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47 Cards in this Set

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5′ cap

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

A site

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.)

alternative RNA splicing

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.

aminoacyl-tRNA synthetase

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

anticodon (an′-tī-kō′-don)

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

codon (kō′-don)

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

exon

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.

frameshift mutation

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.

gene expression

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.

insertion

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

intron (in′-tron)

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.

messenger RNA (mRNA)

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.)

missense mutation

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

mutagen (myū′-tuh-jen)

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

mutation (myū-tā′-shun)

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

nonsense mutation

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

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

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.

P site

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.)

point mutation

A change in a single nucleotide pair of a gene.

poly-A tail

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

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

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

primary transcript

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

primase

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

promoter

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

reading frame

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

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

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

ribosome (rī′-buh-sōm)

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.

ribozyme (rī′-buh-zīm)

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

RNA polymerase

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

RNA processing

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

RNA splicing

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).

signal peptide

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.

signal-recognition particle (SRP)

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.

silent mutation

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.

spliceosome (splī′-sō-sōm)

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.

start point

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

TATA box

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

template strand

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

terminator

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.

transcription

The synthesis of RNA using a DNA template.

transcription factor

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

transcription initiation complex


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

transcription unit

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

transfer RNA (tRNA)

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.

translation

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.

triplet code

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

wobble

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.