fine structure of gene university of mysore

2. Inherited determinant of the phenotypic
iscalledgene.
In 1928 belling suggested that the
chromomers ,which appear like a series
of granules on the chromosomes, might
be the genes.

3.  Gene control biochemical reaction by controlling the
production of enzymes.
 Biochemical reaction in vivo occurs as a series
discrete, stepwise reaction.
 A single enzyme specifically catalyzes each reaction.

4. The genes of almost all organisms are DNA. This
is shown by following observation
 The DNA content of all cells of a species of an
organism is constant .It is halved in the gametes.
 Cells of similar hereditary origin have DNA of
similar composition .The relative amounts of the
four nucleotides are constant.
 Gene mutation can be explained on the basis of
alteRNAtion of DNA structure.

5.  Most plant viruses and some animal viruses
contain RNA as the genetic material
 In the reo group of viruses and in the wound
tumour virus the RNA is present in the double
stranded form. In the tobacco mosaic virus(tmv), a
tobacco virus ,influenza type a virus and bacterial
viruses f2,r17 and ms2 the RNA is single stranded.

6.  The gene has a mutational property as evidence by
the presence and occurrence of allele producing
different phenotypes.
 The gene has a recombination property, as
evidenced by the observation that it can separate
itself from the other genes through crossing over

9.  Length : 10 ̴ 200 bp
 Features : lack of conservation.
 Functions : pass through the ribosome
 Hold the first coding segment
 Promote the entry of mRNA into protein
synthesis

10.  Length : 50 ̴ 600 bp
 Feature : variation in length AATAAA (ATTAAA)
 Function : threads through the ribosome’s
 Hold the mRNA stability
 Termination sites
 Indicate the site for attachment of the poly (A) tail

11.  ENHANCER : located at about thousands
of bp from the gene
 PROMOTER :
 Basal promoter : TATA box , CAAT box or GC
box, located within 20-30 bp from start point.
 Upstream promoter : located at about 100 bp
upstream from start point

12. PROMOTER REGION :
 Initiate transcription
 Recognition point for RNA polymerase.
 Several hundred nucleotides in length
immediately adjacent to the gene
they regulate

13. TATA box :
 Common to almost all eukaryotic mRNA
promoter
 Consensus sequence : TATAA/TA
 20-30 bases upstream of the start point

14. Roles of TATA box:
 Bind RNA polymerase
 Initiate transcription
 Recognized and bound by a general
initiation factor TFIID

15. Intron and exon :
 Lack of correspondence between the DNA and
mRNA
 Intron : do not encode mRNA
 Exon : encode mRNA.
Intron :
 Donot encode for mRNA
 Length : 50 ̴ 30000 bp (average : 200 – 400 bp)
 Present in pre-mRNA only

16. Initiator and terminator :
 Initiator → exons + introns → terminator
 Length : 300 ̴ 1500 bp
 Initiator : ATG(CTG)
 Terminator : TGA , TAA OR TAG.

17. Exon :
 Encode for mRNA
 Four types of exons :
◦ Initial exon.
◦ InteRNAl exon.
◦ Terminal exons.
◦ Single exon(intronless genes)

18.  Some genes encode for protein , others encode for tRNA ,
rRNA etc
 Genes code for mRNA , mRNA code for protein
 The sequence of genes encoding for protein directly
determines their functions (amino acid sequence)
 Genetic code is highly conserved
 Some variation exist - mutations of DNA lead to loss of
function of protein , some may have diseases.