DNA molecules are polymers called
Each polynucleotide is made of
monomers called nucleotides.
Each nucleotide consists of :
• a nitrogenous base (Adenine,
Thymine, Cytosine or Guanine)
• a pentose sugar (DNA = Deoxyribose
• and a phosphate group.
Nucleotide monomers are linked together to
build a polynucleotide.
Adjacent nucleotides are joined by covalent
bonds that form between the –OH group on the
3’ carbon of one nucleotide and the phosphate
on the 5’ carbon on the next nucleotide.
These links create a backbone of sugarphosphate units with nitrogenous bases as
The sequence of bases along a DNA polymer is
unique for each gene.
THE ROLE OF DNA
DNA is vital for all living
beings – even plants.
It is important for:
coding for proteins and
the genetic instruction
guide for life and its
DNA holds the instructions
for an organism's or each
cell’s development and
DNA can replicate itself.
Multicellular eukaryotes have
many introns(non-coding DNA)
within genes and noncoding
DNA between genes.
The bulk of most eukaryotic
genomes consists of noncoding
DNA sequences, often described
in the past as “junk DNA”
Much evidence indicates that
noncoding DNA plays important
roles in the cell.
Sequencing of the human
genome reveals that 98.5% does
not code for proteins, rRNAs, or
Recombinant DNA is used to make transgenic
They are used to make insulin, clotting factor
VIII, human growth hormone and hepatitis B
Transgenic bacteria is used to protect the roots
of plants from insect attack, by producing
• Example = pomato
• Genetically modified to produce potato's
below the ground and tomato's above the
• Foreign genes transferred to cotton, corn, and
potato strains have made these plants
resistant to pests because their cells now
produce an insect toxin.
• Read p. 253 for more examples
Today transgenic bacteria, plants and animals
are called genetically modified organisms
The products that GMO’s produce are called
RNA is made up of:
• Ribose sugar (a pentose sugar with 5
• Phosphate and
• A nitrogenous base; e.g. Purines
(Adenine and Guanine) and
Pyrimidines (Cytosine and Uracil).
RNA exists largely as single nucleotide
chains in living cells.
The RNA strand is made up of alternating
molecules of ribose sugar and phosphate.
• The nitrogen bases are attached to the
sugar molecules in the strand and ’stick
out’ laterally as in DNA.
• A sugar, a nitrogenous base and a
phosphate together form a ribonucleotide.
• An RNA molecule is a polymer of
Williamson, J. 2014. powertpointslides. UJ
Campbell, & Reece. 2010. Biology. Benjamin
Cumming. New York