what does dna look like? dna has.. a sugar/phosphate backbone 4 chemical bases sugar

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What does DNA look like? DNA has.. A sugar/phosphate backbone 4 Chemical bases Suga r

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What does DNA look like?• DNA has..• A sugar/phosphate

backbone • 4 Chemical bases

Sugar

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

Another DNA Polymerase removes the RNA primers and replaces them with DNA.

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

Mutations

• The process by which the sequence of base pairs in a DNA molecule is altered.

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

How else do mutations occur?

Errors can occur in the processes of Mitosis or meiosis

• This is NOT hereditary…. Its just a mistake in procedure!!

This is called NONDISJUNCTION• The chromosomes fail to separate so you

get some homologous chromosomes migration over together instead of separating.