Ask A Scientist© Biology Archive

Author:      D J Ferri
Text:        We are studying genetics and we cannot find a description of a 
"gene."  We have figured that the term is used metaphorical for the part of 
the DNA molecule that encodes the information for one trait.  Is this correct?

Response #:  1 of 2
Author:      wizkid
Text:        In the broadest sense of the term, gene refers to discrete 
heritable factors that encodes for a particular trait.  Specifically, a gene 
is "a segment of a DNA molecule that contains all the information required for 
synthesis of a product (polypeptide chain or RNA molecule), including both 
coding and non-coding sequences.  It is the biological unit of heredity, self-
reproducing, and transmitted from parent to progeny.  Each gene has a specific 
position (locus) on the chromosome map.  From the standpoint of function, 
genes are conceived of as structural, operator, and regulatory genes." - 
Dorland's Illustrated Medical Dictionary, 27th ed.  So, in terms of 
morphology, a gene is a specific sequence of nucleotide in DNA which encodes 
for a specific product.  This DNA sequence is TRANSCRIBED into an RNA 
sequence, which is then TRANSLATED through the function of ribosomes to a 
polypeptide.

Response #:  2 of 2
Author:      booga
Text:        I am sorry that your texts do not describe the structure of a 
gene, but many do.  Try a college level Introductory Biology text like 
Campbell, Keeton, or Curtis.  First of all, a gene does not encode the 
information for one trait.  It does encode the information for one RNA 
sequence, which then usually is used to produce one protein.  The one protein 
can then cause changes in many traits of the organism it is in.  As stated in 
the above answer, a gene is a sequence of nucleotide that encodes a single 
protein.  The structure of genes is varied and intensely researched.  Almost 
all genes have 3 major parts, the promoter, the encoding region, and the stop 
codling.  The promoter is a sequence of nucleotide that the RNA polymerase (an 
enzyme that builds RNA while reading DNA) binds to start transcription.  
Transcription of a gene into RNA involves reading the nucleotide sequence of 
the DNA of the gene and creating a copy of it in the RNA form.  This RNA form 
contains information for one protein, unlike DNA strands which contain 
information for thousands.  The encoding region is the largest part of the 
gene usually.  Groups of three nucleotide make up a codling, which codes for 
one amino acid in the chain that will make up the protein.  In eukayotes (all 
living things besides viruses, bacteria, and cyanobacteria) there are non-
encoding regions interspersed in the coding regions.  These are called introns 
and the coding regions call exons.  Intron regions are skipped by the RNA 
polymerase and do not contribute to the RNA made.  The final part of a gene is 
the "stop codon."  This a another three nucleotide sequence that tells RNA 
polymerase to stop right there.  There are other parts of genes too called 
enhancers, operators, CAP biding sites, and the TATA box.  Look up "operon 
hypothesis."