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
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
Transcription
The synthesis of RNA using a DNA template
Translation
The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of the "language" from nucleotides to amino acids
Primary transcript
An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene
Triplet code
A genetic information system in which sets of three-nucleotide long words specify the amino acids for polypeptide chains
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
Codons
A 3-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code
Reading frame
On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis
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
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
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 unit
A region of DNA that is transcribed into an RNA molecule
Start point
In transcription, the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA
Transcription factors
A regulatory protein that binds to DNA and effects transcription of specific genes
Transcription initiation complex
The completed assembly of transcription factors and RNA polymerase bound to a promoter
TATA Box
A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex
RNA processing
Modification of RNA primary transcripts, including splicing out of introns, joining together of eons and alteration of the 5' and 3' ends
5' cap
A modified form of guanine nucleotide added onto the 5' end of a pre-mRNA molecule
poly-A tail
A sequence of 50-250 adenine nucleotides added onto the 3' end of a pre-mRNA molecule
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)
Introns
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
Exons
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
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
Ribozymes
An RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing
Alternative RNA splicing
A type of eukaryotic gene regulation at the NRA-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
Domains
A discrete structural and functional region of a protein
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
Anticodon
A nucleotide triplet at one end of a tRNA molecule that base-pairs with a particular complementary codon on an mRNA molecule
Aminoacyl-tRNA synthetases
An enzyme that joins each amino acid to the appropriate tRNA
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
Ribosomal RNA (rRNA)
RNA molecules that, together with proteins, make up ribosomes, the most abundant type of RNA
P site
Holds the tRNA carrying the growing polypeptide chain
A site
Holds the tRNA carrying the next amino acid to be added to the polypeptide chain
E site
The place where discharged tRNAs leave the ribosome (exit)
Release Factor
A protein shaped like an aminoacyl tRNA, bunds directly to the stop codon in the A site
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 ER by binding to a receptor protein on the ER
Polyribosomes (Polysomes)
A group of several ribosomes attached to, and translating, the same messenger RNA moleucle
Point mutations
A change in a single nucleotide pair of a gene
Nucleotide-pair substitutions
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
Silent Mutation
A nucleotide-pair substitution that has no observable effect on the phenotype
Missense mutation
A nucleotide-pair substitution that results in a codon that codes for a different amino acid
nonsense mutation
a mutation that changes a amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein
insertions and deletions
a mutation involving the addition or loss of one or more nucleotide pairs to a gene
frameshift mutation
a mutation occurring when nucleotides are inserted in or deleted from a gene and the number inserted or deleted is not multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons
mutagens
a chemical or physical agent that interacts with DNA and can cause a mutation