Bio 161 Chapter 17 Gene Expression: From Gene to Protein

Gene expression

The process by which DNA directs protein synthesis, includes two stages: Transcription and Translation

Alkaptonuria

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Transcription (DNA→mRNA)

Synthesis of RNA using information contained in the DNA; happens in the nucleus

Messenger RNA

complementary RNA that carries the genetic message from the DNA to the protein-synthesizing machinery of the cell (ribosomes)

Translation (mRNA→protein)

Synthesis of a protein (polypeptide) using the information in the mRNA; occurs in the cytoplasm; involves a change in “language” as the cell translates the nucleotide sequence of the mRNA into amino acids

Ribosomes

Where translation occurs—the amino acids are linked together into polypeptide chains

Triplet code (codon)

Three-nucleotide sequences found in the transcribed DNA (mRNA)

Mutations

Changes in the genetic material

Point mutations

Chemical changes in just one base pair of a gene

Nucleotide-pair substitution

Replaces one nucleotide and its partner with another pair of nucleotides

Silent mutations

Mutations that have no effect on the amino acid produced by a codon because of redundancy in the genetic code

Missense mutations

Mutations that still code for an amino acid, but not the correct amino acid

Nonsense mutations

Mutations that change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein

Insertions/deletions

Additions or losses of nucleotide pairs in a gene— disastrous effect on the resulting protein more often than substitutions do

Frameshift mutation

Produced when an insertion or deletion of nucleotides alters the reading frame