Download The chemical basis of heredity Nucleic acid

The chemical basis of heredity
Nucleic acid: is the chemical material that carry genetic
information in all types of living organism.
There are two types of nucleic acid;
1. Deoxy Ribo Nucleic Acid (DNA):this type found in the nucleus
and in all type of living organism except in virus.
2. Ribos Nucleic Acid (RNA): this type found in the cytoplasm and
nucleus and in virus.
The nucleic acid consist of many units called(nucleotides)
and all one of them consist of nitrogen base ,pentose and
phosphate group ,in order to consist of many nucleotides
chain and this nucleotides will be connected by the (di
ester phosphate bond )between three carbon atoms in the
pentose of nucleotide and the five carbon atoms in
another nucleotide.
 The DNA consist from two strand this structure called
(Double helix) but this two strand will be opposite to
each other .in this structure the group of sugar and
phosphate found on external surface of helix while the
nitrogen bases found in side toward the center.
The double helix of DNA structure will be coiled
and all coiled consist from ten pair of nitrogen
bases.the length of all coiled will be 34 A% and
the diameter of helix 20 A%
 There are two types of Nitrogen bases:
1.Purine: Adenine (A) ,Guanine (G).
2.Pyrimidine: Thymin(T) ,Cytosine (C) ,Uracil
(U).
 The A will be linked with the T by two hydrogen
bonds.
 The (U) is found in the RNA instead of (T). so the U
will be linked with the (A).
 The Nitrogen bases will be linked with the number
one of carbon atom of pentose which linked with
the number one of nitrogen atom in state
pyrimidine or nine carbon atom purine,this
molecules that consist of pentose and one of
Nitrogen base called (nucleoside) and the sugar
linked with nitrogen base by the (Glycosidic) bond
.the nucleoside will be linkage with the phosphate
group by the phosphate bond in order to consist
(nucleotide)
 The scientist Chargaff in 1950 found the total sum
of A equal to total sum of T always ,also to the G
and C.
 The ratio of C‫ـ‬G to the T‫ـ‬A will be different from
type of living organism to another but the cell of
liver and sperms in human contain the same ratio
of G‫ـ‬C to A‫ـ‬T this refer to genetic information in
(A‫ـ‬T) similar to genetic information of (G‫ـ‬C) .
Structure of gene
In 1961 the scientist Benzer study the building
gene and write three new expresions to di scripe
the units of genetic material,this are:
1.Cistron: is the active unit and use to expression the
part of DNA that limited one protein chain,the Cistron
very big and has 500 nucleotides.
2.Muton: is the mutation unit,contain small number of
nucleotides about one or don’t more than 5
nucleotides able to product mutation phenotype.
3.Recon: is the new uniting combination or formation
unit .
Is the smaller unit of DNA able to composition new
uniting has one or two nucleotides.
The action of gene:
The modern theory that regulation the create protein
inside the cell called (operon),this theory will be
classify the genes to :
1.structural genes: this type involve the building genes
and responsible about the normal creating of protein.
2.functional or operator genes: this type contact with
structural genes and will be active when the structural
genes in active state and this type will be control on
the working of structural genes.
Ribo Nucleic Acid(RNA):
This type of nucleic acid blay a big role in
transcription of genetic formation that found in DNA
and synthesis of protein.
 The RNA will be different on DNA:
1. the RNA contain ribose sugar.
2. the RNA molecule will be single strand.
3. the RNA contain Uracil(U) instead of Thymine(T) , U
linkage with A
4. there are three types of RNA.
5. the RNA found in nucleus and cytoplasm,but the
DNA found In nucleus only.
6. the RNA found in virus but DNA found in all type of
living organism except virus .
7. the DNA will be double helix for that consist from
two strands coiled with together .
There are three type of RNA:
1.Massenger RNA(mRNA): it is function transport the
genetic information from DNA to ribosomes in sequances
of amino acids in order to synthesis protein chain .the
synthesis process of mRNA from one chain of DNA as
template called (transcription)
DNA transcriptin
mRNA
translation protein synthesis.
2.Transfer RNA (tRNA) : this type found in cytoplasm and
it is job to transport the active amino acid to ribosomes
and contact with the mRNA ,there are number of tRNA
more than amino acid number , there for there are more
than one tRNA for one amino acid .
3.Ribosomal RNA (rRNA) : this type participate in building
of ribosomes and play role in uniting the amino acid to
creating peptide chain .
Protein synthesis process:
In the beginning the first step represented by segregation the two
strands
Of DNA by some enzymes in order to transcription the genetic
Material from DNA to mRNA and used the one strand of DNA as
Atemplate to creating the mRNA strand by help of RNA polymerase
After that the mRNA will be leaving the nucleus to cytoplasm wher
Ribosomes found.
The second step include activation or loading the amino acid by some
Enzyme and contact the active amino acid with the tRNA that special
With it .after that the tRNA transport to ribosomes and contact with
mRNA by the anticodon that found on the tRNA.
The mRNA contain the nucleotides called (codon) and the codon
Must be corresponding with anticodon in this way the amino acid
Will be togather in the ribosomes to creat polypeptide by peptide
Bonds after that the tRNA will be free to attached with another
Amino acid.