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Comparative Biochemistry

Human Biology (Year 12) - Biotechnology as Evidence for Evolution

Ben Whitten

Comparing DNA

DNA is a chemical compound that makes up genes that determine what type of protein a cell can make. All living organisms use the same four bases to code DNA - guanine, adenine, thymine and cytosine, which adds weigh to idea that all living things have evolved from a common ancestor.

The sequence of bases in DNA varies for each organism. New genes may be gained via mutation, and others may be lost via natural selection or genetic drift. When speciation eventually occurs, the new species have similar DNA, but accumulate more differences. Species that are more closely related have less differences in their DNA.

The complete set of DNA in each cell of an organism is called a genome, and it is interesting to note that humans and chimps share about 98% of the same DNA!

What are endogenous retroviruses?

Endogenous retroviruses (ERVs) are sections of non-coding DNA from a viral sequence which has been integrated into the organisms' genome. ERVs work by copying its RNA into the cells' DNA via reverse transcription, hence being inserted into the hosts' chromosomes.

It is only labelled endogenous if it's inserted into the gamete, so it'll be inherited by  the next generations. Offsprings will then have the ERV in the exact same location.

When comparing chromosomes between humans and chimpanzees, we have the same ERVs found on 16 chromosomes; this provides compelling evidence that we share a common ancestor.

What is mitochondrial DNA?

Mitochondria are the organelles in the cell in which cellular respiration occurs. Mitochondria contain small amounts of DNA, labelled mitochondrial DNA (mtDNA). mtDNA is found in the form of small circular molecules.

mtDNA contains 37 genes, where 24 code for the production of tRNA molecules and 13 contain the instructions for producing enzymes for cellular respiration.

Mitochondrial DNA is inherited maternally, meaning it only comes from the mother. The ovum contains a large amount of mitochondria, and once the sperm penetrates the egg, the mitochondria is destroyed. The similarity of mtDNA estimates the closeness of relationship between organisms, and allows for the tracking of ancestry and migration routes.

mtDNA has a very high mutation rate, and therefore slowly diverges from the mtDNA of the original female ancestor as it is passed down onto the next generations of offspring.

What are protein sequences?

Protein sequences provide evidence for evolution. There are tens of thousands of proteins found in all living things, all made by 20 different kinds of amino acids. We can evaluate and analyse the degree of similarity between species by comparing the type and sequence of amino acids across similar proteins.

Animals of the same species are found to have identical amino acid species, whereas those from different species have different amino acids and/or in a different order. The degree of difference enables us to estimate how recent a common ancestor is/what degree of evolution has occurred.

Ubiquitous proteins are proteins that appear in all species. These proteins perform very basic, but essential tasks for life - all carry out the same function. A notable example is Cytochrome C, a protein that plays an essential role in the production of cellular energy. Cytochrome C has changed very little over millions of years, as 37 amino acids are found at the same position for every Cytochrome C molecule - this suggests that we all descended from a common ancestor.

What is bioinformatics?

Bioinformatics combines all areas of biological science and utilises computer science and technologies to describe molecular components of all living things. It involves the acquisition, storage, analysis, and dissemination of biological data, most often DNA and amino acid sequences.

Bioinformatics allows biologists to compare entire genomes, and trace the evolution of many organisms by measuring changes in DNA.

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