CHAPTER 1
HEREDITY AND EVOLUTION
The chromosomes made up of nucleic acids and proteins, present in the nucleus
of the cell ere the components that carry hereditary characters in living
organisms.
The process of transfer of physical and mental characters from parents to the
progeny is called inheritance or heredity.
DNA molecule is made up of two helical strands consisting of deoxyribose sugar,
phosphoric acid and pairs of nitrogenous bases.
Heredity and hereditary changes:
Heredity : The transfer of biological characters from one generation to the next one
with the help of genes is called heredity.
The benefits of science of heredity:
Diagnosis of hereditary disorders.
Treatment of incurable hereditary disorders.
Prevention of hereditary disorders.
Production of hybrid varieties of animals and plants.
Use of microbes in industrial processes.
Transcription, Translation and Translocation :
Transcription :
(1) Synthesis of mRNA as per the nucleotide sequence present on the DNA molecule, is
called the process of transcription.
(2) The nucleotide sequence present in the DNA molecule is called gene. Genes control
the structure and functioning of cells of the body.
(3) Information required for the synthesis of proteins is stored in the genes ie. in the
nucleotide sequences of DNA. The proteins are synthesised according to the need of
the body.
(4) Central Dogma: Synthesis of proteins by DNA through the RNA is called central
dogma.
DNA Transcription →RNA Translation→ Protein
Amjad Sir……….. 9511794292
, (5) Genetic information is thus used from DNA to RNA, then through RNA for protein
synthesis.
(6) mRNA is produced according to the sequence of nucleotides on DNA.
(7) During transcription only one of the two strands of DNA is used.
(8) The sequence of nucleotides present on DNA strand gets copied in mRNA. Hence
there is always complementary sequence produced on the new mRNA molecule.
(9) RNA molecules have uracil instead of thymine present in DNA.
(10) Thus by transcription MRNA molecule which is complementary to DNA is
produced.
Triplet codon :
(1) The code for each amino acid consisting of three nucleotides, is called ‘triplet
codon’.
(2) mRNA formed in nucleus brings the coded message from DNA when it comes in
cytoplasm. This message contains the codes for amino acids.
Dr. Har Govind Khorana, made an important contribution in discovery of triplet codons
for 20 amino acids. He was awarded the Nobel Prize in 1968 for this work, along with
two other scientists.
Thousands of triplet codons are present in each mRNA molecule. As per the message
on mRNA, amino acids are supplied by the tRNA.
Translation : As per the codon on mRNA, the tRNA molecule with complementary
‘anticodon’ is brought near mRNA. this process is called ‘translation’.
Formation of peptide bonds: Every tRNA brings specific amino acid. These individual
amino acids are joined together by peptide bonds with the help of rRNA.
Translocation : The ribosome keeps on moving from one end of mRNA to other end by
the distance of one triplet codon. This process is ‘translocation’.
Many such polypeptide chains come together to form different and complex proteins.
The proteins are essential for controlling various functions of body of living organisms.
Mutation
(1) Sudden change occurring in the genetic material is known as mutation.
(2) Due to transmission of parental genes to offspring, there is remarkable similarity
between parents and their offspring. But if there is mutation in any nucleotide then there
are changes in the characters of the offspring.
(3) Mutations are of two types, viz. minor and major. Minor mutations can also bring
about considerable changes. E.g. Genetic disorders like sickle cell anaemia is caused
Amjad Sir……….. 9511794292
HEREDITY AND EVOLUTION
The chromosomes made up of nucleic acids and proteins, present in the nucleus
of the cell ere the components that carry hereditary characters in living
organisms.
The process of transfer of physical and mental characters from parents to the
progeny is called inheritance or heredity.
DNA molecule is made up of two helical strands consisting of deoxyribose sugar,
phosphoric acid and pairs of nitrogenous bases.
Heredity and hereditary changes:
Heredity : The transfer of biological characters from one generation to the next one
with the help of genes is called heredity.
The benefits of science of heredity:
Diagnosis of hereditary disorders.
Treatment of incurable hereditary disorders.
Prevention of hereditary disorders.
Production of hybrid varieties of animals and plants.
Use of microbes in industrial processes.
Transcription, Translation and Translocation :
Transcription :
(1) Synthesis of mRNA as per the nucleotide sequence present on the DNA molecule, is
called the process of transcription.
(2) The nucleotide sequence present in the DNA molecule is called gene. Genes control
the structure and functioning of cells of the body.
(3) Information required for the synthesis of proteins is stored in the genes ie. in the
nucleotide sequences of DNA. The proteins are synthesised according to the need of
the body.
(4) Central Dogma: Synthesis of proteins by DNA through the RNA is called central
dogma.
DNA Transcription →RNA Translation→ Protein
Amjad Sir……….. 9511794292
, (5) Genetic information is thus used from DNA to RNA, then through RNA for protein
synthesis.
(6) mRNA is produced according to the sequence of nucleotides on DNA.
(7) During transcription only one of the two strands of DNA is used.
(8) The sequence of nucleotides present on DNA strand gets copied in mRNA. Hence
there is always complementary sequence produced on the new mRNA molecule.
(9) RNA molecules have uracil instead of thymine present in DNA.
(10) Thus by transcription MRNA molecule which is complementary to DNA is
produced.
Triplet codon :
(1) The code for each amino acid consisting of three nucleotides, is called ‘triplet
codon’.
(2) mRNA formed in nucleus brings the coded message from DNA when it comes in
cytoplasm. This message contains the codes for amino acids.
Dr. Har Govind Khorana, made an important contribution in discovery of triplet codons
for 20 amino acids. He was awarded the Nobel Prize in 1968 for this work, along with
two other scientists.
Thousands of triplet codons are present in each mRNA molecule. As per the message
on mRNA, amino acids are supplied by the tRNA.
Translation : As per the codon on mRNA, the tRNA molecule with complementary
‘anticodon’ is brought near mRNA. this process is called ‘translation’.
Formation of peptide bonds: Every tRNA brings specific amino acid. These individual
amino acids are joined together by peptide bonds with the help of rRNA.
Translocation : The ribosome keeps on moving from one end of mRNA to other end by
the distance of one triplet codon. This process is ‘translocation’.
Many such polypeptide chains come together to form different and complex proteins.
The proteins are essential for controlling various functions of body of living organisms.
Mutation
(1) Sudden change occurring in the genetic material is known as mutation.
(2) Due to transmission of parental genes to offspring, there is remarkable similarity
between parents and their offspring. But if there is mutation in any nucleotide then there
are changes in the characters of the offspring.
(3) Mutations are of two types, viz. minor and major. Minor mutations can also bring
about considerable changes. E.g. Genetic disorders like sickle cell anaemia is caused
Amjad Sir……….. 9511794292
