DNA Structure,
DNA Replication and
Mitosis
DNA, chromosomes and gene
structure revision
Structure of DNA
DNA is made from
Nucleotides that
have 3 parts:
– 5 carbon Sugar
(deoxyribose)
– Phosphate group
– Nitrogen base
(Adenine, Thymine,
Guanine or Cytosine)
Deoxyribonucleic acid
(DNA) molecule has a
double helix (twisted
ladder) structure with 2
bases of 2 nucleotides
forming the rungs and
the sugar and phosphate
groups forming the sides
Anti-parallel nature of DNA
• Sugar is a 5 carbon ring (joins
ladder sides to rungs)
• Phosphate group attaches to
the 3’ or the 5’ carbon (makes
ladder sides)
This gives direction to each half
of the strand as each strand
(ladder side) runs in the
opposite direction
• Nitrogen bases join anti
parallel strands as A-T and CG only (make ladder rungs)
DNA replication
• The purpose of DNA replication is to make an
exact copy of a DNA molecule prior to cell
division (mitosis) so each daughter cell has the
full set of genetic material.
• Creates a chromosome with two chromatids
• Ensures each resulting cell is able to receive a
complete set of genes from the original cell
• Three main steps
• Animations
1
2
3
Semi-conservative nature of
DNA replication
• Means less opportunity for mistakes to
occur during replication
DNA replication activities
Complete cut out poster showing the semi
conservative nature of DNA replication
Read Biozone pages 133 – 134
• Do exercises 1 – 6 page 134
• Answer self check pg 81
Mitosis
The purpose of mitosis is to make exact
copies of existing cells for growth, repair in
all living organisms and asexual
reproduction in some
• Produces 2 daughter cells genetically
identical to parent cell
• Continuous process but has 4 main stages
• Animation 1
2
Where mitosis occurs in plants
and animals
• Plants – root tips, shoot tips and inside the
bark layer of trees. These are the active
growing sites of plants and many larger
perennial plants continue to grow
throughout their life.
• Animals – in most tissues in immature
animals and wherever cells need replacing
or repair in mature animals.
Mitosis activities
Discuss Factors affecting Mitosis handout
Read Biozone pages 135 – 136
• Do Exercises 1 – 3 page 136
Your task now is to revise and study for the Cell End of
Unit Test, by:
• Read and complete Biozone pages: 97 to 138
(NB some pages not included)
• Complete Key terms: Mix and Match page: 138
(NB some terms not covered)
• Review past or sample external exam papers for
Achievement Standard 91156v1 (AS 2.4) from NZQA
NCEA website
• Check L2 Biology Power-Points and other resources in
MACScience blogsite
• Use other study techniques e.g. Karen Boyes, flip cards,
mind maps
• Ask questions to clarify your understanding before…
• Test date: