Chloë van Beukering Life Sciences Notes 2020
Nucleic Acids
• When a cell is dividing, its chromosomes become visible
• Analysis of the chromatin reveals that it is made of two major components:
• Deoxyribonucleic acid (DNA)
• The DNA is the molecule of heredity within whose structure is coded the information
of inheritance and the information for controlling the cell
• Proteins, called histones, that stabilise the DNA molecules
Chromosomes
• Each chromosome contains one very long DNA molecule that, when unravelled, would
measure about 4.8 cm in length
• The total length of DNA in the nucleus of one single human cell has been estimated to
be about 2.2 m
• The DNA is intricately folded and tightly bound around histones
• For most of the cell cycle, DNA molecules are in very long strands called chromatin, but
prior to cell division, the chromatin condenses
• This replicated DNA molecule, in its now condensed form, is now referred to as a
chromosome
• But, remember, there are two copies attached to each other until nuclear division occurs
• Each of the two copies of a chromosome are designated as a chromatid and they are
physically linked together at a point on the chromosome called the centromere
Nucleic Acids
• Nucleic acids are molecules that were originally thought to occur only in the nucleus
Two types of nucleic acids found in cells:
1. Deoxyribonucleic acid (DNA)
2. Ribonucleic acid (RNA)
• Both of these molecules are long, chain like structures built up from repeating similar
building blocks
• Both are thus, polymers
• Polymer: long chain of similar units joined end-to-end with each other
• Each unit of a polymer is called a monomer (building block)
• In a nucleic acid, the monomers are called nucleotides
Nucleotide consists of three units bonded together:
1. A sugar molecule (ribose or deoxyribose)
- Deoxyribonucleic acid had nucleotides in which the sugar is deoxyribose, while
ribonucleic acid contains the sugar ribose
2. A phosphate group
3. A nitrogenous base
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, Chloë van Beukering Life Sciences Notes 2020
Deoxyribonucleic Acid (DNA)
• In 1953, the scientists James Watson and Frances Crick published the first description of
the structure of DNA based on a model they constructed mainly from experimental
work done by other scientists, including Rosalind Franklin
• DNA is a macromolecule / polymer that provides the template for making the cells
proteins, called the genetic code
• Most of the DNA in a eukaryotic cell is found in the nucleus but there is also DNA in
mitochondria (mtDNA) and chloroplasts
DNA has 2 characteristics:
1. It is a store of genetic information
2. It can copy itself exactly, time after time (called DNA replication)
Each nucleotide in DNA can contain any of four nitrogenous bases:
• A = adenine
• G = guanine
• C = cytosine
• T = thymine
• Within each nucleotide, the nitrogenous base is joined to the deoxyribose sugar and
the phosphate group is attached to the deoxyribose sugar
• Humans have 23 pairs or 46 chromosomes
• These chromosomes are further broken
down into smaller pieces of DNA called
genes, which make up coding DNA for
providing the template for making proteins
• Each DNA molecule consists of two
strands of nucleotides, bonded together
in the middle by weak hydrogen bonds
between pairs of nitrogenous bases
• Adenine can only bond with thymine
• Guanine can only bond with cytosine
• This is the complementary base pairing
rule
• The sides of the double stranded, ladder-like structure are formed by alternating sugar-
phosphate units, while the base pairs form the cross bridges like the rungs on a ladder
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Nucleic Acids
• When a cell is dividing, its chromosomes become visible
• Analysis of the chromatin reveals that it is made of two major components:
• Deoxyribonucleic acid (DNA)
• The DNA is the molecule of heredity within whose structure is coded the information
of inheritance and the information for controlling the cell
• Proteins, called histones, that stabilise the DNA molecules
Chromosomes
• Each chromosome contains one very long DNA molecule that, when unravelled, would
measure about 4.8 cm in length
• The total length of DNA in the nucleus of one single human cell has been estimated to
be about 2.2 m
• The DNA is intricately folded and tightly bound around histones
• For most of the cell cycle, DNA molecules are in very long strands called chromatin, but
prior to cell division, the chromatin condenses
• This replicated DNA molecule, in its now condensed form, is now referred to as a
chromosome
• But, remember, there are two copies attached to each other until nuclear division occurs
• Each of the two copies of a chromosome are designated as a chromatid and they are
physically linked together at a point on the chromosome called the centromere
Nucleic Acids
• Nucleic acids are molecules that were originally thought to occur only in the nucleus
Two types of nucleic acids found in cells:
1. Deoxyribonucleic acid (DNA)
2. Ribonucleic acid (RNA)
• Both of these molecules are long, chain like structures built up from repeating similar
building blocks
• Both are thus, polymers
• Polymer: long chain of similar units joined end-to-end with each other
• Each unit of a polymer is called a monomer (building block)
• In a nucleic acid, the monomers are called nucleotides
Nucleotide consists of three units bonded together:
1. A sugar molecule (ribose or deoxyribose)
- Deoxyribonucleic acid had nucleotides in which the sugar is deoxyribose, while
ribonucleic acid contains the sugar ribose
2. A phosphate group
3. A nitrogenous base
1 of 11
, Chloë van Beukering Life Sciences Notes 2020
Deoxyribonucleic Acid (DNA)
• In 1953, the scientists James Watson and Frances Crick published the first description of
the structure of DNA based on a model they constructed mainly from experimental
work done by other scientists, including Rosalind Franklin
• DNA is a macromolecule / polymer that provides the template for making the cells
proteins, called the genetic code
• Most of the DNA in a eukaryotic cell is found in the nucleus but there is also DNA in
mitochondria (mtDNA) and chloroplasts
DNA has 2 characteristics:
1. It is a store of genetic information
2. It can copy itself exactly, time after time (called DNA replication)
Each nucleotide in DNA can contain any of four nitrogenous bases:
• A = adenine
• G = guanine
• C = cytosine
• T = thymine
• Within each nucleotide, the nitrogenous base is joined to the deoxyribose sugar and
the phosphate group is attached to the deoxyribose sugar
• Humans have 23 pairs or 46 chromosomes
• These chromosomes are further broken
down into smaller pieces of DNA called
genes, which make up coding DNA for
providing the template for making proteins
• Each DNA molecule consists of two
strands of nucleotides, bonded together
in the middle by weak hydrogen bonds
between pairs of nitrogenous bases
• Adenine can only bond with thymine
• Guanine can only bond with cytosine
• This is the complementary base pairing
rule
• The sides of the double stranded, ladder-like structure are formed by alternating sugar-
phosphate units, while the base pairs form the cross bridges like the rungs on a ladder
2 of 11
