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Macromolecule evolution


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Macromolecule evolution

  2. 2. History of life on Earth Billions of years ago before life on Earth began the Earth’s atmosphere was very different from what it is like today. Experiments have shown that organic molecules could have formed under those different conditions.
  3. 3. Miller-Urey experiments Stanley Miller and Harold Urey conducted experiments trying to recreate the conditions of pre-biotic Earth. They succeeded in creating organic molecules. Miller and Urey concluded that organic compounds could have formed on pre-biotic Earth.
  4. 4. Nucleic acids For life to exist organic molecules are not enough. A method of storing and transmitting information to enable the living structures to function is needed. Nucleic acids can perform this role. There are two types of nuclei acid: • DNA – Deoxyribose Nucleic Acid • RNA – Ribose Nucleic Acid
  5. 5. DNA and Evolution All living things use DNA to store and transmit genetic information. Some viruses use RNA as their genetic material (but viruses are not considered living) DNA is the fundamental chemical of living things. The structure of DNA determines the characteristics of the organism made possible by the different arrangements of its building blocks – nucleotides. DNA is universal to all living things.
  6. 6. Two main roles of DNA The fact that all living things share this common genetic code is strong evidence that all life evolved from a common ancestor. 1. To pass on the hereditary characteristics from one generation to another 2. To act as a code for the production of other vital molecules in living things, particularly proteins.
  7. 7. If life had many separate beginnings, we would expect different mechanisms for storing and transmitting genetic information. However, all living organisms use the same genetic code, the same 20 amino acids in their proteins and the same cellular processes. But not all organisms have the same DNA, so changes to genetic information must have occurred over the billions of years since life first evolved. These changes to DNA are called Mutations.
  8. 8. DNA has diversified over billions of years leading to the wide range of different organisms on the Earth.
  9. 9. DNA has diversified Mutations have led to a diversity of DNA which has produced diversity of life. The first organisms (prokaryotes) had circular chromosomes. Eukaryote DNA has since broken up into linear sequences. Now there is more DNA in cells due to increased number of genes and non-coding (junk) DNA. Eukaryote genes contain introns and exons. Exons are translated into proteins Introns are transcribed but removed from mRNA before translation Prokaryotes don’t have introns.
  10. 10. eg Mouse gene for dihydrofolate reductase has 31000 base pairs of which 558 base pairs code for the amino acids required.
  11. 11. Evolution Using information from studies of: • comparative anatomy • comparative embryology • fossil studies Scientists have been able to piece together possible evolutionary pathways. This has provided strong evidence that organisms evolved from a common ancestor.
  12. 12. Comparative anatomy DNA is the genetic code responsible for the features and inheritable characteristics of all living things. Charles Darwin first proposed the theory of evolution claiming that all living things have evolved from common ancestors. He established evolutionary relationships on the basis of structural similarities. Such structures are termed homologous E.g. limbs of different vertebrates We call this comparative anatomy
  13. 13. Modifications to the forelimb of related animals A well documented example of comparative anatomy is the pentadactyl limb of many vertebrates. Similar bone structure has evolved for different functions.
  14. 14. Comparative embryology Another method of making evolutionary links is through Comparative Embryology. Comparing the early embryonic development of different species.
  15. 15. DNA evidence It is now possible with modern technology to analyse and compare the DNA and protein molecules from different organisms. If different species produce proteins what are very similar in their amino acid sequences, it is logical to infer that their DNA is very similar, inherited from a common ancestor.
  16. 16. Phylogenetic trees Scientists have been able to construct evolutionary trees based on DNA analysis of different organisms. Phylogenetic trees show the evolutionary relationships in a variety of organisms based on studying the amino acid sequence of a particular protein. Two proteins studied extensively are: • Cytochrome C • Haemoglobin
  17. 17. If 2 species have evolved from a common ancestor and their separation was recent, it is likely that there will not have been enough time for many new mutations to have taken place. Their DNA sequences should therefore be very similar. They occur close together on a phylogenetic tree.
  18. 18. However, if 2 species have evolved from a common ancestor and they have been separated for a much longer time, it is likely many more mutations have occurred in each species. Their DNA sequences should therefore be very different. They occur further apart on a phylogenetic tree.
  19. 19. Phylogenetic Tree - primates
  20. 20. Cytochrome c A phylogenetic tree indicates the evolutionary relationship of organisms based on studying the amino acid sequence on a particular protein called cytochrome c. Cytochrome c is a protein that is necessary for respiration in all living organisms. It can vary from one species to another. The more similar, the closer the evolutionary relationship.
  21. 21. Cytochrome c The sequences for humans and chimpanzees match all of the 104 amino acid positions. Haemoglobin is another protein molecule used for amino- acid sequencing.
  22. 22. DNA analysis To compare 2 species the same segment of DNA from each species must be analysed. Two techniques are: • DNA Sequencing • DNA Hybridisation
  23. 23. DNA Sequencing • Involves determining the base sequence of a segment of DNA. • Very precise method. • Costly and time consuming. • Only used for small segments. Comparative DNA
  24. 24. Comparative DNA DNA Hybridization • Involves heating DNA from 2 species to get complementary strands. • Upon cooling DNA strands recombine. • The degree of bonding between 1 species DNA and another gives a measure of how closely related the 2 species are.
  25. 25. DNA Hybridization
  26. 26. Comparison of Primate DNA
  27. 27. Mutations A permanent change in the DNA sequence is called a Mutation. ( dna-leads-mutation) Mutation rates can be increased by certain environmental conditions • Radiation • Heat • Mutagenic chemicals Factors that cause increased mutation rates are called Mutagens.
  28. 28. Mutagens While natural mutations do occur spontaneously at a low rate others occur by physical or chemical factors or agents called mutagens. These mutations are often passed from one generation to another They occur during DNA replication or recombination and are called spontaneous mutations. ( repair) All alter genes in control of cell division leading to the development of cancerous cells
  29. 29. Cancer Many forms of cancer are the direct result of mutation. Chemical agents that cause or increase the incidence of cancer are called carcinogens.
  30. 30. In nature, mutations are random events that can be caused by mutagens. The vast majority of mutations are harmful but in some circumstances they can provide a source of variation which nature can select from. This process is called Natural Selection. Natural Selection works on the changes within individuals of a species brought about by mutations.
  31. 31. Base substitutions One nucleotide is substituted for another i.e. wrong base is placed into position on the DNA, leading to a different amino acid placed in the protein Eg sickle cell anemia
  32. 32. Base insertions or deletions Adding or deleting nucleotides on the mRNA will alter the reading of the nucleotide during translation – “frameshift” mutations Bigger mutations involve changes to chromosomes y-chromosome Eg down syndrome
  33. 33. Mutations in DNA
  34. 34. Translocations Part of one chromosome is moved to another Inversions Segment of one chromosome may be flipped upside down from its normal position Duplication Parts of chromosomes appear twice
  35. 35. Inheritable Human Diseases Sickle cell anaemia A fatal blood condition located on chromosome 11, coding for the haemoglobin protein which has an altered base leading to single amino acid alteration. The haemoglobin formed is abnormal gives rise to red blood cells that do not carry oxygen efficiently
  36. 36. Sickled Blood Cells Distorted red blood cells often block blood vessels. Amino acid glutamic acid is replaced by valine
  37. 37. Mutations in Human Chromosomes
  38. 38. Haemophilia Genetic disorder where those afflicted bleed excessively because of an abnormal gene which prevents blood clotting A carrier for the disease may not actually suffer from the disease but can pass on the mutant gene to their offspring.
  39. 39. Inheritance of Haemophilia