AP Bio Chapter 14: Gene Expression: From Gene to Protein

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.

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. (In eukaryotes, the primary RNA transcript must first undergo RNA processing to become this.)

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.

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.

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 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.

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.

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 the sequence was transcribed.

Exon

A sequence within a primary transcript that remains in the RNA after RNA processing; also refers to the region of DNA from which the 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 iron and joining the two adjacent exons.

Ribozyme

An RNA molecule that functions as an enzyme, such as an intron that catalyzes it's own removal during RNA splicing.

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 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.

Ribosomal RNA (rRNA)

RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.

P site

One of a ribosome's three binding site for tRNA during translation. This holds the tRNA carrying the growing polypeptide chain. (Stands for peptidyl tRNA.)

A site

One of a ribosome's three binding sites. This holds the tRNA carrying the next amino acid to be added to the polypeptide chain. (Stands for aminoacyl tRNA.)

E site

One of a ribosome's three binding sites. This is the place where discharged tRNAs leave the ribosome. (Stands for exit.)

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.

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 s

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.

Mutagens

A chemical or physical agent that interacts with DNA and can cause a mutation.