Chapter 5 Evolution M13

 M13.1 Know that DNA IS UNIVERSAL TO MOST LIVING THINGS  DNA is the fundamental chemical of all living things  All living CELLS contain DNA Bacteria only have a single strand but this contains all of the code required to replicate themselves- single circular chromosome or plasmids/small loops of DNA.  Main role of DNA is to pass on hereditary characteristics  Act as the code for the production of other vital molecules in living things-mainly proteins

 Evolution is one of the main areas of modern Biology  Involves the transformation of life on earth from its earliest forms to the vast diversity that we see today.  Modern theory stems from Charles Darwin- Origin of the Species  The fact that there is actually such diversity of life today, despite the origin and DNA similarities is due to mutations

 DNA is said to have been circular in all first organisms  As organisms got larger the strands broke and produced several linear strands of differing lengths  Several starting points existed along the lengths making replication easier and quicker  DNA got bigger : one because of the number of genes now needed and also because there seemed to be developing lots of sections of DNA which coded for nothing  These “bits “ of DNA that don’t appear to code for anything, are junk or non coding bits, called EXONS

 When the exons are cut out by the m RNA they are referred to as INTRONS  The amount of exons seems to increase with the complexity of the organisms  The packaging of DNA also became more complex-proteins called HISTONES began organising the wispy DNA to prevent tangles during division which could have proved that more mutations would occur

 M14.1 Understand that organisms have common features attributable to commonly shared sequences of DNA.  DNA is the genetic code  this means it is responsible for all features and inheritable characteristics  Species that have similar features share many common aspects of their DNA too.

 Evolutionary relationships have been established on the basis of these structural similarities- called comparative anatomy  This means that structures in different organisms may be used for different functions but are fundamentally similar-suggesting a common origin  These are homologous structures  Page 35 of the text shows that bats. Monkeys and pigs have very similar structures in terms of their bones in the wings or limbs, suggesting, scientist believe a common origin 

 Comparison of organisms also involves comparing major organs- heart/lungs  And now DNA:  this involves looking at the proteins  Scientist sequence the amino acids in protein molecules  If these sequences produce proteins, if the sequences are similar then it is inferred a common ancestry—again I see this as if it works, lets just modify, not change it.

 PHYLOGENETIC Trees:  These are diagrams which show evolutionary relationships based on their amino acid sequences  They use the sequence of a protein called cytochrome c  This is a protein that is necessary in the respiration pathways of nearly all living organisms  This protein varies from species to species: with the degree of similarity indicating the closeness in evolutionary relationship  Humans and Chimpanzees match at all 104 amino acid positions

 If you look at the table/diagram on page 36 you will see we vary 9 from a rabbit.13 from a turtle and 45 from yeast!  Compared with fossil and comparative anatomy studies, along with amino acid sequencing, scientist make their valuations as to who’s related to whom in the Kingdom!  Sometimes the protein molecule of haemoglobin is used in amino acid sequencing

 14.2 Explain why the greater the similarity between the sequence of the nucleotides in their DNA, the more likely it is that the separation of the two species is recent.  Species that have a recent common ancestor will usually have similar DNA and protein sequences  The longer the time that species have been separated from one another, the more chance that mutations have occurred and DNA is less similar

 Remember we said that this way of determining evolutionary relationships has been backed up by fossil evidence and comparative anatomy studies  To be more sure it is better to actually compare the DNA sequences in order and arrangement of the nucleotides  This is time consuming & Labour intensive  So……. We use a method called DNA hybridization

 DNA is heated from two different species to the point where the complimentary strands separate from one another  As they cool, the single strands of DNA will recombine to form the double helix again  As the strands recombine we see how closely the different species reattach to another species…closer the match, less time they have been separated on the evolutionary relationship stakes  See page Text, or large text book