Basic Genetics Definitions

* Gene: A gene is a specific segment of DNA in a discrete region of a chromosome that is transcribed and resulting in or leads to the production of a functional RNA or protein.

* Transcription Unit: The stretch of DNA transcribed into an RNA molecule and encodes at least one gene.

http://en.wikipedia.org/wiki/Transcription_(genetics)

Albert Molecular Biology of the Cell 5th Edition p.336

* Coding DNA Sequence (Coding Region): portion of a gene's DNA that codes for protein sequences.

http://en.wikipedia.org/wiki/Coding_region

* Noncoding DNA: DNA sequences (not necessarily inside the gene) that do not encode for protein sequences. For example: introns (which is found inside the gene), DNA sequence (found inside the gene) that corresponds to the 5' UTR or 3' UTR etc.

http://en.wikipedia.org/wiki/Noncoding_DNA#Noncoding_functional_RNA

* Exon: A DNA sequence within a gene whose nucleotides corresponds to those present in the mRNA.

Note that an exon sequence is not necessarily coding. Some of the exons will be wholly or part of the 5' untranslated region (5' UTR) or the 3' untranslated region (3' UTR) of each transcript.

Also, the term exon refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts.

http://en.wikipedia.org/wiki/Exons

Leland Hartwell. Genetics from genes to genomes. 4th edition. G-8

Reece Campbell, Biology, 9th edition. G-13

* Introns: A DNA sequence within a gene whose nucleotides corresponds to those of the RNA molecule that is removed by splicing.

Also, the term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts.

http://en.wikipedia.org/wiki/Introns

Leland Hartwell. Genetics from genes to genomes. 4th edition. G-12

Reece Campbell, Biology, 9th edition. G-19

Introns may have a regulatory function - but role not really clear.

[Dr Kevin Ashton]

http://en.wikipedia.org/wiki/Gene#Evolutionary_concept_of_a_gene

* Untranslated Region: Untranslated region (or UTR) refers to either of two sections on each side of a coding sequence on a strand of mRNA. If it is found on the 5' side, it is called the 5' UTR (or leader sequence), or if it is found on the 3' side, it is called the 3' UTR (or trailer sequence).

http://en.wikipedia.org/wiki/Untranslated_region

They have regulatory roles: mRNA stability, assist ribosome binding and initiation/termination of translation.

* 5' Untranslated Region

For eukaryotes, it is the mRNA region between the 5' cap and the initiation codon. (Note:

It ends at the nucleotide before the start codon)

For prokaryotes, it is the mRNA region between the ribosome binding site and the start codon.

The 5' untranslated region can contain regulatory sequences.

http://en.wikipedia.org/wiki/Five_prime_untranslated_region

From Genes to Genomes 4th Edition p.273

* Initiation (Start) Codon

The start codon is generally defined as the point, sequence, at which a ribosome begins to translate a sequence of RNA into amino acids. The start codon is almost always preceded by an untranslated region 5' UTR. The start codon is AUG. It encodes for methionine which initiates most polypeptides.

Note: the above picture is of a mRNA, that is, after splicing.

* Termination (Stop) Codon

UAA, UAG, UGA. They do not encode any amino acids.

* Promoters

A promoter is a region of DNA that facilitates the transcription of a particular gene. Promoters are located near the genes they regulate, on the same strand and typically upstream (towards the 5' region of the sense strand).

Although promoter regions have a consensus sequence that is the most common sequence at this position, some genes have "strong" promoters that bind the transcription machinery well, and others have "weak" promoters that bind poorly. These weak promoters usually permit a lower rate of transcription than the strong promoters, because the transcription machinery binds to them and initiates transcription less frequently. Other possible regulatory regions include enhancers, which can compensate for a weak promoter. Most regulatory regions are "upstream"--that is, before or toward the 5' end of the transcription initiation site

http://en.wikipedia.org/wiki/Promoter_(genetics)

RNA polymerase recognises and binds to specific sequences in a region of the DNA close to the start of transcription. This region is known as the promoter.

http://en.wikipedia.org/wiki/Promoter_(genetics)

[By Dr Kevin Ashton]

Promoter is a DNA sequence at which RNA polymerase may bind, leading to initiation of transcription.

Leninger Principles of Biochemistry 5th Edition G-13

* Transcription factors: a transcription factor (sometimes called a sequence-specific DNA-binding factor) is a protein that binds to specific DNA sequences, thereby controlling the flow (or transcription) of genetic information from DNA to mRNA.[1][2] Transcription factors perform this function alone or with other proteins