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alternative splicing
Event by which the same gene can specify two or more slightly different proteins. All exons in a pre-mRNA transcript of the gene are retained or some are removed and the rest spliced in various combinations for the mature transcript.
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amino acids
A small organic compound with a carboxylic acid group, an amino group, and a characteristic side group (R); monomer of polypeptide chains.
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anticodon
Series of three nucleotide bases in tRNA that can base-pair with mRNA codons.
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base sequence
Linear order of nucleotides that compose a DNA or RNA strand.
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base-pair substitution
Mutation in which one nucleotide is wrongly substituted for another during DNA replication.
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deletions
Loss of a chromosome segment; often leads to genetic disorders. Also the loss of one or more nucleotide bases from a DNA molecule.
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exons
A base sequence in eukaryotic DNA that is part or all of a protein-encoding gene; may or may not be excised from a pre-mRNA during transcript processing.
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gene mutations
Small-scale change in the nucleotide sequence of a gene; can result in an altered protein product.
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genetic code
Correspondence between triplets of nucleotides in DNA and mRNA, and specific sequences of amino acids in a polypeptide chain; near-universal language of protein synthesis; mitochondria and a few species have a few variant code words.
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insertions
A mutation by which one or more bases are introduced into a DNA strand. Also a movable attachment of muscle to bone.
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introns
One of the noncoding sequences in eukaryotic genes; it is excised from the pre-mRNA transcripts before translation.
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ionizing radiation
Form of radiation with enough energy to eject electrons from atoms.
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messenger RNA
mRNA. A single strand of ribonucleotides transcribed from DNA; the only type of RNA that carries proteinbuilding information to ribosomes.
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mutation rate
Of a given gene locus, the probability that a spontaneous mutation will happen in a specified interval.
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nonionizing radiation
Form of radiation that carries enough energy to boost electrons to higher energy levels but not enough to eject them from an atom.
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polysomes
A series of ribosomes that are all translating the same mRNA molecule at the same time.
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promoter
Short stretch of DNA to which RNA polymerase binds. Transcription then begins at the gene closest to the promoter.
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ribosomal RNA
rRNA. A class of RNA that becomes complexed with proteins to form ribosomes; some catalyze assembly of polypeptide chains.
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ribosomes
The site of polypeptide chain synthesis in all cells. An intact ribosome has two subunits of rRNA and proteins.
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RNA polymerase
Enzyme that catalyzes transcription of DNA into RNA.
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transcription
[L. trans, across, + scribere, to write] First stage of protein synthesis. An RNA strand is assembled from nucleotides using a gene region in DNA as a template.
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transfer RNA
tRNA. One of a class of small RNA molecules that delivers amino acids to a ribosome. Its anticodon pairs with an mRNA codon during translation.
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translation
Second stage of protein synthesis. At ribosomes, information encoded in an mRNA transcript guides the synthesis of a new polypeptide chain from amino acids.
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transposons
Transposable element. A stretch of DNA that jumps spontaneously and randomly to a different location in the genome and may mutate a gene.
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uracil
One of four nitrogencontaining bases in nucleotide monomers of RNA; also applies to a nucleotide with a uracil base component. Like thymine, uracil can base-pair with adenine.
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