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DNA MUTATIONS

Types. Diseases. Mutagens. DNA MUTATIONS. Mutations are any change in the genetic make up of an organism and can occur naturally or can be increased by mutagens. Click on an area for more information. TYPES OF MUTATIONS.

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DNA MUTATIONS

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  1. Types Diseases Mutagens DNA MUTATIONS Mutations are any change in the genetic make up of an organism and can occur naturally or can be increased by mutagens. Click on an area for more information

  2. TYPES OF MUTATIONS Mutations can be spontaneous or natural as a result of errors in DNA replication or gamete production. Error rate is 1 in 1,000,000 replications. Click on an area for more information POINT BLOCK CHROMOSOMAL ABBERATIONS

  3. Change amino acid sequence Change DNA Change protein Three types of point mutation Change organism deletion insertion substitution Click to find out more Point mutations • Involves a change to one of the DNA bases that makes up a gene. • Also known as a MISSENSE mutation. • Consequence varies depending on type of change.

  4. Also But… ATT DNA ATA DNA T A C T T C A A A C C G C G T UAA mRNA UAU Tyr STOP C is replaced by T in the DNA. T A C T T C A A A T C G C G T AGG DNA AGA UCC mRNA UCU Ser Ser Base Substitution • Involves one base in the DNA being substituted by another. • This mutation only affects one codon in the gene. • Known as NONSENSE mutation • Totally different protein made • Effect on organism can be dramatic • End result is a different amino acid in protein. • Generally minor effect on protein/organism. • Serine is still added • Known as a SILENT mutation

  5. DNA T A C T T C A A A C C G C G T Dramatic effect on protein made. Known as frame shift mutations. T A C T T C A A A AC C G C G T A C T T C A A CC G C G T A BASE INSERTION INSERTION Trp Arg Base Insertion/Deletion • Involves one base either being inserted or removed from the DNA sequence. • Both these mutations affect all codons after the insertion or deletion. • The earlier the mutation occurs in the sequence the greater the effect.

  6. Change amino acid sequence Change DNA Change protein Four types of block mutation Change organism inversions deletions translocations duplications Click to find out more Block mutations • Involves large scale changes in DNA segments on chromosome. • Only occur during meiosis, formation of gametes (sex cells). • Can affect the functioning of many genes • Severe effect on functioning and characteristics of organism.

  7. STEP 2 STEP 3 STEP 1 A A B B C C D D F F E E G G H H break genes segment is lost A D F E G H DNA ligase rejoins chromosome Deletion • Section of chromosome is lost, anywhere from three bases to large segments. • The DNA breaks due to the effect of mutagens.

  8. STEP 2 STEP 3 STEP 1 A B C D F E G H 2 2 2 4 4 4 1 1 1 3 3 3 5 5 5 break segment removed DNA ligase joins segment D D F F E E G G H H Translocation • Section of chromosome breaks and is joined to another chromosome. • Problem when gametes formed-some receive extra genes, some deficient.

  9. A A A B B B C C C D D D F F F E E E STEP 2 STEP 3 STEP 1 G G G H H H A B C D F E G H break segment removed D D F F E E G G H H Duplication • Segment of one chromosome is added to the homologous chromosome. • Problem when gametes formed-some have double the genes, some have no genes.

  10. STEP 3 STEP 2 STEP 1 A A B B C C D D F F E E G G H H break segment rotates 180o segment rejoins A C B D F E G H Inversion • Section of chromosome falls out and rotates through 180o. • DNA ligase rejoins section but the genes are in reverse order. • There is no loss of genetic information.

  11. Normal diploid (2N) human cell containing 2 sets of chromosomes. <23, >23 2 x 23 <23, >23 Examples 23 XO XX XXX XY XYY Turner syndrome Normal female Metafemale Normal male Jacob syndrome Through meiosis haploid (N) gametes are produced, containing only one set of chromosomes. 23 Chromosomal abberations • Loss or gain of entire chromosomes- called aneuploidy. • Main cause is non-disjunction of chromosomes during meiosis. • Gametes end up with extra chromosome(s) or fewer than 23 chromosomes. Mainly occurs with sex chromosomes.

  12. Incorporate into genome • Trigger cancers Ionising radiation Alcohol & dietary factors Environmental poisons/irritants Viruses & micro-organisms Types • Nuclear • UV rays • X rays • High fat, alcohol • Trigger cancers • Benzene, asbestos • Tobacco tar, formaldehyde Mutagens • Chemicals or radiation that increase the likelihood of a mutation occurring. • Rate of mutation induced by mutagen is proportional to the dose of mutagen. • Mutagens cause a decrease in the stability of the DNA molecule. • Thus DNA more susceptible to error during replication or meiosis.

  13. Cystic fibrosis Sickle cell disease Down syndrome Diseases Click on a disease to find out more about how it is caused by a mutation.

  14. haemoglobin HBB gene on chromosome 11 normal red blood cell sickle cell This single point mutation has a dramatic effect. Individuals have many health problems, eg weakness, jaundice, anaemia, heart & kidney defects, brain damage, skin lesions and inflamed spleen. Sickle cell disease • Haemoglobin is made up of 4 polypeptide chains (2 alpha & 2 beta chains). • Gene for beta chain is found on chromosome 11 and consists of 438 bases. • A mutation occurs in the gene coding for the beta chain. • The mutation is a substitution where adenine replace thymine on the DNA template strand. • As a result the amino acid valine replaces glutamic acid. • This change the properties of the haemoglobin and results in distorted red blood cells.

  15. CFTR gene on chromosome 7 triplet deleted 506th 507th 508th 509th 510th 506th 507th 508th 509th 510th AAA DNA TAA TAG AAA CCA CAA DNA TAA TAG AAA CCA CAA mRNA mRNA AUU AUC GGU GGU AUU AUC UUU GGU GGU amino acids amino acids ile ile gly val ile ile phe gly val Cystic Fibrosis • Inherited disorder and occurs when an individual has both copies of the faulty gene. • The gene (CFTR) is found on chromosome 7 and normally contains 1480 amino acids. • A mutation occurs whereby the 508th triplet (AAA) is deleted resulting in a mutated CFTR protein of 1479 amino acids. • The abnormal protein is unable to control chloride ion balance in cells. • The build up of chloride ions in cells results in severe effects. • Individuals have reduced life expectancy, high salt levels, blocked airways, pancreatic deficiencies and males are infertile. • Cystic fibrosis is relatively common and occurs 1 in every 2500 individuals.

  16. One of the parent’s sex cells contains two no. 21 chromosomes, due to non-disjunction during meiosis. 23 24 15 21 15/21 Parent 1 Parent 2 Down child 3 no.21 • Arise from having 3 copies of chromosome 21 • known as trisomy-21. Down Syndrome • Individuals have characteristic facial features, are relatively short, slowed intellectual and physical development. • Two main types of Down syndrome-97% non-familial, 3% familial. Non-familial Familial One of the parents has only 45 chromosomes. A translocation has occurred where one of no.15 and one of no. 21 have joined together. One of the sex cells contain 23 but one of the 23 is the 15/21 chromosome.

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