DNA REPLICATION AND POSSIBLE
ERRORS
STANDARD
SB2. Students will analyze how biological traits
are passed on to successive generations.
 Explain the role of DNA in storing and transmitting
cellular information
 Describe the relationships between changes in
DNA and potential appearance of new traits
including


Alternations during replication
 Insertions
 Deletions
 Substitutions
ESSENTIAL QUESTION
 Unit:

Why must organisms be able to grow and
reproduce?
 Today:

How is cellular information stored?
DNA REPLICATION

Review DNA structure
 Double
Helix
 Sugar
Phosphate backbone
 Rungs are the paired bases
 Sugar
 Deoxyribose
 Nucleotides
 Sugar,
phosphate, nitrogenous base
DNA REPLICATION

Review DNA structure

Orientation

Two main ends



5’

phosphate

sugar
3’
Replication occurs in a 5’ → 3’ direction
WHY IS DNA REPLICATED?

To prepare the cell for division
HOW DOES DNA REPLICATE?

DNA helix separates
Each side (strands)
serve as templates
 Original DNA strands
called parental
strands


Result:
Two new DNA helixes
 Each helix has one
strand of parental
DNA and one strand
of new DNA

HOW?

CONTINUED
Steps of DNA Replication
 DNA
unwinds
 Job
 RNA
done by: DNA helicase, an enzyme.
primer added to each unwound strand
 Primer
is a short segment of RNA
 Signals starts of replication
 Job done by: RNA primase (enzyme)
 Complimentary
removed
 Job
nucleotides added and primer
done by: DNA polymerase
 3’ to 5’ direction
THINGS TO KNOW

Leading strand
 New
continuous and elongated strand made as the
DNA unwinds

Lagging strand
 Discontinuous
strand made in pieces
 Pieces called okazaki fragments.
 Linked
together by DNA ligase
APPLY YOUR KNOWLEDGE

Answer the questions on the DNA Replication
worksheet to review DNA and RNA structure
and practice replication.