Chapter 17: From Gene to Protein Flashcards
5’ cap
A modified form of guanine nucleotide added onto the 5′ end of a pre-mRNA molecule.
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.
codon
A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.
domains
(1) A taxonomic category above the kingdom level. The three domains are Archaea, Bacteria, and Eukarya. (2) A discrete structural and functional region of a protein.
E site
One of a ribosome’s three binding sites for tRNA during translation. The E site is the place where discharged tRNAs leave the ribosome. (E stands for exit.)
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
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.
mutagen
A chemical or physical agent that interacts with DNA and can cause a mutation.
mutation
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
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)
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.
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.
ribozyme
An RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing.
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
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.
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 a set 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.
