DNA REPLICATION and MUTATIONS

DNA Replication  Replication – the process of copying a DNA molecule. So that genetic information can be passed on from cell to cell. DNA replicates before cells divide (S phase)

Quick Review… DNA is made up of 2 strands of nucleotides. The strands are held together by HYDROGEN BONDS between each of the bases. The 2 strands are COMPLEMENTARY A pairs with T C pairs with G

 How it Works During replication EACH strand is used as a pattern (template) to make 2 new DNA molecules This is called semi-conservative replication

Original RIGHT with new left strand How it Works AND Original LEFT with new right strand Original RIGHT with new left strand Original DNA

Steps in DNA Replication  Steps in DNA Replication Double helix unwinds. DNA helicase (an ENZYME) “unzips” the DNA molecule, breaking the hydrogen bonds between the strands Unpaired bases DNA helicase (enzyme)

Steps in DNA Replication  Steps in DNA Replication DNA Polymerase (another ENZYME) pairs up free nucleotides in the nucleus with the nucleotides on the DNA strands forming new hydrogen bonds. Where do nucleotides come from? YOU ARE WHAT YOU EAT!

Steps in DNA Replication Original DNA DNA unzips Free nucleotides pair up with the original LEFT strand Free nucleotides pair up with the original RIGHT strand

Steps in DNA Replication  Steps in DNA Replication The DNA winds back up into a double helix. The final products of DNA replication are two molecules of DNA each having half new material and half old material… “Semi-conservative”

DNA Replication Original strand DNA polymerase New strand Growth Replication fork Replication fork Nitrogenous bases New strand Original strand

 Why Replicate? Now all genetic information can be passed onto new cells during cell division. 2 new identical cells DNA copied

Polymerase Chain Reaction (PCR) Can be used to make millions of copies of a DNA sequence from a very small sample Forensics, paternity testing, etc. PCR Video

 Accuracy Replication is also very accurate – only ONE IN A BILLION base pairs are incorrectly paired. When mistakes are made, the DNA molecule can correct itself so the genetic code remains the same. Sometimes they can’t… MUTATIONS

GENE MUTATIONS (in DNA)  GENE MUTATIONS (in DNA)

Point Mutations Happen At Single Nucleotide Points in DNA  Point Mutations Happen At Single Nucleotide Points in DNA Substitution One base changes to (“subs” for) another Insertion Base added (inserted) Deletion Base removed (deleted)

Point Mutation – Deletion

The Dog Ate The Fat Cat Substitution Deletion Insertion The Dog Ate The Fat Rat Deletion The Oga Tet Hef Atr At.. Insertion The Dog Tat Eth Efa Tra t

What kind of point mutation? SUBSTITUTION

What kinds of point mutation? INSERTION DELETION

Insertions and Deletions Can Cause FRAMESHIFTS in the code!  Insertions and Deletions Can Cause FRAMESHIFTS in the code!  Uh Oh! One nucleotide affected every codon down the line—a frameshift!

Now: CHROMOSOMAL MUTATIONS (affect whole chromosomes)  Now: CHROMOSOMAL MUTATIONS (affect whole chromosomes)

What Would You Call It? Deletion

One or more segment is repeated What Would You Call It? normal chromosome one segment repeated three repeats Duplication One or more segment is repeated

A linear stretch of DNA is reversed within the chromosome  What Would You Call It? Inversion A linear stretch of DNA is reversed within the chromosome

 What Would You Call It? chromosome nonhomologous chromosome reciprocal translocation Translocation Entire gene segments are exchanged between non-homologous chromosomes!

Check Point

Mutations may be:  Silent or neutral (no effect) Harmful or Fatal (bad effect) Beneficial (good effect, low probability)