Nucleic Acids and Genetics A Language of Its Own. DNA Structure and Replication. In the mid-1900s, scientists knew that chromosomes, made up of DNA ( deoxyribonucleic acid ) and proteins , contained genetic information.
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By using different radioactively labeled components, they demonstrated that only the virus DNA entered a bacterium to take over the cell and produce new viruses.
In the early 1950s, Rosalind Franklin and her associates began to test X-ray beams with DNA. The X-ray scattering produces a pattern that provides important clues to the structure of many molecules.
This X-ray diffraction photograph of DNA was taken by Franklin. The X-shaped pattern in the center indicates that the structure of DNA is helical.
This is called complementary base pairing because a purine (A and G) is always paired with a pyrimidine (T and C).
The sides of the ladder are the sugar-phosphate backbones, and the rungs of the ladder are the complementary paired bases.
The two DNA strands are anti-parallel – they run in opposite directions.
The process is semiconservative because each new double helix is composed of an old strand of nucleotides from the parent molecule and one newly-formed strand.
Some cancer treatments are aimed at stopping DNA replication in rapidly-dividing cancer cells.
Transcription makes an RNA molecule complementary to a portion of DNA.
Translation occurs when the sequence of bases of mRNA directs the sequence of amino acids in a polypeptide.
As the ribosome moves down the mRNA molecule, new tRNAs arrive, and a polypeptide forms and grows longer.
Translation terminates once the polypeptide is fully formed; the ribosome separates into two subunits and falls off the mRNA.
Several ribosomes may attach and translate the same mRNA, therefore the name polyribosome.
If a point mutation involves the substitution of a different amino acid, the result may be a protein that cannot reach its final shape; this is a missense mutation.
An example is Hbswhich causes sickle-cell disease.
4) Telomeres are DNA segments at the ends of chromosomes that normally get shorter and signal an end to cell division; cancer cells have an enzyme that keeps telomeres long.
Gene mutations vary; some have little effect but some have a dramatic effect.
Loss of genetic control over genes involved in cell growth and/or cell division cause cancer.