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Gene expression
The process by which information encoded in DNA directs the synthesis of protein or, in some cases, RNAs that are not translated into protein and instead function as RNAs.
transcription
The synthesis of RNA using a DNA template.
Messenger RNA
A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein.
Translation
A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein.
Ribosome
A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consisting of a large subunit and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus.
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 a set of three-nucleotide-long words specifies 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.
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.
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.
TRansciption 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 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 polymeras 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 exons, and alteration of the 5' and 3' ends.
5’ cap
A modified form of guanine nucleotide added onto the 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).
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.
Extron
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.
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.
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.
Ribozyme
An RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing.
Transfer RNA
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 synthetase
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.
Ribsomal RNA
RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.
P-site
One of a ribosome's three binding sites for tRNA during translation. Holds the tRNA carrying the growing polypeptide chain. Stands for peptidyl tRNA.
A site
One of a ribosome's three binding sites for tRNA during translation. Holds the tRNA carrying the growing polypeptide chain. Stands for peptidyl tRNA.
E site
One of a ribosome's three binding sites for tRNA during translation. The place where discharged tRNAs leave the ribosome. Stands for exit.
release factor
A protein shaped like an aminoacyl tRNA that binds to the stop codon in the A site and hydrolyzes the bond between the polypeptide and the tRNA in the P 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
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.
mutation
A change in the nucleotide sequence of an organism's DNA or in the DNA or RNA of a virus.
point mutation
A change in a single nucleotide pair of a gene
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.
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.
missense mutation
A nucleotide-pair substitution that results in a codon that codes for a different amino acid.
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.
insertion
A mutation involving the addition of one or more nucleotide pairs to a gene.
deletion
A mutational loss of one or more nucleotide pairs from 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 a multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons.
spontaneous mutation
Mutations that arise by errors during DNA replication or recombination.
mutagen
A chemical or physical agent that interacts with DNA and can cause a mutation.
gene
A region of DNA that can be expressed to produce a final functional product that is either polypeptide or an RNA molecule.
DNA replication
The process by which a DNA molecule is copied; also called DNA synthesis.
Transformation
A change in genotype and phenotype due to the assimilation of external DNA by a cell.
bacteriophage
A virus that infects bacteria; also called a phage.
Phage
A virus that infects bacteria; also called a bacteriophage.
Virus
An infectious particle incapable of replicating outside of a cell, consisting of an RNA or DNA genome surrounded by a protein coat (capsid) and, for some, a membranous envelope.
Double helix
The form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape.
Antiparallel
Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5'->3' directions)
semiconservative
Type of DNA replication in which the replicated double helix consists of one old strand, derived from the parental molecule, and one newly made strand.
origin of replication
Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.
replication fork
A Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are being synthesized.
helicase
An enzyme that untwists the double helix of DNA at replication forks, separating the two strands and making them available as template strands.
single-stranded binding protein
A protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of complementary strands of DNA
topoisomerase
A protein that breaks, swivels, and rejoins DNA strands. During DNA replication, they help to relieve strain in the double helix ahead of the replication fork.
primer
A short stretch of RNA with a free 3' end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication
primase
An enzyme that joins RNA nucleotides to make primer during DNA replication, using the parental DNA strand as a template.
DNA polymerase
An enzyme that catalyzes the elongation of new DNA (for example, at a replication fork) by the addition of nucleotides to the 3' end of an existing chain.
leading strand
The new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5'->3' direction.
lagging strand
A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5'->3' direction away from the replication fork.
Okazaki fragment
A short segment of DNA synthesized away from the replication fork on a template strand during DNA replication. Many are joined together to make up the lagging strand of newly synthesized DNA.
DNA ligase
A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3' end of one DNA fragment (such as an Okazaki fragment) to the 5' end of another DNA fragment (such as a growing DNA chain).
mismatch repair
The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.
nuclease
An enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides.
nucleotide excision repair
A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.
thymine dimer
A structure consisting of adjacent thymine bases on a DNA strand that are covalently linked. Usually caused by exposure to ultraviolet light.
telomerase
An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells, thus restoring their original length and compensating for the shortening that occurs during DNA replication.
nucleoid
A non-membrane-enclosed region in a prokaryotic cell where its chromosome is located.
chromatin
The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, it exists in its dispersed form, as a mass of very long , thin fibers that are not visible with a light microscope.
heterochromatin
Eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed.
euchromatin
The less condensed form of eukaryotic chromatin that is available for transcription.
histone
A small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role in chromatin structure.
nucleosome
The basic, bead-like unit of DNA packing in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of four types of histone.
nucleic acid hybridization
The process of base pairing between a gene and a complementary sequence on another nucleic acid molecule.
plasmid
A small, circular, double-stranded DNA molecule that carries accessory genes separate from those of a bacterial chromosome; in DNA cloning, can be used as a vector carrying up to about 10,000 base pairs (10 kb) of DNA.
recombinant DNA
A DNA molecule made in vitro with segments from different sources.
gene cloning
The production of multiple copies of a gene.
restriction enzyme
An endonuclease (type of enzyme) that recognizes and cuts DNA molecules foreign to a bacterium (such as phage genomes). The enzyme cuts at specific nucleotide sequences (restriction sites).
restriction site
A specific sequence on a DNA strand that is recognized and cut by a restriction enzyme.
restriction frgment
A DNA segment that results from the cutting of DNA by a restriction enzyme.
gel electrophoresis
A technique for separating nucleic acids or proteins on the basis of their size and electrical charge, both of which affect their rate of movement through an electric field in a gel made of agarose or another polymer.
sticky end
A single-stranded end of a double-stranded restriction fragment.
cloning vector
In genetic engineering, a DNA molecule that can carry foreign DNA into a host cell and replicate there. Cloning vectors include plasmids.
polymerase chain reaction
A technique for amplifying DNA in vitro by incubating it with specific primers, a heat-resistant DNA polymerase, and nucleotides.
DNA sequencing
Determining the order of nucleotide bases in a gene or DNA fragment.
telomere
The tandemly repetitive DNA at the end of a eukaryotic chromosome's DNA molecule.
trasformation
A change in genotype and phenotype due to the assimilation of external DNA by a cell.
nucleotide excision repair
A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide
CRISPR-Cas9
A genome editing technology that uses and RNA sequence to guide a nuclease enzyme to a particular location in the genome. Upon RNA binding, the nuclease cleaves the target DNA disabling the gene.
feedback inhibition
A form of regulation of gene expression, that is typical of anabolic (biosynthetic) pathways, where the end product inhibits the activity of the first enzyme in the pathway.
operator
In bacterial and phage DNA, a sequence of nucleotides near the start of an operon to which an active repressor can attach. The binding of the repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon.
operon
A unit of genetic function found in bacteria and phages, consisting of a promoter, an operator, and a coordinately regulated cluster of genes whose products function in a common pathway
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