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