MUTATIONS

Definition of mutation Changes in the genetic material. Mutations are not always a bad thing.

Gene Mutations

Chromosome

Gene

Remember Translation?

What is this? What does it tell us?

What Amino Acid does the codon GCA code for?

What about CGU?

Organisms have evolved many ways to Organisms have evolved many ways to protect their DNA from changes.protect their DNA from changes.

MutationsMutations

In spite of these mechanisms, however, In spite of these mechanisms, however, changes in the DNA occasionally do occur.changes in the DNA occasionally do occur.

Any change in DNA sequence is called a Any change in DNA sequence is called a mutationmutation..

Mutations can be caused by errors in Mutations can be caused by errors in replication, transcription, cell replication, transcription, cell division, or by external agents.division, or by external agents.

Mutations can affect the reproductive Mutations can affect the reproductive cells of an organism by changing the cells of an organism by changing the sequence of nucleotides within a gene in sequence of nucleotides within a gene in a sperm or an egg cell.a sperm or an egg cell.

Mutations in reproductive cellsMutations in reproductive cells

If this cell takes part in fertilization, the If this cell takes part in fertilization, the altered gene would become part of the altered gene would become part of the genetic makeup of the offspring.genetic makeup of the offspring.

Two major types of mutations:A. Gene mutation

a. Point mutation1. Substitution

b. Frameshift mutation1. Insertion2. Deletion

B. Chromosomal mutationa. Deletionb. Duplicationc. Inversiond. Translocation

Gene Mutations:1. Point mutation

- changes involving one or a few (2-3) nucleotides.

Example - Substitution

Point Mutations:1. Substitution

Oringinal Strand - GCAMutated Strand - GTA

Effects only one Amino Acidin the sequence.

DNA RNA Amino Acid

GCA CGU Arginine

GTA CAU Histidine

Gene Mutations:Frameshift mutations

a shift in the “reading frame” of the genetic message.

Or – changes the whole sequence.

Frameshift Mutations:1. Insertion –

Inserting an additional base into the genetic sequence.

2. Deletion - Deleting a base from the genetic sequence.

The cow jumped over the moon.becomes

The coj umpedo vert hem oon.

INSERTIONOriginal Strand - TACGCATGGAATMutated Strand - TATCGCATGGAAT

Changes the entire message. It is no longer the same sequence – so it is no longer making the same protein.

RNA Amino Acid Sequence

AUG-CGU-ACC-UUA Met – Arg – Thr – Leu

AUA-GCG-UAC-CUU-A Iso – Hal – Tyr – Leu

DELETIONOringinal Strand - TACGCATGGAATMutated Strand - ACGCATGGAAT

Again, it changes the entire message. It is no longer the same sequence – so it is

no longer making the same protein.

RNA Amino Acid SequenceAUG-CGU-ACC-UUA… Met – Arg – Thr – Leu

UGC-CUA-CCU-UA… Ser – Leu – Pro

Chromosomal Mutations

Chromosome

Gene

Chromosomal Mutations changes in the structure of a chromosome.

– Deletion – deleting part of the chromosome

– Duplication – duplicating part of the chromosome

– Inversion – inverting two sections of a chromosome

- Translocation: when a section of each

chromatid trade places.

Chromosomal Mutations

Deletion: deleting part of the chromosome

So, what is actually being deleted?

Chromosomal Mutations

Duplication: duplicating part of the chromosome

So, what is actually being duplicated?

Chromosomal Mutations

Inversion: inverting two sections of a chromosome

Chromosomal Mutations

Translocation: when a section of each chromatid trade places.

Any agent that can cause a change in DNA is called a mutagen.

Mutagens include radiation, chemicals, and even high temperatures.

Forms of radiation, such as X rays, cosmic rays, ultraviolet light, and nuclear radiation, are dangerous mutagens because the energy they contain can damage or break apart DNA.

Causes of Mutations

Causes of Mutations The breaking and reforming of a double-

stranded DNA molecule can result in deletions.

Chemical mutagens include dioxins, asbestos, benzene, and formaldehyde, substances that are commonly found in buildings and in the environment.

Chemical mutagens usually cause substitution mutations.

Repairing DNA

Repair mechanisms that fix mutations in cells have evolved.

Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides.

These repair mechanisms work extremely well, but they are not perfect.

The greater the exposure to a mutagen such as UV light, the more likely is the chance that a mistake will not be corrected.