Lesson 1: Genes, Genetic Code, and DNA Replication

Lesson 1: Genes, Genetic Code, and DNA Replication

A gene is a segment of a DNA molecule that carries the coded information for a product (a polypeptide chain or RNA).

Protein-coding genes typically consist of three nucleotide sequence regions:

• Regulatory region: Located at the 3′ end of the coding strand of the gene, it carries signals that initiate and control the transcription process.

• Coding region: Contains the information that encodes amino acids.

• Termination region: Located at the 5′ end of the coding strand of the gene, it carries the signal to terminate transcription.

Uninterrupted genes (common in prokaryotes) have a continuous coding region.

Interrupted genes (mostly in eukaryotes) have coding segments for amino acids (exons) interspersed with non-coding segments (introns).

Structural genes carry information that codes for products that make up the structural or functional components of a cell.

Regulatory genes produce products that control the activity of other genes.

DNA is composed of four types of nucleotides: A, T, G, X.

The genetic code is a triplet code, meaning that three consecutive nucleotides code for one amino acid.

The genetic code in DNA is transcribed into mRNA.

There are 64 triplets on mRNA (codons) corresponding to 64 triplets (triplets) on DNA that code for amino acids that were experimentally deciphered in 1966.

Properties of the genetic code:

• Specificity: One triplet codes for only one type of amino acid.

• Degeneracy (redundancy): Multiple different triplets can code for the same type of amino acid, except for AUG and UGG.

• Universality: All species share the same genetic code, except for a few exceptions.

Stop codons: UAA, UAG, UGA, indicate the signal to end translation.

Start codon: AUG, defines the start point of translation and codes for methionine in eukaryotes / formylmethionine in prokaryotes.

DNA replication process:

DNA replication in prokaryotic cells, eukaryotic cells, and virus DNA (double-stranded form) all follow the principle of complementarity and semi-conservative replication.