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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.
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 “language” from nucleotides to amino acids.
Ribosomes
A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists 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.
Reading frame
On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis.
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.
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 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.
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 affects transcription of specific genes.
Transcription initiation complex
The completed assembly of transcription factors and RNA polymerase bound to a promoter.
5’ cap
A modified form of guanine nucleotide added onto the end of pre-mRNA molecule
Poly- A tail
A sequence of 50-250 adenine nucleotides added onto the 3’ end of a pre- mRNA molecule.
Splicing
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.
Alternative RNA splicing
A type of eukaryotic gene regulation at the RNA - processing 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 by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons.
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.
Ribosomal RNAs (rRNAs)
RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.
Mutations
A change in the nucleotide sequence of an organism’s DNA or in the DNA or RNA of a virus.
Point mutations
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 had 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 mutations
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.
Insertions
A mutation involving the addition of one ore more nucleotide pairs to a gene.
Deletions
A mutational loss of one or more nucleotide pairs form 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.
Mutagen
A chemical or physical agent that interacts with DNA and can cause a mutation.
