Definition of Gene

Central Dogma

Definition of Gene

Proof that DNA
is Genetic Material

DNA Structure

Restriction Modification
System

Nucleic Acid
Hybriddizations

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Definition of Gene

Many molecular definitions of a gene relate to their role in directing the production of specific proteins. This stems from the analysis of mutants where it was shown that the absence of a specific protein was related to the mutation. Proteins are key components in the central dogma as polymerases but they also have other key metabolic roles. These role are:

Enzymatic
Structural components
Regulatory roles

Original Concept of the Gene: One gene = one enzyme

This concept does not hold for those proteins that are heteromeric or consist two of two or more different subunits.

Example: RUBISCO (ribulose bisphosphate carboxylase oxygenase)

CO₂ + 5-C-sugar --------------------> 2 3-C-sugars

RUBISCO is a multimeric protein of 16 peptides

8 small subunits (nuclear encoded)
8 large subunits (chloroplast encoded)

--thus two genes are responsible for this enzyme

Revised Concept: One gene = one peptide

Newest Discovery - Glucose 6-phosphate dehydrogenase is an enzyme found in human red blood cells. The major form this peptide is encoded from information from two chromosomes.

Minor form: NH₄--------------------CO₃
(The sequences encoding the gene are on the X chromosome.)

Major form: NH₄xx------------------CO₃
(Amino acids 1-53 are encoded on chromosome 6, and amino acids 54-479 are encoded on the X chromosome.)

Conclusion: This gene fits the one gene = one peptide model stated above, if you are willing to accept that not all genes reside on a single continuous stretch of DNA.