfreplicating
molecule and its replication
takes place during interphase in
cell division.
The DNA in mitochondria and
chloroplasts also replicates
each time these organelles
divide.…read more

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The nucleotides join together to form a new molecule of DNA
Mutations may occur in
replicating the genetic code.
These mutations occur when
DNA is not accurately copied
and when the wrong
nucleotide is inserted into
the strand. Some mutations
are harmful, such as
achondroplasia (a form of
dwarfism), Marfan syndrome
(a connective tissue
disorder), and Huntington
disease (a degenerative
disease of the nervous
system). Some are not, such
as red hair.
Mutations can be passed on and inherited from parents or can occur spontaneously.…read more

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Exons are regions of the RNA strand that code for the amino acids of the protein being
synthesized whereas introns are segments that do not code for the protein and are not
Introns are cut out and the exon regions are spliced together to form a long chain of
The mRNA chain progresses out of the nucleus and over onto the rough endoplasmic
reticulum that has the ribosomes on it
Ribosomes are made up of two subunits
Transfer RNA molecules bring amino…read more

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The newly synthesized polypeptide is folded into its shape to form the protein…read more


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