Grade 12 Life Sciences: Detailed Notes on Nucleic
Acids
Introduction
Nucleic acids are complex organic molecules that store and transmit genetic information in living organisms. They are
essential for heredity, protein synthesis, growth, development, and reproduction. The two main types of nucleic acids
are DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).
Structure of Nucleic Acids
Nucleic acids are made up of smaller units called nucleotides. Each nucleotide consists of three components: a
phosphate group, a pentose sugar, and a nitrogenous base. The sugar in DNA is deoxyribose, while the sugar in RNA
is ribose.
Nitrogenous Bases
DNA contains four nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). RNA contains
Adenine (A), Uracil (U), Cytosine (C), and Guanine (G). In DNA, Adenine pairs with Thymine, while Cytosine pairs
with Guanine.
DNA Structure
DNA consists of two strands twisted together to form a double helix. The strands are held together by hydrogen bonds
between complementary nitrogenous bases. The structure of DNA was discovered by James Watson and Francis
Crick in 1953.
Functions of DNA
DNA stores hereditary information, controls protein synthesis, and ensures that genetic information is passed from
one generation to the next. DNA also controls cell activities through the production of proteins and enzymes.
DNA Replication
DNA replication is the process by which DNA makes an identical copy of itself before cell division. The DNA double
helix unwinds and unzips as hydrogen bonds break. Free nucleotides attach to exposed bases according to
complementary base pairing. DNA polymerase joins nucleotides together to form new strands.
RNA
RNA is usually single-stranded and plays an important role in protein synthesis. There are three main types of RNA:
messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
Acids
Introduction
Nucleic acids are complex organic molecules that store and transmit genetic information in living organisms. They are
essential for heredity, protein synthesis, growth, development, and reproduction. The two main types of nucleic acids
are DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).
Structure of Nucleic Acids
Nucleic acids are made up of smaller units called nucleotides. Each nucleotide consists of three components: a
phosphate group, a pentose sugar, and a nitrogenous base. The sugar in DNA is deoxyribose, while the sugar in RNA
is ribose.
Nitrogenous Bases
DNA contains four nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). RNA contains
Adenine (A), Uracil (U), Cytosine (C), and Guanine (G). In DNA, Adenine pairs with Thymine, while Cytosine pairs
with Guanine.
DNA Structure
DNA consists of two strands twisted together to form a double helix. The strands are held together by hydrogen bonds
between complementary nitrogenous bases. The structure of DNA was discovered by James Watson and Francis
Crick in 1953.
Functions of DNA
DNA stores hereditary information, controls protein synthesis, and ensures that genetic information is passed from
one generation to the next. DNA also controls cell activities through the production of proteins and enzymes.
DNA Replication
DNA replication is the process by which DNA makes an identical copy of itself before cell division. The DNA double
helix unwinds and unzips as hydrogen bonds break. Free nucleotides attach to exposed bases according to
complementary base pairing. DNA polymerase joins nucleotides together to form new strands.
RNA
RNA is usually single-stranded and plays an important role in protein synthesis. There are three main types of RNA:
messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
