Campbell Biology- From Gene To Protein (Ch. #17)

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5′ cap

Back 1

A modified form of guanine nucleotide added onto the 5′ end of a pre-mRNA molecule.

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A site

Back 2

One of a ribosome’s three binding sites for tRNA during translation. The A site holds the tRNA carrying the next amino acid to be added to the polypeptide chain. (A stands for aminoacyl tRNA.)

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alternative RNA splicing

Back 3

A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.

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aminoacyl-tRNA synthetase

Back 4

An enzyme that joins each amino acid to the appropriate tRNA.

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anticodon (an′-tī-kō′-don)

Back 5

A nucleotide triplet at one end of a tRNA molecule that base-pairs with a particular complementary codon on an mRNA molecule.

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codon (kō′-don)

Back 6

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.

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exon

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A sequence within a primary transcript that remains in the RNA after RNA processing; also refers to the region of DNA from which this sequence was transcribed.

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frameshift mutation

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A mutation occurring when nucleotides are inserted in or deleted from a gene and the number inserted or deleted is not a multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons.

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gene expression

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The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs.

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insertion

Back 10

A mutation involving the addition of one or more nucleotide pairs to a gene.

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intron (in′-tron)

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A noncoding, intervening sequence within a primary transcript that is removed from the transcript during RNA processing; also refers to the region of DNA from which this sequence was transcribed.

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messenger RNA (mRNA)

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A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein. (In eukaryotes, the primary RNA transcript must undergo RNA processing to become mRNA.)

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missense mutation

Back 13

A nucleotide-pair substitution that results in a codon that codes for a different amino acid.

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mutagen (myū′-tuh-jen)

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A chemical or physical agent that interacts with DNA and can cause a mutation.

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mutation (myū-tā′-shun)

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A change in the nucleotide sequence of an organism’s DNA or in the DNA or RNA of a virus.

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nonsense mutation

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A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

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nucleotide-pair substitution (nū′-klē-ō-tīd′)

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A type of point mutation in which one nucleotide in a DNA strand and its partner in the complementary strand are replaced by another pair of nucleotides.

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P site

Back 18

One of a ribosome’s three binding sites for tRNA during translation. The P site holds the tRNA carrying the growing polypeptide chain. (P stands for peptidyl tRNA.)

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point mutation

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A change in a single nucleotide pair of a gene.

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poly-A tail

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A sequence of 50–250 adenine nucleotides added onto the 3′ end of a pre-mRNA molecule.

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polyribosome (polysome) (pol′-ē-rī′-buh-sōm′)

Back 21

A group of several ribosomes attached to, and translating, the same messenger RNA molecule.

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primary transcript

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An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene.

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primase

Back 23

An enzyme that joins RNA nucleotides to make a primer during DNA replication, using the parental DNA strand as a template.

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promoter

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A specific nucleotide sequence in the DNA of a gene that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.

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reading frame

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On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis.

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ribosomal RNA (rRNA) (rī′-buh-sō′-mul)

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RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.

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ribosome (rī′-buh-sōm)

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A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus. See alsonucleolus.

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ribozyme (rī′-buh-zīm)

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An RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing.

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RNA polymerase

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An enzyme that links ribonucleotides into a growing RNA chain during transcription, based on complementary binding to nucleotides on a DNA template strand.

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RNA processing

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Modification of RNA primary transcripts, including splicing out of introns, joining together of exons, and alteration of the 5′ and 3′ ends.

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RNA splicing

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After synthesis of a eukaryotic primary RNA transcript, the removal of portions of the transcript (introns) that will not be included in the mRNA and the joining together of the remaining portions (exons).

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signal peptide

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A sequence of about 20 amino acids at or near the leading (amino) end of a polypeptide that targets it to the endoplasmic reticulum or other organelles in a eukaryotic cell.

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signal-recognition particle (SRP)

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A protein-RNA complex that recognizes a signal peptide as it emerges from a ribosome and helps direct the ribosome to the endoplasmic reticulum (ER) by binding to a receptor protein on the ER.

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silent mutation

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A nucleotide-pair substitution that has no observable effect on the phenotype; for example, within a gene, a mutation that results in a codon that codes for the same amino acid.

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spliceosome (splī′-sō-sōm)

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A large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons.

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start point

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In transcription, the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA.

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TATA box

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A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex.

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template strand

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The DNA strand that provides the pattern, or template, for ordering, by complementary base pairing, the sequence of nucleotides in an RNA transcript.

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terminator

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In bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA.

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transcription

Back 40

The synthesis of RNA using a DNA template.

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transcription factor

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A regulatory protein that binds to DNA and affects transcription of specific genes.

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transcription initiation complex

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The completed assembly of transcription factors and RNA polymerase bound to a promoter.

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transcription unit

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A region of DNA that is transcribed into an RNA molecule.

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transfer RNA (tRNA)

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An RNA molecule that functions as a translator between nucleic acid and protein languages by carrying specific amino acids to the ribosome, where they recognize the appropriate codons in the mRNA.

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translation

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The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of “language” from nucleotides to amino acids.

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triplet code

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A genetic information system in which sets of three-nucleotide-long words specify the amino acids for polypeptide chains.

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wobble

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Flexibility in the base-pairing rules in which the nucleotide at the 5′ end of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position (3′ end) of a codon.