DNA Replication
Replicationbubble
Replicationfork
Replicationfork
Hydrogen bond
Replication occurs during Interphase
DNA replication is the process where an entire double-stranded DNA is copied to produce a second, identical DNA double helix.
DNA Replication
• Helicase unwinds the double helix starting at a replication bubble.
• The two strands separate as the hydrogen bonds between base pairs are broken.
• Two replication forks form and the DNA is unwound in opposite directions.
DNAhelicase
DNA Replication
• Helicase has completed unwinding the DNA strand.
• Single strand Binding Proteins (SSB) keep the two strands from re-annealing (coming back
together).
DNA Replication
Primase RNA Primer
• Primase is an RNA polymerase that makes the RNA primer.
• These primers “tell” the DNA polymerase where to start copying the DNA.
Leading Strand
Lagging Strand
DNA Replication
DNA Polymerase
• The DNA polymerase starts at the 3’ end of the RNA primer of the leading stand CONTINUOUSLY.• DNA is copied in 5’ to 3’ direction.• DNA polymerase copies the lagging strand DIS- continuously.
Leading Strand
Lagging Strand
3’ 5’
5’ 3’
Direction of Replication
Direction of Replication
DNA Replication
• The dis-continuous pieces of DNA copied on the lagging strand are known as Okazaki fragments.
DNA Replication
Finally the gaps in the sugar phosphate backbone are sealed by DNA ligase
There are now 2 identical double helices of DNA.
ligase
What is a mutation?
• Any change in DNA• Any abnormal change in genetic material.• Some can be inherited by the next generation.
• Remember that genes are located in DNA!!!
What causes a mutation?
• 1.) Changes in the environment OR mutagens• a. ultraviolet radiation• b. pollutants and chemicals• c. tar from tobacco• 2.) Errors during replication, transcription,
or translation
Types of mutations
• Point mutations• small (but significant) changes, often in a
single nucleotide base.• Deletions• remove information from the gene. A
deletion could be as small as a single base or as large as the gene itself.
Types of mutations
• Insertions
occur when extra DNA is added into an existing gene.
• Frame Shift
when either addition or deletion of one or two nucleotide bases. When this occurs, the “reading frame” is changed so that all the codons read after the mutation are incorrect.
Guess which type of mutation..
Normal:
As the man saw the dog hit the can end it is
As the man saw the doT hit the can end
Point mutation
As the man saw thehit the can end
deletion
Guess which type of mutations…
As the man saw the FAT dog hit the can end
Insertation
As the man saw the ogh itt hec ane nd it
Frame shift