2C - Genes

gene

a section of DNA that carries the code to make a protein

transcription

the process whereby a sequence of DNA is used as a template to produce a complementary sequence of mRNA

translation

the process where an mRNA sequence is read to produce a corresponding amino acid sequence to build a polypeptide

compare triplets and codons

In DNA, a group of three adjacent DNA nucleotides is known as a triplet, and when a DNA triplet is transcribed into an mRNA molecule, the three nucleotides become known as a codon.

why are codons and triplets crucial to the production of proteins?

Codons and triplets are crucial to the production of proteins, as each triplet or codon codes for a specific amino acid in the final polypeptide chain.

start codon

the sequence of three nucleotides in mRNA that signals the start of translation

stop codon

 the sequence of three nucleotides in mRNA that signals the end of translation

Properties of genetic code: universal

Nearly all living organisms use the same codons to code for specific amino acids.

Properties of the genetic code: Unambiguous

Each codon is only capable of coding for one specific amino acid. For example, the codon UUA only codes for the amino acid leucine.

Properties of the genetic code: Degenerate

While each codon only codes for one amino acid (unambiguous), each amino acid may be coded for by multiple different codons (degenerate). For example, both the codons UUA and UUG code for the amino acid leucine.

Properties of the genetic code: Non-overlapping

Each triplet or codon is read independently, without overlapping from adjacent triplets or codons.

Regions of a gene: Promoter

The promoter region (a sequence of DNA) is an upstream binding site for RNA polymerase, which is an enzyme responsible for transcription. When RNA polymerase binds to the promoter region of a gene, it allows for the transcription of that particular gene. Therefore, the promoter region effectively denotes the starting position and direction of transcription. In eukaryotes, the promoter region is often the sequence of bases ‘TATAAA’, commonly known as the TATA box.

Regions of a gene: Introns

Introns are regions of non-coding DNA that do not contribute to the final protein as they are removed during RNA processing (post-transcriptional modifications). Importantly, only eukaryotic genes contain introns – prokaryotic genes do not contain introns.

Regions of a gene: Exons

Exons are regions of coding DNA, which are transcribed and translated into the final protein. These can be found in both eukaryotes and prokaryotes.

Regions of a gene: Termination sequence

The termination sequence represents a sequence of DNA that signals for the end of transcription.

Regions of a gene: Operator

The operator region serves as the binding site for repressor proteins, which can then inhibit gene expression. This region is typically only found in prokaryotic genes, as eukaryotes have different regions for regulating gene expression.

Regions of a gene: Leader

 the segment of DNA or mRNA that immediately precedes the coding region.