Mutation: DNA changes

DO NOW: 3/16

Objective:Define mutation, identify several types, and describe their effect

on organisms.

Task: If all mRNA molecules begin with the sequence 5’ AUG 3’, what DNA sequence might be the beginning of a gene?

Back to the DNA… Refresher:

DNA mRNA Protein

Transcrip

tion

TranslationReplication

Transcription: DNA mRNA• The information carried by DNA is copied

into mRNA form by the enzyme RNA polymerase (and others).

Translation: mRNA Protein• The information carried by mRNA is translated

into a sequence of amino acids. This requires a ribosome (containing rRNA) and tRNA to bring the correct amino acids to the mRNA

DNA changes

• Sometimes, a gene can be “turned on” (induced, or activated) and cause a protein to be made, while at other times it can be “turned off” (inhibited or repressed) to save energy - like a light bulb

• Genes also change over time, like people do. A mutation is a change in a DNA sequence.

MUTATION: A Change in a DNA Sequence

• Any change to a DNA sequence is a

mutation.

• Very few mutations are advantageous, some are harmful, but most make no difference at all (silent mutations), since about 95% or more of your DNA does not code for proteins.

• Note: only mutations present in gametes can be passed on to offspring!

Mutant Flies

Recombinant DNA = genetic engineering

• Recombinant DNA: A human-made combination of DNA sequences from 2 or more organisms.

Mutation Type 1

• Genome Mutations (nondisjunction): a change in chromosome number. Always serious, often lethal.

Mutation Type 2: Chromosomal Mutations

Chromosomal mutations affect large pieces of chromosomes. Their effects vary.

Examples:

Deletion (A)Inversion (B)Translocation (C)Duplication (D)

Mutation Type 3: Single Gene Mutations

• As the name implies, single gene mutations affect only a single gene.

.

Types of Single Gene Mutations

• Deletions: One or more bases is removed from a sequence.– ATTAGG becomes ATGG

• Insertions: One or more bases is added.– ATTAGG becomes ATTAAGG

• Point Mutations: One or more bases is replaced with a different base– ATTAGG becomes ATAAGG

More Mutation Examples

• Missense: (point mutation)– The cat ate the rat The cat ate the hat

• Nonsense: (new stop signal)– The cat ate the rat The cat ate

• Frameshift: (insertion or deletion changes reading frame)– The cat ate the rat Ath eca tat eth era t.

Mutations that Matter

• Most mutations have no effect.

• Those that do have an effect are usually bad:– Cancer– Loss of function (protein doesn’t work anymore)

• A tiny fraction of a fraction have a positive effect– Increased survival & reproduction (Michale Phelps,

etc…)

Do you have it?

• A mutation is:A. When a gene is turned on

B. When a gene is turned off

C. A change in a DNA sequence

D. Always bad for the organism that has it

Do you have it?

• These types of mutations are the most serious because they can change the whole protein structure, not just one amino acid:

A. Point mutations

B. Frameshift mutations

C. Insertions of 3 nucleotides

D. Always bad for the organism that has it

Do you have it?

• The lac gene produces an enzyme that breaks down lactose (a type of sugar) and provides energy to a cell. The gene needs to be _____________ if lactose is to be used.

A. inducedB. inhibitedC. mutatedD. recombinant

Do you have it?

• Mutations in which of the following cells can be passed on to offspring?

A. Neurons (brain cells)

B. Epithelial (skin) cells

C. red or white blood cells

D. Germ (gonad) cells