RNA and Mutations!

– RNA = ribonucleic acid (3 types)• mRNA – messenger RNA

takes information for protein to be made from DNA to the ribosome

• tRNA – transfer RNA carries amino acids to ribosomes, lines them up in the correct order according to mRNA

• rRNA – ribosomal RNA makes up the structure of the ribosome

RNA

– RNA nucleotides are composed of

• phosphate

• ribose (sugar)

• and a base (adenine, guanine, cytosine and uracil)

RNA

Mutations• Random change Random change

in DNA in DNA sequence or sequence or genetic materialgenetic material

• Caused by errors Caused by errors inin– ReplicationReplication– TranscriptionTranscription– Cell divisionCell division– External agentsExternal agents

• ChemicalsChemicals• RadiationRadiation• VirusesViruses

Mutagens

Mutations may be:

• Helpful – longer beaks in a birdHelpful – longer beaks in a bird

• Harmful – causes a disease like Harmful – causes a disease like cancercancer

• No effect – no change in proteinNo effect – no change in protein

Inheriting Mutations• Two Types of CellsTwo Types of Cells

– Body (somatic) CellsBody (somatic) Cells

– Sex (germ) CellsSex (germ) Cells

– Mutations must be in Mutations must be in sex cellssex cells to be passed to be passed on to offspringon to offspring

• Skin cancer Skin cancer cannot be cannot be passed on from passed on from a parent’s skin a parent’s skin cell to a child’s cell to a child’s cells.cells.

GENE MUTATIONSGENE MUTATIONS

• Point Mutations–Occur at a single point in the DNA

sequence• Ex: DNA TAC GCA TGG AAT

RNA AUG CGU ACC UUA

AA MET-ARG-THR-LEU

– But how does this affect the proteins being made?

• A substitution occurs and C is substituted with T

DNA TAC GTA TGG AAT

RNA AUG CAU ACC UUA

AA MET – HIS- THR-LEU

GENE MUTATIONSGENE MUTATIONS• Frameshift Mutations

– Occurs when a nucleotide is deleted or inserted in a DNA strand

• Bases are still read in groups of 3, so…it shifts the reading of all of the codons from that nucleotide on.

– Ex: DNA TAC GCA TGG AAT

RNA AUG CGU ACC UUA

AA MET- ARG- THR-LEU

– But how does this affect the proteins being made? DNA TAT CGC ATG GAA T

RNA AUA GCG UAC CUU A

AA ILE – ALA- TYR-LEU

A human example of a frameshift mutation is Tay Sachs disease.

• Genes or groups of genes can become incorrectly placed on a chromosome and cause a mutation

Types:• Insertion• Deletion• Inversion• Translocation• Inversion

• Non-disjunction – when sister chromatids fail to separate correctly during meiosis

• Ex: Trisomy 21

• Genes can be turned “off” or “on”– Activated or deactivated

• Activated – means the gene is expressed or the protein is made• Deactivated means the gene is not expressed or no protein is

made

• Exons and introns – – Much of the mRNA that is transcribed in the nucleus

does not actually get translated– Some mRNA gets clipped out, enzymes do this called

processing, maturing, or editing• The part taken out = introns (interferring)• The part that actually codes for the needed protein and goes to

the ribosome to be translated is called the exon (that which is expressed)