DNA MUTATIONS A mutation is a change in the DNA code. Can be caused by pollution (chemicals), radiation, bacteria or viruses, and UV light……These things are called MUTAGENIC AGENTS.

EFFECTS OF MUTATION MOST mutations are harmful and lead to the DEATH of a cell or organism. If the mutations are GERMINAL mutations (mutations to sperm or egg) they could effect all the cells of the zygote. (& genetic disease may result) If the mutations are SOMATIC (body) mutations, CANCER could result.

CHROMOSOMAL MUTATIONS This is when whole chromosomes change which can alter the order, number, or expression of genes. Can be from non-disjunction giving more or fewer whole chromosomes. Pieces of chromosomes can break off, turn around, or get put in at other places on the chromosome.

CHROMOSOMAL MUTATIONS

POINT MUTATIONS in GENES Mutations can also be small changes in segments of the DNA. These may be base SUBSTITUTIONS, DELETIONS, or ADDITIONS. A mutation might not have any effect (silent), it could cause a different amino acid to be inserted (missense), or might cause a stop to protein synthesis (nonsense).

SUBSTITUTION: NO CHANGE: mRNA MET LYS PHE GLY STOP Protein If a substitution is made where the C is replaced with a U, what happens? No change (especially if in the THIRD base of the codon. This is called the “wobble effect”

SUBSTITUTION: MISSENSE: A U G A A G U U U G A G C U A A mRNA MET LYS PHE SER GLY STOP Protein What if a G was replaced by an A? There is now a change in the amino acid sequence which could affect protein function.

SUBSTITUTION: NONSENSE: A U G A U A G U U U G G C U A A mRNA MET STOP LYS PHE GLY STOP Protein What if an A was replaced by a U? Translation of the protein will STOP and the protein will not function properly.

INSERTION OR DELETION If a base is inserted or deleted from the DNA (or RNA) this could cause a FRAMESHIFT MUTATION. Since the code is read in 3-letter CODONS, a change in order will cause a new set of codons.

DELETION: THE CAT ATE THE FAT RAT What happens if you delete the first C?

DELETION: THE ATA TET HEF ATR AT The reading frame shifts to the left and becomes nonsense.

INSERTION: THE CAT ATE THE FAT RAT Z What happens if you add a letter before “CAT”?

INSERTION: THE ZCA TAT ETH EFA TRA T The reading frame shifts to the right and becomes nonsense.

INSERTION OR DELETION In DNA these frameshifts could lead to different amino acids being translated or stop codons terminating translation too soon.

TYPES OF GENES: ONCOGENES seem to be genes that turn on abnormal cell growth and division leading to cancer. STRUCTURAL GENES: are translated into needed, functional proteins. REGULATOR GENES: acts as a switch to turn on and off structural genes.

Regulatory genes act like an ON or OFF switch for structural genes by making a protein that can start or stop the structural gene’s action

Cancer & oncogenes Proto-oncogenes - normal genes that control cell division and growth are called proto-oncogenes Oncogenes - if something happens to mutate these genes they become oncogenes….genes that can cause cancer