- during transcription, one strand of the genes DNA serves as a template for synthesizing many copies of mRNA
- the key enzyme in transcription is RNA polymerase
- each gene has a sequence (a promoter) at which RNA polymerase begins transcription. transcription stops after RNA polymerase encounters encounters special transcription termination sequences
- the mRNA molecule is constructed according to specific base-pairing rules: A, U, C and G in mRNA pair with T,A, G, and C, respectively, in the template strand of DNA
- newly made, or preliminary, eukaryotic mRNA must be processed while it is still in the nucleus to (among other things) splice out noncoding sequences of DNA (introns) found in many genes. the remaining, protein-encoding segments of mRNA (exons) are then joined in a mature mRNA molecule that is exported to the ribosomes for translation into protein
a mutation is any alteration in the info coded within an individuals DNA. sometimes the effects of that change can be detected as a change in the inherited characteristics of that individual (a phenotypic change). but in other cases, the mutation may be silent, with no outward sign that it has occurred. most mutations are neutral in their impact on the individual, neither benefiting ot nor harming it. some mutations have harmful effects, and rarely, a mutation might produce a change that enhances the individuals ability to survive and reproduce in a particular environment.
a very large number of our genes carry info for the construction of specific proteins. that info is carried in the form of a sequence of chemical units, called nitrogenous bases, that in turn specify the sequence in which the amino acid in a protein are strung together (proteins are built from amino acids, and each unique protein has a unique sequence of amino acids). when the base sequence of a protein-coding gene changes, the amino acid sequ3ence of its protein is altered as well. every protein has special chemical and biological properties that are critical to its function ,and most of those properties stem from the precise sequence of amino acids in it. if the amino acid sequence of a protein changes because of a mutation in the gene that codes for it, the biological function of that protein may change as well
to produce domesticated species, humans have manipulated the reproduction of other organisms, selecting for desirable qualities that, over time, have become standard in domesticated species. although such selection practices do lead to changes in the DNA of organisms (that is, they lead to an increase in the frequencies of allels that control the inheritance of the traits we select for), genetic engineering enables us to make much greater changes in a much shorter span of time. using such methods, we can manipulate the DNA of organisms directly, and we can transfer genes from one species to another. transfers of DNA from, say, a human to a bacterium (as is done in the production of human insulin) far exceed the scope of DNA transfers that occur in nature or are possible through conventional breeding of crops and farm animals . we can also selectively change specific DNA sequences - something e could never do before. overall, we can now manipulate DNA with gretater power and precision than we could when we domesticated species such as dogs, corn, and cows the advantage of DNA cloning id that it is easier to study a gene and its function, and to manipulate that function for practical benefits, once you have many copies of it. once a gene has been cloned, it can be sequenced, transferred to other organisms, or used in various experiments. today, many lifesaving pharmaceuticals, such as human insulin, human growth hormone, human blood-clotting proteins, and anticancer drugs, are manufactured by bacteria that have been genetically modified by having cloned human genes inserted into them Kenneth R. Miller, Levine Christy C. Hayhoe, Doug Hayhoe, Jeff Major, Maurice DiGiuseppe Kenneth R. Miller, Levine