DNA REPLICATION and MUTATIONS DNA Replication n Replication

DNA REPLICATION and MUTATIONS

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

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

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

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

Steps in DNA Replication 1. 2. Double helix unwinds. DNA helicase (an ENZYME) “unzips” the DNA molecule, breaking the hydrogen bonds between the strands DNA helicase (enzyme) Unpaired bases

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? 3. n YOU ARE WHAT YOU EAT!

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

Steps in DNA Replication 4. n 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 DNA polymerase Growth Replication fork New strand Original strand Nitrogenous bases

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

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

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

GENE MUTATIONS (in DNA)

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

Point Mutation – Deletion

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

What kind of point mutation? N O I T U T I T S B U S

What kinds of point mutation? N O I T R E S IN N O I T E L E D

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

Now: CHROMOSOMAL MUTATIONS (affect whole chromosomes)

What Would You Call It? Deletion

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

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: n Silent or neutral (no effect) n Harmful or Fatal (bad effect) n Beneficial (good effect, low probability)