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DNA by Mind Map: DNA
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Nucleotide polymer; double helix; hydrogen bonding; complementary base pairing (A-T; C-G). Differs from RNA in that the sugar in RNA is ribose, thymine is replace with uracil in RNA and that RNA is single stranded.


Encode genetic information


Restriction enzyme digestion


Restriction fragment Length Polymorphism (RFLP)


Cell cycle. The lifecycle of a cell is composed of four distinct stages, which constitute a cycle. The cell cycle contains several checkpoint, which prevent a cell from progressing to the next stage of the cycle unless the cell is compliant with all conditions. A cell's passage through the cell cycle is regulated by the cyclin-CdK system. CdK is present in a cell's cytoplasm all the time, but cyclins are synthesised at the checkpoint, to drive the cell into the next phase of the cycle. Once the cell enters the next phase, the cyclins are destroyed. Cyclins are synthesised in response to growth factor signalling. If cells are able to bypass the checkpoints in an unregulated manner, then the cell becomes cancerous.


Only 1.5% of human genome encodes for proteins. The remaining components are considered to be 'junk' DNA


Miescher discovered nucleic acids in nuclei.

Geneticists confirm that chromosomes are involved in sex-determination and heredity. Chromosome are the 'heritable factors' described by Mendel. But chromosomes are composed of DNA and proteins. Proteins are more diverse, leading to the suspicion that proteins were the molecules of heredity.

Fred Griffiths discovers the transformation principle, which is able to transform non-pathogenic Streptococcus bacteria (R form) into pathogenic ones (S form). The transformation can be transmitted to subsequent generations, indicating that it is heritable. Avery and co-workers prove that the transforming principle is DNA, not RNA or proteins.

Using radioactive phosphorus (found in DNA, but not proteins) and radioactive sulphur (found in proteins, but not DNA), Hershey and Chase confirm, using bacteriophages, that DNA is the molecule of heredity. Only when the 'parent virus'' DNA was labelled did the progeny viruses also contain radioactive DNA.

Waston, Crick, Franklin, Wilkins discover the structure of DNA using X-ray crystallography.

Evolutionary genomics

Large scale changes in genomes are often the result of errors during meiosis. This results in cells having extra DNA, which is the raw material on which evolution works.


Science is an exploration of the natural world. It produces a body of knowledge that describes and explains the universe at large.


The underlying principles of evolution were developed by many scientists over a long period of time, but were 'formalised' by Darwin and Wallace. Darwin called his ideas 'descent with modification'.


Mutations. Mutations are changes to the genetic script that an individual inherits. Mutation may occur between generations through meiosis. Errors during DNA replication is another source of mutations. They may be caused by chemicals in the environment (carcinogens) or by ionising radiations.

Reproduction & Development

Fertilisation: union of two dissimilar nuclei. Binding of sperm onto eggs induces acrosome reaction, which leads to the fusion of sperm and egg cell membranes. It also stimulates the cortical reaction in eggs, which prevents other sperms from fertilising the egg. This is the first stage of development in multicellular organisms. The product of fertilisation is a zygote.