Glossary of Chapter 17 - From Gene to Protein

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nutritional mutants that cannot survive on a minimal medium, but require additional supplements to facilitate metabolism
One gene – one polypeptide hypothesis
a specific hypothesis that suggests that a single gene codes for a single specific polypeptide
the synthesis of RNA under the direction of DNA; process in which genetic information is merely copied from one nucleic acid to another, it provides a template for assembling a sequence of RNA nucleotides
Messenger RNA (mRNA)
an RNA molecule that is a transcript of the gene’s protein-building instructions; it carries a genetic message from the DNA to the protein-synthesizing machinery of the cell
the actual synthesis of a polypeptide, which occurs under the direction of mRNA; process during which the genetic information in the nucleic acid has to be converted to amino acids; occurs in the ribosomes
Triplet code
the genetic instructions for a polypeptide chain aree written in the DNA as a series of three-nucleotide combinations; there are 64 possible triplet combinations
Template strand
one of the two DNA strands that is transcribed; provides the template for ordering the sequence of nucleotides in an RNA transcript
mRNA base triplets
RNA polymerase
an enzyme that pries the two strands of DNA apart and hooks together the RNA nucleotides as they base-pair along the DNA template
Transcription unit
the stretch of DNA that is transcribed into an RNA molecule
a region of DNA where RNA polymerase attaches and initiates transcription; includes the transcription start point and extends several nucleotides “upstream” from the start point; determines where transcription starts as well as which of the two strands of the DNA helix is used as the template
Transcription factors
a collection of proteins in eukaryotes that mediate the binding of RNA polymerase and the initiation of transcription
Transcription initiation complex
the completed assembly of transcription factors and RNA polymerase bound to the promoter
a DNA sequence which, when transcribed by the RNA polymerase, terminates the transcription process; the transcribed terminator (RNA sequence) actually serves as the terminator
5’ cap
the end of a pre-mRNA molecule is capped off with a modified form of a guanine molecule; helps protect the mRNA from degradation by hydrolytic enzymes and acts as an identifier molecule for ribosomes once the mRNA is in the cytoplasm
Poly(A) tail
an addition to the 3’ end of a mRNA molecule in eukaryotic nuclei; consists of 30-200 adenine nucleotides; inhibits degradation of the from hydrolytic reactions and acts as an identifier molecule for ribosomes once the mRNA is in the cytoplasm; helps facilitate the export of mRNA from the nucleus into the cytoplasm
RNA splicing
the removal of a large portion of the RNA molecule that is initially synthesized in order to condense the molecule into the crucial codons
aka: intervening sequences; the noncoding segments of nucleic acid that lie between coding regions
called so because the are eventually expressed or translated into amino acid sequences
a molecule that is nearly equal in size to a ribosome; the combination of several different snRNPs joined together with additional proteins; interacts with the splice sites at the ends of an intron by cutting at specific points to release the intron and then immediately joins together the two exons that flanked the intron
RNA molecules that function as enzymes; gave rise to the idea of the catalytic role of snRNA in gene splicing
Transfer RNA
a nucleic acid that functions to transfer amino acids from the cytoplasm’s amino acid pool to a ribosome
a nucleotide triplet that comprises one end of a tRNA molecule; binds, according to base-pairing rules, to a complementary codon on mRNA
a relaxation of the base-pairing rules in relation to tRNA molecules
Aminoacyl-tRNA synthetase
an enzyme that attaches the correct amino acid to each tRNA molecule; catalyzes the covalent attachment of the amino acid to its tRNA in a process driven by the hydrolysis of ATP
Ribosomal RNA
the most abundant type of RNA found in a cell; compose about 60% of a ribosome (proteins compose the other 40%)
P site (peptidyl-tRNA site)
the site on a ribosome that holds the tRNA that is carrying the growing polypeptide chain
A site (aminoacyl-tRNA site)
the site on a ribosome that holds the tRNA that is carrying the next amino acid to be added to the chain
E site (exit site)
the site on a ribosome that functions as an exit site for discharged tRNAs from the ribosome
strings of ribosomes that produce many copies of a protein simultaneously
Signal peptide
a peptide about 20 amino acids in length at or near the leading end of the protein; signals the peptide to be moved to the ER for packaging and secretion or utilization in the endomembrane system
Signal recognition particle (SRP)
a protein-RNA complex that functions as an adaptor that brings the ribosome to a receptor protein built into the ER membrane; recognizes the signal peptide and responds
changes in the genetic material of a cell
Point mutations
chemical changes in just one or a few base pairs in a single gene
Base-pair substitution
the replacement of one nucleotide and its partner in the complementary DNA strand with another pair of nucleotides
Missense mutations
the altered codon still codes for an amino acid and thus makes sense, although not necessarily the right sense
Nonsense mutations
alterations that change an amino acid codon to a stop signal; usually lead to nonfunctional proteins
Insertions or deletions
additions or losses of one or more nucleotide pairs in a gene; usually have a disastrous effect upon the resulting protein
Frameshift mutation
occurs whenever the number of nucleotides inserted or deleted is not a multiple of 3, causing an improper production of many of the amino acids in the chain
physical and chemical agents that interact with DNA to cause mutations
Ames test
developed by Bruce Ames; tests mutagenic properties of chemicals; uses easily grown bacteria with a mutation that prevents them from growing in culture; radiation causes back-mutation that renders the bacteria viable for growth in culture

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